On Tue, 18 Mar 2008 10:54:46 -0700, Bob McGowan wrote:

>>> Now the crontab reads:
>>>
>>>  * * * * *    root    is_burning || logger get executed.
>>>
>>> + set -x
>>> + ps -eaf
>>> + grep -E  -[dts]ao |cdrdao *write|growisofs.*speed='
>>> root     15306 15295  0 09:29 ?        00:00:00 grep -E cdrecord.* 
>>> -[dts]ao |cdrdao *write|growisofs.*speed=
>>> + exit 0
>>>
>>> $ is_burning || echo not burning CD/DVD
>>> not burning CD/DVD
>>>
>>> I.e., having put the 'ps | grep' part into a shell script, the 
>>> behavior is still the same.
>>> Does it has anything to do with busybox?
> 
> If I followed the above discussion correctly, the OP's concern is that 
> sometimes the grep will return a result, even when the specified cd 
> related programs are not running, and that this happens when the grep is 
> run from cron but not from the command line.

Exactly. Right ON!
 
> If this is correct, the results you're seeing can in fact happen in 
> either case.  Whether you see a result or not is totally dependent on 
> the process scheduler, timing of execution slices and perhaps your 
> processor speed and/or if it's an SMP environment.
> 
> What's happening is the grep you're running is sometimes finding itself. 
>   For example:
> 
>    ps -ef|grep firefox|cut -c1-60
>    rmcgowan 17073 16974  0 08:13 ?        00:00:00 /bin/sh /usr
>    rmcgowan 17080 17073  0 08:13 ?        00:00:00 /bin/sh /usr
>    rmcgowan 17106 17080  0 08:13 ?        00:00:59 /usr/local/f
>    rmcgowan 30742 17130  0 10:49 pts/1    00:00:00 grep firefox
> 
> The last line is the grep that ran.  So, one line is sometimes returned, 
> even when firefox is not running.
> 
> There are a number of ways to get around the problem.  My favorite is to 
> use something that will show up in the ps output for the grep itself but 
> which will not be part of what you're looking for.  But this does 
> require using either the -l or -f options (which it looks like you are).
> 
>    ps -ef | grep '[f]irefox'
> 
> will eliminate the grep command itself because the pattern can never 
> match itself. . . 
>
> I hope this helps solve your problem.

Bingo!!!

That's exactly the reason. As you can see from my script that I've already
applied the '[]' trick, but the trick wasn't applied to all 3 grep cases.
Having added '[]' to each of the grep cases, I finally see:

 Mar 18 21:29:01 cxmr logger: get executed.

Bravo!!! 

Thanks a lot to everyone who replied!

-- 
Tong (remove underscore(s) to reply)
  http://xpt.sourceforge.net/techdocs/
  http://xpt.sourceforge.net/tools/


-- 
To UNSUBSCRIBE, email to [EMAIL PROTECTED] 
with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]

Reply via email to