lockfile - conditional semaphore-file creator
lockfile -sleeptime | -r retries
| -l locktimeout | -s suspend |
-! | -ml | -mu | filename
lockfile can be used to create one or more
semaphore files. If lockfile can't create all the
specified files (in the specified order), it waits
sleeptime (defaults to 8) seconds and retries the
last file that didn't succeed. You can specify the number of
retries to do until failure is returned. If the
number of retries is -1 (default, i.e., -r-1)
lockfile will retry forever.
If the number of retries expires before all files
have been created, lockfile returns failure and removes all
the files it created up till that point.
Using lockfile as the condition of a loop in a shell script
can be done easily by using the -! flag to invert the
exit status. To prevent infinite loops, failures for any
reason other than the lockfile already existing are not
inverted to success but rather are still returned as
All flags can be specified anywhere on the command line,
they will be processed when encountered. The command line is
simply parsed from left to right.
All files created by lockfile will be read-only, and
therefore will have to be removed with __rm
If you specify a locktimeout then a lockfile will be
removed by force after locktimeout seconds have passed since
the lockfile was last modified/created (most likely by some
other program that unexpectedly died a long time ago, and
hence could not clean up any leftover lockfiles). Lockfile
is clock skew immune. After a lockfile has been removed by
force, a suspension of suspend seconds (defaults to
16) is taken into account, in order to prevent the
inadvertent immediate removal of any newly created lockfile
by another program (compare SUSPEND in
If the permissions on the system mail spool directory allow
it, or if lockfile is suitably setgid, it will be able to
lock and unlock your system mailbox by using the options
-ml and -mu respectively.
Suppose you want to make sure that access to the file
Now if all the scripts that access
LOGNAME used as a hint to determine the invoker's
/etc/passwd to verify and/or correct the invoker's
loginname (and to find out his HOME directory, if
lockfile for the system mailbox, the environment variables
present in here will not be taken from the environment, but
will be determined by looking in /etc/passwd
rm(1), mail(1), binmail(1)?,
Filename too long, ...
Use shorter filenames.
Forced unlock denied on
No write permission in the directo- ry where lockfile
Forcing lock on
Out of memory, ...
The system is out of swap space.
Signal received, ...
Lockfile will remove anything it created till now and
Sorry, ... The retries limit has been
Try praying, ...
Missing subdirectories or insuffi- cient
Definitely less than one.
The behavior of the -! flag, while useful, is not
neces- sarily intuitive or consistent. When testing
lockfile's return value, shell script writers should
consider care- fully whether they want to use the -!
flag, simply re- verse the test, or do a switch on the exact
exitcode. In general, the -! flag should only be used
when lockfile is the conditional of a loop.
Lockfile is NFS-resistant and eight-bit clean.
Calling up lockfile with the -h or -? options will cause it
to display a command-line help page. Calling it up with the
- v option will cause it to display its version
Multiple -! flags will toggle the return
Since flags can occur anywhere on the command line, any
filename starting with a '-' has to be preceded by
The number of retries will not be reset when any
following file is being created (i.e., they are simply used
up). It can, however, be reset by specifying
- rnewretries after every file on the command
Although files with any name can be used as lockfiles, it is
common practice to use the extension `.lock' to lock
mailfolders (it is appended to the mailfolder name). In case
one does not want to have to worry about too long filenames
and does not have to conform to any other lock- filename
convention, then an excellent way to generate a lockfilename
corresponding to some already existing file is by taking the
prefix `lock.' and appending the i-node number of the file
which is to be locked.
This program is part of the procmail
mail-processing-pack- age (v3.22) available at
http://www.procmail.org/ or ftp.procmail.org in
There exists a mailinglist for questions relating to any
- program in the procmail package
for subscription requests.
If you would like to stay informed about new versions and
official patches send a subscription request to
(this is a readonly list).
Stephen R. van den Berg
Philip A. Guenther