POSTFIX-WRAPPER(5)                                          POSTFIX-WRAPPER(5)

       postfix-wrapper - Postfix multi-instance API

       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.

       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,

              # postfix status

       This enumerates the status of all Postfix  instances  within  a  multi-
       instance configuration.

       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

       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 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

                  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 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-


              : ${command_directory?"do not invoke this command directly"}

              instance_dirs=`$POSTCONF -h multi_instance_directories |
                              sed 's/,/ /'` || exit 1

              for dir in $config_directory $instance_dirs
                  case "$1" in
                      test "`$POSTCONF -c $dir -h multi_instance_enable`" \
                          = yes || continue;;
                      test "`$POSTCONF -c $dir -h multi_instance_enable`" \
                          = yes || {
                          $POSTFIX -c $dir check || err=$?
                  $POSTFIX -c $dir "$@" || err=$?

              exit $err

       Each Postfix instance has its own  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

       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 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.

       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  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

       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 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'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

              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.

       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.

       config_directory (see 'postconf -d' output)
              The default location of the Postfix and  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.

       postfix(1) Postfix control program
       postmulti(1) full-blown multi-instance manager
       $daemon_directory/postfix-wrapper simple multi-instance manager

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       Wietse Venema
       IBM T.J. Watson Research
       P.O. Box 704
       Yorktown Heights, NY 10598, USA