Provided by: postfix_3.4.10-1ubuntu1_amd64 bug


       postfix-wrapper - Postfix multi-instance API


       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
       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.


       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.


       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.


       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 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 configuration directory pathnames of additional Postfix instances.  For example:

                  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

       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 implementation:


              : ${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-permissions" or "upgrade-configuration", and it will replace "start"  by  "check"  so
       that problems will be reported even when the instance is disabled.


       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 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 manager  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 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  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 instance.


              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.


       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


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

       data_directory (see 'postconf -d' output)
              The  directory with Postfix-writable data files (for example: caches, pseudo-random

       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


       The Secure Mailer license must be distributed with this software.


       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