START-INFO-DIR-ENTRY * tar: (tar). Making tape (or disk) archives. END-INFO-DIR-ENTRY This file documents GNU `tar', a utility used to store, backup, and transport files. Copyright (C) 1992, 1994, 1995, 1996, 1997 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the Foundation. This file documents GNU `tar', which is a utility used to store, backup, and transport files. `tar' is a tape (or disk) archiver. This manual documents the release 1.12. Introduction ************ Welcome to the GNU `tar' manual. GNU `tar' is used to create and manipulate files ("archives") which are actually collections of many other files; the program provides users with an organized and systematic method for controlling a large amount of data. What this Book Contains ======================= The first part of this chapter introduces you to various terms that will recur throughout the book. It also tells you who has worked on GNU `tar' and its documentation, and where you should send bug reports or comments. The second chapter is a tutorial (*note Tutorial::.) which provides a gentle introduction for people who are new to using `tar'. It is meant to be self contained, not requiring any reading from subsequent chapters to make sense. It moves from topic to topic in a logical, progressive order, building on information already explained. Although the tutorial is paced and structured to allow beginners to learn how to use `tar', it is not intended solely for beginners. The tutorial explains how to use the three most frequently used operations (`create', `list', and `extract') as well as two frequently used options (`file' and `verbose'). The other chapters do not refer to the tutorial frequently; however, if a section discusses something which is a complex variant of a basic concept, there may be a cross reference to that basic concept. (The entire book, including the tutorial, assumes that the reader understands some basic concepts of using a Unix-type operating system; *note Tutorial::..) The third chapter presents the remaining five operations, and information about using `tar' options and option syntax. The other chapters are meant to be used as a reference. Each chapter presents everything that needs to be said about a specific topic. One of the chapters (*note Date input formats::.) exists in its entirety in other GNU manuals, and is mostly self-contained. In addition, one section of this manual (*note Standard::.) contains a big quote which is taken directly from `tar' sources. In general, we give both the long and short (abbreviated) option names at least once in each section where the relevant option is covered, so that novice readers will become familiar with both styles. (A few options have no short versions, and the relevant sections will indicate this.) Some Definitions ================ The `tar' program is used to create and manipulate `tar' archives. An "archive" is a single file which contains the contents of many files, while still identifying the names of the files, their owner(s), and so forth. (In addition, archives record access permissions, user and group, size in bytes, and last modification time. Some archives also record the file names in each archived directory, as well as other file and directory information.) You can use `tar' to "create" a new archive in a specified directory. The files inside an archive are called "members". Within this manual, we use the term "file" to refer only to files accessible in the normal ways (by `ls', `cat', and so forth), and the term "member" to refer only to the members of an archive. Similarly, a "file name" is the name of a file, as it resides in the filesystem, and a "member name" is the name of an archive member within the archive. The term "extraction" refers to the process of copying an archive member (or multiple members) into a file in the filesystem. Extracting all the members of an archive is often called "extracting the archive". The term "unpack" can also be used to refer to the extraction of many or all the members of an archive. Extracting an archive does not destroy the archive's structure, just as creating an archive does not destroy the copies of the files that exist outside of the archive. You may also "list" the members in a given archive (this is often thought of as "printing" them to the standard output, or the command line), or "append" members to a pre-existing archive. All of these operations can be peformed using `tar'. What `tar' Does =============== The `tar' program provides the ability to create `tar' archives, as well as various other kinds of manipulation. For example, you can use `tar' on previously created archives to extract files, to store additional files, or to update or list files which were already stored. Initially, `tar' archives were used to store files conveniently on magnetic tape. The name `tar' comes from this use; it stands for `t'ape `ar'chiver. Despite the utility's name, `tar' can direct its output to available devices, files, or other programs (using pipes). `tar' may even access remote devices or files (as archives). You can use `tar' archives in many ways. We want to stress a few of them: storage, backup, and transportation. Storage Often, `tar' archives are used to store related files for convenient file transfer over a network. For example, the GNU Project distributes its software bundled into `tar' archives, so that all the files relating to a particular program (or set of related programs) can be transferred as a single unit. A magnetic tape can store several files in sequence. However, the tape has no names for these files; it only knows their relative position on the tape. One way to store several files on one tape and retain their names is by creating a `tar' archive. Even when the basic transfer mechanism can keep track of names, as FTP can, the nuisance of handling multiple files, directories, and multiple links makes `tar' archives useful. Archive files are also used for long-term storage. You can think of this as transportation from the present into the future. (It is a science-fiction idiom that you can move through time as well as in space; the idea here is that `tar' can be used to move archives in all dimensions, even time!) Backup Because the archive created by `tar' is capable of preserving file information and directory structure, `tar' is commonly used for performing full and incremental backups of disks. A backup puts a collection of files (possibly pertaining to many users and projects) together on a disk or a tape. This guards against accidental destruction of the information in those files. GNU `tar' has special features that allow it to be used to make incremental and full dumps of all the files in a filesystem. Transportation You can create an archive on one system, transfer it to another system, and extract the contents there. This allows you to transport a group of files from one system to another. How `tar' Archives are Named ============================ Conventionally, `tar' archives are given names ending with `.tar'. This is not necessary for `tar' to operate properly, but this manual follows that convention in order to accustom readers to it and to make examples more clear. Often, people refer to `tar' archives as "`tar' files," and archive members as "files" or "entries". For people familiar with the operation of `tar', this causes no difficulty. However, in this manual, we consistently refer to "archives" and "archive members" to make learning to use `tar' easier for novice users. POSIX Compliance ================ We make some of our recommendations throughout this book for one reason in addition to what we think of as "good sense". The main additional reason for a recommendation is to be compliant with the POSIX standards. If you set the shell environment variable `POSIXLY_CORRECT', GNU `tar' will force you to adhere to these standards. Therefore, if this variable is set and you violate one of the POSIX standards in the way you phrase a command, for example, GNU `tar' will not allow the command and will signal an error message. You would then have to reorder the options or rephrase the command to comply with the POSIX standards. There is a chance in the future that, if you set this environment variable, your archives will be forced to comply with POSIX standards, also. No GNU `tar' extensions will be allowed. GNU `tar' Authors ================= GNU `tar' was originally written by John Gilmore, and modified by many people. The GNU enhancements were written by Jay Fenlason, then Joy Kendall, and the whole package has been further maintained by Thomas Bushnell, n/BSG, and finally Franc,ois Pinard, with the help of numerous and kind users. We wish to stress that `tar' is a collective work, and owes much to all those people who reported problems, offered solutions and other insights, or shared their thoughts and suggestions. An impressive, yet partial list of those contributors can be found in the `THANKS' file from the GNU `tar' distribution. Jay Fenlason put together a draft of a GNU `tar' manual, borrowing notes from the original man page from John Gilmore. This draft has been distributed in `tar' versions 1.04 (or even before?) through 1.10, then withdrawn in version 1.11. Thomas Bushnell, n/BSG and Amy Gorin worked on a tutorial and manual for GNU `tar'. Franc,ois Pinard put version 1.11.8 of the manual together by taking information from all these sources and merging them. Melissa Weisshaus finally edited and redesigned the book to create version 1.12. For version 1.12, Daniel Hagerty contributed a great deal of technical consulting. In particular, he is the primary author of *Note Backups::. Reporting bugs or suggestions ============================= If you find problems or have suggestions about this program or manual, please report them to `bug-gnu-utils@prep.ai.mit.edu'. Tutorial Introduction to `tar' ****************************** This chapter guides you through some basic examples of three `tar' operations: `--create', `--list', and `--extract'. If you already know how to use some other version of `tar', then you may not need to read this chapter. This chapter omits most complicated details about how `tar' works. Assumptions this Tutorial Makes =============================== This chapter is paced to allow beginners to learn about `tar' slowly. At the same time, we will try to cover all the basic aspects of these three operations. In order to accomplish both of these tasks, we have made certain assumptions about your knowledge before reading this manual, and the hardware you will be using: * Before you start to work through this tutorial, you should understand what the terms "archive" and "archive member" mean (*note Definitions::.). In addition, you should understand something about how Unix-type operating systems work, and you should know how to use some basic utilities. For example, you should know how to create, list, copy, rename, edit, and delete files and directories; how to change between directories; and how to figure out where you are in the filesystem. You should have some basic understanding of directory structure and how files are named according to which directory they are in. You should understand concepts such as standard output and standard input, what various definitions of the term "argument" mean, the differences between relative and absolute path names, and . * This manual assumes that you are working from your own home directory (unless we state otherwise). In this tutorial, you will create a directory to practice `tar' commands in. When we show path names, we will assume that those paths are relative to your home directory. For example, my home directory path is `/home/fsf/melissa'. All of my examples are in a subdirectory of the directory named by that path name; the subdirectory is called `practice'. * In general, we show examples of archives which exist on (or can be written to, or worked with from) a directory on a hard disk. In most cases, you could write those archives to, or work with them on any other device, such as a tape drive. However, some of the later examples in the tutorial and next chapter will not work on tape drives. Additionally, working with tapes is much more complicated than working with hard disks. For these reasons, the tutorial does not cover working with tape drives. *Note Media:: for complete information on using `tar' archives with tape drives. Stylistic Conventions ===================== In the examples, `$' represents a typical shell prompt. It precedes lines you should type; to make this more clear, those lines are shown in `this font', as opposed to lines which represent the computer's response; those lines are shown in `this font', or sometimes `like this'. When we have lines which are too long to be displayed in any other way, we will show them like this: This is an example of a line which would otherwise not fit in this space. Basic `tar' Operations and Options ================================== `tar' can take a wide variety of arguments which specify and define the actions it will have on the particular set of files or the archive. The main types of arguments to `tar' fall into one of two classes: operations, and options. Some arguments fall into a class called "operations"; exactly one of these is both allowed and required for any instance of using `tar'; you may *not* specify more than one. People sometimes speak of "operating modes". You are in a particular operating mode when you have specified the operation which specifies it; there are eight operations in total, and thus there are eight operating modes. The other arguments fall into the class known as "options". You are not required to specify any options, and you are allowed to specify more than one at a time (depending on the way you are using `tar' at that time). Some options are used so frequently, and are so useful for helping you type commands more carefully that they are effectively "required". We will discuss them in this chapter. You can write most of the `tar' operations and options in any of three forms: long (mnemonic) form, short form, and old style. Some of the operations and options have no short or "old" forms; however, the operations and options which we will cover in this tutorial have corresponding abbreviations. We will indicate those abbreviations appropriately to get you used to seeing them. (Note that the "old style" option forms exist in GNU `tar' for compatibility with Unix `tar'. We present a full discussion of this way of writing options and operations appears in *Note Old Options::, and we discuss the other two styles of writing options in *Note Mnemonic Options:: and *Note Short Options::.) In the examples and in the text of this tutorial, we usually use the long forms of operations and options; but the "short" forms produce the same result and can make typing long `tar' commands easier. For example, instead of typing tar --create --verbose --file=afiles.tar apple angst aspic you can type tar -c -v -f afiles.tar apple angst aspic or even tar -cvf afiles.tar apple angst aspic For more information on option syntax, see *Note Advanced tar::. In discussions in the text, when we name an option by its long form, we also give the corresponding short option in parentheses. The term, "option", can be confusing at times, since "operations" are often lumped in with the actual, *optional* "options" in certain general class statements. For example, we just talked about "short and long forms of options and operations". However, experienced `tar' users