{"id":247,"date":"2010-07-14T16:08:13","date_gmt":"2010-07-14T16:08:13","guid":{"rendered":"http:\/\/poojanwagh.opalstacked.com\/techblog\/?p=247"},"modified":"2010-07-14T16:08:13","modified_gmt":"2010-07-14T16:08:13","slug":"using-linux-command-lockfile-in-bash-scripts","status":"publish","type":"post","link":"https:\/\/tech.poojanblog.com\/blog\/unix-linux\/using-linux-command-lockfile-in-bash-scripts\/","title":{"rendered":"Using Linux command lockfile in bash scripts"},"content":{"rendered":"

I needed to create a script that runs a regression test. I intended to schedule this with a cron job. However, I found that sometimes, my cron jobs would collide with each other.<\/p>\n

So, I looked to Linux’ lockfile<\/code> command to create a file lock as a semaphore.<\/p>\n

Here’s the incantation:<\/p>\n

[cc_bash]<\/p>\n

# if we’re already running, exit
\nif ! lockfile -r 0 regression.lock; then
\n echo “regression.sh already running in area $1”
\n exit 1
\nfi
\n.\/tools\/regression.py
\nrm -f regression.lock<\/p>\n

[\/cc_bash]
\nIn this case, lockfile is set with a retry count of 0 -r 0<\/code>. However, I can chose to make this a retry of 1000 (for example). <\/p>\n

One can specify a timeout period (for example 60 seconds) with -s 60<\/code>. Note, however, that this timeout period starts when the lockfile was last modified\/created, and it forces the removal of the lockfile. This helps prevent zombie processes that were killed before they could remove their lockfile.<\/p>\n