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Old 07-10-2007, 08:35 AM   #1
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Registered: May 2005
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Weird interaction between wget and cron


I've written a cron script to monitor a website for downtime. Essentially it wgets the website, greps it for a known string, and if the string doesn't show up, emails me. It also has a check to make sure it emails me at most once an hour, so my box doesn't fill up:

rm runlast
date >> runlast

y="The following services on are broken!  Oh noes!  "

wget -O openmrs1.html
x=`cat openmrs1.html|grep /openmrs/dwr/interface/DWRAlertService.js`
if [ ! -n "$x" ]
y=$y" "

wget -O openmrs2.html
x=`cat openmrs2.html|grep Meeting,Community,Developers,Developers`
if [ ! -n "$x" ]
y=$y" "

wget -O openmrs3.html
x=`cat openmrs3.html|grep /wiki/WikiStart?action=diff`
if [ ! -n "$x" ]
y=$y" "

wget -O openmrs4.html
x=`cat openmrs4.html|grep templates/subSilver/images/openmrs-small-logo.gif`
if [ ! -n "$x" ]
y=$y" "

if test $z -eq 1
a=`cat olddate`
b=`perl -le 'print time'`
c=`expr $b - $a`
echo `date`" "$y$c >> openmrslog
        if test $c -ge 3600
        rm olddate
        echo $b >> olddate
        echo $y | mail
The script works when run via ssh, but when run via cron it emails me, but the wgets fail. That is, if the correct files are already there, it will not email me regardless of whether the website is down: it doesn't try to fetch them! Along the same line, if the correct files aren't already there (eg openmrs1.html, openmrs2.html... aren't there), then it will not try to download them, and will just email me. I don't understand this -- why does it work via ssh, but not cron, and, more importantly, how can I fix it?!

My crontab -l output is:
0,10,20,30,40,50 * * * * /u/1/a/ata2114/>/dev/null 2>&1
Any help would be appreciated!

Old 07-10-2007, 10:09 AM   #2
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Registered: Dec 2005
Location: Campinas/SP - Brazil
Distribution: SuSE, RHEL, Fedora, Ubuntu
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My first guess is maybe there is no PATH to wget, perl or other program you call in your script; the environment in a cronjob is not the same as is in a interactive shell.

To check, remove the redirections in the cronjob, to get the output and errors to help to diagnose the problem.

Last edited by marozsas; 07-10-2007 at 10:23 AM.
Old 07-11-2007, 02:29 AM   #3
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Registered: Aug 2004
Location: Sydney
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cron doesn't have hardly any shell vars or PATH (by default) unless you set them, so always specify complete dirpaths to all progs and files.
Incidentally cron usually emails root if it has a problem.


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