often refer to these by shorthand terms such as, "short and long options". This term assumes that the "operations" are included, also. Context will help you determine which definition of "options" to use. Similarly, the term "command" can be confusing, as it is often used in two different ways. People sometimes refer to `tar' "commands". A `tar' "command" is the entire command line of user input which tells `tar' what to do -- including the operation, options, and any arguments (file names, pipes, other commands, etc). However, you will also sometimes hear the term "the `tar' command". When the word "command" is used specifically like this, a person is usually referring to the `tar' *operation*, not the whole line. Again, use context to figure out which of the meanings the speaker intends. The Three Most Frequently Used Operations ========================================= Here are the three most frequently used operations (both short and long forms), as well as a brief description of their meanings. The rest of this chapter will cover how to use these operations in detail. We will present the rest of the operations in the next chapter. `--create' `-c' Create a new `tar' archive. `--list' `-t' List the contents of an archive. `--extract' `-x' Extract one or more members from an archive. Two Frequently Used Options =========================== To understand how to run `tar' in the three operating modes listed previously, you also need to understand how to use two of the options to `tar': `--file' (which takes an archive file as an argument) and `--verbose'. (You are usually not *required* to specify either of these options when you run `tar', but they can be very useful in making things more clear and helping you avoid errors.) The `--file' Option ------------------- `--file=ARCHIVE-NAME' `-f ARCHIVE-NAME' Specify the name of an archive file. You can specify an argument for the `--file=ARCHIVE-NAME' (`-f ARCHIVE-NAME') option whenever you use `tar'; this option determines the name of the archive file that `tar' will work on. If you don't specify this argument, then `tar' will use a default, usually some physical tape drive attached to your machine. If there is no tape drive attached, or the default is not meaningful, then `tar' will print an error message. The error message might look roughly like one of the following: tar: can't open /dev/rmt8 : No such device or address tar: can't open /dev/rsmt0 : I/O error To avoid confusion, we recommend that you always specfiy an archive file name by using `--file=ARCHIVE-NAME' (`-f ARCHIVE-NAME') when writing your `tar' commands. For more information on using the `--file=ARCHIVE-NAME' (`-f ARCHIVE-NAME') option, see *Note file::. The `--verbose' Option ---------------------- `--verbose' `-v' Show the files being worked on as `tar' is running. `--verbose' (`-v') shows details about the results of running `tar'. This can be especially useful when the results might not be obvious. For example, if you want to see the progress of `tar' as it writes files into the archive, you can use the `--verbose' option. In the beginning, you may find it useful to use `--verbose' at all times; when you are more accustomed to `tar', you will likely want to use it at certain times but not at others. We will use `--verbose' at times to help make something clear, and we will give many examples both using and not using `--verbose' to show the differences. Sometimes, a single instance of `--verbose' on the command line will show a full, `ls' style listing of an archive or files, giving sizes, owners, and similar information. Other times, `--verbose' will only show files or members that the particular operation is operating on at the time. In the latter case, you can use `--verbose' twice in a command to get a listing such as that in the former case. For example, instead of saying tar -cvf afiles.tar apple angst aspic above, you might say tar -cvvf afiles.tar apple angst aspic This works equally well using short or long forms of options. Using long forms, you would simply write out the mnemonic form of the option twice, like this: $ tar --create --verbose --verbose ... Note that you must double the hyphens properly each time. Later in the tutorial, we will give examples using `--verbose --verbose'. Getting Help: Using the `--help' Option --------------------------------------- `--help' The `--help' option to `tar' prints out a very brief list of all operations and option available for the current version of `tar' available on your system. How to Create Archives ====================== *(This message will disappear, once this node revised.)* One of the basic operations of `tar' is `--create' (`-c'), which you use to create a `tar' archive. We will explain `--create' first because, in order to learn about the other operations, you will find it useful to have an archive available to practice on. To make this easier, in this section you will first create a directory containing three files. Then, we will show you how to create an *archive* (inside the new directory). Both the directory, and the archive are specifically for you to practice on. The rest of this chapter and the next chapter will show many examples using this directory and the files you will create: some of those files may be other directories and other archives. The three files you will archive in this example are called `blues', `folk', and `jazz'. The archive is called `collection.tar'. This section will proceed slowly, detailing how to use `--create' in `verbose' mode, and showing examples using both short and long forms. In the rest of the tutorial, and in the examples in the next chapter, we will proceed at a slightly quicker pace. This section moves more slowly to allow beginning users to understand how `tar' works. Preparing a Practice Directory for Examples ------------------------------------------- To follow along with this and future examples, create a new directory called `practice' containing files called `blues', `folk' and `jazz'. The files can contain any information you like: ideally, they should contain information which relates to their names, and be of different lengths. Our examples assume that `practice' is a subdirectory of your home directory. Now `cd' to the directory named `practice'; `practice' is now your "working directory". (*Please note*: Although the full path name of this directory is `/HOMEDIR/practice', in our examples we will refer to this directory as `practice'; the HOMEDIR is presumed. In general, you should check that the files to be archived exist where you think they do (in the working directory) by running `ls'. Because you just created the directory and the files and have changed to that directory, you probably don't need to do that this time. It is very important to make sure there isn't already a file in the working directory with the archive name you intend to use (in this case, `collection.tar'), or that you don't care about its contents. Whenever you use `create', `tar' will erase the current contents of the file named by `--file=ARCHIVE-NAME' (`-f ARCHIVE-NAME') if it exists. `tar' will not tell you if you are about to overwrite a file unless you specify an option which does this . To add files to an existing archive, you need to use a different option, such as `--append' (`-r'); see *Note append:: for information on how to do this. Creating the Archive -------------------- To place the files `blues', `folk', and `jazz' into an archive named `collection.tar', use the following command: $ tar --create --file=collection.tar blues folk jazz The order of the arguments is not very important, *when using long option forms*. You could also say: $ tar blues --create folk --file=collection.tar jazz However, you can see that this order is harder to understand; this is why we will list the arguments in the order that makes the commands easiest to understand (and we encourage you to do the same when you use `tar', to avoid errors). Note that the part of the command which says, `--file=collection.tar' is considered to be *one* argument. If you substituted any other string of characters for ``collection.tar'', then that string would become the name of the archive file you create. The order of the options becomes more important when you begin to use short forms. With short forms, if you type commands in the wrong order (even if you type them correctly in all other ways), you may end up with results you don't expect. For this reason, it is a good idea to get into the habit of typing options in the order that makes inherent sense. *Note short create:: for more information on this. In this example, you type the command as shown above: `--create' is the operation which creates the new archive (`collection.tar'), and `--file' is the option which lets you give it the name you chose. The files, `blues', `folk', and `jazz', are now members of the archive, `collection.tar' (they are "file name arguments" to the `--create' operation) . Now that they are are in the archive, they are called *archive members*, not files . When you create an archive, you *must* specify which files you want placed in the archive. If you do not specify any archive members, GNU `tar' will complain. If you now list the contents of the working directory (`ls'), you will find the archive file listed as well as the files you saw previously: blues folk jazz collection.tar Creating the archive `collection.tar' did not destroy the copies of the files in the directory. Keep in mind that if you don't indicate an operation, `tar' will not run and will prompt you for one. If you don't name any files, `tar' will complain. You must have write access to the working directory, or else you will not be able to create an archive in that directory. *Caution*: Do not attempt to use `--create' (`-c') to add files to an existing archive; it will delete the archive and write a new one. Use `--append' (`-r') instead. *Note append::. Running `--create' with `--verbose' ----------------------------------- If you include the `--verbose' (`-v') option on the command line, `tar' will list the files it is acting on as it is working. In verbose mode, the `create' example above would appear as: $ tar --create --verbose --file=collection.tar blues folk jazz blues folk jazz This example is just like the example we showed which did not use `--verbose', except that `tar' generated the remaining lines . In the rest of the examples in this chapter, we will frequently use `verbose' mode so we can show actions or `tar' responses that you would otherwise not see, and which are important for you to understand. Short Forms with `create' ------------------------- As we said before, the `--create' (`-c') operation is one of the most basic uses of `tar', and you will use it countless times. Eventually, you will probably want to use abbreviated (or "short") forms of options. A full discussion of the three different forms that options can take appears in *Note Styles::; for now, here is what the previous example (including the `--verbose' (`-v') option) looks like using short option forms: $ tar -cvf collection.tar blues folk jazz blues folk jazz As you can see, the system responds the same no matter whether you use long or short option forms. One difference between using short and long option forms is that, although the exact placement of arguments following options is no more specific when using short forms, it is easier to become confused and make a mistake when using short forms. For example, suppose you attempted the above example in the following way: $ tar -cfv collection.tar blues folk jazz In this case, `tar' will make an archive file called `v', containing the files `blues', `folk', and `jazz', because the `v' is the closest "file name" to the `-f' option, and is thus taken to be the chosen archive file name. `tar' will try to add a file called `collection.tar' to the `v' archive file; if the file `collection.tar' did not already exist, `tar' will report an error indicating that this file does not exist. If the file `collection.tar' does already exist (e.g., from a previous command you may have run), then `tar' will add this file to the archive. Because the `-v' option did not get registered, `tar' will not run under `verbose' mode, and will not report its progress. The end result is that you may be quite confused about what happened, and possibly overwrite a file. To illustrate this further, we will show you how an example we showed previously would look using short forms. This example, $ tar blues --create folk --file=collection.tar jazz is confusing as it is. When shown using short forms, however, it becomes much more so: $ tar blues -c folk -f collection.tar jazz It would be very easy to put the wrong string of characters immediately following the `-f', but doing that could sacrifice valuable data. For this reason, we recommend that you pay very careful attention to the order of options and placement of file and archive names, especially when using short option forms. Not having the option name written out mnemonically can affect how well you remember which option does what, and therefore where different names have to be placed. (Placing options in an unusual order can also cause `tar' to report an error if you have set the shell environment variable, `POSIXLY_CORRECT'; *note posix compliance::. for more information on this.) Archiving Directories --------------------- You can archive a directory by specifying its directory name as a file name argument to `tar'. The files in the directory will be archived relative to the working directory, and the directory will be re-created along with its contents when the archive is extracted. To archive a directory, first move to its superior directory. If you have followed the previous instructions in this tutorial, you should type: $ cd .. $ This will put you into the directory which contains `practice', i.e. your home directory. Once in the superior directory, you can specify the subdirectory, `practice', as a file name argument. To store `practice' in the new archive file `music.tar', type: $ tar --create --verbose --file=music.tar practice `tar' should output: practice/ practice/blues practice/folk practice/jazz practice/collection.tar Note that the archive thus created is not in the subdirectory `practice', but rather in the current working directory--the directory from which `tar' was invoked. Before trying to archive a directory from its superior directory, you should make sure you have write access to the superior directory itself, not only the directory you are trying archive with `tar'. For example, you will probably not be able to store your home directory in an archive by invoking `tar' from the root directory; *Note absolute::. (Note also that `collection.tar', the original archive file, has itself been archived. `tar' will accept any file as a file to be archived, regardless of its content. When `music.tar' is extracted, the archive file `collection.tar' will be re-written into the file system). If you give `tar' a command such as $ tar --create --file=foo.tar . `tar' will report `tar: foo.tar is the archive; not dumped'. This happens because `tar' creates the archive `foo.tar' in the current directory before putting any files into it. Then, when `tar' attempts to add all the files in the directory `.' to the archive, it notices that the file `foo.tar' is the same as the archive, and skips it. (It makes no sense to put an archive into itself.) GNU `tar' will continue in this case, and create the archive normally, except