Crontab

Index

Options:：

-e: Edit the timer settings for the specified user;
-l: List the timer settings for the specified user;
-r: Remove the timer settings for the specified user;
-u: Specify the username for which the timer is to be set;

The crontab file located in the /etc directory manages periodic tasks such as writing cached data to the disk and cleaning logs. It serves as the configuration file for system task scheduling.
Tasks that users wish to perform periodically, such as data backups and scheduled email reminders, can be customized using the crontab tool. All user-defined crontab files are stored in the /var/spool/cron directory.

Template file

# /etc/crontab: system-wide crontab
# Unlike any other crontab you don't have to run the `crontab'
# command to install the new version when you edit this file
# and files in /etc/cron.d. These files also have username fields,
# that none of the other crontabs do.

# Specifies the shell the system should use
SHELL=/bin/sh
# Specifies the path to execute system commands
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
# Specifies that crond's task execution information will be sent via email to the root user
MAILTO=root

# For details, refer to man 4 crontabs

# Example of job definition:
# .---------------- minute (0 - 59)
# |  .------------- hour (0 - 23)
# |  |  .---------- day of month (1 - 31)
# |  |  |  .------- month (1 - 12) OR jan,feb,mar,apr ...
# |  |  |  |  .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat
# |  |  |  |  |
# *  *  *  *  * user-name  command to be executed

Example

# Write the script content to the null device
*/5 * * * * /root/XXXX.sh &>/dev/null 2>&1
# Write the script content to the specified file
*/5 * * * * /root/XXXX.sh > /tmp/load.log 2>&1 &

# Execute every minute
* * * * * command
# Execute at the 3rd and 15th minute of every hour
3,15 * * * * command
# Execute at the 3rd and 15th minute of 8 to 11 in the morning
3,15 8-11 * * * command
# Execute at the 3rd and 15th minute of 8 to 11 in the morning every Monday
3,15 8-11 * * 1 command
# Restart smb at 21:30 every night
30 21 * * * /etc/init.d/smb restart
# Restart smb at 4:45 on the 1st, 10th, and 22nd of every month
45 4 1,10,22 * * /etc/init.d/smb restart
# Restart smb at 1:10 on Saturdays and Sundays
10 1 * * 6,0 /etc/init.d/smb restart
# Restart smb every 30 minutes between 18:00 and 23:00 every day
0,30 18-23 * * * /etc/init.d/smb restart
# Restart smb every hour between 23:00 and 07:00
* 23-7/1 * * * /etc/init.d/smb restart
# Restart smb on the 4th of every month and at 11:00 on Mondays to Wednesdays
0 11 4 * mon-wed /etc/init.d/smb restart
# Restart smb at 4:00 on the 1st of January
0 4 1 jan * /etc/init.d/smb restart

【Note】

It is essential to use absolute paths in the crontab file, including for any custom scripts you have written.