application background
Suppose your network has been connected, and now you want to update the entire system, and you need to automatically update the system at 2:15 am every day. How to do it?
solution
Step 1: Run the system update command, the first update will take a long time.
[root@localhost bin]# yum -y update
Step 2: Execute the same command for the second time, the speed is very fast, and the command is executed as follows.
[root@localhost bin]# yum -y update
Loaded plugins: fastestmirror, langpacks
Loading mirror speeds from cached hostfile
* base: centos.ustc.edu.cn
* extras: centos.ustc.edu.cn
* updates: centos.ustc.edu.cn
No packages marked for update
Step 3: Edit the crontab file of the scheduled task, the key is the last line
[root@localhost bin]# vim /etc/crontab
SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root
# For details see 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
15 2 * * * root /usr/bin/yum -y update