for the exclusion of that one file. (*Please note:* Other versions of `tar' are not so clever; they will enter an infinite loop when this happens, so you should not depend on this behavior unless you are certain you are running GNU `tar'. ) How to List Archives ==================== Frequently, you will find yourself wanting to determine exactly what a particular archive contains. You can use the `--list' (`-t') operation to get the member names as they currently appear in the archive, as well as various attributes of the files at the time they were archived. For example, you can examine the archive `collection.tar' that you created in the last section with the command, $ tar --list --file=collection.tar The output of `tar' would then be: blues folk jazz The archive `bfiles.tar' would list as follows: ./birds baboon ./box Be sure to use a `--file=ARCHIVE-NAME' (`-f ARCHIVE-NAME') option just as with `--create' (`-c') to specify the name of the archive. If you use the `--verbose' (`-v') option with `--list', then `tar' will print out a listing reminiscent of `ls -l', showing owner, file size, and so forth. If you had used `--verbose' (`-v') mode, the example above would look like: $ tar --list --verbose --file=collection.tar folk -rw-rw-rw- myself user 62 1990-05-23 10:55 folk You can specify one or more individual member names as arguments when using `list'. In this case, `tar' will only list the names of members you identify. For example, `tar --list --file=afiles.tar apple' would only print `apple'. Because `tar' preserves paths, file names must be specified as they appear in the archive (ie., relative to the directory from which the archive was created). Therefore, it is essential when specifying member names to `tar' that you give the exact member names. For example, `tar --list --file=bfiles birds' would produce an error message something like `tar: birds: Not found in archive', because there is no member named `birds', only one named `./birds'. While the names `birds' and `./birds' name the same file, *member* names are compared using a simplistic name comparison, in which an exact match is necessary. *Note absolute::. However, `tar --list --file=collection.tar folk' would respond with `folk', because `folk' is in the archive file `collection.tar'. If you are not sure of the exact file name, try listing all the files in the archive and searching for the one you expect to find; remember that if you use `--list' with no file names as arguments, `tar' will print the names of all the members stored in the specified archive. Listing the Contents of a Stored Directory ------------------------------------------ *(This message will disappear, once this node revised.)* To get information about the contents of an archived directory, use the directory name as a file name argument in conjunction with `--list' (`-t'). To find out file attributes, include the `--verbose' (`-v') option. For example, to find out about files in the directory `practice', in the archive file `music.tar', type: $ tar --list --verbose --file=music.tar practice `tar' responds: drwxrwxrwx myself user 0 1990-05-31 21:49 practice/ -rw-rw-rw- myself user 42 1990-05-21 13:29 practice/blues -rw-rw-rw- myself user 62 1990-05-23 10:55 practice/folk -rw-rw-rw- myself user 40 1990-05-21 13:30 practice/jazz -rw-rw-rw- myself user 10240 1990-05-31 21:49 practice/collection.tar When you use a directory name as a file name argument, `tar' acts on all the files (including sub-directories) in that directory. How to Extract Members from an Archive ====================================== *(This message will disappear, once this node revised.)* Creating an archive is only half the job--there is no point in storing files in an archive if you can't retrieve them. The act of retrieving members from an archive so they can be used and manipulated as unarchived files again is called "extraction". To extract files from an archive, use the `--extract' (`--get', `-x') operation. As with `--create' (`-c'), specify the name of the archive with `--file=ARCHIVE-NAME' (`-f ARCHIVE-NAME'). Extracting an archive does not modify the archive in any way; you can extract it multiple times if you want or need to. Using `--extract', you can extract an entire archive, or specific files. The files can be directories containing other files, or not. As with `--create' (`-c') and `--list' (`-t'), you may use the short or the long form of the operation without affecting the performance. Extracting an Entire Archive ---------------------------- To extract an entire archive, specify the archive file name only, with no individual file names as arguments. For example, $ tar -xvf collection.tar produces this: -rw-rw-rw- me user 28 1996-10-18 16:31 jazz -rw-rw-rw- me user 21 1996-09-23 16:44 blues -rw-rw-rw- me user 20 1996-09-23 16:44 folk Extracting Specific Files ------------------------- To extract specific archive members, give their exact member names as arguments, as printed by `--list' (`-t'). If you had mistakenly deleted one of the files you had placed in the archive `collection.tar' earlier (say, `blues'), you can extract it from the archive without changing the archive's structure. It will be identical to the original file `blues' that you deleted. First, make sure you are in the `practice' directory, and list the files in the directory. Now, delete the file, `blues', and list the files in the directory again. You can now extract the member `blues' from the archive file `collection.tar' like this: $ tar --extract --file=collection.tar blues If you list the files in the directory again, you will see that the file `blues' has been restored, with its original permissions, creation times, and owner. (These parameters will be identical to those which the file had when you originally placed it in the archive; any changes you may have made before deleting the file from the file system, however, will *not* have been made to the archive member.) The archive file, `collection.tar', is the same as it was before you extracted `blues'. You can confirm this by running `tar' with `--list' (`-t'). Remember that as with other operations, specifying the exact member name is important. `tar --extract --file=bfiles.tar birds' will fail, because there is no member named `birds'. To extract the member named `./birds', you must specify `tar --extract --file=bfiles.tar ./birds'. To find the exact member names of the members of an archive, use `--list' (`-t') (*note list::.). If you give the `--verbose' (`-v') option, then `--extract' (`--get', `-x') will print the names of the archive members as it extracts them. Extracting Files that are Directories ------------------------------------- Extracting directories which are members of an archive is similar to extracting other files. The main difference to be aware of is that if the extracted directory has the same name as any directory already in the working directory, then files in the extracted directory will be placed into the directory of the same name. Likewise, if there are files in the pre-existing directory with the same names as the members which you extract, the files from the extracted archive will overwrite the files already in the working directory (and possible subdirectories). This will happen regardless of whether or not the files in the working directory were more recent than those extracted. However, if a file was stored with a directory name as part of its file name, and that directory does not exist under the working directory when the file is extracted, `tar' will create the directory. We can demonstrate how to use `--extract' to extract a directory file with an example. Change to the `practice' directory if you weren't there, and remove the files `folk' and `jazz'. Then, go back to the parent directory and extract the archive `music.tar'. You may either extract the entire archive, or you may extract only the files you just deleted. To extract the entire archive, don't give any file names as arguments after the archive name `music.tar'. To extract only the files you deleted, use the following command: $ tar -xvf music.tar practice/folk practice/jazz Because you created the directory with `practice' as part of the file names of each of the files by archiving the `practice' directory as `practice', you must give `practice' as part of the file names when you extract those files from the archive. Commands That Will Fail ----------------------- Here are some sample commands you might try which will not work, and why they won't work. If you try to use this command, $ tar -xvf music.tar folk jazz you will get the following response: tar: folk: Not found in archive tar: jazz: Not found in archive $ This is because these files were not originally *in* the parent directory `..', where the archive is located; they were in the `practice' directory, and their file names reflect this: $ tar -tvf music.tar practice/folk practice/jazz practice/rock Likewise, if you try to use this command, $ tar -tvf music.tar folk jazz you would get a similar response. Members with those names are not in the archive. You must use the correct member names in order to extract the files from the archive. If you have forgotten the correct names of the files in the archive, use `tar --list --verbose' to list them correctly. Going Further Ahead in this Manual ================================== Invoking GNU `tar' ****************** *(This message will disappear, once this node revised.)* This chapter is about how one invokes the GNU `tar' command, from the command synopsis (*note Synopsis::.). There are numerous options, and many styles for writing them. One mandatory option specifies the operation `tar' should perform (*note Operation Summary::.), other options are meant to detail how this operation should be performed (*note Option Summary::.). Non-option arguments are not always interpreted the same way, depending on what the operation is. You will find in this chapter everything about option styles and rules for writing them (*note Styles::.). On the other hand, operations and options are fully described elsewhere, in other chapters. Here, you will find only synthetic descriptions for operations and options, together with pointers to other parts of the `tar' manual. Some options are so special they are fully described right in this chapter. They have the effect of inhibiting the normal operation of `tar' or else, they globally alter the amount of feedback the user receives about what is going on. These are the `--help' and `--version' (*note help::.), `--verbose' (`-v') (*note verbose::.) and `--interactive' (`-w') options (*note interactive::.). General Synopsis of `tar' ========================= The GNU `tar' program is invoked as either one of: tar OPTION... [NAME]... tar LETTER... [ARGUMENT]... [OPTION]... [NAME]... The second form is for when old options are being used. You can use `tar' to store files in an archive, to extract them from an archive, and to do other types of archive manipulation. The primary argument to `tar', which is called the "operation", specifies which action to take. The other arguments to `tar' are either "options", which change the way `tar' performs an operation, or file names or archive members, which specify the files or members `tar' is to act on. You can actually type in arguments in any order, even if in this manual the options always precede the other arguments, to make examples easier to understand. Further, the option stating the main operation mode (the `tar' main command) is usually given first. Each NAME in the synopsis above is interpreted as an archive member name when the main command is one of `--compare' (`--diff', `-d'), `--delete', `--extract' (`--get', `-x'), `--list' (`-t') or `--update' (`-u'). When naming archive members, you must give the exact name of the member in the archive, as it is printed by `--list' (`-t'). For `--append' (`-r') and `--create' (`-c'), these NAME arguments specify the names of either files or directory hierarchies to place in the archive. These files or hierarchies should already exist in the file system, prior to the execution of the `tar' command. `tar' interprets relative file names as being relative to the working directory. `tar' will make all file names relative (by removing leading slashes when archiving or restoring files), unless you specify otherwise (using the `--absolute-names' (`-P') option). *Note absolute::, for more information about `--absolute-names' (`-P'). If you give the name of a directory as either a file name or a member name, then `tar' acts recursively on all the files and directories beneath that directory. For example, the name `/' identifies all the files in the filesystem to `tar'. The distinction between file names and archive member names is especially important when shell globbing is used, and sometimes a source of confusion for newcomers. *Note Wildcards::, for more information about globbing. The problem is that shells may only glob using existing files in the file system. Only `tar' itself may glob on archive members, so when needed, you must ensure that wildcard characters reach `tar' without being interpreted by the shell first. Using a backslash before `*' or `?', or putting the whole argument between quotes, is usually sufficient for this. Even if NAMEs are often specified on the command line, they can also be read from a text file in the file system, using the `--files-from=FILE-OF-NAMES' (`-T FILE-OF-NAMES') option. If you don't use any file name arguments, `--append' (`-r'), `--delete' and `--concatenate' (`--catenate', `-A') will do nothing, while `--create' (`-c') will usually yield a diagnostic and inhibit `tar' execution. The other operations of `tar' (`--list' (`-t'), `--extract' (`--get', `-x'), `--compare' (`--diff', `-d'), and `--update' (`-u')) will act on the entire contents of the archive. Besides successful exits, GNU `tar' may fail for many reasons. Some reasons correspond to bad usage, that is, when the `tar' command is improperly written. Errors may be encountered later, while encountering an error processing the archive or the files. Some errors are recoverable, in which case the failure is delayed until `tar' has completed all its work. Some errors are such that it would not meaningful, or at least risky, to continue processing: `tar' then aborts processing immediately. All abnormal exits, whether immediate or delayed, should always be clearly diagnosed on `stderr', after a line stating the nature of the error. GNU `tar' returns only a few exit statuses. I'm really aiming simplicity in that area, for now. If you are not using the `--compare' (`--diff', `-d') option, zero means that everything went well, besides maybe innocuous warnings. Nonzero means that something went wrong. Right now, as of today, "nonzero" is almost always 2, except for remote operations, where it may be 128. Using `tar' Options =================== GNU `tar' has a total of eight operating modes which allow you to perform a variety of tasks. You are required to choose one operating mode each time you employ the `tar' program by specifying one, and only one operation as an argument to the `tar' command (two lists of four operations each may be found at *Note frequent operations:: and *Note Operations::). Depending on circumstances, you may also wish to customize how the chosen operating mode behaves. For example, you may wish to change the way the output looks, or the format of the files that you wish to archive may require you to do something special in order to