POSTPONE(1)                                                        POSTPONE(1)



NAME
       postpone  -  schedules  a  command to be executed later when a lockfile
       disappears

SYNOPSIS
       postpone [-dfv] [-lwLoO FILE] command args ...

DESCRIPTION
       Postpone schedules a command to be executed later when a lockfile  dis‐
       appears. Intended usage is when a command is executed possibly multiple
       times, but running once  is  sufficient.  This  happens  in  maintainer
       scripts  of  Debian packages, for example, the menu system will need to
       run update-menus every time a menu file is installed or removed, but if
       several  packages  are  processed at once, a single update-menus run at
       the end is sufficient. In fact, postpone is a generalization of similar
       code  found  in  update-menus  that is already able to postpone itself.
       Another prominent use case are TeX packages that need to  rebuild  sev‐
       eral indices.

       On  startup,  postpone  will  look  if any of the lock files given with
       --wait exists. If not, it will run command immediately  in  foreground.
       Otherwise,  it will fork to background, waiting for the lock file(s) to
       disappear. At the same time, the --lock file is created to indicate  to
       other  postpone  instances that command is already scheduled for execu‐
       tion; the other instances will exit without further action.

       Additionally, --extra-lock will be acquired just before  the  execution
       of  command, this allows the serialization of several (different) back‐
       ground jobs.

       All lockfiles are optional. See below for examples.

OPTIONS
       -w FILE or --wait FILE
              Wait for FILE before  running  command.  Can  be  given  several
              times.   This  activates  the  main feature of postpone ‐‐ delay
              execution  until  some  other  task  has  exited  (specifically,
              released its fcntl() lock).

       -l FILE or --lock FILE
              Creates lockfile FILE. If postpone is called again with the same
              FILE, it will exit, assuming the task is already postponed. Make
              sure  that  the  (effects  of the) commands are the same for the
              same lockfile.

       -L FILE or --extra-lock FILE
              Before running command, acquire lock on FILE. Use this to  seri‐
              alize several (most likely different) postponed commands.

       -d or --debian
              Equivalent    to    --wait    /var/lib/dpkg/lock    --extra-lock
              /var/lib/dpkg/postpone.lock. Meant for use in maintainer scripts
              of  Debian  packages, will wait for dpkg and apt‐get to exit and
              serialize the postponed commands.

       -o FILE or --output FILE
              Redirect stdout and stderr output to FILE when running in  back‐
              ground.   (Discarded  otherwise.)  If  FILE  ends with "XXXXXX",
              mkstemp is used.

       -O FILE or --all-output FILE
              Like --output, but always redirect stdout and stderr  output  to
              FILE.

       -f or --foreground
              Do not detach while waiting for locks.

       -v or --verbose
              Verbose output. Repeat for debugging output.

       --help Print options summary and exit.

       --version
              Print version information and exit.

       --version-string
              Print version information in machine readable form and exit.

EXAMPLES
       Example usage in a texlive postinst maintainer script:

           if [ -x /usr/bin/postpone ] ; then
               postpone --verbose --lock /var/run/updmap-sys.lock --debian \
                   --all-output /tmp/updmap.XXXXXXXX \
                   updmap-sys
           else
               updmap-sys
           fi

FILES
       /var/lib/dpkg/lock
              Dpkg’s default lockfile.

       /var/lib/dpkg/postpone.lock
              Default extra lockfile when running with --debian.

BUGS
       Postpone  currently only uses fcntl() to acquire locks on --wait, usage
       with applications using flock() will fail gracefully. (The command will
       run immediately.) --lock and --extra-lock use flock().

COMPATIBILITY
       For  compatibility,  using  unknown options does not abort the program.
       Applications can use --version-string if they need to compare the post�‐
       pone version number.

SEE ALSO
       update-menus(1), fcntl(2), flock(2), mkstemp(3), dpkg(1).

COPYRIGHT
       Copyright (C) 2007  Christoph Berg

       Based on code from:
       Debian menu system ‐‐ update-menus
       update-menus/update-menus.cc

       Copyright (C) 1996‐2003  Joost Witteveen
       Copyright (C) 2002‐2004  Bill Allombert and Morten Brix Pedersen

       This program is free software; you can redistribute it and/or modify it
       under the terms of the GNU General Public License as published  by  the
       Free  Software Foundation; either version 2 of the License, or (at your
       option) any later version.

       This program is distributed in the hope that it  will  be  useful,  but
       WITHOUT  ANY  WARRANTY;  without  even  the  implied  warranty  of MER‐
       CHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU  General
       Public License for more details.



                                 June 9th 2007                     POSTPONE(1)