User management in Linux system

1. Commonly used configuration files

User information file: /etc/password
Password file: /etc/shadow
User group file: /etc/group
User group password file ：/etc/gshadow

1.1 /etc/password file

vim /etc/password

fubh:x:1020:1000::/home/fubh :/bin/bash

man 5 password #View configuration file help

(Password file) There is one record per line, and each line has this format:

account :password:UID:GID:GECOS:directory:shell
(Account:Password:User ID:Group ID:General information:Host directory:shell)

The field description is as follows:

Account users' name in the system, it cannot contain the cipher of the capital letters.

UID user ID number.

GID The user's primary group ID number.

                                                                                                                                                                                                          GECOS    Typically, it contains the user's full name.

directory The user's $HOME directory.

shell The program to run at login (if empty, use /bin/sh if set For a non-existent execution (program), the user cannot log in through login(1).)

1.1.1 User classification

UID=0 is a super user
UID=500~ 60000 is an ordinary user
UID=1~499 It is a pseudo user (related to system and program services)



1.2 /etc/shadow file

root:# 21312sd$44:wd323%cds:14945:0:99999:7:::

Username: Encrypted password: Last modification time: Minimum time interval: Maximum time interval: Warning time: Account idle time: Expiration time:

1.3 /etc/group file

vim /etc/group

sudo:x:27:web,yanghuang,zhoumin,duyp,taofh,luanqq

group_name:password:GID:user_list
(Group name:Group password:Group ID:Group members)




2. Common commands:

Add a user: useradd [-ugGdsce] user name

useradd -g webadmin -G root,web -c 'test suer' bob

-u UID

-g Default user group GID
-G Specify that the user belongs to multiple groups
-d Host directory
-s Command parser Shell
-c Description information
-e Specify user expiration time

Settings Password: passwd Username

Modify user information:
Modify username: usermod -l New username Old username
Add user group: usermod -G sys bob_fu

Delete a user: userdel [-r] username (-r deletes the user's home directory)

Set a password for the group: gpasswd group name
gpasswd [-adArR] username group name
- a Add a user to a group
-d Delete the user from the group
-A Set the user group administrator
-r Delete the user group password
-R Prohibit the user from switching to regroup

For example:
gpasswd webadmin
gpasswd -a bob_fu webadmin
gpasswd -A bob_fu webadmin
gpasswd -r webadmin

Lock a user: passwd -l jack / usermod -L jack
Unlock a user: passwd -uf jack / usermod -U jack

Switch the group: newgrp webadmin
View the group: groups lisi

Add a group: groupadd [-g GID] Group name (View: grep webadmin /etc/group)

Delete group: groupdel webadmin

Rename group: groupmod -n New name Old name

3. Other commands:

pwck Detect /etc/passwd file (lock file)
vipw Edit /etc/passwd file view (lock file)
id View user id and group information
finger View user details
su Switch users (su - username)
passwd -S View user password status
who, w View current Denghu user information
grpck User group configuration file Detect
vigr Edit /etc/group file (lock file)
chage [-lmM] Set password (available under LINUX)
-l View user password settings chage -l jack
-m Password modification The minimum number of days
 -M The maximum number of days for password modification
 -d The date the password was last modified
 -I The number of days to determine the account after the password expires
 -E Set the password expiration date, if it is 0 , indicating that the password will expire immediately, if it is -1, it will never expire
-W Set the number of days to start warning before the password expires

4. Case: Authorize the safeware directory to jack and mary Have write permission

root creates a directory:
mkdir /software

Add two users:
useradd jack
useradd mary

Set password:
password jack
password mary

Add a group
groupadd softadm

Add user to group
usermod -G softadm jack
gpasswd -a mary softadm

View group members:
grep softadm /etc/group

Authorize the root group in the directory to the softadm group
chgrp softadm ./software

Give Add directory write permission to the group
chmod g+w ./software

5. Extension (RedHead series)

5.1 Add users in batches

<1> The newusers command imports the user information file
For example, the content of user.info is as follows
test01::10001:503::/home/test01:/bin/bash
test02::10002:503:: /home/test02:/bin/bash
test03::10003:503::/home/test03:/bin/bash
test04::10004:503::/home/test04:/bin/bash
test05::10005:503::/home/test05:/bin/bash
test06::10006:503::/home/test06:/bin/bash

newusers < user. info

<2> The pwunconv command cancels the shadow password function

pwunconv

<3> The chpasswd command imports the password

For example, the content of pass.info is as follows
test01:admin+01
test02:admin+02
test03:admin+03
test04:admin+04
test05:admin+05
test06:admin+06

chpasswd
<4> The pwconv command writes the password to the shadow file

pwconv

Optimization solution: write a script

#!/bin/bash
#add-some-users.sh
#The script is add some users to a new group.

echo "Welcome to the add some users!"
echo -n "Please input the new group(example : mygroup) : "

read  my_new_group  
groupadd $my_new_group

echo -n "Add the $my_new_group group is successful!"
echo "&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&"
echo "Then add some users to the $my_new_group group!"

echo -n "Please input the username(example: student) : "
read new_user
echo -n "Please input the username(begin_id)(example: 1 ) : "
read begin_id
echo -n "Please input the username(end_id)(example: 10 ) : "
read end_id

echo "&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&"

for ((i=$begin_id;i<=$end_id;i++))
do

#add the new_user to the my_new_group,and no add new_user&#39;s group

useradd -n -g $my_new_group $new_user$i

#delete the new_user password

passwd -d $new_user$i

chage -d 0 $new_user$i     //

done

echo "&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&"

5.2 Restrict user su to root

groupadd sugroup

chmod 4550 /bin/su
chgrp sugroup /bin.su
ls -l /bin/ After su
is set, only users in the sugroup group can use su to switch root
sueradd bob
passwd bob
usermod -G sugroup bob

5.3 Replace with sudo su

sudo configuration file/etc/sudoers

(Administrator) edit configuration file command:
visudo
Format: user name (group name) host address (host name )=command (absolute path)

For example:
User authorization: bob 192.186.9.3=/usr/sbin/useradd,/usr/sbin/userdel
Group authorization: %webadmin host1=/ bin/vim /etc/httpd/conf/httpd.conf

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