Cron Manual

Files

• “username” user’s cron file location

  /var/spool/cron/{username}

• Root’s crontab file

  /var/spool/cron/root

• Configuration file for cron,

  /etc/crontab

Cron service

service crontd status
service crontd start
service crontd stop
service crontd restart

Valid values for cron job

• Minutes – from 0 to 59
• Hours – from 0 to 23
• Day of month – from 1 to 31
• Month – from 1 to 12 (also from jan to dec)
• Day of week – from 0 to 6 (0 is sunday, also from sun to sat)

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Cron monitoring commands

• Check cron config

  chkconfig --list | grep crond
  ps -ef | grep cron

• Show current cron jobs of user

  crontab -l

• Show current cron jobs of user root

  crontab -u root -l

• Delete cur cron jobs

  crontab -r

• Delete user’s cur cron jobscrontab -u root -r
• Edit the cron tab jobscrontab -e
• Edit the user’s cron tab jobs

  crontab -u root -e

• Install cron job for user root from file /var/spool/cron/root content

  crontab -i -u root /var/spool/cron/root

Example of cron file

# Cron example file /var/spool/cron/root
# (Created for Boot1935)
SHELL=/bin/bash
MAILTO=root

# 1-12 hours
* 0,1,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23 * * * /root/reich3/saytime.sh
# minutes with 5 minute interval
5,10,15,20,25,30,35,40,45,50,55 * * * * /root/reich3/saytime.sh
# hours 0-1, 9-23
* 0-2,9-23 * * * play /root/reich3/saytime.wav
# every minute
0-59 * * * * /root/reich3/saytime.sh