How to log cron jobs?

Question

I want to know how I can see exactly what the cron jobs are doing on each execution. Where are the log files located? Or can I send the output to my email? I have set the email address to send the log when the cron job runs but I haven't received anything yet.

Answer 1

cron already sends the standard output and standard error of every job it runs by mail to the owner of the cron job.

You can use MAILTO=recipient in the crontab file to have the emails sent to a different account.

For this to work, you need to have mail working properly. Delivering to a local mailbox is usually not a problem (in fact, chances are ls -l "$MAIL" will reveal that you have already been receiving some) but getting it off the box and out onto the internet requires the MTA (Postfix, Sendmail, what have you) to be properly configured to connect to the world.

Answer 2

* * * * * myjob.sh >> /var/log/myjob.log 2>&1

will log all output from the cron job to /var/log/myjob.log

You might use mail to send emails. Most systems will send unhandled cron job output by email to root or the corresponding user.

Answer 3

There are at least three different types of logging:

1. The logging BEFORE the program is executed, which only logs IF the cronjob TRIED to execute the command. That one is located in /var/log/syslog, as already mentioned by @Matthew Lock.

2. The logging of errors AFTER the program tried to execute, which can be sent to an email or to a file, as mentioned by @Spliffster. I prefer logging to a file, because with email THEN you have a NEW source of problems, and its checking if email sending and reception is working perfectly. Sometimes it is, sometimes it's not. For example, in a simple common desktop machine in which you are not interested in configuring an smtp, sometimes you will prefer logging to a file:

    * * * *  COMMAND_ABSOLUTE_PATH > /ABSOLUTE_PATH_TO_LOG 2>&1
   

   • I would also consider checking the permissions of /ABSOLUTE_PATH_TO_LOG, and run the command from that user's permissions. Just for verification, while you test whether it might be a potential source of problems.
3. The logging of the program itself, with its own error-handling and logging for tracking purposes.

There are some common sources of problems with cronjobs: * The ABSOLUTE PATH of the binary to be executed. When you run it from your shell, it might work, but the cron process seems to use another environment, and hence it doesn't always find binaries if you don't use the absolute path. * The LIBRARIES used by a binary. It's more or less the same previous point, but make sure that, if simply putting the NAME of the command, is referring to exactly the binary which uses the very same library, or better, check if the binary you are referring with the absolute path is the very same you refer when you use the console directly. The binaries can be found using the locate command, for example:

$locate python

Be sure that the binary you will refer, is the very same the binary you are calling in your shell, or simply test again in your shell using the absolute path that you plan to put in the cronjob.

• Another common source of problems is the syntax in the cronjob. Remember that there are special characters you can use for lists (commas), to define ranges (dashes -), to define increment of ranges (slashes), etc. Take a look: http://www.softpanorama.org/Utilities/cron.shtml

Answer 4

By default cron logs to /var/log/syslog so you can see cron related entries by using:

grep CRON /var/log/syslog

https://askubuntu.com/questions/56683/where-is-the-cron-crontab-log

Answer 5

Incase you're running some command with sudo, it won't allow it. Sudo needs a tty.

Answer 6

Here is my code:

* * * * * your_script_fullpath >> your_log_path 2>&1