LOCKFILE linux command manual

LOCKFILE(1)                                                    LOCKFILE(1)



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 lock-
       file 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 pre-
       vent 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 mod-
       ified/created  (most  likely  by  some other program that unexpectedly
       died a long time ago, and hence could not clean up any leftover  lock-
       files).   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 SUS-
       PEND 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 login-
                              name (and to find out his  HOME  directory,  if
                              needed)

       /var/mail/$LOGNAME.lock
                              lockfile  for  the system mailbox, the environ-
                              ment variables present  in  here  will  not  be
                              taken  from the environment, but will be deter-
                              mined by looking in /etc/passwd

SEE ALSO
       rm(1), mail(1), binmail(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  privi-
                              leges.

BUGS
       Definitely less than one.

WARNINGS
       The  behavior  of the -!  flag, while useful, is not necessarily intu-
       itive 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  exit-
       code.   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 be-
       ing created (i.e., they are simply used up).  It can, however, be  re-
       set 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  ap-
       pended  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  (v3.22)
       available at http://www.procmail.org/ or ftp.procmail.org in pub/proc-
       mail/.

MAILINGLIST
       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
              procmail-announce-request@procmail.org
       (this is a readonly list).

AUTHORS
       Stephen R. van den Berg
              
       Philip A. Guenther
              



BuGless                           2001/06/23                      LOCKFILE(1)