A cronjob is a time-based task scheduler in Unix-like computer operating systems. Cron allows users to schedule jobs (commands or shell scripts) to run regularly at specific times or dates. It is commonly used to automate system maintenance or administration.
Cron is controlled by a crontab file (cron table), which is a configuration file that specifies shell commands to be executed at specific times. The crontab files are stored where the job lists and other instructions to the cron daemon are kept. Users can have their own individual crontab files, and often there is a system-wide crontab file (usually in /etc or a subdirectory of /etc) that only system administrators can edit.
Each user can edit their own crontab file using the command-line utility called crontab.