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crontab format

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Article ID: 67
by: Reese K.
Posted: 08 Oct, 2012
Last updated: 10 Oct, 2014
Views: 1933

Here's a quick comment that can be added to users crontabs as a reminder to the crontab format:

# m h dom mon dow command

There are various ways to schedule a command to run, such as every 5 minutes, that would be considered acceptable format by some linux distributions, and not accepted by Solaris.

This kb article was intended to be kept simple as a reminder to what order the fields go, something that can be found easily by reading the man page.

[root@linux01 ~]# crontab -l
# m h dom mon dow command
#
# ssh blackhole to prevent brute force attacks
* * * * * /root/scripts/ssh-blackhole.bsh >/dev/null 2>&1
#* * * * * /root/scripts/ssh-blackhole2.bsh &>/tmp/ssh-blackhole.troubleshoot.log

# For details see man 4 crontabs

# Example of job definition:
# .---------------- minute (0 - 59)
# |  .------------- hour (0 - 23)
# |  |  .---------- day of month (1 - 31)
# |  |  |  .------- month (1 - 12) OR jan,feb,mar,apr ...
# |  |  |  |  .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat
# |  |  |  |  |
# *  *  *  *  * user-name command to be executed (full path name to command must be used)

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folder UNIX -> Linux
folder UNIX -> Solaris
folder UNIX -> Scripting

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