make the archive look right. You can customize and control `tar''s performance by running `tar' with one or more options (such as `--verbose' (`-v'), which we used in the tutorial). As we said in the tutorial, "options" are arguments to `tar' which are (as their name suggests) optional. Depending on the operating mode, you may specify one or more options. Different options will have different effects, but in general they all change details of the operation, such as archive format, archive name, or level of user interaction. Some options make sense with all operating modes, while others are meaningful only with particular modes. You will likely use some options frequently, while you will only use others infrequently, or not at all. (A full list of options is available in *note All Options::..) Note that `tar' options are case sensitive. For example, the options `-T' and `-t' are different; the first requires an argument for stating the name of a file providing a list of NAMEs, while the second does not require an argument and is another way to write `--list' (`-t'). In addition to the eight operations, there are many options to `tar', and three different styles for writing both: long (mnemonic) form, short form, and old style. These styles are discussed below. Both the options and the operations can be written in any of these three styles. The Three Option Styles ======================= There are three styles for writing operations and options to the command line invoking `tar'. The different styles were developed at different times during the history of `tar'. These styles will be presented below, from the most recent to the oldest. Some options must take an argument. (For example, `--file=ARCHIVE-NAME' (`-f ARCHIVE-NAME') takes the name of an archive file as an argument. If you do not supply an archive file name, `tar' will use a default, but this can be confusing; thus, we recommend that you always supply a specific archive file name.) Where you *place* the arguments generally depends on which style of options you choose. We will detail specific information relevant to each option style in the sections on the different option styles, below. The differences are subtle, yet can often be very important; incorrect option placement can cause you to overwrite a number of important files. We urge you to note these differences, and only use the option style(s) which makes the most sense to you until you feel comfortable with the others. Mnemonic Option Style --------------------- Each option has at least one long (or mnemonic) name starting with two dashes in a row, e.g. `list'. The long names are more clear than their corresponding short or old names. It sometimes happens that a single mnemonic option has many different different names which are synonymous, such as `--compare' and `--diff'. In addition, long option names can be given unique abbreviations. For example, `--cre' can be used in place of `--create' because there is no other mnemonic option which begins with `cre'. (One way to find this out is by trying it and seeing what happens; if a particular abbreviation could represent more than one option, `tar' will tell you that that abbreviation is ambiguous and you'll know that that abbreviation won't work. You may also choose to run `tar --help' to see a list of options. Be aware that if you run `tar' with a unique abbreviation for the long name of an option you didn't want to use, you are stuck; `tar' will perform the command as ordered.) Mnemonic options are meant to be obvious and easy to remember, and their meanings are generally easier to discern than those of their corresponding short options (see below). For example: $ tar --create --verbose --blocking-factor=20 --file=/dev/rmt0 gives a fairly good set of hints about what the command does, even for those not fully acquainted with `tar'. Mnemonic options which require arguments take those arguments immediately following the option name; they are introduced by an equal sign. For example, the `--file' option (which tells the name of the `tar' archive) is given a file such as `archive.tar' as argument by using the notation `--file=archive.tar' for the mnemonic option. Short Option Style ------------------ Most options also have a short option name. Short options start with a single dash, and are followed by a single character, e.g. `-t' (which is equivalent to `--list'). The forms are absolutely identical in function; they are interchangeable. The short option names are faster to type than long option names. Short options which require arguments take their arguments immediately following the option, usually separated by white space. It is also possible to stick the argument right after the short option name, using no intervening space. For example, you might write `-f archive.tar' or `-farchive.tar' instead of using `--file=archive.tar'. Both `--file=ARCHIVE-NAME' and `-f ARCHIVE-NAME' denote the option which indicates a specific archive, here named `archive.tar'. Short options' letters may be clumped together, but you are not required to do this (as compared to old options; see below). When short options are clumped as a set, use one (single) dash for them all, e.g. ``tar' -cvf'. Only the last option in such a set is allowed to have an argument(1). When the options are separated, the argument for each option which requires an argument directly follows that option, as is usual for Unix programs. For example: $ tar -c -v -b 20 -f /dev/rmt0 If you reorder short options' locations, be sure to move any arguments that belong to them. If you do not move the arguments properly, you may end up overwriting files. ---------- Footnotes ---------- (1) Clustering many options, the last of which has an argument, is a rather opaque way to write options. Some wonder if GNU `getopt' should not even be made helpful enough for considering such usages as invalid. Old Option Style ---------------- *(This message will disappear, once this node revised.)* Like short options, old options are single letters. However, old options must be written together as a single clumped set, without spaces separating them or dashes preceding them(1). This set of letters must be the first to appear on the command line, after the `tar' program name and some whitespace; old options cannot appear anywhere else. The letter of an old option is exactly the same letter as the corresponding short option. For example, the old option `t' is the same as the short option `-t', and consequently, the same as the mnemonic option `--list'. So for example, the command `tar cv' specifies the option `-v' in addition to the operation `-c'. When options that need arguments are given together with the command, all the associated arguments follow, in the same order as the options. Thus, the example given previously could also be written in the old style as follows: $ tar cvbf 20 /dev/rmt0 Here, `20' is the argument of `-b' and `/dev/rmt0' is the argument of `-f'. On the other hand, this old style syntax makes it difficult to match option letters with their corresponding arguments, and is often confusing. In the command `tar cvbf 20 /dev/rmt0', for example, `20' is the argument for `-b', `/dev/rmt0' is the argument for `-f', and `-v' does not have a corresponding argument. Even using short options like in `tar -c -v -b 20 -f /dev/rmt0' is clearer, putting all arguments next to the option they pertain to. If you want to reorder the letters in the old option argument, be sure to reorder any corresponding argument appropriately. This old way of writing `tar' options can surprise even experienced users. For example, the two commands: tar cfz archive.tar.gz file tar -cfz archive.tar.gz file are quite different. The first example uses `archive.tar.gz' as the value for option `f' and recognizes the option `z'. The second example, however, uses `z' as the value for option `f'--probably not what was intended. Old options are kept for compatibility with old versions of `tar'. This second example could be corrected in many ways, among which the following are equivalent: tar -czf archive.tar.gz file tar -cf archive.tar.gz -z file tar cf archive.tar.gz -z file As far as we know, all `tar' programs, GNU and non-GNU, support old options. GNU `tar' supports them not only for historical reasons, but also because many people are used to them. For compatibility with Unix `tar', the first argument is always treated as containing command and option letters even if it doesn't start with `-'. Thus, `tar c' is equivalent to `tar -c': both of them specify the `--create' (`-c') command to create an archive. ---------- Footnotes ---------- (1) Beware that if you precede options with a dash, you are announcing the short option style instead of the old option style; short options are decoded differently. Mixing Option Styles -------------------- All three styles may be intermixed in a single `tar' command, so long as the rules for each style are fully respected(1). Old style options and either of the modern styles of options may be mixed within a single `tar' command. However, old style options must be introduced as the first arguments only, following the rule for old options (old options must appear directly after the `tar' command and some whitespace). Modern options may be given only after all arguments to the old options have been collected. If this rule is not respected, a modern option might be falsely interpreted as the value of the argument to one of the old style options. For example, all the following commands are wholly equivalent, and illustrate the many combinations and orderings of option styles. tar --create --file=archive.tar tar --create -f archive.tar tar --create -farchive.tar tar --file=archive.tar --create tar --file=archive.tar -c tar -c --file=archive.tar tar -c -f archive.tar tar -c -farchive.tar tar -cf archive.tar tar -cfarchive.tar tar -f archive.tar --create tar -f archive.tar -c tar -farchive.tar --create tar -farchive.tar -c tar c --file=archive.tar tar c -f archive.tar tar c -farchive.tar tar cf archive.tar tar f archive.tar --create tar f archive.tar -c tar fc archive.tar On the other hand, the following commands are *not* equivalent to the previous set: tar -f -c archive.tar tar -fc archive.tar tar -fcarchive.tar tar -farchive.tarc tar cfarchive.tar These last examples mean something completely different from what the user intended (judging based on the example in the previous set which uses long options, whose intent is therefore very clear). The first four specify that the `tar' archive would be a file named `-c', `c', `carchive.tar' or `archive.tarc', respectively. The first two examples also specify a single non-option, NAME argument having the value `archive.tar'. The last example contains only old style option letters (repeating option `c' twice), not all of which are meaningful (eg., `.', `h', or `i'), with no argument value. ---------- Footnotes ---------- (1) Before GNU `tar' version 1.11.6, a bug prevented intermixing old style options with mnemonic options in some cases. All `tar' Options ================= The coming manual sections contain an alphabetical listing of all `tar' operations and options, with brief descriptions and cross references to more in-depth explanations in the body of the manual. They also contain an alphabetically arranged table of the short option forms with their corresponding long option. You can use this table as a reference for deciphering `tar' commands in scripts. Operations ---------- `--append' `-r' Appends files to the end of the archive. *Note append::. `--catenate' `-A' Same as `--concatenate'. *Note concatenate::. `--compare' `-d' Compares archive members with their counterparts in the file system, and reports differences in file size, mode, owner, modification date and contents. *Note compare::. `--concatenate' `-A' Appends other `tar' archives to the end of the archive. *Note concatenate::. `--create' `-c' Creates a new `tar' archive. *Note create::. `--delete' Deletes members from the archive. Don't try this on a archive on a tape! *Note delete::. `--diff' `-d' Same `--compare'. *Note compare::. `--extract' `-x' Extracts members from the archive into the file system. *Note extract::. `--get' `-x' Same as `--extract'. *Note extract::. `--list' `-t' Lists the members in an archive. *Note list::. `--update' `-u' Adds files to the end of the archive, but only if they are newer than their counterparts already in the archive, or if they do not already exist in the archive. *Note update::. `tar' Options ------------- `--absolute-names' `-P' Normally when creating an archive, `tar' strips an initial `/' from member names. This option disables that behavior. . `--after-date' (See `--newer'; .) `--atime-preserve' Tells `tar' to preserve the access time field in a file's inode when dumping it. . `--backup=BACKUP-TYPE' Rather than deleting files from the file system, `tar' will back them up using simple or numbered backups, depending upon BACKUP-TYPE. . `--block-number' `-R' With this option present, `tar' prints error messages for read errors with the block number in the archive file. . `--blocking-factor=BLOCKING' `-b BLOCKING' Sets the blocking factor `tar' uses to BLOCKING x 512 bytes per record. . `--checkpoint' This option directs `tar' to print periodic checkpoint messages as it reads through the archive. Its intended for when you want a visual indication that `tar' is still running, but don't want to see `--verbose' output. . `--compress' `--uncompress' `-Z' `tar' will use the `compress' program when reading or writing the archive. This allows you to directly act on archives while saving space. . `--confirmation' (See `--interactive'; .) `--dereference' `-h' When creating a `tar' archive, `tar' will archive the file that a symbolic link points to, rather than archiving the symlink. . `--directory=DIR' `-C DIR' When this option is specified, `tar' will change its current directory to DIR before performing any operations. When this option is used during archive creation, it is order sensitive. . `--exclude=PATTERN' When performing operations, `tar' will skip files that match PATTERN. . `--exclude-from=FILE' `-X FILE' Similar to `--exclude', except `tar' will use the list of patterns in the file FILE. . `--file=ARCHIVE' `-f ARCHIVE' `tar' will use the file ARCHIVE as the `tar' archive it performs operations on, rather than `tar''s compilation dependent default. . `--files-from=FILE' `-T FILE' `tar' will use the contents of FILE as a list of archive members or files to operate on, in addition to those specified on the command-line. . `--force-local' Forces `tar' to interpret the filename given to `--file' as a local file, even if it looks like a remote tape drive name. . `--group=GROUP' Files added to the `tar' archive will have a group id of GROUP, rather than the group from the source file. GROUP is first decoded as a group symbolic name, but if this interpretation fails, it has to be a decimal numeric group ID. . Also see the comments for the `--owner=USER' option. `--gunzip' (See `--gzip'; .) `--gzip' `--gunzip' `--ungzip' `-z' This option tells `tar' to read or write archives through `gzip', allowing `tar' to directly operate on several kinds of compressed archives transparently. . `--help' `tar' will print out a short message summarizing the operations and options to `tar' and exit. . `--ignore-failed-read' Instructs `tar' to exit successfully if it encounters an unreadable file. *Note Reading::. `--ignore-umask' (See `--preserve-permissions'; *note