Ed Avis Ed Avis - 3 years ago 166
Linux Question

crontab (cronie), run certain days of the month

I want to make a crontab entry which will run on every weekday except the 1st, 2nd, and 3rd of each month. Here's what I have:

45 8,12,16 4-31 * 1-5 my_program


I thought that this had the following meaning:

minutes: 45 past the hour
hours: 8, 12, and 16
day of month: 4th to 31st inclusive
month: all
day of week: Monday to Friday inclusive


That is what I read in the
crontab(5)
manual page. However, I can see that the job ran at 08:45 today, Monday 2nd October. I am certain the crontab file was loaded correctly (and
crontab -l
shows it); it wasn't changed recently. The system date and time as shown by
date
is also correct.

What am I missing to make sure my cron job only runs from the 4th onwards? I am using Fedora Linux:

% rpm -qf `which crontab`
cronie-1.5.0-3.fc23.x86_64
% rpm -q fedora-release
fedora-release-23-1.noarch

Answer Source

From crontab manual:

Note: The day of a command's execution can be specified by two fields — day of month, and day of week. If both fields are restricted (i.e., aren't *), the command will be run when either field matches the current time. For example, ``30 4 1,15 * 5'' would cause a command to be run at 4:30 am on the 1st and 15th of each month, plus every Friday. One can, however, achieve the desired result by adding a test to the command (see the last example in EXAMPLE CRON FILE below).

The mentioned example looks like this:

0 4 8-14 * *    test $(date +\%u) -eq 6 && echo "2nd Saturday"

So in your case it would be like this (not tested):

45   8,12,16 4-31 * *  test $(date +\%u) -lt 6 && my_program
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