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dotlock(1) User Manuals dotlock(1)


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.


Just try. mutt_dotlock won't actually lock a file, but inform the invoking process if it's at all possible to lock file.
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.
Unlock. mutt_dotlock will remove file.lock.
Delete. mutt_dotlock will lock file, remove it if it has length 0, and afterwards remove file.lock.
Use privileges. If given this option, mutt_dotlock will operate with group mail privileges when creating and deleting lock files.
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.


The lock file mutt_dotlock generates.


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


mutt_dotlock gives all diagnostics in its return values:

0 - DL_EX_OK
The program was successful.
An unspecified error such as bad command line parameters, lack of system memory and the like has occurred.
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.
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.
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 <>

AUGUST 1999 Unix