CRON JOB | CHEAT SHEET

Cron Jobs

  • Cron – A time based job scheduling service
  • Crontab -A program to create, read, update, and delete your schedules.
  • Use cron to schedule and automate tasks.

A crontab or table is used to specify when commands will be executed by cron. Any line starting with “#” within the editor will be ignored, as It’s for comments.
*   *   *   *   *   Command
|    |    |    |    |
|    |    |    |    + — Day of the week (0-6)
|    |    |    +   —- Month of the Year (1-12)
|    |    +    ——–Day of the month (1-31)
|    +   ————-Hour  (0-23)
+   —————–Minute (0 – 59)

 

Example : # Run every monday at 7 AM
0   7   *   *    1   /opt/sales/bin/weekly-report
|     |    |    |    |
|     |    |    |    + — Day of the week (0-6)
|     |    |    +   —- Month of the Year (1-12)
|     |    +    ——–Day of the month (1-31)
|     +   ————-Hour  (0-23)
+   —————–Minute (0 – 59)

If any output is generated by a cron job, it will be mailed by you.
Example: #Run at 2:00 every day and send the output to a file log

0    2    *    *    *    /root/backupdb > /tmp/db.log 2>&1

If you want to run a command to run every thirty minutes simply use a 0,30 or 0/2 in the minutes tab. If you want to run a command every 5 minutes at the top of an hour, use 0-4 in the minutes tab.

Shortcuts:
@yearly      0   0   1   1   *
@anually    0   0   1   1   *
@monthly   0   0   1   *   *
@weekly     0   0   *   *   0
@daily         0   0   *   *   *
@midnight   0   0   *   *   *
@hourly       0   *   *   *   *

Using the Crontab Command:

# crontab file  – Install a new crontab from file
# crontab -l    – List your cron jobs
# crontab -e  – Edit your cron jobs, will take you to the editor
# crontab -r   – Remove all of your cron jobs

As usual, you can view the manpage for additional option and any answers to your questions.

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