Section: User Commands (1)
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lockfile - conditional semaphore-file creator
can be used to create one or more
If lockfile can't create all the specified files (in the specified order),
(defaults to 8) seconds and retries the last file that didn't
succeed. You can specify the number of
to do until failure is returned.
If the number of
is -1 (default, i.e.,
lockfile will retry forever.
If the number of
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 failures.
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
If you specify a
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
seconds (defaults to 16) is taken into account, in order to prevent
the inadvertent immediate removal of any newly created lockfile by another
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
Suppose you want to make sure that access to the file "important" is
serialised, i.e., no more than one program or shell script should be allowed
to access it. For simplicity's sake, let's suppose that it is a shell
script. In this case you could solve it like this:
rm -f important.lock
Now if all the scripts that access "important" follow this guideline, you
will be assured that at most one script will be executing between the
`lockfile' and the `rm' commands.
used as a hint to determine the invoker's loginname
to verify and/or correct the invoker's loginname (and to find out his HOME
directory, if needed)
lockfile for the system mailbox, the environment variables present in here
will not be taken from the environment, but will be determined by looking
Filename too long, ...
Use shorter filenames.
Forced unlock denied on "x"
No write permission in the directory where lockfile "x" resides, or more than
one lockfile trying to force a lock at exactly the same time.
Forcing lock on "x"
Lockfile "x" is going to be removed by force because of a timeout
Out of memory, ...
The system is out of swap space.
Signal received, ...
Lockfile will remove anything it created till now and terminate.
limit has been reached.
Truncating "x" and retrying lock
"x" does not seem to be a valid filename.
Try praying, ...
Missing subdirectories or insufficient privileges.
Definitely less than one.
The behavior of the
flag, while useful, is not necessarily intuitive or consistent. When
testing lockfile's return value, shell script writers should consider
carefully whether they want to use the
flag, simply reverse 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 information.
flags will toggle the return status.
Since flags can occur anywhere on the command line, any filename starting
with a '-' has to be preceded by './'.
The number of
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
after every file on the command line.
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 lockfilename 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
(v3.23pre) available at http://www.procmail.org/
There exists a mailinglist for questions relating to any program in the
- for submitting questions/answers.
- 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
- Mailbox locks
- SEE ALSO