…with an open minded approach

incron

There is a great linux kernel functionality called “inotify” – which can emmit events on file changes. Its just great, have a look at its home page, I think its one of those linux pearls not much widely known…

Well, the thing is that using inotify, a tool called incron has been made, which is like a cron for file events (instead of time events), and that is really usefull when we want to detect file changes and react accordingly :) very usefull for server scripts :)

And so, without further delay, here it goes, the best resume I found so far detailing how to use incron: http://www.howtoforge.com/triggering-commands-on-file-or-directory-changes-with-incron

NOTES: there be dragons…

Inside you incrontabs, you must leave *only* 1 space between the <path> <mask> <cmd>. If you leave 2 or more spaces, then the 2nd (and more) spaces will be considered part of the <mask> or <cmd> and it will fail… I was leaving 2 spaces between <mask> and <cmd>, and incron did not work and in /var/log/syslog there were these messages

incrond[27693]: cannot exec process: No such file or directory

This was because of having 2 spaces… when I corrected to only 1 space, it began working correctly. Keep it in mind, so you dont suffer as much as I did to find it out :)

 

After editing with “incrontab -e”, check that “incrontab -l” shows the rules. If it does not show some rule, then that is because that rule has some error and was not recognized.

 

To debug what is happening behind the curtains, its usefull to have a “tail -f /var/log/syslog” on another terminal…

 

Cheers

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One response

  1. I started using incron. Awesome tool. Thanks for sharing the link. It is a nice and clear write up.

    March 30, 2014 at 21:24

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