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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 neces-
sary.
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 de-
fault value is 5. mutt_dotlock waits one second between successive locking at-
tempts.
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 gener-
ate 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 re-
turn 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 AT does-not-exist.org>
Unix AUGUST 1999 dotlock(1)
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