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)
Check Out this Related Man Page
dotlock(1) Mail Avenger 0.8.3 dotlock(1)NAME
dotlock - execute a command with a lock on a mailbox
SYNOPSIS
dotlock [-LPW] mbox-file command [arg ...]
DESCRIPTION
dotlock acquires a lock on the mailbox file mbox-file using both flock and a lock file, then executes command with any arguments specified.
When command exits, dotlock releases the lock.
dotlock attempts to clean up stale lockfiles. If it succeeds in locking an mbox-file with flock, and roughly 30 seconds elapse without
there being any changes to mbox-file or the lockfile, then dotlock will delete the lockfile and try again.
While it holds a lock, lockfile will keep updating the modification time of the lockfile every 15 seconds, to prevent the lock from getting
cleaned up in the event that command is slow.
OPTION
--noflock (-L)
Ordinarily, dotlock uses both flock and dotfile locking. (It uses flock first, but releases that lock in the even that dotfile locking
fails, so as to avoid deadlocking with applications that proceed in the reverse order.) The -L option disables flock locking, so that
dotlock only uses dotfile locking.
This is primarily useful as a wrapper around an application that already does flock locking, but to which you want to add dotfile
locking. (Even if your mail delivery system doesn't use flock, flock actually improves the efficiency of dotlock, so there is no
reason to disable it.)
--fcntl (-P)
This option enables fcntl (a.k.a. POSIX) file locking of mail spools, in addition to flock and dotfile locking. The advantage of fcntl
locking is that it may do the right thing over NFS. However, if either the NFS client or server does not properly support fcntl
locking, or if the file system is not mounted with the appropriate options, fcntl locking can fail in one of several ways. It can
allow different processes to lock the same file concurrently--even on the same machine. It can simply hang when trying to acquire a
lock, even if no other process holds a lock on the file. Also, on some OSes it can interact badly with flock locking, because those
OSes actually implement flock in terms of fcntl.
--nowait (-W)
With this option, dotlock simply exits non-zero and does not run command if it cannot immediately acquire the lock.
SEE ALSO avenger(1), deliver(1), avenger.local(8)
The Mail Avenger home page: <http://www.mailavenger.org/>.
BUGS
dotlock does not perform fcntl/lockf-style locking by default. Thus, if your mail reader exclusively uses fcntl for locking, there will be
race conditions unless you specify the --fcntl option.
flock does not work over network file systems. Thus, because of dotlock's mechanism for cleaning stale lock files, there is a possibility
that a network outage could lead to a race condition where the lockfile is cleared before command finishes executing. If lockfile detects
that the lock has been stolen, it prints a message to standard error, but does not do anything else (like try to kill command).
AUTHOR
David Mazieres
Mail Avenger 0.8.3 2012-04-05 dotlock(1)