POSTFIX-WRAPPER(5) File Formats Manual POSTFIX-WRAPPER(5)
NAME
postfix-wrapper - Postfix multi-instance API
DESCRIPTION
Support for managing multiple Postfix instances is available as of ver-
sion 2.6. Instances share executable files and documentation, but have
their own directories for configuration, queue and data files.
This document describes how the familiar "postfix start" etc. user in-
terface can be used to manage one or multiple Postfix instances, and
gives details of an API to coordinate activities between the postfix(1)
command and a multi-instance manager program.
With multi-instance support, the default Postfix instance is always re-
quired. This instance is identified by the config_directory parameter's
default value.
GENERAL OPERATION
Multi-instance support is backwards compatible: when you run only one
Postfix instance, commands such as "postfix start" will not change be-
havior at all.
Even with multiple Postfix instances, you can keep using the same post-
fix commands in boot scripts, upgrade procedures, and other places. The
commands do more work, but humans are not forced to learn new tricks.
For example, to start all Postfix instances, use:
# postfix start
Other postfix(1) commands also work as expected. For example, to find
out what Postfix instances exist in a multi-instance configuration, use:
# postfix status
This enumerates the status of all Postfix instances within a multi-in-
stance configuration.
MANAGING AN INDIVIDUAL POSTFIX INSTANCE
To manage a specific Postfix instance, specify its configuration direc-
tory on the postfix(1) command line:
# postfix -c /path/to/config_directory command
Alternatively, the postfix(1) command accepts the instance's configura-
tion directory via the MAIL_CONFIG environment variable (the -c com-
mand-line option has higher precedence).
Otherwise, the postfix(1) command will operate on all Postfix instances.
ENABLING POSTFIX(1) MULTI-INSTANCE MODE
By default, the postfix(1) command operates in single-instance mode. In
this mode the command invokes the postfix-script file directly (cur-
rently installed in the daemon directory). This file contains the com-
mands that start or stop one Postfix instance, that upgrade the configu-
ration of one Postfix instance, and so on.
When the postfix(1) command operates in multi-instance mode as discussed
below, the command needs to execute start, stop, etc. commands for each
Postfix instance. This multiplication of commands is handled by a
multi-instance manager program.
Turning on postfix(1) multi-instance mode goes as follows: in the de-
fault Postfix instance's main.cf file, 1) specify the pathname of a
multi-instance manager program with the multi_instance_wrapper parame-
ter; 2) populate the multi_instance_directories parameter with the con-
figuration directory pathnames of additional Postfix instances. For ex-
ample:
/etc/postfix/main.cf:
multi_instance_wrapper = $daemon_directory/postfix-wrapper
multi_instance_directories = /etc/postfix-test
The $daemon_directory/postfix-wrapper file implements a simple manager
and contains instructions for creating Postfix instances by hand. The
postmulti(1) command provides a more extensive implementation including
support for life-cycle management.
The multi_instance_directories and other main.cf parameters are listed
below in the CONFIGURATION PARAMETERS section.
In multi-instance mode, the postfix(1) command invokes the $multi_in-
stance_wrapper command instead of the postfix-script file. This
multi-instance manager in turn executes the postfix(1) command in sin-
gle-instance mode for each Postfix instance.
To illustrate the main ideas behind multi-instance operation, below is
an example of a simple but useful multi-instance manager implementation:
#!/bin/sh
: ${command_directory?"do not invoke this command directly"}
POSTCONF=$command_directory/postconf
POSTFIX=$command_directory/postfix
instance_dirs=`$POSTCONF -h multi_instance_directories |
sed 'y/,/ /'` || exit 1
err=0
for dir in $config_directory $instance_dirs
do
case "$1" in
stop|abort|flush|reload|drain)
test "`$POSTCONF -c $dir -h multi_instance_enable`" \
= yes || continue;;
start)
test "`$POSTCONF -c $dir -h multi_instance_enable`" \
= yes || {
$POSTFIX -c $dir check || err=$?
continue
};;
esac
$POSTFIX -c $dir "$@" || err=$?
done
exit $err
PER-INSTANCE MULTI-INSTANCE MANAGER CONTROLS
Each Postfix instance has its own main.cf file with parameters that con-
trol how the multi-instance manager operates on that instance. This
section discusses the most important settings.
The setting "multi_instance_enable = yes" allows the multi-instance man-
ager to start (stop, etc.) the corresponding Postfix instance. For
safety reasons, this setting is not the default.