Writing::..) `--ignore-zeros' `-i' With this option, `tar' will ignore zeroed blocks in the archive, which normally signals EOF. *Note Reading::. `--incremental' `-G' Used to inform `tar' that it is working with an old GNU-format incremental backup archive. It is intended primarily for backwards compatibility only. . `--info-script=SCRIPT-FILE' `--new-volume-script=SCRIPT-FILE' `-F SCRIPT-FILE' When `tar' is performing multi-tape backups, SCRIPT-FILE is run at the end of each tape. . `--interactive' `--confirmation' `-w' Specifies that `tar' should ask the user for confirmation before performing potentially destructive options, such as overwriting files. . `--keep-old-files' `-k' When extracting files from an archive, `tar' will not overwrite existing files if this option is present. *Note Writing::. `--label=NAME' `-V NAME' When creating an archive, instructs `tar' to write NAME as a name record in the archive. When extracting or listing archives, `tar' will only operate on archives that have a label matching the pattern specified in NAME. . `--listed-incremental=SNAPSHOT-FILE' `-g SNAPSHOT-FILE' During a `--create' operation, specifies that the archive that `tar' creates is a new GNU-format incremental backup, using SNAPSHOT-FILE to determine which files to backup. With other operations, informs `tar' that the archive is in incremental format. . `--mode=PERMISSIONS' When adding files to an archive, `tar' will use PERMISSIONS for the archive members, rather than the permissions from the files. The program `chmod' and this `tar' option share the same syntax for what PERMISSIONS might be. *Note Permissions: (filetutils)File permissions. This reference also has useful information for those not being overly familiar with the Unix permission system. Of course, PERMISSIONS might be plainly specified as an octal number. However, by using generic symbolic modifications to mode bits, this allows more flexibility. For example, the value `a+rw' adds read and write permissions for everybody, while retaining executable bits on directories or on any other file already marked as executable. `--multi-volume' `-M' Informs `tar' that it should create or otherwise operate on a multi-volume `tar' archive. . `--new-volume-script' (see -info-script) `--newer=DATE' `--after-date=DATE' `-N' When creating an archive, `tar' will only add files that have changed since DATE. . `--newer-mtime' In conjunction with `--newer', `tar' will only add files whose contents have changed (as opposed to just `--newer', which will also back up files for which any status information has changed). `--no-recursion' With this option, `tar' will not recurse into directories unless a directory is explicitly named as an argument to `tar'. . `--null' When `tar' is using the `--files-from' option, this option instructs `tar' to expect filenames terminated with `NUL', so `tar' can correctly work with file names that contain newlines. . `--numeric-owner' This option will notify `tar' that it should use numeric user and group IDs when creating a `tar' file, rather than names. . `--old-archive' (See `--portability'; .) `--one-file-system' `-l' Used when creating an archive. Prevents `tar' from recursing into directories that are on different file systems from the current directory. . `--owner=USER' Specifies that `tar' should use USER as the owner of members when creating archives, instead of the user associated with the source file. USER is first decoded as a user symbolic name, but if this interpretation fails, it has to be a decimal numeric user ID. . There is no value indicating a missing number, and `0' usually means `root'. Some people like to force `0' as the value to offer in their distributions for the owner of files, because the `root' user is anonymous anyway, so that might as well be the owner of anonymous archives. `--portability' `--old-archive' `-o' Tells `tar' to create an archive that is compatible with Unix V7 `tar'. . `--posix' Instructs `tar' to create a POSIX compliant `tar' archive. . `--preserve' Synonymous with specifying both `--preserve-permissions' and `--same-order'. . `--preserve-order' (See `--same-order'; *note Reading::..) `--preserve-permissions' `--same-permissions' `-p' When `tar' is extracting an archive, it normally subtracts the users' umask from the permissions specified in the archive and uses that number as the permissions to create the destination file. Specifying this option instructs `tar' that it should use the permissions directly from the archive. *Note Writing::. `--read-full-records' `-B' Specifies that `tar' should reblock its input, for reading from pipes on systems with buggy implementations. *Note Reading::. `--record-size=SIZE' Instructs `tar' to use SIZE bytes per record when accessing the archive. . `--recursive-unlink' Similar to the `--unlink-first' option, removing existing directory hierarchies before extracting directories of the same name from the archive. *Note Writing::. `--remove-files' Directs `tar' to remove the source file from the file system after appending it to an archive. . `--rsh-command=CMD' Notifies `tar' that is should use CMD to communicate with remote devices. . `--same-order' `--preserve-order' `-s' This option is an optimization for `tar' when running on machines with small amounts of memory. It informs `tar' that the list of file arguments has already been sorted to match the order of files in the archive. *Note Reading::. `--same-owner' When extracting an archive, `tar' will attempt to preserve the owner specified in the `tar' archive with this option present. . `--same-permissions' (See `--preserve-permissions'; *note Writing::..) `--show-omitted-dirs' Instructs `tar' to mention directories its skipping over when operating on a `tar' archive. . `--sparse' `-S' Invokes a GNU extension when adding files to an archive that handles sparse files efficiently. . `--starting-file=NAME' `-K NAME' This option affects extraction only; `tar' will skip extracting files in the archive until it finds one that matches NAME. *Note Scarce::. `--suffix=SUFFIX' Alters the suffix `tar' uses when backing up files from the default `~'. . `--tape-length=NUM' `-L NUM' Specifies the length of tapes that `tar' is writing as being NUM x 1024 bytes long. . `--to-stdout' `-O' During extraction, `tar' will extract files to stdout rather than to the file system. *Note Writing::. `--totals' Displays the total number of bytes written after creating an archive. . `--touch' `-m' Sets the modification time of extracted files to the extraction time, rather than the modification time stored in the archive. *Note Writing::. `--uncompress' (See `--compress'; .) `--ungzip' (See `--gzip'; .) `--unlink-first' `-U' Directs `tar' to remove the corresponding file from the file system before extracting it from the archive. *Note Writing::. `--use-compress-program=PROG' Instructs `tar' to access the archive through PROG, which is presumed to be a compression program of some sort. . `--verbose' `-v' Specifies that `tar' should be more verbose about the operations its performing. This option can be specified multiple times for some operations to increase the amount of information displayed. . `--verify' `-W' Verifies that the archive was correctly written when creating an archive. . `--version' `tar' will print an informational message about what version it is and a copyright message, some credits, and then exit. . `--volno-file=FILE' Used in conjunction with `--multi-volume'. `tar' will keep track of which volume of a multi-volume archive its working in FILE. . Short Options Cross Reference ----------------------------- Here is an alphabetized list of all of the short option forms, matching them with the equivalent long option. `-A' `--concatenate' `-B' `--read-full-records' `-C' `--directory' `-F' `--info-script' `-G' `--incremental' `-K' `--starting-file' `-L' `--tape-length' `-M' `--multi-volume' `-N' `--newer' `-O' `--to-stdout' `-P' `--absolute-names' `-R' `--block-number' `-S' `--sparse' `-T' `--files-from' `-U' `--unlink-first' `-V' `--label' `-W' `--verify' `-X' `--exclude-from' `-Z' `--compress' `-b' `--blocking-factor' `-c' `--create' `-d' `--compare' `-f' `--file' `-g' `--listed-incremental' `-h' `--dereference' `-i' `--ignore-zeros' `-k' `--keep-old-files' `-l' `--one-file-system' `-m' `--touch' `-o' `--portability' `-p' `--preserve-permissions' `-r' `--append' `-s' `--same-order' `-t' `--list' `-u' `--update' `-v' `--verbose' `-w' `--interactive' `-x' `--extract' `-z' `--gzip' GNU `tar' documentation ======================= Being careful, the first thing is really checking that you are using GNU `tar', indeed. The `--version' option will generate a message giving confirmation that you are using GNU `tar', with the precise version of GNU `tar' you are using. `tar' identifies itself and prints the version number to the standard output, then immediately exits successfully, without doing anything else, ignoring all other options. For example, `tar --version' might return: tar (GNU tar) 1.12 The first occurrence of `tar' in the result above is the program name in the package (for example, `rmt' is another program), while the second occurrence of `tar' is the name of the package itself, containing possibly many programs. The package is currently named `tar', after the name of the main program it contains(1). Another thing you might want to do is checking the spelling or meaning of some particular `tar' option, without resorting to this manual, for once you have carefully read it. GNU `tar' has a short help feature, triggerable through the `--help' option. By using this option, `tar' will print a usage message listing all available options on standard output, then exit successfully, without doing anything else and ignoring all other options. Even if this is only a brief summary, it may be several screens long. So, if you are not using some kind of scrollable window, you might prefer to use something like: $ tar --help | less presuming, here, that you like using `less' for a pager. Other popular pagers are `more' and `pg'. If you know about some KEYWORD which interests you and do not want to read all the `--help' output, another common idiom is doing: tar --help | grep KEYWORD for getting only the pertinent lines. The perceptive reader would have noticed some contradiction in the previous paragraphs. It is written that both `--version' and `--help' print something, and have all other options ignored. In fact, they cannot ignore each other, and one of them has to win. We do not specify which is stronger, here; experiment if you really wonder! The short help output is quite succint, and you might have to get back to the full documentation for precise points. If you are reading this paragraph, you already have the `tar' manual in some form. This manual is available in printed form, as a kind of small book. It may printed out of the GNU `tar' distribution, provided you have TeX already installed somewhere, and a laser printer around. Just configure the distribution, execute the command `make dvi', then print `doc/tar.dvi' the usual way (contact your local guru to know how). If GNU `tar' has been conveniently installed at your place, this manual is also available in interactive, hypertextual form as an Info file. Just call `info tar' or, if you do not have the `info' program handy, use the Info reader provided within GNU Emacs, calling `tar' from the main Info menu. There is currently no `man' page for GNU `tar'. If you observe such a `man' page on the system you are running, either it does not long to GNU `tar', or it has not been produced by GNU. Currently, GNU `tar' documentation is provided in Texinfo format only, if we except, of course, the short result of `tar --help'. ---------- Footnotes ---------- (1) There are plans to merge the `cpio' and `tar' packages into a single one which would be called `paxutils'. So, who knows if, one of this days, the `--version' would not yield `tar (GNU paxutils) 3.2' Checking `tar' progress ======================= Typically, `tar' performs most operations without reporting any information to the user except error messages. When using `tar' with many options, particularly ones with complicated or difficult-to-predict behavior, it is possible to make serious mistakes. `tar' provides several options that make observing `tar' easier. These options cause `tar' to print information as it progresses in its job, and you might want to use them just for being more careful about what is going on, or merely for entertaining yourself. If you have encountered a problem when operating on an archive, however, you may need more information than just an error message in order to solve the problem. The following options can be helpful diagnostic tools. Normally, the `--list' (`-t') command to list an archive prints just the file names (one per line) and the other commands are silent. When used with most operations, the `--verbose' (`-v') option causes `tar' to print the name of each file or archive member as it is processed. This and the other options which make `tar' print status information can be useful in monitoring `tar'. With `--create' (`-c') or `--extract' (`--get', `-x'), `--verbose' (`-v') used once just prints the names of the files or members as they are processed. Using it twice causes `tar' to print a longer listing (reminiscent of `ls -l') for each member. Since `--list' (`-t') already prints the names of the members, `--verbose' (`-v') used once with `--list' (`-t') causes `tar' to print an `ls -l' type listing of the files in the archive. The following examples both extract members with long list output: $ tar --extract --file=archive.tar --verbose --verbose $ tar xvv archive.tar Verbose output appears on the standard output except when an archive is being written to the standard output, as with `tar --create --file=- --verbose' (`tar cfv -', or even `tar cv'--if the installer let standard output be the default archive). In that case `tar' writes verbose output to the standard error stream. The `--totals' option--which is only meaningful when used with `--create' (`-c')--causes `tar' to print the total amount written to the archive, after it has been fully created. The `--checkpoint' option prints an occasional message as `tar' reads or writes the archive. In fact, it print directory names while reading the archive. It is designed for those who don't need the more detailed (and voluminous) output of `--block-number' (`-R'), but do want visual confirmation that `tar' is actually making forward progress. The `--show-omitted-dirs' option, when reading an archive--with `--list' (`-t') or `--extract' (`--get', `-x'), for example--causes a message to be printed for each directory in the archive which is skipped. This happens regardless of the reason for skipping: the directory might not have been named on the command line (implicitly or explicitly), it might be excluded by the use of the `--exclude=PATTERN' option, or some other reason. If `--block-number' (`-R') is used, `tar' prints, along with every message it would normally produce, the block number within the archive where the message was triggered. Also, supplementary messages are triggered when reading blocks full of NULs, or when hitting end of file on the archive. As of now, if the archive if properly terminated with a NUL block, the reading of the file may stop before end of file is met, so the position of end of file will not usually show when `--block-number' (`-R') is used. Note that GNU `tar' drains the archive before exiting when reading the archive