    POSTFIX-WRAPPER(5)                                          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
           interface 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
           required.  This  instance is identified by the config_directory parame-
           ter'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 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-instance 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 config-
           uration of one Postfix instance, and so on.

           When  the  postfix(1)  command  operates in multi-instance mode as dis-
           cussed 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  parame-
           ter; 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 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_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 operation, below  is
           an  example  of  a simple but useful multi-instance manager implementa-
           tion:

                  #!/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
           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 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
           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-per-
           missions"  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 sec-
           tion 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.   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_instance_enable  configuration parameter. The multi-instance man-
           ager  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 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  parameter  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) com-
                  mands 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
                  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  con-
                  figuration 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)