Running a cron job on Linux every six hours

Question

How can I run command every six hours every day?

I tried the following, but it did not work:

/6 * * * * *  mycommand

Answer 1

You should include a path to your command, since cron runs with an extensively cut-down environment. You won't have all the environment variables you have in your interactive shell session.

It's a good idea to specify an absolute path to your script/binary, or define PATH in the crontab itself. To help debug any issues I would also redirect stdout/err to a log file.