How to run SUDO... commands in cronjobs in Ubuntu 16.04?

Question

There are certain terminal commands which can only be run as a root user. If we try to execute them without sudo keyword, they fail with the Permission denied error. An example would be a command to make a directory/folder in certain locations.

I need to run one such command as a part of a cron job in my Ubuntu 16.04. Normally I could run the command with the sudo keyword in the terminal and I would be prompted to enter the root user's password and then the command would be executed successfully.

But now that I have to enter this command as a part of a cron job in my crontab file, how do I do this? How do I run such a command as a part of a cronjob?

Solution 1

Simply run crontab -e as root user . This would run your command with root permission and there is no need to add sudo before it .

However you can't login with root user and you need to perform your job as cron job you should specified full path in cron file :

 $ * * * * * /usr/bin/sudo /your/command

Also you can add NOPASSWD in front of your command in /etc/sudoers file to run command as root but without password .

Solution 2

Another option is to put it in the system-wide crontab at /etc/crontab (or in a file in /etc/cron.d), where you can specify the user each task is run at:

* * * * * root mkdir /foo/bar

Comments

[Pilot6]

cron runs with root. You don't need to add sudo.

[steeldriver]

Usually, one would put such jobs in root's crontab (sudo crontab -e rather than plain crontab -e) or use the system cron file /etc/crontab directly. Is there some particular reason you need to use a user crontab?

[George Udosen]

@steeldriver please what's the difference between sudo crontab -e and crontab -e?

[steeldriver]

@George sudo crontab -e inserts the command into root's crontab file /var/spool/cron/crontabs/root, whereas crontab -e inserts it into $USER's crontab file /var/spool/cron/crontabs/$USER

[George Udosen]

@steeldriver I guess my hunch was right!

[Sopalajo de Arrierez]

I don't think CRON runs as root, @Pilot6 . If you add * * * * * echo "hello" > /tmp/test.txt to CronTab as normal user, the newly created file will have your username's owner, group and permissions.

[Pilot6]

You can't add anything to crontab "as normal user".

[fkraiem]

There is no need for sudo since the task will run as root already.

[Ali Ghasempour]

@fkraiem As i said if you don't have access to root account for making new cron as root , you can use sudo .

[fkraiem]

If you have access to sudo, you typically have access to root.