Shell script: Ensure that script isn't executed if already running [duplicate]

This question already has answers here: Closed 10 years ago.

Possible Duplicate:

Quick-and-dirty way to ensure only one instance of a shell s开发者_如何转开发cript is running at a time

I've set up a cronjob to backup my folders properly which I am quite proud of. However I've found out, by looking at the results from the backups, that my backup script has been called more than once by Crontab, resulting in multiple backups running at the same time.

Is there any way I can ensure that a certain shell script to not run if the very same script already is executing?

---

A solution without race condition or early exit problems is to use a lock file. The flock utility handles this very well and can be used like this:

flock -n /var/run/your.lockfile -c /your/script

It will return immediately with a non 0 status if the script is already running.

---

The usual and simple way to do this is to put something like:

if [[ -f /tmp/myscript.running ]] ; then
    exit
fi
touch /tmp/myscript.running

at the top of you script and

rm -f /tmp/myscript.running

at the end, and in trap functions in case it doesn't reach the end.

This still has a few potential problems (such as a race condition at the top) but will do for the vast majority of cases.

---

A good way without a lock file:

ps | grep $0 | grep -v grep > /var/tmp/$0.pid
pids=$(cat /var/tmp/$0.pid | cut -d ' ' -f 1)
for pid in $pids
do
   if [ $pid -ne $$ ]; then
      logprint " $0 is already running. Exiting"
      exit 7
   fi
done
rm -f /var/tmp/$0.pid

This does it without a lock file, which is cool. ps into a temp file, scrape the first field (pid #) and look for ourselves. If we find a different one, then somebody's already running. The grep $0 is to shorten the list to just those instances of this program, and the grep -v grep gets rid of the line that is the grep itself:)

---

You can use a tmp file.
Named it tmpCronBkp.a, tmpCronBkp.b, tmpCronBkp.c... etc. Releated of yout backup script.

Create it on script start and delete it at the end...

In a while, check if file exist or not and what file exist.

Have you tried this way?