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.

GID The user's primary group ID number.

directory The user's $HOME directory.

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

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

1.3 /etc/group file

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




2. Common commands:

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

-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'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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