Linux User and User group management

1 User Profiles

1.1 User Information file /etc/passwd

View Help man 5 passwd

--Account:password:UID:GID:GECOS:directory:shell

-account User name Notice specification

-PASSWD password flag x indicates password specific password in shadow

-uid user ID 0: superuser, determined by UID, not determined by user name

1-499: System User (pseudo user), cannot log on, cannot be deleted, called by system service or command

500-65535: Normal User

-gid Group ID Initial group ID user created groups, each user can only have one initial group, not recommended changes, specifically which group to see/etc/group

Additional groups: One user can also join multiple other user groups

-gecos User Description

-directory User home Directory Super User:/root/Normal User:/hoshme/user name/

-shell Login After the shell is the Linux command interpreter standard Shell:/bin/bash and/sbin/nologin cannot log in

1.2 Shadow file /etc/shadow

-1 User Name

-2 Encryption Password SHA512 hash encryption algorithm "!!" or "*" means no password and cannot log in

-3 Password Last modified date of the Linux timestamp after the nth day of 1970-1-1

-42 time interval for password modification

-5 Password Expiration date

-6 number of warning days before password modification expires

-7 grace days after password expiration 0 or no: Expiration immediately expires-1: No Expiration

-8 account Expiration Time timestamp indication

Timestamp-Date: date-d "1970-01-01 16066 Days"

Date-time stamp: Echo $ (($ (Date--date= "2015/10/13" +%s)/86400+1))

-9 Reserved fields

1.3.1 Group information file /etc/group

-1 Group names

-2 sets of password flags specific passwords are not recommended for use in /etc/gshadow

-3 GID group ID and UID are similar

-4 groups of additional users and passwd to know the initial user

1.3.2 Group password file/etc/gshadow

-1 Group names

-2 sets of passwords

-3 Group Administrator user names

-Additional users in Group 4

2 user Management related files are automatically created when users are added

2.1 User's Home directory

$ normal User/home/user name/Permissions 700

# Super User/root/Permissions 550

2.2 User's mailbox

/var/spool/mail/User Name

2.3 User Templates Directory

/etc/skel/

3 User Management commands

　　Useradd [Options] User name

-u UID: Specify UID manually

-D Home Directory: Manually specify the home directory

-C User Description: Manually specify the user's description

-G Group Name: Manually specify the initial group

-G Group Name: Specify the user's additional group comma separated

-S Shell: Manually Specify the user's login shell. Default/bin/bash

　　　　

User Default value File/etc/default/useradd

/etc/login.defs

　　

　　passwd Options [User Name]

Only Superuser can add [username], the normal user directly passwd

-S query the status of user passwords only for Superuser

-L lock User is actually changing the password bit in shadow with double exclamation marks

-U Unlock User

--stdin using a string as the user's password

echo "123" | passwd--stdin Zoro can be added in bulk by user shell programming

Linux User and User group management