Linux Learning-User and user group management

I. User Profile 1 user information file/etc/passwd

　　　　　　vim/etc/passwd

　　　　　　

First field: User name

Second field: Password flag (x indicates a password)

Third field: User ID (UID)

0: Super User

1-499: System User (pseudo user)

500-65536: Normal User

Fourth field: User initial group ID (GID)

Initial group: Refers to the user immediately login to have this group of relevant permissions, each user initial group only one, generally with the user name as the user's initial group name.

Additional groups: Users can join multiple additional groups and have permissions for those groups

Fifth field: User description

Sixth field: Home directory

Super User home directory:/root/

Normal User home directory:/home/user name/

Seventh field: Shall after logging in

Shell is the command interpreter for Linux

/bin/bash Allow log in

/sbin/nologin not allowed to log in

2 Shadow File/etc/shadow

　　　　　　Vim/etc/shadow

First field: User name

Second field: Encrypt password

SHA512 Hashing Encryption algorithm

If the password bit is "!!" or "*", it means no password and cannot log in

Third field: Password Last modified date

Use 1970.1.1 as standard time, every day time stamp plus 1

Time Stamp Conversion
Date, time stamp	Echo $ (($ (Date--date= "2014/01/06" +%s)/86400 + 1))
Time Stamp, date	Date-d "1970-01-01 16066 Days"

Fourth field: two times password modification interval

Fifth field: Password expiration

Sixth field: Number of days before expiration of the password expiration date

Seventh field: The number of days after which the password expires

0: Expire immediately after the password expires

-1: The representative password will never expire

Eighth field: Account Expiration time (timestamp indication)

Nineth field: Reserved

3 Set of information files/etc/group

　　　　　　Vim/etc/group

　　　　　　

First field: Group name

Second field: Group password flag

Third field: Group ID (GID)

Fourth field: Additional users in the group

4 set of password files/etc/gshadow

Vim/etc/gshadow

　　　　　　

First field: Group name

Second field: group password

Third field: Group Administrator user name

Fourth field: Additional users in the group

II. user Management Related documents 1 user's home directory

Normal User:/home/user name/

Super User:/root/

2 User's mailbox file

　　　　　　/var/spool/mail/User Name

3 User Templates Directory

　　　　　　/etc/skel/

Used to save files that are automatically generated when a new user is created, such as creating a new file in the directory notice.msg the notice.msg file is created automatically when you create the user

4 Adding a user default value file

　　　　　　/etc/default/useradd

group=100	User Default Group
Home=/home	User home Directory
Inactive=-1	Password Expiration Grace days
Expire=	Password Expiration Time
Shell=/bin/bash	Default shell
Skel=/etc/skel	Template Catalog
Create_mail_spool=yes	Whether to create a mailbox

　　　　　　/etc/login.defs

Pass_max_days 99999	Password expiration
Pass_min_days 0	Password modification interval
Pass_min_len 5	Password minimum 5 bit
Pass_warn_age 7	Password Expiry warning time
Uid_min 500 Uid_max 6000	Minimum maximum UID Range
Encrypt_method SHA512	Encryption mode

III. User Management Commands 1 adding users

　　　　　　Useradd [-udcggs] User name

-U UID

-D Home Directory

-C User Description

-G Group name (initial group)

-G Group name (additional group)

-s command interpreter shell (default/bin/bash)

Example: Useradd-u 666-g root,bin-c "test user"-d/home/zhw-s/bin/bash ZHW

2 Modifying user passwords

　　　　　　passwd [Options] [user name]

Cases:

Passwd-s user1 Query the password status of User1 password (root user only)

Passwd-l User1 temporarily lock user (root user only)

Passwd-u user1 unlock user (root only)

echo "123" | passwd--stdin Use a string as the user's password

3 Modifying user Information

　　　　　　Usermod [-ucggdlu] [user name]

-U UID

-D Home Directory

-C User Description

-G Group name (initial group)

-G Group name (additional group)

-s command interpreter shell (default/bin/bash)

-L Lock User

-U Unlock User

4 Modifying User Password status

　　　　　　chage [-ldmmwie] User name

-l list user detailed password status

-D Change the password last changed date ( when-D 0 requires the user to change the password as soon as it is logged in )

-M two times password change interval

-M Password expiration date

-W warning days before password expires

-I Grace days after password expires (I)

-E Account Expiry time

5 Deleting a user

　　　　　　Userdel [-r] User name

-R Delete User's home directory while deleting user

6 Viewing user IDs

　　　　　　ID User name to view the UID, GID, and owning group of the user

7 See which user is currently

　　　　　　WhoAmI

8 Viewing User Environment variables

Env

9 User Switching

　　　　　　Su-User name switches the user's environment variables together

　　　　　　su-root-c "Useradd user2" add a user with root privileges user2

10 viewing logged-in user information

　　　　　　W.H.O.

Display: Log in username login Terminal login time

TTY indicates local terminal

PTS indicates a remote terminal

11 View Log in User details

　　　　　　W

Display: Current time continuous run time (uptime) Number of users load Balancing index

Login Username-Login terminal-Login IP address-Login time-idle time-Cumulative CPU time-current CPU time-work command

Iv. User Group Management Command 1 adding user groups

　　　　　　Groupadd [-g] Group name

-G Specify Group ID

2 Modifying user groups

　　　　　　Groupmod [-GN] group name

-G Modify Group ID

-N Modify Group name

Example: Groupmod-n G2 G1 Change the name of the group G1 to G2

3 Deleting a group

　　　　　　Groupdel Group Name

Note: You cannot delete the user's initial group, delete the user and then delete the group, but the user's additional group can be deleted

4 Adding a user to a group or removing it from a group

　　　　　　gpasswd-a User name Group name join a user to a group

　　　　　　gpasswd-d User Name Group name removes the user from the group

Linux Learning-User and user group management