dotlockfile man page on ElementaryOS

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DOTLOCKFILE(1)		       Cistron Utilities		DOTLOCKFILE(1)

NAME
       dotlockfile - Utility to manage lockfiles

SYNOPSIS
       /usr/bin/dotlockfile [-l [-r retries] |-u|-t|-c] [-p] [-m|lockfile]

DESCRIPTION
       dotlockfile  is	a  command  line  utility to reliably create, test and
       remove lockfiles.  It creates  lockfiles	 reliably  on  local  and  NFS
       filesystems,  because  the  crucial  steps of testing for a preexisting
       lockfile and creating it are performed atomically by a single  call  to
       link(2).	 Manpage lockfile_create(3) describes the used algorithm.

       dotlockfile  is	installed with attribute SETGID mail and thus can also
       be used to lock and unlock mailboxes even if the mailspool directory is
       only writable by group mail.

       The  name  dotlockfile  comes  from  the	 way  mailboxes are locked for
       updates on a lot of UNIX systems.  A lockfile is created with the  same
       filename as the mailbox but with the string ".lock" appended.

       The names dotlock and lockfile were already taken - hence the name dot‐
       lockfile :).

OPTIONS
       -l     Create a lockfile if no preexisting  valid  lockfile  is	found,
	      else  wait and retry according to option -r.  This option is the
	      default.

	      A lockfile is treated as valid,
	      ·	 if it holds the process-id of a running process,
	      ·	 or if it does not hold any process-id and  has	 been  touched
	      less than 5 minutes ago (timestamp is younger than 5 minutes).

       -r retries
	      The  number  of times dotlockfile retries to acquire the lock if
	      it failed the first time before giving up.   The	initial	 sleep
	      after  failing  to  acquire  the	lock is 5 seconds.  After each
	      retry the sleep intervall is increased incrementally  by	5 sec‐
	      onds  up	to  a  maximum sleep of 60 seconds between tries.  The
	      default number of retries is 5.  To try only once, use  "-r  0".
	      To try indefinitely, use "-r -1".

       -u     Remove a lockfile.

       -t     Touch  an	 existing lockfile (update the timestamp).  Useful for
	      lockfiles on NFS filesystems.  For lockfiles on  local  filesys‐
	      tems the -p option is preferable.

       -c     For  debugging  only:   Check for the existence of a valid lock‐
	      file.

	      Note:  Testing for a preexisting lockfile	 and  writing  of  the
	      lockfile	must be done by the same "dotlockfile -l" or "dotlock‐
	      file -m" command, else the lockfile creation cannot be reliable.

       -p     Write the process-id of the calling process into	the  lockfile.
	      Also  when  testing for an existing lockfile, check the contents
	      for the process-id of a running process to verify if  the	 lock‐
	      file  is	still  valid.	Obviously useful only for lockfiles on
	      local filesystems.

       -m     Lock or unlock the current users mailbox.	 The path to the mail‐
	      box   is	 the   default	system	mailspool  directory  (usually
	      /var/mail) with the username as gotten from getpwuid() appended.
	      If  the environment variable $MAIL is set, that is used instead.
	      Then the string ".lock" is appended  to  get  the	 name  of  the
	      actual lockfile.

       lockfile
	      The  lockfile  to be created or removed.	Must not be specified,
	      if the -m option is in effect.

RETURN VALUE
       Zero on success, and non-zero on failure.  For the  -c  option,	sucess
       means  that  a  valid  lockfile	is already present.  When locking (the
       default, or with the -l option) dotlockfile returns the same values  as
       the  library  function  lockfile_create(3).   Unlocking	a non-existant
       lockfile is not an error.

NOTES
       The lockfile is created exactly as named	 on  the  command  line.   The
       extension ".lock" is not automatically appended.

       This  utility is a lot like the lockfile(1) utility included with proc‐
       mail, and the mutt_dotlock(1) utility included with mutt.  However  the
       command-line  arguments	differ,	 and so does the return status.	 It is
       believed, that dotlockfile is the most flexible	implementation,	 since
       it  automatically  detects  when	 it  needs to use priviliges to lock a
       mailbox, and does it safely.

       The above  mentioned  lockfile_create(3)	 manpage  is  present  in  the
       liblockfile-dev package.

BUGS
       None known.

SEE ALSO
       lockfile_create(3), maillock(3)

AUTHOR
       Miquel van Smoorenburg, miquels@cistron.nl

			       September 8, 2009		DOTLOCKFILE(1)
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