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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 removing 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 option) 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
       attacks against other users' spool files. The code carefully avoids
       race conditions 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
       created to avoid running mutt with group mail privileges.

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

Unix                              AUGUST 1999                       dotlock(1)