use cron to automate on ubuntu
Summary
- Cron is a job scheduler
- Install cron ,
apt install cron - It doesn't restart when a crontab file modified.
- The command crontab allows the user to modify entries to cron.
Use crontab
- Edit entries with
crontab -e - Add below lines to crontab file ```
Every minute write hello world to greetings.txt file.
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- echo “Hello World at $(date)” >> $HOME/greetings.txt ```
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Tail $HOME/greetings.txt
Cron job syntax
- [min] [hour] [ay of month] [month] [day of week] [command]
- field|values|
- [min]|0-59|
- [hour]|0-23|
- [day of month]|1-31|
- [month]|1-12|
- [day of week]|0-6|
- *|Every allowed value(minute)|
- 0-5|0th-5th minute|
Why is the cron jobs not running
su user- if you would like to run cron jobs with a user account
- check cron service
service cron status - if it doesn't run, run via
service cron start - check the cron job was loaded
crontab -l - edit the cron jobs
crontab -e``` -
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- echo “Hello World at $(date)” >> $HOME/greetings.txt ```
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tail $HOME/greetings.txt
Important
if you edit cron job with vim, please quit vim to load the cron jobs.
Reference
- https://blog.csdn.net/liaoyanyunde/article/details/86572370
- https://askubuntu.com/questions/1165969/ubuntu-18-04-on-wsl-cron-daemon-not-running-after-reboot
- https://askubuntu.com/questions/1241397/ubuntu-20-04-service-autostart
- https://www.cherryservers.com/blog/how-to-use-cron-to-automate-linux-jobs-on-ubuntu-20-04
- https://www.geeksforgeeks.org/tail-command-linux-examples/
- https://stackoverflow.com/questions/66314858/how-we-can-see-all-running-services-linux-machine
- https://askubuntu.com/questions/390201/how-to-see-login-history
- Why is the cron jobs not running