watchdog script to keep process running with cron

Thanks, but I'm actually trying to keep an SSH tunnel alive for a database connection, and the:

/path/to/myprogram & > $HOME/tmp/myprogram.log &

line doesn't seem to work out-of-the-box for ssh.

The above is a general format applicable to all programs. Specifically for SSH, you should try something like this:

/usr/bin/ssh -N "-L 12671:127.0.0.1:3306" -oServerAliveInterval=60 -oServerAliveCountMax=3 -oBatchMode=yes -oConnectTimeout=10 "USERNAME@webNNN.webfaction.com" &

Where the following would be replaced by your information:

• 12671 - your local port on your server. The source of the tunnel.
• 3306 - the destination port of the tunnel. Would point to the database port. (use 3306 for mysql, 5432 for postgresql)
• USERNAME - your username.
• webNNN - the number of your webserver; for example, web200.webfaction.com

To be more aggressive in automatically handling migrations and/or IP changes by ignoring host credentials, add the -oUserKnownHostsFile=/dev/null -oStrictHostKeyChecking=no options to the above command as well.

I'm new to Bash scripting, and have a problem with the watchdog script. My user name is replicounts, and the program that needs an occasional restart is aff.py.

The crontab is working fine, and my watchdog.sh script (below) is being executed when it should. But the resulting watchdog.log is:

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/home/replicounts/cron/watchdog.sh: line 7: python3.1: command not found

I manually run the program (in webapps/aff/htdocs) with:

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nohup python3.1 aff.py &

The python3.1 is available interactively in all my directories. Also note:

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[replicounts@web214 cron]$ echo $PATH
/usr/kerberos/bin:/usr/local/bin:/bin:/usr/bin:/home/replicounts/bin
[replicounts@web214 cron]$ ls -a /home/replicounts/bin
.  ..  .ph

FYI, my watchdog.sh script is:

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[replicounts@web214 cron]$ cat watchdog.sh
#!/usr/bin/env bash
PIDFILE="$HOME/tmp/aff.pid"
if [ -e "${PIDFILE}" ] && (ps -u $USER -f | grep "[ ]$(cat ${PIDFILE})[ ]"); then
  echo "Already running."
  exit 99
fi
python3.1 $HOME/webapps/aff/htdocs/aff.py > $HOME/tmp/aff.log &
echo $! > "${PIDFILE}"
chmod 644 "${PIDFILE}"

What needs to be changed?

John

cron doesn't operate with the same PATH as your shell account, so try using the full path to everything in your script and in your cron jobs. For example, instead of python3.1, use /usr/local/bin/python3.1. You can find the full path for a particular tool with the which command, eg:

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[root@web214 ~]# which python3.1
/usr/local/bin/python3.1

Or, you can explicitly set the PATH in your script.

Hope that helps!

For reference, here is cron's environment:

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SHELL=/bin/sh
USER=<username>
PATH=/usr/bin:/bin
PWD=/home/<username>
SHLVL=1
HOME=/home/<username>
LOGNAME=<username>

Additionally, cron runs the commands directly from your $HOME directory. To test cron commands, I like to run something like this:

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cd $HOME
unset $(env | awk -F= '/^\w/ {print $1}' | xargs)
export USER=$(/usr/bin/whoami)
export SHELL=/bin/sh
export PATH=/usr/bin:/bin
export PWD=/home/$USER
export SHLVL=1
export HOME=/home/$USER
export LOGNAME=$USER

And then run the command exactly as it appears in the crontab.