cron job on centOS 6.5

Question

I have used these 2 references to insert a new crontab entry.

redhat

ubuntu

I have created a new bash file and moved it to /usr/bin. That sh file has execute permissions for the root user and the admin group. The bash file just echos a line to a log file and then calls a java program. I have tested the sh file as root, manually. It runs fine. My crontab entry looks like this...

 @hourly      /usr/bin/foo.blah.sh

It's supposed to run at the top of every hour. The echo statement is not getting printed to the log file so I don't think crond is calling it at all. Also, when I visually monitor processes in "top", the job never appears. I have run "service crond status" to verify the cron daemon is running. The documentation says that restarting the daemon is not necessary. What else could I be doing wrong?

Answer 1

You don't actually say where the crontab entry is, but based on your comment that crontab -l outputs no crontab for root, I would hazard a guess that you have added a file under one of the /etc/cron.* directories, which contains files corresponding to various cron jobs. This answer assumes that that is the case.

Those files have a format that is slightly different from the user-specific crontab that you edit through crontab -e. Specifically, they include a username field just before the command, which is not included in the user-specific crontab (which at least on my system are stored under /var/spool/cron/crontabs, but please don't abuse that information; the exact location is an implementation detail of the cron daemon you happen to be running, and you should use the documented interfaces for managing those files).

As a result, you should change

@hourly      /usr/bin/foo.blah.sh

to

@hourly user /usr/bin/foo.blah.sh

where user is the name of the user account to run the script as. It should then run fine.

I really encourage you to not run cron jobs as root unless you must; doing anything as the superuser is always a security risk. If possible, give the script its own account with restricted access. (This is the principle of least privilege; least, that is, that is required for it to do its job.) As a general rule, you should place system-local files into /usr/local to avoid clashes with the system package manager; additionally, to avoid confusion, don't place things in any bin directory that need root privileges to work, use sbin instead.

Answer 2

In the past, when adding scripts to cron, I always led the line with sh, like so:

@hourly    sh /usr/bin/foo.blah.sh