cron job question (for checking kernel updates)

[Ranjan Maitra]

On Wed, 2 Oct 2013 13:34:36 -0700 Rick Stevens <ricks at alldigital.com>
wrote:

> On 10/02/2013 01:06 PM, Ranjan Maitra issued this missive:
> > On Wed, 2 Oct 2013 09:26:32 -0700 Rick Stevens <ricks at alldigital.com>
> > wrote:
> >
> >> On 10/02/2013 08:10 AM, Ranjan Maitra issued this missive:
> >>> Hi,
> >>>
> >>> I have a cron job running which yum updates all my machines once a day.
> >>> All of these work fine.
> >>>
> >>> I also have a cron job which checks for kernel updates every hour and
> >>> sends me a message if an updated kernel has been installed. Here is the
> >>> relevant script:
> >>>
> >>> --- begin file called check-kernel.sh in my scripts/yum directory---
> >>>
> >>> #!/bin/bash
> >>>
> >>> latestkernel=$(rpm -q kernel |tail -n1|sed -e 's/kernel-//')
> >>>
> >>> #echo "$latestkernel"
> >>>
> >>> if uname -a | grep -qv "$latestkernel"; then
> >>> notify-send "Kernel UPDATE on ${HOSTNAME}: Running Kernel is $(uname
> >>> -r) but lat est installed rpm is ${latestkernel}; REBOOT required"
> >>> fi;
> >>>
> >>>
> >>> --- end file called check-kernel.sh ---
> >>>
> >>> (A bit wordy, I know.)
> >>>
> >>> I have verified that this is executable and works from the commandline
> >>> without any errors.
> >>>
> >>> I have the following set up via crontab -e:
> >>>
> >>> 0,15,30,45 * * * * nice -n 19 $HOME/.xplanet/download_xplanet_cloudmap
> >>> 5 * * * * nice -n 19 $HOME/scripts/yum/check-kernel.sh
> >>>
> >>> The first line downloads cloudmaps for use with xplanet and works just
> >>> fine (or appears to) and has done so for aeons.
> >>>
> >>> However, nothing happens (or appears to) for the second line.
> >>>
> >>> What is wrong here?
> >>
> >> The most common problem I've seen is that cron jobs typically have very
> >> limited paths and the executables you're running (notify-send, uname)
> >> may not be in the path the cronjob has. For giggles, do "echo $PATH" as
> >> the user the cronjob will run as. Then build a cron job that echos
> >> cron's concept of the path:
> >>
> >> 	#!/bin/bash
> >> 	echo $PATH >/tmp/pathecho.txt
> >>
> >> and have cron run that once as the same user. Look at the data in
> >> /tmp/pathecho.txt and I'll bet you'll find its far more restricted than
> >> that of an interactive shell.
> >
> > I tried this: here is what I got --
> >
> > $ echo $PATH
> > /bin:/usr/bin:/usr/local/bin:/usr/local/sbin:/usr/sbin:/home/user/bin
> >
> > $ cat /tmp/pathecho.txt
> > /usr/bin:/bin
> >
> > Clearly more restrictive as you suggest.
> >
> > However, what I do not understand is why this does not "work" though. I
> > do not understand because notify-send is in /usr/bin as well as in /bin:
> >
> > $ which notify-send
> > notify-send is /bin/notify-send
> > notify-send is /usr/bin/notify-send
> >
> > Both appear to be in the path. So where is the problem?
> >
> > I will also try the suggestions in the references in Matthew Miller's
> > response now.
> 
> You could try adding a "set -x" after the shebang line:
> 
> 	#!/bin/bash
> 	set -x
> 
> That tells bash to print out every expansion. Then change your cron
> entry to have a ">/tmp/test.txt 2>&1" at the end:
> 
> 	5 * * * * nice -n 19 $HOME/scripts/yum/check-kernel.sh >/tmp/test.txt 2>&1
> 
> Let the script run, then examine the /tmp/test.txt file to see what bash
> doesn't like. Don't forget to remove the "set -x" from the script and
> the ">... 2>&1" stuff from the crontab entry when you're done. Odds are
> it's a path issue or something that isn't expanding as you think it
> would because it's not an interactive shell running the script.
> -----------------------------------------------------------------

Here is what I get:

$ more /tmp/test.txt 
++ tail -n1
++ rpm -q kernel
++ sed -e s/kernel-//
+ latestkernel=3.11.2-201.fc19.i686
+ grep -qv 3.11.2-201.fc19.i686
+ uname -a
++ uname -r
+ notify-send 'Kernel UPDATE on subarnarekha.stat.iastate.edu: Running
Kernel is 3.11.1-200.fc19.i686 but latest installed rpm is
3.11.2-201.fc19.i686; REBOOT r equired'


I also tried explicitly putting in /usr/bin/notify-send (hardcoding it
in) to the original code, but no effect.

THanks,
Ranjan

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