The default setting "multi_instance_enable = no" is useful for manual
testing with "postfix -c /path/name start" etc. The multi-instance man-
ager will not start such an instance, and it will skip commands such as
"stop" or "flush" that require a running Postfix instance. The
multi-instance manager will execute commands such as "check", "set-per-
missions" or "upgrade-configuration", and it will replace "start" by
"check" so that problems will be reported even when the instance is dis-
abled.
MAINTAINING SHARED AND NON-SHARED FILES
Some files are shared between Postfix instances, such as executables and
manpages, and some files are per-instance, such as configuration files,
mail queue files, and data files. See the NON-SHARED FILES section be-
low for a list of per-instance files.
Before Postfix multi-instance support was implemented, the executables,
manpages, etc., have always been maintained as part of the default Post-
fix instance.
With multi-instance support, we simply continue to do this. Specifi-
cally, a Postfix instance will not check or update shared files when
that instance's config_directory value is listed with the default
main.cf file's multi_instance_directories parameter.
The consequence of this approach is that the default Postfix instance
should be checked and updated before any other instances.
MULTI-INSTANCE API SUMMARY
Only the multi-instance manager implements support for the multi_in-
stance_enable configuration parameter. The multi-instance manager will
start only Postfix instances whose main.cf file has "multi_instance_en-
able = yes". A setting of "no" allows a Postfix instance to be tested by
hand.
The postfix(1) command operates on only one Postfix instance when the -c
option is specified, or when MAIL_CONFIG is present in the process envi-
ronment. This is necessary to terminate recursion.
Otherwise, when the multi_instance_directories parameter value is
non-empty, the postfix(1) command executes the command specified with
the multi_instance_wrapper parameter, instead of executing the commands
in postfix-script.
The multi-instance manager skips commands such as "stop" or "reload"
that require a running Postfix instance, when an instance does not have
"multi_instance_enable = yes". This avoids false error messages.
The multi-instance manager replaces a "start" command by "check" when a
Postfix instance's main.cf file does not have "multi_instance_enable =
yes". This substitution ensures that problems will be reported even when
the instance is disabled.
No Postfix command or script will update or check shared files when its
config_directory value is listed in the default main.cf's multi_in-
stance_directories parameter value. Therefore, the default instance
should be checked and updated before any Postfix instances that depend
on it.
Set-gid commands such as postdrop(1) and postqueue(1) effectively append
the multi_instance_directories parameter value to the legacy alter-
nate_config_directories parameter value. The commands use this informa-
tion to determine whether a -c option or MAIL_CONFIG environment setting
specifies a legitimate value.
The legacy alternate_config_directories parameter remains necessary for
non-default Postfix instances that are running different versions of
Postfix, or that are not managed together with the default Postfix in-
stance.
ENVIRONMENT VARIABLES
MAIL_CONFIG
When present, this forces the postfix(1) command to operate only
on the specified Postfix instance. This environment variable is
exported by the postfix(1) -c option, so that postfix(1) commands
in descendant processes will work correctly.
CONFIGURATION PARAMETERS
The text below provides only a parameter summary. See postconf(5) for
more details.
multi_instance_directories (empty)
An optional list of non-default Postfix configuration directo-
ries; these directories belong to additional Postfix instances
that share the Postfix executable files and documentation with
the default Postfix instance, and that are started, stopped,
etc., together with the default Postfix instance.
multi_instance_wrapper (empty)
The pathname of a multi-instance manager command that the post-
fix(1) command invokes when the multi_instance_directories para-
meter value is non-empty.
multi_instance_name (empty)
The optional instance name of this Postfix instance.
multi_instance_group (empty)
The optional instance group name of this Postfix instance.
multi_instance_enable (no)
Allow this Postfix instance to be started, stopped, etc., by a
multi-instance manager.
NON-SHARED FILES
config_directory (see 'postconf -d' output)
The default location of the Postfix main.cf and master.cf config-
uration files.
data_directory (see 'postconf -d' output)
The directory with Postfix-writable data files (for example:
caches, pseudo-random numbers).
queue_directory (see 'postconf -d' output)
The location of the Postfix top-level queue directory.
SEE ALSO
postfix(1) Postfix control program
postmulti(1) full-blown multi-instance manager
$daemon_directory/postfix-wrapper simple multi-instance manager
LICENSE
The Secure Mailer license must be distributed with this software.
AUTHOR(S)
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
POSTFIX-WRAPPER(5)
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