Theory: ------------Account and permission management

Overview of user accounts and group accounts

Linux controls resource access based on user identity

• user account
  • Super user, ordinary user, program user
• Group account
  • Basic group (private group)
  • Additional group (public group)
• UID and GID
  • UID (User IDentity, user identification number)
  • GID (Group IDentify, group identification number)

User account file

Save basic information such as user name, host directory, and login shell

• File location: /etc/passwd
• Each row corresponds to a user account record
  

Save user password, account validity period and other information

/etc/shadow

Add user account

useradd command
useradd [options] username

• -u: ------------------------------------ Specify how much UID
• -d: ------------------------------------Specify the host directory
• -e: ------------------------------------ Specify the account expiration time
• -g: ------------------------------------Specify user basic group
• -G: ------------------------------------Specify the user additional group, which can belong to the user group or Can belong to other
• -M: ------------------------------------Do not create a host directory
• -s: ------------------------------------Specify the login shelluser

Set/change user password passwd

passwd command
passwd [options] username

• -d: ------------------------------------clear password
• -l: ------------------------------------ lock account
• -s: ------------------------------------Check whether the account is locked
• -u:------------------------------------Unlock user account

Example:

passwd tom            ##账户设置密码
passwd -l tom		##锁定tom
cat /etc/passwd 		##看下tom 
passwd -u tom			##解锁tom

passwd -l lisi 				##会看到shadow lisi有2个锁定的”！“号
usermod -U lisi				##这个命令敲2次可以解锁

Modify the attributes of a user account usermod

usermod command

usermod [options] username

• -u ------------------------------------ modify user UID
• -d ------------------------------------ modify the user's home directory location
• -e ------------------------------------ Modify the user account expiration time can be YYYY-MM-DD date
• -g ------------------------------------ modify the user's basic group name
• -G ------------------------------------ modify the user's additional group name
• -s ------------------------------------Specify the user's login shell
• -l ------------------------------------ change user login name
• -L ------------------------------------ lock account
• -U ------------------------------------Unlock user account

Example:

usermod -l A B				##将B的登录名称改成A
mkdir /data				##创建A新的宿主目录/data
usermod -d /data A			##修改A的宿主目录
usermod -s /sbin/nologin A		##修改A的shell环境为：不能登录

Delete user account userdel

userdel command
userdel [-r] username

• When the -r option is added, it means to delete even the user's home directory

The initial configuration file of the user account 3 important hidden files

1. .bash_profile --------The commands in the file will be executed every time the user logs in
2. .bashrc --------The commands in the file are executed every time the /bin/Bash program (including login) is loaded
3. .bash_logout --------The commands in the file will be executed every time you log out

Both .bashrc and .bash_profile are started on boot, and .bashrc is more refined than .bash_profile.
Bash_logout is understandable, wipe your ass, wipe your footprints after doing bad things.

Group account file

Similar to user account file

• /etc/group: save the basic information of the group account
• /etc/gshadow: save the password information of the group account

Add group account groupadd

groupadd command
groupadd [-g GID] group account name

Example:

groupadd -g 1000 market				##指定GID号

Add and delete group members gpasswd and group account groupdel

gpasswd command
gpasswd [option] group account name

• -a: --------------Add a user to the group
• -d: -------------- Remove a user member from the group
• -M: --------------Define the list of group members, separated by commas

groupdel command
groupdel group account name

Example:

groupdel market					##删除组账号market

Query account information

groups Username---------------View the group
id the user belongs to Username---------------View user information
finger Username--- ------------Query the detailed information of the user account
w, who, users command---------------Query the information of the user who has logged in to the host

File/directory permissions and ownership

access permission

• Read r: Allow to view file content and display directory list
• Write w: allow to modify the content of the file, allow to create, move and delete files or subdirectories in the directory
• Executable x: Allow programs and switch directories

Ownership (ownership)

• Owner: the user account that owns the file or directory
• Group: the group account that owns the file or directory

Set permissions of files and directories chmod

chmod [option] permission directory file name

• -R:----------------- Modify directory permissions recursively
• u:-----------------user owner
• g:-----------------group belongs to the group
• o:-----------------other other
• a:-----------------all all
• +:-----------------Add permissions
• -:-----------------Reduce permissions
• =:-----------------Set permissions

Set the ownership chown of files and directories

chown Owner: group file directory -----------------######Set the ownership of the file directory
-R------------ -----Recursively modify the ownership of the directory