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Automating routine maintenance—like database backups or log rotations—ensures a reliable Linux server. In this guide, you’ll learn how to schedule both recurring and one-off tasks using three core utilities: cron, anacron, and at.
The image features an icon of an alarm clock and the text "Schedule Tasks To Run At a Set Time" on a dark background.

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Scheduling Utilities Overview

UtilityUse CaseConfiguration File or Command
cronRepetitive jobs (minutes, hours, days)/etc/crontab & crontab -e
anacronPeriodic jobs when system may be off/etc/anacrontab
atOne-time, non-recurring tasksat <time> / atq / atrm

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1. cron

cron runs tasks on a fixed schedule. The system-wide crontab at /etc/crontab also serves as a syntax reference: 
# /etc/crontab
SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root

# ┌──────── minute (0 - 59)
# │ ┌────── hour (0 - 23)
# │ │ ┌──── day of month (1 - 31)
# │ │ │ ┌── month (1 - 12 or jan–dec)
# │ │ │ │ ┌ day of week (0 - 6 or sun–sat)
# │ │ │ │ │
35 6 * * * root /bin/some_command --some_options

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Field Descriptions

  • Minute: 0–59
  • Hour: 0–23 (0 = midnight)
  • Day of Month: 1–31
  • Month: 1–12 or jan–dec
  • Day of Week: 0–6 (Sunday = 0 or 7) or sun–sat
Special operators:
  • * : every valid value
  • , : value list (e.g., 15,45)
  • - : range (e.g., 2-4)
  • / : step (e.g., */4 for every 4th unit)
Always use full paths in your cron jobs. For example, find touch with which touch and use /usr/bin/touch.

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Edit Your User Crontab

  1. Open the editor: 
    crontab -e
  2. Add a job (runs daily at 06:35): 
    35 6 * * * /usr/bin/touch ~/test_passed

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Common cron Examples

  • Every Sunday at 03:00: 
    0 3 * * sun /usr/bin/touch weekly_backup
  • On the 15th of each month at 03:00: 
    0 3 15 * * /usr/bin/touch midmonth_task
  • Daily at 03:00: 
    0 3 * * * /usr/bin/touch daily_task
  • Hourly on the hour: 
    0 * * * * /usr/bin/touch hourly_task

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Managing crontabs

ActionCommand
List your crontabcrontab -l
List root’s crontabsudo crontab -l
Edit another user’s crontabsudo crontab -u username -e
Remove your crontabcrontab -r
Remove another user’s crontabsudo crontab -u username -r

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/etc/cron.* Directories

Place scripts in these directories to run at fixed intervals:
  • /etc/cron.hourly/
  • /etc/cron.daily/
  • /etc/cron.weekly/
  • /etc/cron.monthly/
Example—install an hourly script: 
touch myscript.sh
sudo cp myscript.sh /etc/cron.hourly/
sudo chmod +x /etc/cron.hourly/myscript.sh
Remove it with: 
sudo rm /etc/cron.hourly/myscript.sh

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2. anacron

When a system is off during a scheduled job, anacron runs missed tasks at boot. The file /etc/anacrontab uses this format: 
# period days   delay minutes   job-identifier   command
1               5               cron.daily       nice run-parts /etc/cron.daily
7              25               cron.weekly      nice run-parts /etc/cron.weekly
@monthly       45               cron.monthly     nice run-parts /etc/cron.monthly
3              10               test_job         /usr/bin/touch /root/anacron_created_this
  • period days: 1 = daily; 7 = weekly; @monthly
  • delay minutes: wait before running
  • job-identifier: unique name for logging
  • command: full path to execute
Example: Runs test_job every 3 days, 10 minutes after boot. Verify your configuration without executing jobs: 
sudo anacron -T
A silent output means the syntax is correct.

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3. at

Use at for one-off tasks. Schedule in 24-hour or relative formats: 
# Schedule a one-time job at 15:00 today
at 15:00
# at> /usr/bin/touch file_created_by_at
# at> <Ctrl+D>
Supported time formats:
  • Absolute: at '2:30 Aug 20 2022'
  • Relative: at 'now + 30 minutes'
  • Other: at 'now + 3 days', at 'now + 3 weeks', etc.
Ensure the atd daemon is running; otherwise at jobs won’t execute.

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Managing at Jobs

ActionCommand
List pending jobsatq
View job detailsat -c <job-number>
Remove a jobatrm <job-number>
Example—list and remove: 
atq
atrm 20
Practice with these tools to automate backups, cleanup tasks, and custom scripts. Proper scheduling keeps your Linux system reliable and maintenance-free.

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