mutt_dotlock - Lock mail spool files.
mutt_dotlock [-t|-f|-u|-d] [-p] [-r retries]
file
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.
- -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.
- file.lock
- The lock file mutt_dotlock generates.
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.
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.
mutt_dotlock is part of the Mutt mail user agent package.
It has been created to avoid running mutt with group mail privileges.
Thomas Roessler <roessler@does-not-exist.org>