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LOCKFILE !!!LOCKFILE NAME SYNOPSIS DESCRIPTION EXAMPLES ENVIRONMENT FILES SEE ALSO DIAGNOSTICS BUGS WARNINGS MISCELLANEOUS NOTES SOURCE MAILINGLIST AUTHORS ---- !!NAME lockfile - conditional semaphore-file creator !!SYNOPSIS __lockfile -__''sleeptime'' | __-r__ ''retries'' | __-l__ ''locktimeout'' | __-s__ ''suspend'' | __-!__ | __-ml__ | __-mu__ | ''filename'' ... !!DESCRIPTION __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 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 __rm -f__. 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 procmail(1)). __Mailbox locks__ 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. !!EXAMPLES Suppose you want to make sure that access to the file ... lockfile important.lock ... access_ Now if all the scripts that access !!ENVIRONMENT __LOGNAME__ used as a hint to determine the invoker's loginname !!FILES __/etc/passwd__ to verify and/or correct the invoker's loginname (and to find out his HOME directory, if needed) __/var/mail/$LOGNAME.lock__ 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 !!SEE ALSO rm(1), mail(1), binmail(1), sendmail(8), procmail(1) !!DIAGNOSTICS Filename too long, ... Use shorter filenames. Forced unlock denied on No write permission in the directo- ry where lockfile Forcing lock on Lockfile LOCKTIMEOUT__ in procmail(1)). Out of memory, ... The system is out of swap space. Signal received, ... Lockfile will remove anything it created till now and terminate. Sorry, ... The ''retries'' limit has been reached. Truncating Try praying, ... Missing subdirectories or insuffi- cient privileges. !!BUGS Definitely less than one. !!WARNINGS 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. !!MISCELLANEOUS Lockfile is NFS-resistant and eight-bit clean. !!NOTES 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. Multiple __-!__ 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 ''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 -r''newretries'' 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 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. !!SOURCE This program is part of the ''procmail mail-processing-pack- age'' (v3.22) available at http://www.procmail.org/ or ftp.procmail.org in __pub/procmail/__. !!MAILINGLIST 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 procmail-announce-request@procmail.org (this is a readonly list). !!AUTHORS Stephen R. van den Berg Philip A. Guenther ----
6 pages link to
lockfile(1)
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procmail(1)
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