exim_lock(8) [debian man page]

EXIM_LOCK(8)						      System Manager's Manual						      EXIM_LOCK(8)

NAME

       exim_lock - Mailbox maintenance

SYNOPSIS

       exim_lock [options]mailbox-file

DESCRIPTION

       The  exim_lock  utility	locks  a  mailbox  file  using	the same algorithm as Exim.  For a discussion of locking issues, see section 25.2.
       exim_lock can be used to prevent any modification of a mailbox by Exim or a user agent while investigating a problem.  The utility requires
       the  name  of  the file as its first argument.  If the locking is successful, the second argument is run as a command (using C's "system()"
       function); if there is no second argument, the value of the SHELL environment variable is used; if this is unset or empty, /bin/sh is  run.
       When the command finishes, the mailbox is unlocked and the utility ends.  The following options are available:

       -fcntl Use "fcntl()" locking on the open mailbox.

       -interval
	      This must be followed by a number, which is a number of seconds; it sets the interval to sleep between retries (default 3).

       -lockfile
	      Create a lock file before opening the mailbox.

       -mbx   Lock the mailbox using MBX rules.

       -q     Suppress verification output.

       -retries
	      This must be followed by a number; it sets the number of times to try to get the lock (default 10).

       -timeout
	      This must be followed by a number, which is a number of seconds; it sets a timeout to be used with a blocking "fcntl()" lock.  If it
	      is not set (the default), a non-blocking call is used.

       -v     Generate verbose output.

	      If none of -fcntl, -lockfile or -mbx are given, the default is to create a lock file and also use "fcntl()" locking on the  mailbox,
	      which  is  the same as Exim's default.  The use of -fcntl requires that the file be writable; the use of -lockfile requires that the
	      directory containing the file be writable.  Locking by lock file does not last for ever; Exim assumes that a lock file is expired if
	      it is more than 30 minutes old.

	      The  -mbx  option  is mutually exclusive with -fcntl.  It causes a shared lock to be taken out on the open mailbox, and an exclusive
	      lock on the file /tmp/.n.m where n and m are the device number and inode number of the mailbox file.  When the locking is  released,
	      if an exclusive lock can be obtained for the mailbox, the file in /tmp is deleted.

	      The  default  output  contains verification of the locking that takes place.  The -v option causes some additional information to be
	      given.  The -q option suppresses all output except error messages.

       A command such as

	 exim_lock /var/spool/mail/spqr

       runs an interactive shell while the file is locked, whereas

	 exim_lock -q /var/spool/mail/spqr <<End
	 <some commands>
	 End

       runs a specific non-interactive sequence of commands while the file is locked, suppressing all verification output.  A single  command  can
       be run by a command such as

	 exim_lock -q /var/spool/mail/spqr     "cp /var/spool/mail/spqr /some/where"

       Note that if a command is supplied, it must be entirely contained within the second argument - hence the quotes.

BUGS

       This manual page needs a major re-work. If somebody knows better groff than us and has more experience in writing manual pages, any patches
       would be greatly appreciated.

SEE ALSO

       exim(8), /usr/share/doc/exim4-base/

AUTHOR

       This manual page was stitched together from spec.txt by Andreas Metzler <ametzler at downhill.at.eu.org>, for the Debian  GNU/Linux  system
       (but may be used by others).

								  March 26, 2003						      EXIM_LOCK(8)

lockfile-progs(1)						 Lockfile programs						 lockfile-progs(1)

NAME

       lockfile-progs - command-line programs to safely lock and unlock files and mailboxes (via liblockfile).

SYNOPSIS

       mail-lock [--use-pid] [--retry retry-count]
       mail-unlock
       mail-touchlock [--oneshot]

       lockfile-create [--use-pid] [--retry retry-count] [--lock-name] filename
       lockfile-remove [--lock-name] filename
       lockfile-touch [--oneshot] [--lock-name] filename
       lockfile-check [--use-pid] [--lock-name] filename

DESCRIPTION

       Lockfile-progs provides a set a programs that can be used to lock and unlock mailboxes and files safely (via liblockfile):

	   mail-lock - lock the current user's mailbox
	   mail-unlock - unlock the current user's mailbox
	   mail-touchlock - touch the lock on the current user's mailbox

	   lockfile-create - lock a given file
	   lockfile-remove - remove the lock on a given file
	   lockfile-touch - touch the lock on a given file
	   lockfile-check - check the lock on a given file

       By  default,  the filename argument refers to the name of the file to be locked, and the name of the lockfile will be filename .lock.  How-
       ever, if the --lock-name argument is specified, then filename will be taken as the name of the lockfile itself.

       Each of the mail locking commands attempts to lock /var/spool/mail/<user>, where <user> is the name associated with the effective user  ID,
       as determined by via geteuid(2).

       Once  a file is locked, the lock must be touched at least once every five minutes or the lock will be considered stale, and subsequent lock
       attempts will succeed.  Also see the --use-pid option and the lockfile_create(3) manpage.

       The lockfile-check command tests whether or not a valid lock already exists.

OPTIONS

       -q, --quiet
	   Suppress any output.  Success or failure will only be indicated by the exit status.

       -v, --verbose
	   Enable diagnostic output.

       -l, --lock-name
	   Do not append .lock to the filename.  This option applies to lockfile-create, lockfile-remove, lockfile-touch, or lockfile-check.

       -p, --use-pid
	   Write the current process id (PID) to the lockfile whenever a lockfile is created, and use that pid when checking  a  lock's  validity.
	   See	the lockfile_create(3) manpage for more information.  This option applies to lockfile-create, lockfile-remove, lockfile-touch, and
	   lockfile-check.

       -o, --oneshot
	   Touch the lock and exit immediately.  This option applies to lockfile-touch and mail-touchlock.  When not provided, these commands will
	   run forever, touching the lock once every minute until killed.

       -r retry-count, --retry retry-count
	   Try	to  lock filename retry-count times before giving up.  Each attempt will be delayed a bit longer than the last (in 5 second incre-
	   ments) until reaching a maximum delay of one minute between retries.  If retry-count is unspecified, the default is 9 which	will  give
	   up after 180 seconds (3 minutes) if all 9 lock attempts fail.

EXAMPLES

       Locking a file during a lengthy process:

	 lockfile-create /some/file
	 lockfile-touch /some/file &
	 # Save the PID of the lockfile-touch process
	 BADGER="$!"
	 do-something-important-with /some/file
	 kill "${BADGER}"
	 lockfile-remove /some/file

EXIT STATUS

       0
	   For lockfile-check this indicates that a valid lock exists, otherwise it just indicates successful program execution.

       Not 0
	   For	lockfile-check	a  non-zero  exit  status indicates that the specified lock does not exist or is not valid.  For other programs it
	   indicates that some problem was encountered.

SEE ALSO

       maillock(3)
       touchlock(3)
       mailunlock(3)
       lockfile_create(3)
       lockfile_remove(3)
       lockfile_touch(3)
       lockfile_check(3)

AUTHOR

       Written by Rob Browning <rlb@defaultvalue.org>

0.1.12								    2008-02-10							 lockfile-progs(1)