POSTFIX-WRAPPER(5) POSTFIX-WRAPPER(5)
NAME
postfix-wrapper - Postfix multi-instance API
DESCRIPTION
Postfix versions 2.6 and later provide support for multi-
ple Postfix instances. Instances share executable files
and documentation, but have their own directories for con-
figuration, queue and data files.
This document describes how the familiar "postfix start"
etc. user interface can be used to manage one or multiple
Postfix instances, and gives details of an API to coordi-
nate activities between the postfix(1) command and a
multi-instance manager program.
With multi-instance support, the default Postfix instance
is always required. The config_directory parameter's
default value specifies that instance's configuration file
location.
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 proce-
dures, 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 exam-
ple, 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 config-
uration 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
environment variable (the -c command-line option has
higher precedence).
When no Postfix instance information is specified, 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 post-
fix-script file directly (currently installed in the dae-
mon directory). This file contains the commands that
start or stop one Postfix instance, that upgrade the con-
figuration 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) populate the
multi_instance_directories parameter with the configura-
tion directory pathnames of additional Postfix instances.
For example:
/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 pro-
vides a more extensive implementation including support
for life-cycle management.
The multi_instance_directories and other main.cf parame-
ters are listed below in the CONFIGURATION PARAMETERS sec-
tion.
In multi-instance mode, the postfix(1) command invokes the
$multi_instance_wrapper command instead of the 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 opera-
tion, 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 param-
eters that control how the multi-instance manager operates
on that instance. This section discusses the most impor-
tant 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 set-
ting 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 maintained
as part of the default Postfix instance.
With multi-instance support, we simply continue to do
this. Specifically, 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 Post-
fix instance should be checked and updated before any
other instances.
MULTI-INSTANCE API SUMMARY
Only the multi-instance manager implements support for the
multi_instance_enable configuration parameter. The multi-
instance manager will start only Postfix instances whose
main.cf file has "multi_instance_enable = 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 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 parame-
ter, 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 parame-
ter 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 run-
ning different versions of Postfix, or that are not man-
aged 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 post-
fix(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 configura-
tion 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
config_directory (see 'postconf -d' output)
The default location of the Postfix main.cf and
master.cf configuration 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 direc-
tory.
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
POSTFIX-WRAPPER(5)