1, Classification

1. Classification by access control of account identity

① User account (identified by UID)

② Group account number (identified by GID)

2. Classification by user account

① Super user root

② System user

③ Ordinary users

3. Classification by group account (group account is used to distinguish permissions, not for login)

Basic group (private group)

Additional group (subordinate group)

2, Account file and password file

1. The local account data is stored in the local disk, including the user account data file and the group account data file

1) User account data file

/etc/passwd (user account file)

/etc/shadow (user password file)

2) Group account data file

/etc/group (group account file)

/etc/gshadow (group password file)

2. User initial profile

1) Profile source

When creating a new user, copy according to the /etc/skel template directory

2) Primary initial profile

~/. bash profile: execute every login

~/. bashrc: execute every time you enter a new Bash environment

Global configuration files: /etc/bashrc, /etc/profile

3. User account file

1) /etc/passwd save basic information of user account

2) Instance

One line per user record to: split into 7 fields Field 1: name of user account Field 2: password string or placeholder x Field 3: UID number of user account Field 4: GID number of the basic group to which it belongs Field 5: full user name Field 6: home directory Field 7: interpreter used for login

4. User password file

1) /etc/shadow save password string / validity period and other information

2) Instance

One line per user record to: split into 9 fields Field 1: name of user account Field 2: encrypted password string Field 3: time when the password was last modified Field 4: minimum effective days of password, 0 by default Field 5: the longest valid days of the password, 99999 by default Field 6: warning days before password expiration, default 7 Field 7: how many days after the password expires to disable this user account Field 8: account expiration time. The default value is blank Field 9: reserved field (not used)

5. Group account file

1) /etc/group saves the basic information of the group number

2) Instance

One row per group record to: split into 4 fields Field 1: name of group account Field 2: password placeholder x Field 3: GID number of group account Field 4: list of member users of this group

6. Group password file

1) /etc/gshadow save the management information of the group account

2) Instance

One row per group record to: split into 4 fields Field 1: name of group account Field 2: encrypted password string Field 3: list of administrators in this group Field 4: list of member users of this group

3, Related commands

1. useradd command

1) Function

useradd add user

2) Format

useradd [options] user name

3) Common command options

-u: Specify UID

-d: Specify the home directory. The default is / home / user name

-G: Specify the additional group to which you belong

-s: Login interpreter for the specified user

4) Instance

2. usermod command

1) Function

usermod modify user

2) Format

usermod d[options] user name

3) Common command options

-l: Change the login name of the user account

-u: User id

-d: Home directory

-s: Login interpreter

-G: Additional group (reset additional group)

4) Instance

3. passwd command

1) Function

Set user password

2) Format

passwd [options] user name

3) Common command options

--stdin: read password from standard input (such as pipeline operation)

4) Instance

4. userdel command

1) Function

userdel delete user

2) Format

userdel [options] username

3) Common command options

-r: delete along with home directory / user mail

4) Instance

5. id command

1) Function

Query account id

2) Format

id [options] user name

3) Instance

6. groupadd command

1) Function

groupadd add group account

2) Format

groupadd [options] group name

3) Common command options

-g: Specify GID

4) Instance

7. gpasswd command

1) Function

gpasswd management group members

2) Format

gpasswd [options] Group name

3) Common command options

-A: Define group administrator list

-a: Add group members (only one at a time)

-d: Delete group members (only one can be deleted at a time)

-M: Define group member user list (multiple can be set)

4) Instance

8. groupdel command

1) Function

groupdel delete group (the deleted target group cannot be the user's basic group)

2) Format

groupdel group name

3) Instance