from a pipe. This option is especially useful when reading damaged archives, since it helps pinpoint the damaged sections. It can also be used with `--list' (`-t') when listing a file-system backup tape, allowing you to choose among several backup tapes when retrieving a file later, in favor of the tape where the file appears earliest (closest to the front of the tape). . Asking for Confirmation During Operations ========================================= Typically, `tar' carries out a command without stopping for further instructions. In some situations however, you may want to exclude some files and archive members from the operation (for instance if disk or storage space is tight). You can do this by excluding certain files automatically (*note Choosing::.), or by performing an operation interactively, using the `--interactive' (`-w') option. `tar' also accepts `--confirmation' for this option. When the `--interactive' (`-w') option is specified, before reading, writing, or deleting files, `tar' first prints a message for each such file, telling what operation it intends to take, then asks for confirmation on the terminal. The actions which require confirmation include adding a file to the archive, extracting a file from the archive, deleting a file from the archive, and deleting a file from disk. To confirm the action, you must type a line of input beginning with `y'. If your input line begins with anything other than `y', `tar' skips that file. If `tar' is reading the archive from the standard input, `tar' opens the file `/dev/tty' to support the interactive communications. Verbose output is normally sent to standard output, separate from other error messages. However, if the archive is produced directly on standard output, then verbose output is mixed with errors on `stderr'. Producing the archive on standard output may be used as a way to avoid using disk space, when the archive is soon to be consumed by another process reading it, say. Some people felt the need of producing an archive on stdout, still willing to segregate between verbose output and error output. A possible approach would be using a named pipe to receive the archive, and having the consumer process to read from that named pipe. This has the advantage of letting standard output free to receive verbose output, all separate from errors. GNU `tar' Operations ******************** Basic GNU `tar' Operations ========================== The basic `tar' operations, `--create' (`-c'), `--list' (`-t') and `--extract' (`--get', `-x'), are currently presented and described in the tutorial chapter of this manual. This section provides some complementary notes for these operations. `--create' (`-c') Creating an empty archive would have some kind of elegance. One can initialize an empty archive and later use `--append' (`-r') for adding all members. Some applications would not welcome making an exception in the way of adding the first archive member. On the other hand, many people reported that it is dangerously too easy for `tar' to destroy a magnetic tape with an empty archive(1). The two most common errors are: 1. Mistakingly using `create' instead of `extract', when the intent was to extract the full contents of an archive. This error is likely: keys `c' and `x' are right next ot each other on the QWERTY keyboard. Instead of being unpacked, the archive then gets wholly destroyed. When users speak about "exploding" an archive, they usually mean something else :-). 2. Forgetting the argument to `file', when the intent was to create an archive with a single file in it. This error is likely because a tired user can easily add the `f' key to the cluster of option letters, by the mere force of habit, without realizing the full consequence of doing so. The usual consequence is that the single file, which was meant to be saved, is rather destroyed. So, recognizing the likelihood and the catastrophical nature of these errors, GNU `tar' now takes some distance from elegance, and cowardly refuses to create an archive when `--create' (`-c') option is given, there are no arguments besides options, and `--files-from=FILE-OF-NAMES' (`-T FILE-OF-NAMES') option is *not* used. To get around the cautiousness of GNU `tar' and nevertheless create an archive with nothing in it, one may still use, as the value for the `--files-from=FILE-OF-NAMES' (`-T FILE-OF-NAMES') option, a file with no names in it, as shown in the following commands: tar --create --file=empty-archive.tar --files-from=/dev/null tar cfT empty-archive.tar /dev/null `--extract' (`--get', `-x') A socket is stored, within a GNU `tar' archive, as a pipe. `--list' (`-t') GNU `tar' now shows dates as `1996-11-09', while it used to show them as `Nov 11 1996'. (One can revert to the old behavior by defining `USE_OLD_CTIME' in `src/list.c' before reinstalling.) But preferrably, people you should get used to ISO 8601 dates. Local American dates should be made available again with full date localisation support, once ready. In the meantime, programs not being localisable for dates should prefer international dates, that's really the way to go. Look up `http://www.ft.uni-erlangen.de/~mskuhn/iso-time.html' if you are curious, it contains a detailed explanation of the ISO 8601 standard. ---------- Footnotes ---------- (1) This is well described in `Unix-haters Handbook', by Simson Garfinkel, Daniel Weise & Steven Strassmann, IDG Books, ISBN 1-56884-203-1. Advanced GNU `tar' Operations ============================= Now that you have learned the basics of using GNU `tar', you may want to learn about further ways in which `tar' can help you. This chapter presents five, more advanced operations which you probably won't use on a daily basis, but which serve more specialized functions. We also explain the different styles of options and why you might want to use one or another, or a combination of them in your `tar' commands. Additionally, this chapter includes options which allow you to define the output from `tar' more carefully, and provide help and error correction in special circumstances. The Five Advanced `tar' Operations ---------------------------------- *(This message will disappear, once this node revised.)* In the last chapter, you learned about the first three operations to `tar'. This chapter presents the remaining five operations to `tar': `--append', `--update', `--concatenate', `--delete', and `--compare'. You are not likely to use these operations as frequently as those covered in the last chapter; however, since they perform specialized functions, they are quite useful when you do need to use them. We will give examples using the same directory and files that you created in the last chapter. As you may recall, the directory is called `practice', the files are `jazz', `blues', `folk', `rock', and the two archive files you created are `collection.tar' and `music.tar'. We will also use the archive files `afiles.tar' and `bfiles.tar'. `afiles.tar' contains the members `apple', `angst', and `aspic'. `bfiles.tar' contains the members `./birds', `baboon', and `./box'. Unless we state otherwise, all practicing you do and examples you follow in this chapter will take place in the `practice' directory that you created in the previous chapter; see *Note prepare for examples::. (Below in this section, we will remind you of the state of the examples where the last chapter left them.) The five operations that we will cover in this chapter are: `--append' `-r' Add new entries to an archive that already exists. `--update' `-r' Add more recent copies of archive members to the end of an archive, if they exist. `--concatenate' `--catenate' `-A' Add one or more pre-existing archives to the end of another archive. `--delete' Delete items from an archive (does not work on tapes). `--compare' `--diff' `-d' Compare archive members to their counterparts in the file system. The Current State of the Practice Files --------------------------------------- Currently, the listing of the directory using `ls' is as follows: The archive file `collection.tar' looks like this: $ tar -tvf collection.tar The archive file `music.tar' looks like this: $ tar -tvf music.tar How to Add Files to Existing Archives: `--append' ------------------------------------------------- *(This message will disappear, once this node revised.)* If you want to add files to an existing archive, you don't need to create a new archive; you can use `--append' (`-r'). The archive must already exist in order to use `--append'. (A related operation is the `--update' operation; you can use this to add newer versions of archive members to an existing archive. To learn how to do this with `--update', *note update::..) If you use `--append' (`-r') to add a file that has the same name as an archive member to an archive containing that archive member, then the old member is not deleted. What does happen, however, is somewhat complex. `tar' *allows* you to have infinite numbers of files with the same name. Some operations treat these same-named members no differently than any other set of archive members: for example, if you view an archive with `--list' (`-t'), you will see all of those members listed, with their modification times, owners, etc. Other operations don't deal with these members as perfectly as you might prefer; if you were to use `--extract' (`--get', `-x') to extract the archive, only the most recently added copy of a member with the same name as four other members would end up in the working directory. This is because `--extract' extracts an archive in the order the members appeared in the archive; the most recently archived members will be extracted last. Additionally, an extracted member will *overwrite* a file of the same name which existed in the directory already, and `tar' will not prompt you about this. Thus, only the most recently archived member will end up being extracted, as it will overwrite the one extracted before it, and so on. There are a few ways to get around this. . If you want to replace an archive member, use `--delete' to delete the member you want to remove from the archive, , and then use `--append' to add the member you want to be in the archive. Note that you can not change the order of the archive; the most recently added member will still appear last. In this sense, you cannot truely "replace" one member with another. (Replacing one member with another will not work on certain types of media, such as tapes; see *Note delete:: and *Note Media::, for more information.) Appending Files to an Archive ............................. *(This message will disappear, once this node revised.)* The simplest way to add a file to an already existing archive is the `--append' (`-r') operation, which writes specified files into the archive whether or not they are already among the archived files. When you use `--append', you *must* specify file name arguments, as there is no default. If you specify a file that already exists in the archive, another copy of the file will be added to the end of the archive. As with other operations, the member names of the newly added files will be exactly the same as their names given on the command line. The `--verbose' (`-v') option will print out the names of the files as they are written into the archive. `--append' cannot be performed on some tape drives, unfortunately, due to deficiencies in the formats those tape drives use. The archive must be a valid `tar' archive, or else the results of using this operation will be unpredictable. *Note Media::. To demonstrate using `--append' to add a file to an archive, create a file called `rock' in the `practice' directory. Make sure you are in the `practice' directory. Then, run the following `tar' command to add `rock' to `collection.tar': $ tar --append --file=collection.tar rock If you now use the `--list' (`-t') operation, you will see that `rock' has been added to the archive: $ tar --list --file=collection.tar -rw-rw-rw- me user 28 1996-10-18 16:31 jazz -rw-rw-rw- me user 21 1996-09-23 16:44 blues -rw-rw-rw- me user 20 1996-09-23 16:44 folk -rw-rw-rw- me user 20 1996-09-23 16:44 rock Multiple Files with the Same Name ................................. You can use `--append' (`-r') to add copies of files which have been updated since the archive was created. (However, we do not recommend doing this since there is another `tar' option called `--update'; *note update::. for more information. We describe this use of `--append' here for the sake of completeness.) When you extract the archive, the older version will be effectively lost. This works because files are extracted from an archive in the order in which they were archived. Thus, when the archive is extracted, a file archived later in time will overwrite a file of the same name which was archived earlier, even though the older version of the file will remain in the archive unless you delete all versions of the file. Supposing you change the file `blues' and then append the changed version to `collection.tar'. As you saw above, the original `blues' is in the archive `collection.tar'. If you change the file and append the new version of the file to the archive, there will be two copies in the archive. When you extract the archive, the older version of the file will be extracted first, and then overwritten by the newer version when it is extracted. You can append the new, changed copy of the file `blues' to the archive in this way: $ tar --append --verbose --file=collection.tar blues blues Because you specified the `--verbose' option, `tar' has printed the name of the file being appended as it was acted on. Now list the contents of the archive: $ tar --list --verbose --file=collection.tar -rw-rw-rw- me user 28 1996-10-18 16:31 jazz -rw-rw-rw- me user 21 1996-09-23 16:44 blues -rw-rw-rw- me user 20 1996-09-23 16:44 folk -rw-rw-rw- me user 20 1996-09-23 16:44 rock -rw-rw-rw- me user 58 1996-10-24 18:30 blues The newest version of `blues' is now at the end of the archive (note the different creation dates and file sizes). If you extract the archive, the older version of the file `blues' will be overwritten by the newer version. You can confirm this by extracting the archive and running `ls' on the directory. *Note Writing:: for more information. (*Please note:* This is the case unless you employ the `--backup' option; .) Updating an Archive ------------------- *(This message will disappear, once this node revised.)