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=====Cron=====
return to DevLinux

====Basic Commands====
%%
# load a file as user's cron
$ crontab ~/mycrons/master.cron

# list user's cron
$ crontab -l
%%

====Syntax====
===Notes===
~- ""<tt>*</tt>"" in min field means run every minute
~- ""<tt>*/4</tt>"" in min field means **run every** 4 minutes (**not** 60/4 or every 15 minutes)

===Basic cron file line syntax===
%%
# cron (run every minute)
# M H DM MO DW SCRIPT
* * * * * touch /tmp/klenwell_test_cron

# cron.d (run every 15 minutes every other day)
# M H DM MO DW USER SCRIPT
*/15 * * * */2 klenwell touch /tmp/cron_test.txt
%%
Cron Fields:
M : Minutes
H : Hours
DM : Day of Month
MO : Month
DW : Day of Week

====cron.d====
To enable a cron file through the cron.d directory, create a symbolic link. For example:
%%
$ sudo ln -s ~/mycrons/crond-test.cron /etc/cron.d/crond-test
%%

===Sample cron.d File===
%%(bash)
# cron.d file
# to activate, link to /etc/cron.d: [sudo] ln -s [path/]fname.cron /etc/cron.d/link_name

# +---------------- minute (0 - 59)
# | +------------- hour (0 - 23)
# | | +---------- day of month (1 - 31)
# | | | +------- month (1 - 12)
# | | | | +---- day of week (0 - 6) (Sunday=0 or 7)
# | | | | |
# M H DM MO DW USER SCRIPT
* * * * * klenwell touch /tmp/crontest.txt
%%

====References====
[[http://www.unixgeeks.org/security/newbie/unix/cron-1.html | Intro to Cron]] (unixgeeks.org)