man > postfix-wrapper(5)

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 multiple Postfix instances, and gives details of an API to  coordinate  activi‐
       ties 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,  com‐
       mands 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 in‐
       stances 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 environment 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 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 default Postfix  instance's
       main.cf  file, 1) specify the pathname of a multi-instance manager program with the multi_in‐
       stance_wrapper parameter; 2) populate the multi_instance_directories parameter with the  con‐
       figuration 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 instruc‐
       tions for creating Postfix instances by hand.  The postmulti(1) command provides a  more  ex‐
       tensive implementation including support for life-cycle management.

       The  multi_instance_directories and other main.cf parameters are listed below in the CONFIGU‐
       RATION PARAMETERS section.

       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 post‐
       fix(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-in‐
       stance manager operates on that instance.  This section discusses  the  most  important  set‐
       tings.

       The  setting  "multi_instance_enable = yes" allows the multi-instance manager to start (stop,
       etc.) the corresponding Postfix instance. For safety reasons, this setting  is  not  the  de‐
       fault.

       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 "up‐
       grade-configuration", and it will replace "start" by "check" so that  problems  will  be  re‐
       ported 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 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_instance_enable  configura‐
       tion  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 re‐
       cursion.

       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.   There‐
       fore,  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_in‐
       stance_directories  parameter  value  to  the  legacy  alternate_config_directories parameter
       value. The commands use this information to determine whether a -c option or MAIL_CONFIG  en‐
       vironment 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 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 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 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

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