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 version 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 interface can be used to manage one or mul‐
tiple 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 required. 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 behavior at all.
Even with multiple Postfix instances, you can keep using the same postfix 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-instance configuration.
MANAGING AN INDIVIDUAL POSTFIX INSTANCE
To manage a specific Postfix instance, specify its configuration directory on the postfix(1) command line:
# postfix -c /path/to/config_directory command
Alternatively, the postfix(1) command accepts the instance's configuration directory via the MAIL_CONFIG envi‐
ronment variable (the -c command-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 (currently installed in the daemon directory). This file contains the commands
that start or stop one Postfix instance, that upgrade the configuration 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 default Postfix instance's main.cf file, 1)
specify the pathname of a multi-instance manager program with the multi_instance_wrapper parameter; 2) popu‐
late the multi_instance_directories parameter with the configuration directory pathnames of additional Postfix
instances. For example:
postfix-script file. This multi-instance manager in turn executes the postfix(1) command in single-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 's/,/ /'` || 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 control 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 manager to start (stop, etc.) the corre‐
sponding 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 manager 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-permissions" or "upgrade-configuration", and it will replace "start" by "check" so that
problems will be reported even when the instance is disabled.
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
below for a list of per-instance files.
Before Postfix multi-instance support was implemented, the executables, manpages, etc., have always been main‐
tained as part of the default Postfix instance.
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 environment. 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_instance_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 param‐
eter value to the legacy alternate_config_directories parameter value. The commands use this information 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 instance.
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 directories; these directories belong to addi‐
tional 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 postfix(1) command invokes when the
multi_instance_directories parameter 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
$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
POSTFIX-WRAPPER(5)
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