SHLOCK(1)SHLOCK(1)NAMEshlock - create lock files for use in shell scripts
SYNOPSISshlock-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 packages.
-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=<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
BUGSshlock assumes that it will not be used in an environment with multiple
locks/unlocks in a short time (due to a race condition). That is,
shlock is intended for daily or hourly jobs.
HISTORY
Written by Rich $alz <rsalz@uunet.uu.net> after a description of HDB
UUCP locking given by Peter Honeyman. This is revision 5794, dated
2002-10-01.
SEE ALSOinn.conf(5)SHLOCK(1)
