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LOCKFILE(1)                                                        LOCKFILE(1)

       lockfile - conditional semaphore-file creator

       lockfile -sleeptime | -r retries |
            -l locktimeout | -s suspend | -!  | -ml | -mu | filename ...

       lockfile  can  be used to create one or more semaphore files.  If lockfile can't create all the specified files
       (in the specified order), it waits sleeptime (defaults to 8) seconds and retries the last file that didn't suc-
       ceed.   You  can specify the number of retries to do until failure is returned.  If the number of retries is -1
       (default, i.e., -r-1) lockfile will retry forever.

       If the number of retries expires before all files have been created, lockfile returns failure and  removes  all
       the files it created up till that point.

       Using  lockfile as the condition of a loop in a shell script can be done easily by using the -!  flag to invert
       the exit status.  To prevent infinite loops, failures for any reason other than the lockfile  already  existing
       are not inverted to success but rather are still returned as failures.

       All  flags can be specified anywhere on the command line, they will be processed when encountered.  The command
       line is simply parsed from left to right.

       All files created by lockfile will be read-only, and therefore will have to be removed with rm -f.

       If you specify a locktimeout then a lockfile will be removed by force after  locktimeout  seconds  have  passed
       since  the  lockfile was last modified/created (most likely by some other program that unexpectedly died a long
       time ago, and hence could not clean up any leftover lockfiles).  Lockfile is clock skew immune.  After a  lock-
       file  has  been  removed  by  force, a suspension of suspend seconds (defaults to 16) is taken into account, in
       order to prevent the inadvertent immediate removal of any newly created lockfile by  another  program  (compare
       SUSPEND in procmail(1)).

   Mailbox locks
       If  the  permissions on the system mail spool directory allow it, or if lockfile is suitably setgid, it will be
       able to lock and unlock your system mailbox by using the options -ml and -mu respectively.

       Suppose you want to make sure that access to the file "important" is serialised, i.e., no more than one program
       or  shell  script  should  be  allowed  to  access it.  For simplicity's sake, let's suppose that it is a shell
       script.  In this case you could solve it like this:
              lockfile important.lock
              rm -f important.lock
       Now if all the scripts that access "important" follow this guideline, you will be  assured  that  at  most  one
       script will be executing between the 'lockfile' and the 'rm' commands.

       LOGNAME                used as a hint to determine the invoker's loginname

       /etc/passwd            to verify and/or correct the invoker's loginname (and to find out his HOME directory, if

                              lockfile for the system mailbox, the environment variables present in here will  not  be
                              taken from the environment, but will be determined by looking in /etc/passwd

       rm(1), mail(1), binmail(1), sendmail(8), procmail(1)

       Filename too long, ... Use shorter filenames.

       Forced unlock denied on "x"
                              No  write permission in the directory where lockfile "x" resides, or more than one lock-
                              file trying to force a lock at exactly the same time.

       Forcing lock on "x"    Lockfile "x" is going to be removed by force because of a timeout  (compare  LOCKTIMEOUT
                              in procmail(1)).

       Out of memory, ...     The system is out of swap space.

       Signal received, ...   Lockfile will remove anything it created till now and terminate.

       Sorry, ...             The retries limit has been reached.

       Truncating "x" and retrying lock
                              "x" does not seem to be a valid filename.

       Try praying, ...       Missing subdirectories or insufficient privileges.

       Definitely less than one.

       The  behavior  of  the  -!  flag, while useful, is not necessarily intuitive or consistent.  When testing lock-
       file's return value, shell script writers should consider carefully whether they want to use the -!  flag, sim-
       ply  reverse the test, or do a switch on the exact exitcode.  In general, the -!  flag should only be used when
       lockfile is the conditional of a loop.

       Lockfile is NFS-resistant and eight-bit clean.

       Calling up lockfile with the -h or -? options will cause it to display a command-line help page.  Calling it up
       with the -v option will cause it to display its version information.

       Multiple -!  flags will toggle the return status.

       Since  flags  can  occur  anywhere  on the command line, any filename starting with a '-' has to be preceded by

       The number of retries will not be reset when any following file is being created (i.e., they  are  simply  used
       up).  It can, however, be reset by specifying -rnewretries after every file on the command line.

       Although  files  with  any name can be used as lockfiles, it is common practice to use the extension '.lock' to
       lock mailfolders (it is appended to the mailfolder name).  In case one does not want to have to worry about too
       long filenames and does not have to conform to any other lockfilename convention, then an excellent way to gen-
       erate a lockfilename corresponding to some already existing file is by taking the prefix 'lock.' and  appending
       the i-node number of the file which is to be locked.

       This  program  is part of the procmail mail-processing-package (v3.22) available at or in pub/procmail/.

       There exists a mailinglist for questions relating to any program in the procmail package:
                     for submitting questions/answers.
                     for subscription requests.

       If you would like to stay informed about new versions and official patches send a subscription request to
       (this is a readonly list).

       Stephen R. van den Berg
       Philip A. Guenther

BuGless                           2001/06/23                       LOCKFILE(1)