dotlock(1)							   User Manuals 							dotlock(1)

NAME

       lbdb_dotlock - Lock mail spool files.

SYNOPSIS

       lbdb_dotlock [-t|-f|-u|-d] [-r retries] file

DESCRIPTION

       dotlock implements the traditional mail spool file locking method: To lock file, a file named file.lock is created.

OPTIONS

       -t     Just try.  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, dotlock will break that lock by
	      removing the lockfile.

       -u     Unlock.  dotlock will remove file.lock.

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

       -r retries
	      This command line option tells 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.  dotlock waits one second between successive locking attempts.

FILES

       file.lock
	      The lock file dotlock generates.

SEE ALSO

       fcntl(2), flock(2), lockfile(1), lbdb-fetchaddr(1)

DIAGNOSTICS

       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 occured.

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

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

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

NOTES

       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, 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 com-
       ments in dotlock.c.

HISTORY

       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@guug.de>

Unix								   OCTOBER 2005 							dotlock(1)