bionic (5) postfix-wrapper.5.gz

Provided by: postfix_3.3.0-1ubuntu0.4_amd64 bug

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 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.

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 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  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 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 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  configuration  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 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-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.

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 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  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)
              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

                                                                                              POSTFIX-WRAPPER(5)