* In the previous section, you learned how to use `--append' (`-r') to add a file to an existing archive. A related operation is `--update' (`-u'). The `--update' operation updates a `tar' archive by comparing the date of the specified archive members against the date of the file with the same name. If the file has been modified more recently than the archive member, then the newer version of the file is added to the archive (as with `--append' (`-r')). Unfortunately, you cannot use `--update' with magnetic tape drives. The operation will fail. Both `--update' and `--append' work by adding to the end of the archive. When you extract a file from the archive, only the version stored last will wind up in the file system, unless you use the `--backup' option (). How to Update an Archive Using `--update' ......................................... You must use file name arguments with the `--update' (`-u') operation. If you don't specify any files, `tar' won't act on any files and won't tell you that it didn't do anything (which may end up confusing you). To see the `--update' option at work, create a new file, `classical', in your practice directory, and some extra text to the file `blues', using any text editor. Then invoke `tar' with the `update' operation and the `--verbose' (`-v') option specified, using the names of all the files in the practice directory as file name arguments: $ tar --update -v -f collection.tar blues folk rock classical blues classical $ Because we have specified verbose mode, `tar' prints out the names of the files it is working on, which in this case are the names of the files that needed to be updated. If you run `tar --list' and look at the archive, you will see `blues' and `classical' at its end. There will be a total of two versions of the member `blues'; the one at the end will be newer and larger, since you added text before updating it. (The reason `tar' does not overwrite the older file when updating it is because writing to the middle of a section of tape is a difficult process. Tapes are not designed to go backward. *Note Media:: for more information about tapes. `--update' (`-u') is not suitable for performing backups for two reasons: it does not change directory content entries, and it lengthens the archive every time it is used. The GNU `tar' options intended specifically for backups are more efficient. If you need to run backups, please consult *Note Backups::. Combining Archives with `--concatenate' --------------------------------------- Sometimes it may be convenient to add a second archive onto the end of an archive rather than adding individual files to the archive. To add one or more archives to the end of another archive, you should use the `--concatenate' (`--catenate', `-A') operation. To use `--concatenate', name the archives to be concatenated on the command line. (Nothing happens if you don't list any.) The members, and their member names, will be copied verbatim from those archives. If this causes multiple members to have the same name, it does not delete any members; all the members with the same name coexist. For information on how this affects reading the archive, . To demonstrate how `--concatenate' works, create two small archives called `bluesrock.tar' and `folkjazz.tar', using the relevant files from `practice': $ tar -cvf bluesrock.tar blues rock blues classical $ tar -cvf folkjazz.tar folk jazz folk jazz If you like, You can run `tar --list' to make sure the archives contain what they are supposed to: $ tar -tvf bluesrock.tar -rw-rw-rw- melissa user 105 1997-01-21 19:42 blues -rw-rw-rw- melissa user 33 1997-01-20 15:34 rock $ tar -tvf folkjazz.tar -rw-rw-rw- melissa user 20 1996-09-23 16:44 folk -rw-rw-rw- melissa user 65 1997-01-30 14:15 jazz We can concatenate these two archives with `tar': $ cd .. $ tar --concatenate --file=bluesrock.tar jazzfolk.tar If you now list the contents of the `bluesclass.tar', you will see that now it also contains the archive members of `jazzfolk.tar': $ tar --list --file=bluesrock.tar blues rock jazz folk When you use `--concatenate', the source and target archives must already exist and must have been created using compatable format parameters (). The new, concatenated archive will be called by the same name as the first archive listed on the command line. Like `--append' (`-r'), this operation cannot be performed on some tape drives, due to deficiencies in the formats those tape drives use. It may seem more intuitive to you to want or try to use `cat' to concatenate two archives instead of using the `--concatenate' operation; after all, `cat' is the utility for combining files. However, `tar' archives incorporate an end-of-file marker which must be removed if the concatenated archives are to be read properly as one archive. `--concatenate' removes the end-of-archive marker from the target archive before each new archive is appended. If you use `cat' to combine the archives, the result will not be a valid `tar' format archive. If you need to retrieve files from an archive that was added to using the `cat' utility, use the `--ignore-zeros' (`-i') option. *Note Ignore Zeros:: for further information on dealing with archives improperly combined using the `cat' shell utility. You must specify the source archives using `--file=ARCHIVE-NAME' (`-f ARCHIVE-NAME') (*note file::.). If you do not specify the target archive, `tar' uses the value of the environment variable `TAPE', or, if this has not been set, the default archive name. Removing Archive Members Using `--delete' ----------------------------------------- *(This message will disappear, once this node revised.)* You can remove members from an archive by using the `--delete' option. Specify the name of the archive with `--file=ARCHIVE-NAME' (`-f ARCHIVE-NAME') and then specify the names of the members to be deleted; if you list no member names, nothing will be deleted. The `--verbose' (`-v') option will cause `tar' to print the names of the members as they are deleted. As with `--extract' (`--get', `-x'), you must give the exact member names when using `tar --delete'. `--delete' will remove all versions of the named file from the archive. The `--delete' operation can run very slowly. Unlike other operations, `--delete' has no short form. This operation will rewrite the archive. You can only use `--delete' on an archive if the archive device allows you to write to any point on the media, such as a disk; because of this, it does not work on magnetic tapes. Do not try to delete an archive member from a magnetic tape; the action will not succeed, and you will be likely to scramble the archive and damage your tape. There is no safe way (except by completely re-writing the archive) to delete files from most kinds of magnetic tape. *Note Media::. To delete all versions of the file `blues' from the archive `collection.tar' in the `practice' directory, make sure you are in that directory, and then, $ tar --list --file=collection.tar blues folk jazz rock practice/blues practice/folk practice/jazz practice/rock practice/blues $ tar --delete --file=collection.tar blues $ tar --list --file=collection.tar folk jazz rock $ The `--delete' option has been reported to work properly when `tar' acts as a filter from `stdin' to `stdout'. Comparing Archive Members with the File System ---------------------------------------------- *(This message will disappear, once this node revised.)* The `--compare' (`-d'), or `--diff' operation compares specified archive members against files with the same names, and then reports differences in file size, mode, owner, modification date and contents. You should *only* specify archive member names, not file names. If you do not name any members, then `tar' will compare the entire archive. If a file is represented in the archive but does not exist in the file system, `tar' reports a difference. You have to specify the record size of the archive when modifying an archive with a non-default record size. `tar' ignores files in the file system that do not have corresponding members in the archive. The following example compares the archive members `rock', `blues' and `funk' in the archive `bluesrock.tar' with files of the same name in the file system. (Note that there is no file, `funk'; `tar' will report an error message.) $ tar --compare --file=bluesrock.tar rock blues funk rock blues tar: funk not found in archive Depending on the system where you are running `tar' and the version you are running, `tar' may have a different error message, such as: funk: does not exist The spirit behind the `--compare' (`--diff', `-d') option is to check whether the archive represents the current state of files on disk, more than validating the integrity of the archive media. For this later goal, *Note verify::. Options Used by `--extract' =========================== *(This message will disappear, once this node revised.)* The previous chapter showed how to use `--extract' (`--get', `-x') to extract an archive into the filesystem. Various options cause `tar' to extract more information than just file contents, such as the owner, the permissions, the modification date, and so forth. This section presents options to be used with `--extract' when certain special considerations arise. You may review the information presented in *Note extract:: for more basic information about the `--extract' operation. Options to Help Read Archives ----------------------------- *(This message will disappear, once this node revised.)* Normally, `tar' will request data in full record increments from an archive storage device. If the device cannot return a full record, `tar' will report an error. However, some devices do not always return full records, or do not require the last record of an archive to be padded out to the next record boundary. To keep reading until you obtain a full record, or to accept an incomplete record if it contains an end-of-archive marker, specify the `--read-full-records' (`-B') option in conjunction with the `--extract' (`--get', `-x') or `--list' (`-t') operations. *Note Blocking::. The `--read-full-records' (`-B') option is turned on by default when `tar' reads an archive from standard input, or from a remote machine. This is because on BSD Unix systems, attempting to read a pipe returns however much happens to be in the pipe, even if it is less than was requested. If this option were not enabled, `tar' would fail as soon as it read an incomplete record from the pipe. If you're not sure of the blocking factor of an archive, you can read the archive by specifying `--read-full-records' (`-B') and `--blocking-factor=512-SIZE' (`-b 512-SIZE'), using a blocking factor larger than what the archive uses. This lets you avoid having to determine the blocking factor of an archive. *Note Blocking Factor::. Reading Full Records .................... `--read-full-records' `-B' Use in conjunction with `--extract' (`--get', `-x') to read an archive which contains incomplete records, or one which has a blocking factor less than the one specified. Ignoring Blocks of Zeros ........................ Normally, `tar' stops reading when it encounters a block of zeros between file entries (which usually indicates the end of the archive). `--ignore-zeros' (`-i') allows `tar' to completely read an archive which contains a block of zeros before the end (i.e. a damaged archive, or one which was created by `cat'-ing several archives together). The `--ignore-zeros' (`-i') option is turned off by default because many versions of `tar' write garbage after the end-of-archive entry, since that part of the media is never supposed to be read. GNU `tar' does not write after the end of an archive, but seeks to maintain compatablity among archiving utilities. `--ignore-zeros' `-i' To ignore blocks of zeros (ie. end-of-archive entries) which may be encountered while reading an archive. Use in conjunction with `--extract' (`--get', `-x') or `--list' (`-t'). Ignore Fail Read ................ `--ignore-failed-read' Do not exit with nonzero on unreadable files or directories. Changing How `tar' Writes Files ------------------------------- *(This message will disappear, once this node revised.)* Options to Prevent Overwriting Files .................................... Normally, `tar' writes extracted files into the file system without regard to the files already on the system; i.e., files with the same names as archive members are overwritten when the archive is extracted. If the name of a corresponding file name is a symbolic link, the file pointed to by the symbolic link will be overwritten instead of the symbolic link itself (if this is possible). Moreover, special devices, empty directories and even symbolic links are automatically removed if they are found to be on the way of the proper extraction. To prevent `tar' from extracting an archive member from an archive if doing so will overwrite a file in the file system, use `--keep-old-files' (`-k') in conjunction with `--extract'. When this option is specified, `tar' will report an error stating the name of the files in conflict instead of overwriting the file with the corresponding extracted archive member. The `--unlink-first' (`-U') option removes existing files, symbolic links, empty directories, devices, etc., *prior* to extracting over them. In particular, using this option will prevent replacing an already existing symbolic link by the name of an extracted file, since the link itself is removed prior to the extraction, rather than the file it points to. On some systems, the backing store for the executable *is* the original program text. You could use the `--unlink-first' (`-U') option to prevent segmentation violations or other woes when extracting arbitrary executables over currently running copies. Note that if something goes wrong with the extraction and you *did* use this option, you might end up with no file at all. Without this option, if something goes wrong with the extraction, the existing file is not overwritten and preserved. If you specify the `--recursive-unlink' option, `tar' removes *anything* that keeps you from extracting a file as far as current permissions will allow it. This could include removal of the contents of a full directory hierarchy. For example, someone using this feature may be very surprised at the results when extracting a directory entry from the archive. This option can be dangerous; be very aware of what you are doing if you choose to use it. Keep Old Files .............. `--keep-old-files' `-k' Do not overwrite existing files from archive. The `--keep-old-files' (`-k') option prevents `tar' from over-writing existing files with files with the same name from the archive. The `--keep-old-files' (`-k') option is meaningless with `--list' (`-t'). Prevents `tar' from overwriting files in the file system during extraction. Unlink First ............ `--unlink-first' `-U' Try removing files before extracting over them, instead of trying to overwrite them. Recursive Unlink ................ `--recursive-unlink' When this option is specified, try removing files and directory hierarchies before extracting over them. *This is a dangerous option!