Provided by: procmail_3.22-21_amd64 bug

NAME

       lockfile - conditional semaphore-file creator

SYNOPSIS

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

DESCRIPTION

       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 succeed.  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 lockfile 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.

EXAMPLES

       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
              ...
              access_"important"_to_your_hearts_content
              ...
              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.

ENVIRONMENT

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

FILES

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

       /var/mail/$LOGNAME.lock
                              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

SEE ALSO

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

DIAGNOSTICS

       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 lockfile 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.

BUGS

       Definitely less than one.

WARNINGS

       The behavior of the -!  flag, while useful, is not necessarily  intuitive  or  consistent.
       When  testing  lockfile's  return  value,  shell  script writers should consider carefully
       whether they want to use the -!  flag, simply 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.

MISCELLANEOUS

       Lockfile is NFS-resistant and eight-bit clean.

NOTES

       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 generate 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.

SOURCE

       This  program  is  part  of  the  procmail mail-processing-package (v3.23pre) available at
       http://www.procmail.org/ or ftp.procmail.org in pub/procmail/.

MAILINGLIST

       There exists a mailinglist for questions relating to any program in the procmail package:
              <procmail-users@procmail.org>
                     for submitting questions/answers.
              <procmail-users-request@procmail.org>
                     for subscription requests.

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

AUTHORS

       Stephen R. van den Berg
              <srb@cuci.nl>
       Philip A. Guenther
              <guenther@sendmail.com>