Instead of just removing the lock file, you might want to determine whether or not the script is still running.
A fairly common way to do this is to have the script that creates the lock file writes its PID into the lock file (echo $$ > lock). Then if the lock file is present when it isn't expected, you can cat the lock file and look for that PID in the output from ps to determine if the lock owner is still running or died before removing the lock file.
Even easier than using ps, you can use something like:
as long as the process that created the lock and the process running the above code are running with the same UID and permissions.
Last edited by Don Cragun; 05-17-2014 at 09:40 PM..
Reason: Add ps alternative.
This User Gave Thanks to Don Cragun For This Post:
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Discussion started by: apatil65
7 Replies
LEARN ABOUT HPUX
shlock
SHLOCK(1) General Commands Manual SHLOCK(1)NAME
shlock - create lock files for use in shell scripts
SYNOPSIS
shlock -p pid -f name [ -b ] [ -u ] [ -c ]
DESCRIPTION
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.
OPTIONS -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.
EXAMPLES
The following example shows how shlock would be used within a shell script:
LOCK=/var/run/innd/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
HISTORY
Written by Rich $alz <rsalz@uunet.uu.net> after a description of HDB UUCP locking given by Peter Honeyman. This is revision 1.9, dated
1996/10/29.
SHLOCK(1)