Dexter wants to master the usage of the cron command for his upcoming RHEL-based LFCS exam. Please give him a high level overview of the top 3 things he needs to know about cron with examples.
Sure, here are the top 3 things Dexter needs to know about cron:
- Cron syntax: Cron uses a specific syntax to define the time and frequency of the tasks to be executed. The syntax consists of five fields, separated by spaces: minute (0-59), hour (0-23), day of the month (1-31), month (1-12), and day of the week (0-6, where Sunday is 0). The following example runs a command every day at 2:30 AM:
- 30 2 * * * /path/to/command
- Scheduling jobs in cron: To schedule jobs in cron, users can edit their own crontab file using the
crontab -ecommand. The crontab file contains lines of commands or scripts to be executed, each followed by the time and frequency using cron syntax. Here's an example to run a script every Monday at 1:00 PM:
- 0 13 * * 1 /path/to/script
- Cron commands: Users can manage their cron jobs using the
crontabcommand, which has a few useful subcommands. The
crontab -lcommand lists the user's current crontab file,
crontab -rremoves the user's crontab file, and
crontab -uis used to manage the crontab file of another user. Here's an example of how to remove a user's crontab file:
- crontab -r
By understanding the syntax, scheduling, and management of cron jobs, Dexter can effectively use cron to schedule and automate tasks in his RHEL system.