cron
time-based job scheduler daemon
TLDR
SYNOPSIS
crontab [options] [file]cron [options]
DESCRIPTION
cron is the daemon that executes scheduled commands. crontab manages per-user cron tables. Together they provide time-based job scheduling for automated system maintenance, backups, log rotation, and recurring tasks.The cron daemon starts at boot and runs continuously, waking up every minute to check all crontab files for jobs that need execution. Each user can have their own crontab file, and the system has crontabs for system-wide maintenance. Jobs run in the background without user interaction, making cron essential for Unix/Linux system administration.
CONFIGURATION
/etc/crontab
System-wide crontab file with additional user field for running jobs as specific users./etc/cron.d/
Directory containing system crontab files in the same format as /etc/crontab./var/spool/cron/
Directory containing per-user crontab files managed via the crontab command.
CRONTAB OPTIONS
-e
Edit crontab-l
List crontab-r
Remove crontab-u user
Operate on user's crontab (requires root)-i
Prompt before removal
CRON DAEMON OPTIONS
-n
Run in foreground-m command
Mail command (or "off" to disable)-s
Log to syslog-p
Accept any user crontab
CRONTAB SYNTAX
│ │ │ │ │
│ │ │ │ └─ Day of week (0-7, Sun=0 or 7)
│ │ │ └─── Month (1-12)
│ │ └───── Day of month (1-31)
│ └─────── Hour (0-23)
└───────── Minute (0-59)
SPECIAL STRINGS
@reboot: Run at startup@hourly: 0 * * * *@daily: 0 0 * * *@weekly: 0 0 * * 0@monthly: 0 0 1 * *@yearly: 0 0 1 1 *
INSTALL
CAVEATS
Jobs run with limited environment. Set PATH explicitly in crontab. Output mailed to user unless redirected. Use MAILTO="" to disable mail.
