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RedHat 9 (Linux i386) - man page for shlock (redhat section 1)

SHLOCK(1)						      General Commands Manual							 SHLOCK(1)

shlock - create lock files for use in shell scripts
shlock -p pid -f name [ -b ] [ -u ] [ -c ]
Shlock tries to create a lock file named name and write the process ID pid into it. If the file already exists, shlock will read the process ID from the file and test to see if the process is currently running. If the process exists, then the file will not be created. Shlock exits with a zero status if it was able to create the lock file, or non-zero if the file refers to currently-active process.
-b Process IDs are normally read and written in ASCII. If the ``-b'' flag is used, then they will be written as a binary int. For compatibility with other systems, the ``-u'' flag is accepted as a synonym for ``-b'' since binary locks are used by many UUCP pack- ages. -c If the ``-c'' flag is used, then shlock will not create a lock file, but will instead use the file to see if the lock is held by another program. If the lock is valid, the program will exit with a non-zero status; if the lock is not valid (i.e., invoking shlock without the flag would have succeeded), then the program will exit with a zero status.
The following example shows how shlock would be used within a shell script: LOCK=<pathrun in inn.conf>/LOCK.send trap 'rm -f ${LOCK} ; exit 1' 1 2 3 15 if shlock -p $$ -f ${LOCK} ; then # Do appropriate work else echo Locked by `cat ${LOCK}` fi
shlock does not assumed to be used under a number of lock/unlock environment in a short time. Namely, shlock should be used for an envi- ronment like daily or hourly based job.
Written by Rich $alz <> after a description of HDB UUCP locking given by Peter Honeyman. This is revision, dated 2002/09/24.
inn.conf(5) SHLOCK(1)