* Some people argue that GNU `tar' should not hesitate to overwrite files with other files when extracting. When extracting a `tar' archive, they expect to see a faithful copy of the state of the filesystem when the archive was created. It is debatable that this would always be a proper behaviour. For example, suppose one has an archive in which `usr/local' is a link to `usr/local2'. Since then, maybe the site removed the link and renamed the whole hierarchy from `/usr/local2' to `/usr/local'. Such things happen all the time. I guess it would not be welcome at all that GNU `tar' removes the whole hierarchy just to make room for the link to be reinstated (unless it *also* simultaneously restores the full `/usr/local2', of course! GNU `tar' is indeed able to remove a whole hierarchy to reestablish a symbolic link, for example, but *only if* `--recursive-unlink' is specified to allow this behaviour. In any case, single files are silently removed. Setting Modification Times .......................... Normally, `tar' sets the modification times of extracted files to the modification times recorded for the files in the archive, but limits the permissions of extracted files by the current `umask' setting. To set the modification times of extracted files to the time when the files were extracted, use the `--touch' (`-m') option in conjunction with `--extract' (`--get', `-x'). `--touch' `-m' Sets the modification time of extracted archive members to the time they were extracted, not the time recorded for them in the archive. Use in conjunction with `--extract' (`--get', `-x'). Setting Access Permissions .......................... To set the modes (access permissions) of extracted files to those recorded for those files in the archive, use `--same-persmissions' in conjunction with the `--extract' (`--get', `-x') operation. `--preserve-permission' `--same-permission' `--ignore-umask' `-p' Set modes of extracted archive members to those recorded in the archive, instead of current umask settings. Use in conjunction with `--extract' (`--get', `-x'). Writing to Standard Output .......................... To write the extracted files to the standard output, instead of creating the files on the file system, use `--to-stdout' (`-O') in conjunction with `--extract' (`--get', `-x'). This option is useful if you are extracting files to send them through a pipe, and do not need to preserve them in the file system. If you extract multiple members, they appear on standard output concatenated, in the order they are found in the archive. `--to-stdout' `-O' Writes files to the standard output. Used in conjunction with `--extract' (`--get', `-x'). Extract files to standard output. When this option is used, instead of creating the files specified, `tar' writes the contents of the files extracted to its standard output. This may be useful if you are only extracting the files in order to send them through a pipe. This option is meaningless with `--list' (`-t'). Removing Files .............. `--remove-files' Remove files after adding them to the archive. Coping with Scarce Resources ---------------------------- *(This message will disappear, once this node revised.)* Starting File ............. `--starting-file=NAME' `-K NAME' Starts an operation in the middle of an archive. Use in conjunction with `--extract' (`--get', `-x') or `--list' (`-t'). If a previous attempt to extract files failed due to lack of disk space, you can use `--starting-file=NAME' (`-K NAME') to start extracting only after member NAME of the archive. This assumes, of course, that there is now free space, or that you are now extracting into a different file system. (You could also choose to suspend `tar', remove unnecessary files from the file system, and then restart the same `tar' operation. In this case, `--starting-file=NAME' (`-K NAME') is not necessary. *Note Inc Dumps::, *Note interactive::, and *Note exclude::.) Same Order .......... `--same-order' `--preserve-order' `-s' To process large lists of file names on machines with small amounts of memory. Use in conjunction with `--compare' (`--diff', `-d'), `--list' (`-t') or `--extract' (`--get', `-x'). The `--same-order' (`--preserve-order', `-s') option tells `tar' that the list of file names to be listed or extracted is sorted in the same order as the files in the archive. This allows a large list of names to be used, even on a small machine that would not otherwise be able to hold all the names in memory at the same time. Such a sorted list can easily be created by running `tar -t' on the archive and editing its output. This option is probably never needed on modern computer systems. Backup options ============== GNU `tar' offers options for making backups of files before writing new versions. These options control the details of these backups. They may apply to the archive itself before it is created or rewritten, as well as individual extracted members. Other GNU programs (`cp', `install', `ln', and `mv', for example) offer similar options. Backup options may prove unexpectedly useful when extracting archives containing many members having identical name, or when extracting archives on systems having file name limitations, making different members appear has having similar names through the side-effect of name truncation. (This is true only if we have a good scheme for truncated backup names, which I'm not sure at all: I suspect work is needed in this area.) When any existing file is backed up before being overwritten by extraction, then clashing files are automatically be renamed to be unique, and the true name is kept for only the last file of a series of clashing files. By using verbose mode, users may track exactly what happens. At the detail level, some decisions are still experimental, and may change in the future, we are waiting comments from our users. So, please do not learn to depend blindly on the details of the backup features. For example, currently, directories themselves are never renamed through using these options, so, extracting a file over a directory still has good chances to fail. Also, backup options apply to created archives, not only to extracted members. For created archives, backups will not be attempted when the archive is a block or character device, or when it refers to a remote file. For the sake of simplicity and efficiency, backups are made by renaming old files prior to creation or extraction, and not by copying. The original name is restored if the file creation fails. If a failure occurs after a partial extraction of a file, both the backup and the partially extracted file are kept. `--backup' Make backups of files that are about to be overwritten or removed. Without this option, the original versions are destroyed. `--suffix=SUFFIX' Append SUFFIX to each backup file made with `-b'. If this option is not specified, the value of the `SIMPLE_BACKUP_SUFFIX' environment variable is used. And if `SIMPLE_BACKUP_SUFFIX' is not set, the default is `~', just as in Emacs. `--version-control=METHOD' Use METHOD to determine the type of backups made with `--backup'. If this option is not specified, the value of the `VERSION_CONTROL' environment variable is used. And if `VERSION_CONTROL' is not set, the default backup type is `existing'. This option corresponds to the Emacs variable `version-control'; the same values for METHOD are accepted as in Emacs. This options also more descriptive name. The valid METHODs (unique abbreviations are accepted): `t' `numbered' Always make numbered backups. `nil' `existing' Make numbered backups of files that already have them, simple backups of the others. `never' `simple' Always make simple backups. Some people express the desire to *always* use the OP-BACKUP option, by defining some kind of alias or script. This is not as easy as one may thing, due to the fact old style options should appear first and consume arguments a bit inpredictably for an alias or script. But, if you are ready to give up using old style options, you may resort to using something like (a Bourne shell function here): tar () { /usr/local/bin/tar --backup $*; } Notable `tar' Usages ==================== *(This message will disappear, once this node revised.)* You can easily use archive files to transport a group of files from one system to another: put all relevant files into an archive on one computer system, transfer the archive to another system, and extract the contents there. The basic transfer medium might be magnetic tape, Internet FTP, or even electronic mail (though you must encode the archive with `uuencode' in order to transport it properly by mail). Both machines do not have to use the same operating system, as long as they both support the `tar' program. For example, here is how you might copy a directory's contents from one disk to another, while preserving the dates, modes, owners and link-structure of all the files therein. In this case, the transfer medium is a "pipe", which is one a Unix redirection mechanism: $ cd sourcedir; tar -cf - . | (cd targetdir; tar -xf -) The command also works using short option forms: $ cd sourcedir; tar --create --file=- . | (cd targetdir; tar --extract --file=-) This is one of the easiest methods to transfer a `tar' archive. Looking Ahead: The Rest of this Manual ====================================== You have now seen how to use all eight of the operations available to `tar', and a number of the possible options. The next chapter explains how to choose and change file and archive names, how to use files to store names of other files which you can then call as arguments to `tar' (this can help you save time if you expect to archive the same list of files a number of times), and how to If there are too many files to conveniently list on the command line, you can list the names in a file, and `tar' will read that file. *Note files::. There are various ways of causing `tar' to skip over some files, and not archive them. *Note Choosing::. Performing Backups and Restoring Files ************************************** *(This message will disappear, once this node revised.)* GNU `tar' is distributed along with the scripts which the Free Software Foundation uses for performing backups. There is no corresponding scripts available yet for doing restoration of files. Even if there is a good chance those scripts may be satisfying to you, they are not the only scripts or methods available for doing backups and restore. You may well create your own, or use more sophisticated packages dedicated to that purpose. Some users are enthusiastic about `Amanda' (The Advanced Maryland Automatic Network Disk Archiver), a backup system developed by James da Silva `jds@cs.umd.edu' and available on many Unix systems. This is free software, and it is available at these places: http://www.cs.umd.edu/projects/amanda/amanda.html ftp://ftp.cs.umd.edu/pub/amanda Here is a possible plan for a future documentation about the backuping scripts which are provided within the GNU `tar' distribution. .* dumps . + what are dumps . + different levels of dumps . - full dump = dump everything . - level 1, level 2 dumps etc, - A level n dump dumps everything changed since the last level n-1 dump (?) . + how to use scripts for dumps (ie, the concept) . - scripts to run after editing backup specs (details) . + Backup Specs, what is it. . - how to customize . - actual text of script [/sp/dump/backup-specs] . + Problems . - rsh doesn't work . - rtape isn't installed . - (others?) . + the --incremental option of tar . + tapes . - write protection . - types of media . : different sizes and types, useful for different things . - files and tape marks one tape mark between files, two at end. . - positioning the tape MT writes two at end of write, backspaces over one when writing again. This chapter documents both the provided FSF scripts and `tar' options which are more specific to usage as a backup tool. To "back up" a file system means to create archives that contain all the files in that file system. Those archives can then be used to restore any or all of those files (for instance if a disk crashes or a file is accidently deleted). File system "backups" are also called "dumps". Using `tar' to Perform Full Dumps ================================= *(This message will disappear, once this node revised.)* Full dumps should only be made when no other people or programs are modifying files in the filesystem. If files are modified while `tar' is making the backup, they may not be stored properly in the archive, in which case you won't be able to restore them if you have to. (Files not being modified are written with no trouble, and do not corrupt the entire archive.) You will want to use the `--label=ARCHIVE-LABEL' (`-V ARCHIVE-LABEL') option to give the archive a volume label, so you can tell what this archive is even if the label falls off the tape, or anything like that. Unless the filesystem you are dumping is guaranteed to fit on one volume, you will need to use the `--multi-volume' (`-M') option. Make sure you have enough tapes on hand to complete the backup. If you want to dump each filesystem separately you will need to use the `--one-file-system' (`-l') option to prevent `tar' from crossing filesystem boundaries when storing (sub)directories. The `--incremental' (`-G') option is not needed, since this is a complete copy of everything in the filesystem, and a full restore from this backup would only be done onto a completely empty disk. Unless you are in a hurry, and trust the `tar' program (and your tapes), it is a good idea to use the `--verify' (`-W') option, to make sure your files really made it onto the dump properly. This will also detect cases where the file was modified while (or just after) it was being archived. Not all media (notably cartridge tapes) are capable of being verified, unfortunately. `--listed-incremental=SNAPSHOT-FILE' (`-g SNAPSHOT-FILE') take a file name argument always. If the file doesn't exist, run a level zero dump, creating the file. If the file exists, uses that file to see what has changed. `--incremental' (`-G') `--incremental' (`-G') handle old GNU-format incremental backup. This option should only be used when creating an incremental backup of a filesystem. When the `--incremental' (`-G') option is used, `tar' writes, at the beginning of the archive, an entry for each of the directories that will be operated on. The entry for a directory includes a list of all the files in the directory at the time the dump was done, and a flag for each file indicating whether the file is going to be put in the archive. This information is used when doing a complete incremental restore. Note that this option causes `tar' to create a non-standard archive that may not be readable by non-GNU versions of the `tar' program. The `--incremental' (`-G') option means the archive is an incremental backup. Its meaning depends on the command that it modifies. If the `--incremental' (`-G') option is used with `--list' (`-t'), `tar' will list, for each directory in the archive, the list of files in that directory at the time the archive was created. This information is put out in a format that is not easy for humans to read, but which is unambiguous for a program: each file name is preceded by either a `Y' if the file is present in the archive, an `N' if the file is not included in the archive, or a `D' if the file is a directory (and is included in the archive). Each file name is terminated by a null character. The last file is followed by an additional null and a newline to indicate the end of the data. If the `--incremental' (`-G') option is used with `--extract' (`--get', `-x'), then when the entry for a directory is found, all files that currently exist in that directory but are not listed in the archive *are deleted from the directory*. This behavior is convenient when you are restoring a damaged file system from a succession of incremental backups: it restores the entire state of the file system to that which obtained when the backup was made. If you don't use `--incremental' (`-G'), the file system will probably fill up with files that shouldn't exist any more. `--listed-incremental=SNAPSHOT-FILE' (`-g SNAPSHOT-FILE') handle new GNU-format incremental backup. This option handles new GNU-format incremental backup. It has much the same effect as `--incremental' (`-G'), but also the time when the dump is done and the list of directories dumped is written to the given FILE. When restoring, only files newer than the saved time are restored, and the direcotyr list is used to speed up operations. `--listed-incremental=SNAPSHOT-FILE' (`-g SNAPSHOT-FILE') acts like `--incremental' (`-G'), but when used in conjunction with `--create' (`-c') will also cause `tar' to use the file FILE, which contains information about the state of the filesystem at the time of the last backup, to decide which files to include in the archive being created. That file will then be updated by `tar'. If the file FILE does not exist when this option is specified, `tar' will create it, and includ