NAME

       dotlockfile - Utility to manage lockfiles

SYNOPSIS

       dotlockfile -l [-r retries] [-i interval] [-p] [-q] <-m | lockfile>
       dotlockfile -l [-r retries] [-i interval] [-p] [-q] <-m | lockfile> [-P] cmd args ...
       dotlockfile -u | -t

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 dotlockfile :).

OPTIONS

       -l     Create a lockfile if no preexisting valid lockfile is found, else  wait  and  retry  according  to
              option -r.  Retry interval can be explicitly set with option -i.  This option (-l) is the default,
              so it can be left off.

              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  interval  is  increased incrementally by 5 seconds up to a maximum sleep of 60 seconds
              between tries unless overridden by -i.  The default number of retries is 5.  To try only once, use
              "-r 0".  To try indefinitely, use "-r -1".

       -i interval
              Sets a consistent retry interval.

       -u     Remove a lockfile.

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

       -p     Write the process-id of the calling process (or dotlockfile itself if a command is executed)  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  lockfile  is  still  valid.   Obviously  useful  only  for
              lockfiles on local filesystems.

       -m     Lock or unlock the current users mailbox.  The path to the mailbox 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.

       -q     Don't print warnings or errors to the standard error output. Used internally by  liblockfile  when
              it spawns dotlockfile as a helper program.

       -P     On  successful  "lock  and  spawn command", don't exit with status zero, but pass through the exit
              value of the spawned command.

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

       command argument ...
              Create lockfile, run the command , wait for it to exit, and remove lockfile.

RETURN VALUE

       Zero on success, and non-zero on failure.  When locking (the default, or with the -l option)  dotlockfile
       returns the same values as the library function lockfile_create(3).  Unlocking a non-existent lockfile is
       not an error.

       Unless the -P option was supplied, when a command is executed, the return value does not correspond  with
       that of the command that was run.  If locking and unlocking was successful, the exit status is zero.

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  procmail,  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 privileges 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

                                                January 10, 2017                                  DOTLOCKFILE(1)