Provided by: procmail_3.24-1ubuntu2_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  LOCK‐
                              TIMEOUT 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 on‐
       ly 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  ex‐
       cellent  way to generate a lockfilename corresponding to some already existing file is by taking the pre‐
       fix `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  (v3.24)  available  at  http://www.proc‐
       mail.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>

                                                     BuGless                                         LOCKFILE(1)