UNIX for Dummies Questions & Answers

Hello All,

I was wondering if someone could take a quick glance at this Cron job and tell me if it's going to do what I am expecting.

I want it to run everyday at 8:00 am and 5:00 pm.

And the line in Crontab looks like:

Code:

0 8,17 * * * /usr/local/myScript.sh

Does that look correct?

Thanks in Advance,
Matt

Looks like the correct format.

Hey Joey, thanks for the quick reply!

Cool, thanks for taking a look. Its a pretty important server so I just wanted to make sure it was correct before I put it into effect...

Thanks Again Much Appreciated,
Matt

Just a few suggestions:

1. Your script should definitely not reside in "/usr/local", but in "/usr/local/bin". See the File System Hierarchy Standard, which is a very good guideline for what to place where.

2. Have you made sure you do not fall for the Cron Problem Number One?

3. You should redirect <stdout> and <stderr> in your cron line, either to a log file or to "/dev/null". Otherwise you will get strange mails to the user account the cron job runs under. Modify your line to something like this:

Code:

0 8,17 * * * /usr/local/bin/myScript.sh 1>/dev/null 2>/dev/null

Corollary: you might ask yourself why i did not use "> /dev/null 2>&1". First, i find this easier to read. Second, this will do the same regardless of order, while "2>&1 > /dev/null" will not do the same when written this way or the other way round.

I hope this helps.

bakunin

Hey bakunin, thanks for the reply.

Sorry I didn't put my actual path in there I was just throwing something in there as a placeholder more or less...

The script is actually located at "/usr/local/nagios/libexec/...."
Was the "Cron Problem Number One" page just saying don't use relative paths, use absolute? If that's the case then I'm ok there.

Also, my script doesn't have any real STDOUT. The script interacts with the Nagios' NSCA Daemon which works with the
Nagios Host Server, by sending some output in a specific format to the Nagios Server for processing.

What my script does is write its output to a txt file, then while still in the script I execute the "send_nsca" Command which
is what actually sends the contents of the txt file to the Nagios Server...

I put those cron jobs into effect yesterday before I left work and added a line in my script temporarily (which I removed this
morning) that wrote the Date/Time and which option was used (because there a 5 commands in cron, same script for all,
but each with a different CLI Option) to a makeshift log file to see if everything was executed at the correct times and what not,
and when I checked this morning the times and CLI Options matched perfectly with what I wanted it to do!


Thanks Again guys for all your tips, the info is much appreciated!


Thanks Again,
Matt

Actually this is a small part of it. The basic problem is: a scirpt started from commandline inherits the environment of the login shell, but a script started from cron inherits the environment of "init", which is next to empty. Guess what happens to heirs of poor processes? Sometimes they go broke, so to say. ;-))

This usually lands here in the form of: "my script worked perfectly from commandline, then i put it in a crontab and since then i doesn't work any more". We have these threads about once a week, which is why i started to call this "Cron Problem Number One". As you relate that your script works this seems not to be the case, but that was not clear from the start so i thought i'd mention it to put it on your checklist.

Regarding the suggested redirections: you just need to have some error condition and some command will write something to stdout. I would redirect any job in cron in the way i mentioned, just to be sure.

I hope this helps.

bakunin

Hey Bakunin, thanks for the reply!

No worries, I'm always willing to take some constructive criticism...
Thanks for the info about cron, didn't know that (that it inherits the environment from init).

I'll be sure to add some logging stuff to the script and have it redirected as suggested.


Thanks again for the help, very much appreciated!


Thanks Again,
Matt