One, for conditional loop statement
for variable name in value list for user name in list file
do do
Command sequence Create user and set password
done done
Two, while conditional loop statement
while conditional test operation while not guessing the correct price
do do
Command sequence Repeatedly guess the price of goods
done done
Three, case conditional test statement
case variable value in
Mode 1)
Command sequence 1
；；
Mode 2)
Command sequence 2
；；
.......
*)
Default command sequence
esac
Four, planning task service procedures
1. One-time scheduled task: at 19:10 at>reboot at>ctrl+D key combination at -l (to view the one-time scheduled task that has been set but not executed); at -c (to view the detailed content of the scheduled task) ; At -q (name the scheduled task); atrm the number of the scheduled task (delete the scheduled task).
2. Long-term scheduled tasks: crontab -e (create and edit scheduled tasks); crontab -l (view current scheduled tasks); crontab -r (delete a scheduled task); crontab -u (edit other's scheduled tasks)
Use crond to set the parameter format of the task: minute, hour, day, month and week. Command (the minute field must have a value, and it must not be empty or *)
crontab -e Create a new scheduled task and enter the following information, save and exit
25 3 * * 1,3,5 /user/bin/tar -czvf backup.tar.gz /home/wwwroot Every Monday, Wednesday, and Friday at 3:25 in the morning, use the tar command to check the data directory of a website Pack and process it as a backup file
systemctl status crond View the status of the crond service to see if it is started
systemctl restart crond
systemctl enable crond
*/10 * * * * /user/bin/reboot restart every 10 minutes
10 2,5,10 * * * /user/bin/reboot every day at 2:5:10 and 10 minutes
Five, user identity and capabilities
Administrator UID (User IDentification) is 0: system administrator user
Redhat 5/6 system user UID 1-499 ordinary user UID 500-65535
Redhat 7/8 system user UID 1-999 ordinary user UID 1000~~~~
When each user is created, a basic user group with the same name will be automatically created. This basic user group has only this user. If the user is included in another user group in the future, this other user group is called an extended user group. A user has only one basic user group, but there can be multiple extended user groups.
1. useradd: used to create a new user, the format is "useradd [option] username"
Parameters: -d (specify the user's home directory); -e (account expiration time, format is YYYY-MM-DD); -u (specify the user's default UID); -G (specify one or more extended users Group); -g (specify an initial user basic group); -N (not create a basic user group with the same name of the user); -s (specify the user's default Shell interpreter)
2. groupadd: used to create a user group, the format is "groupadd [option] group name"
groupadd -g 88888 haha
useradd -g 88888 xiaotan
id xiaotan
vim /etc/group can enter it to modify, delete the added extended group, save and exit
3.usermod: Used to modify the attributes of the user, the format is "usermod [option] username"
usermod -u 8889 abc Modify the UID number value of abc users
4. passwd: used to modify user password, expiration time, authentication information, etc., the format is "passwd [option] [user name]"
5.userdel: Used to delete users, the format is "userdel [option] username"
Parameters: -f (force delete user); -r (delete user and user home directory at the same time)