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 re-
tries times before giving up or (if invoked with the -f command
line option) break a lock. The default value is 5. mutt_dot-
lock 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)