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DOTLOCKFILE(1)		       Cistron Utilities		DOTLOCKFILE(1)

NAME
       dotlockfile - Utility to manage lockfiles

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

DESCRIPTION
       Dotlockfile is a command line utility to safely create, test and remove
       lockfiles. Lockfiles are created in an NFS-safe	way.  Dotlockfile  can
       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. This is the default.

       -u     Remove a lockfile.

       -c     Check for the existence of a valid lockfile.

       -t     Touch an existing lockfile (update the timestamp).

       -p     Write  the  process-id of the calling process into the lockfile.
	      Also when testing for an existing lockfile, check	 the  contents
	      for a process-id to find out if the lockfile is still valid.

       -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 next
	      try, a sleep of 5 seconds extra occurs up to a maximum sleep  of
	      60 seconds between tries.	 The default number of retries is 5.

       -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/removed, unless 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  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 added.

       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	 mail‐
       box, 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

				  15 May 2003			DOTLOCKFILE(1)
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