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 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

   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.


   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


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

                          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), 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  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

   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


   Definitely less than one.


   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.


   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 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.


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


   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


Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.

Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.

Free Software

Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.

Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.

Free Books

The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.

Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.


Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.

Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.