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]
