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dotlock(1)			  User Manuals			      dotlock(1)

NAME
     mutt_dotlock - Lock mail spool files.

SYNOPSIS
     mutt_dotlock [-t|-f|-u|-d] [-p] [-r retries] file

DESCRIPTION
     mutt_dotlock  implements the traditional mail spool file locking method: To
     lock file, a file named file.lock is created.  The  program  operates  with
     group mail privileges if necessary.

OPTIONS
     -t     Just  try.	 mutt_dotlock won't actually lock a file, but inform the
	    invoking process if it's at all possible to lock file.

     -f     Force the lock.  If another process holds a lock on file longer than
	    a certain amount of time, mutt_dotlock will break that lock  by  re-
	    moving the lockfile.

     -u     Unlock.  mutt_dotlock will remove file.lock.

     -d     Delete.   mutt_dotlock will lock file, remove it if it has length 0,
	    and afterwards remove file.lock.

     -p     Use privileges.  If given this  option,  mutt_dotlock  will  operate
	    with group mail privileges when creating and deleting lock files.

     -r retries
	    This  command  line option tells mutt_dotlock to try locking retries
	    times before giving up or (if invoked with the -f command  line  op-
	    tion) break a lock.  The default value is 5.  mutt_dotlock waits one
	    second between successive locking attempts.

FILES
     file.lock
	    The lock file mutt_dotlock generates.

SEE ALSO
     fcntl(2), flock(2), lockfile(1), mutt(1)

DIAGNOSTICS
     mutt_dotlock gives all diagnostics in its return values:

     0 - DL_EX_OK
	    The program was successful.

     1 - DL_EX_ERROR
	    An	unspecified  error  such as bad command line parameters, lack of
	    system memory and the like has occurred.

     3 - DL_EX_EXIST
	    The user wants to lock a file  which  has  been  locked  by  another
	    process  already.	If  mutt_dotlock  is invoked with the -f command
	    line option, mutt_dotlock won't generate this error, but break other
	    processes' locks.

     4 - DL_EX_NEED_RPIVS
	    This return value only occurs if mutt_dotlock has been invoked  with
	    the -t command line option.  It means that mutt_dotlock will have to
	    use its group mail privileges to lock file.

     5 - DL_EX_IMPOSSIBLE
	    This  return value only occurs if mutt_dotlock has been invoked with
	    the -t command line option.  It means that mutt_dotlock is unable to
	    lock file even with group mail privileges.

NOTES
     mutt_dotlock tries to implement an NFS-safe  dotlocking  method  which  was
     borrowed from lockfile (1).

     If  the  user  can't  open  file  for  reading  with his normal privileges,
     mutt_dotlock will return the DL_EX_ERROR exit value to  avoid  certain  at-
     tacks against other users' spool files. The code carefully avoids race con-
     ditions when checking permissions; for details of all this see the comments
     in dotlock.c.

HISTORY
     mutt_dotlock is part of the Mutt mail user agent package.	It has been cre-
     ated to avoid running mutt with group mail privileges.

AUTHOR
     Thomas Roessler <roessler@does-not-exist.org>

Unix				   AUGUST 1999			      dotlock(1)

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