RHCSA5

user 、 Group and sudo
Every user has a id Number
root Of uid Number is 0
uid 1-200 Users automatically created by the system
uid 201-999 Install third-party applications
uid 1000+ Other ordinary users created manually

/etc/passwd
Storage content
First column ： user name
Second column ：x（ Originally password , Move back ）
The third column ：uid
The fourth column ：gid
Followed by notes 、 Home directory 、 Login mode

Group
Each user belongs to a group , Defined as a collection of users

/etc/group
Storage content
First column ： Group name
Second column ：x（ Originally password , Move back ）
The third column ：gid

obtain root jurisdiction
su Switching users , Temporary switching ,root No password is required for switching , The home directory doesn't change , I won't use the environment variables of new users
su - Switching users , Home directory transformation , Will use the environment variables of new users

sudo Raise the right
visudo To write
vim /etc/sudoers.d

visudo Specific operation
visudo
Cursor to end

rewrite ,student Can perform all privileges

rewrite ,student It can be executed useradd and su

Log of execution

/var/log/secure

Create user
useradd
-d Specify home directory （ Home directory exists , Default home）
-e Specify expiration date
-g Appoint gid

tail -1 /etc/passwd

tail /etc/shadow
Random string ; password （hash）, Creation time （ Days , The current date -1970.7.1）; The password should be changed on the day when it is created ; Change the password for the number of days used ; Password expiration warning time

useradd No password , Use passwd To set the password

usermod
-u Group number user
-G Specify a new additional group
-a Specify to add an additional group
-L Lock the user , Unable to log in temporarily
-u user Unlock

groupadd Create group
groupmems
-d Delete a user of the Group -g The specified group

groupdel -r
userdel -r
-r Use as much as possible

chage The number of days to change the user's password