.\"	$NetBSD: spawn.8,v 1.5 2025/02/25 19:15:43 christos Exp $
.\"
.TH SPAWN 8 
.ad
.fi
.SH NAME
spawn
\-
Postfix external command spawner
.SH "SYNOPSIS"
.na
.nf
\fBspawn\fR [generic Postfix daemon options] command_attributes...
.SH DESCRIPTION
.ad
.fi
The \fBspawn\fR(8) daemon monitors a TCP or UNIX\-domain stream
socket, configured in \fBmaster.cf\fR with a service type
\fBinet\fR or \fBunix\fR.

This daemon spawns an external command whenever a connection
is established, with the standard input, output and error file
descriptors connected to the remote client.

The command process is subject to the time limit specified
with the parameter \fItransport\fR_time_limit (default:
command_time_limit) where \fItransport\fR equals the service
name field in master.cf. A process that exceeds the time limit
will receive a SIGKILL signal.

The \fBspawn\fR(8) daemon service typically has a process limit >
1 in its \fBmaster.cf\fR service definition, so that the number
of processes can scale with demand.
.SH "COMMAND ATTRIBUTE SYNTAX"
.na
.nf
.ad
.fi
The external command attributes are given in the \fBmaster.cf\fR
file at the end of a service definition.  The syntax is as follows:
.IP "\fBuser\fR=\fIusername\fR (required)"
.IP "\fBuser\fR=\fIusername\fR:\fIgroupname\fR"
The external command is executed with the rights of the
specified \fIusername\fR.  The software refuses to execute
commands with root privileges, or with the privileges of the
mail system owner. If \fIgroupname\fR is specified, the
corresponding group ID is used instead of the group ID
of \fIusername\fR.
.IP "\fBargv\fR=\fIcommand\fR... (required)"
The command to be executed. This must be specified as the
last command attribute.
The command is executed directly, i.e. without interpretation of
shell meta characters by a shell command interpreter.
.sp
If a command argument must contain whitespace, or if a command
argument must begin with "{", enclose the argument with "{" and
"}". This form will ignore whitespace after the outer "{" and
before the outer "}". Example:
.sp
.fi
    argv=/bin/sh \-c { shell syntax here }
.SH DIAGNOSTICS
.ad
.fi
The \fBspawn\fR(8) daemon reports abnormal child exits.
Problems are logged to \fBsyslogd\fR(8) or \fBpostlogd\fR(8).
.SH "SECURITY"
.na
.nf
.fi
.ad
The \fBspawn\fR(8) daemon needs root privilege in order to
execute external commands as the specified user. It is therefore
security sensitive.

However, the \fBspawn\fR(8) daemon does not receive data from
or about service clients or external commands, and thus is not
vulnerable to data\-driven attacks.
.SH "CONFIGURATION PARAMETERS"
.na
.nf
.ad
.fi
Changes to \fBmain.cf\fR are picked up automatically as \fBspawn\fR(8)
processes run for only a limited amount of time. Use the command
"\fBpostfix reload\fR" to speed up a change.

The text below provides only a parameter summary. See
\fBpostconf\fR(5) for more details including examples.

In the text below, \fItransport\fR is the first field of the entry
in the \fBmaster.cf\fR file.
.SH "RESOURCE AND RATE CONTROL"
.na
.nf
.ad
.fi
.IP "\fBtransport_time_limit ($command_time_limit)\fR"
A transport\-specific override for the command_time_limit parameter
value, where \fItransport\fR is the master.cf name of the message
delivery transport.
.SH "MISCELLANEOUS"
.na
.nf
.ad
.fi
.IP "\fBconfig_directory (see 'postconf -d' output)\fR"
The default location of the Postfix main.cf and master.cf
configuration files.
.IP "\fBdaemon_timeout (18000s)\fR"
How much time a Postfix daemon process may take to handle a
request before it is terminated by a built\-in watchdog timer.
.IP "\fBexport_environment (see 'postconf -d' output)\fR"
The list of environment variables that a Postfix process will export
to non\-Postfix processes.
.IP "\fBipc_timeout (3600s)\fR"
The time limit for sending or receiving information over an internal
communication channel.
.IP "\fBmail_owner (postfix)\fR"
The UNIX system account that owns the Postfix queue and most Postfix
daemon processes.
.IP "\fBmax_idle (100s)\fR"
The maximum amount of time that an idle Postfix daemon process waits
for an incoming connection before terminating voluntarily.
.IP "\fBmax_use (100)\fR"
The maximal number of incoming connections that a Postfix daemon
process will service before terminating voluntarily.
.IP "\fBprocess_id (read\-only)\fR"
The process ID of a Postfix command or daemon process.
.IP "\fBprocess_name (read\-only)\fR"
The process name of a Postfix command or daemon process.
.IP "\fBqueue_directory (see 'postconf -d' output)\fR"
The location of the Postfix top\-level queue directory.
.IP "\fBsyslog_facility (mail)\fR"
The syslog facility of Postfix logging.
.IP "\fBsyslog_name (see 'postconf -d' output)\fR"
A prefix that is prepended to the process name in syslog
records, so that, for example, "smtpd" becomes "prefix/smtpd".
.PP
Available in Postfix 3.3 and later:
.IP "\fBservice_name (read\-only)\fR"
The master.cf service name of a Postfix daemon process.
.SH "SEE ALSO"
.na
.nf
postconf(5), configuration parameters
master(8), process manager
postlogd(8), Postfix logging
syslogd(8), system logging
.SH "LICENSE"
.na
.nf
.ad
.fi
The Secure Mailer license must be distributed with this software.
.SH "AUTHOR(S)"
.na
.nf
Wietse Venema
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA

Wietse Venema
Google, Inc.
111 8th Avenue
New York, NY 10011, USA