Late Post

Linux 101: The best way to use cron

Persevering with along with his Linux 101 sequence, Jack Wallen introduces you to the fundamentals of process scheduling with cron.

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For the admins who’re new to Linux, I wish to introduce you to the cron device. What’s cron? Merely acknowledged, cron means that you can create scheduled jobs on a Linux system. Say, as an example, you could have a backup script, known as backup.sh. You’ve got positioned that script in /usr/native/bin, so it may be executed globally and also you wish to be certain the backup occurs at both a selected time of day or commonly on a sure day of the week. 

How do you do that? You invoke cron. 

To make use of this, you add conjobs to your consumer’s crontab file. Go browsing to your Linux server and challenge the command:  

crontab -l

This may listing out all current cron jobs. To create a brand new cron job, you edit the crontab file. To do that, challenge the command: 

crontab -e

You’ll then add a line on the backside of that file to schedule the operating of your backup script. This is the place it will get a bit tough. The primary part of the road is the place you declare when the job is to run. At the start of that line there are 5 slots for time, that are (from left to proper): Minutes (0-59), hours (0-23), day of month (1-31), month (1-12), day of week (0-6, though you need to use Sunday, Monday, Tuesday, and so on., and Sunday may be represented by 0, 7, or Sunday). 

For instance you need that backup job to run each Sunday at 11pm. That entry may very well be 0 23 * * 0. A star signifies the job is to occur each iteration. On this case we have indicated the job ought to occur Sunday at 11pm, each week and each month. The remainder of this line would come with the express path to the executable, so /usr/native/bin/backup.sh. 

Our whole line could be 0 23 * * 0 /usr/native/bin/backup.sh. Save the crontab file with the Ctrl+X mixture (if nano is your editor of alternative), and the job is scheduled. You would possibly wish to be certain your job is listed with the crontab -l command. 

Congratulations, you’ve got simply scheduled your first cron job. This needs to be simply sufficient to get you going with this highly effective Linux scheduling device.

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