Cron jobs

Cron tabs can be used to automate jobs on your system by running programs or scripts at prdefined times, dates or days, each user can have their own cron tabs or they can be run as root. To open a crontab, type the following in a [Terminal];

crontab -e

this will open in the vi text editor, but if you prefere the gedit text editor, run the following command;

export VISUAL=gedit

If you stick with vi then use Control+o followed by [Enter] to save your tab, then Control+x to [Exit].

When you run crontab -e, you will get an empty crontab with just the following [or similar] dispalyed;

# m h dom mon dow command

the headings are described below and I usually add these to the top of the file to make things easier to edit. So my crontab looks like this:

# m h dom mon dow command

# mins -> minutes (0-59)

# hours -> hour (0-24)

# DayOfMonth -> day of month (1-31)

# month -> month (1-12)

# DayOfWeek -> day of week (0-6) [Sunday is 0], or

# DayOfWeek -> day of week (mon – sun)

# You can use ‘,’ ‘-’ to give you 1,2,3,5 or 1-5 etc

# The * is used as a wildcard i.e every month

# m h dom mon dow command

# * * * * * /command

Examples;

each of the 6 command requires a space between them, here are a few examples;

### runs cron 2 mins past every hour ###

2 * * * * /home/martin/bin/play_sound.sh

### runs cron every 2 minutes ###

# m h dom mon dow command

*/2 * * * * /home/martin/bin/play_sound.sh

#01 * * * * root run-parts /etc/cron.hourly

#The run-parts script is simple enough: it just runs all the executables in the specified directory

### runs cron every fri at 15:30 ###

# m h dom mon dow command

30 15 * * * fri /home/martin/bin/backup.sh

Advertisements

Tags: , , , , , , ,

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s


%d bloggers like this: