User and group operations are not done frequently and will be forgotten, so I will summarize them.

User-related commands

Check user list

cat /etc/passwd
###Execution result############
user_name1:1001:1001::/home/user_name1:/bin/bash
user_name2:x:1002:1002::/home/user_name2:/bin/bash

User created

useradd {user_name}

User deletion

userdel {user_name}

Group related commands

Group list confirmation

cat /etc/group
###Execution result############
root:x:0:
~ ~ Omitted ~ ~
group_name1:x:1003:user_name1,user_name2
group_name2:x:1004:user_name1

Group creation

groupadd {group_name}

Group deletion

groupdel {group_name}

Confirmation of users belonging to the group

getent group {group_name}
###Execution result############
group_name1:x:1003:user_name1,user_name2

Check the group to which the user belongs

groups {user_name}
#Execution result
user_name1 : user_name1 group_name1 group_name2

If you also want to know the UID and GID

id {user_name}
###Execution result############
uid=1001(user_name1) gid=1001(user_name1) groups=1001(user_name1),1003(group_name1),1004(group_name2)

gid= ... Primary group groups = ... the first is the Primary group, the second is the Secondary group

Change primary group

usermod -g {group_name} {user_name}

Other (secondary or later) affiliation group change / multiple addition

※※Caution※※ The -G option ** ignores and overwrites existing groups **. If you want to add a group while keeping the existing group, you need to ** specify the existing group as well **. You can check the existing group with ʻid {user_name} `.

usermod -G {group_name} {user_name}

To specify more than one, separate them with , (comma).

usermod -G {group_name1},{group_name2} {user_name}

Delete other (secondary or later) affiliated groups

Take advantage of the property of ** ignoring and overwriting ** existing groups of the -G option. Check the existing group with ʻid {user_name} `, and specify the group you want to delete.

usermod -G {group_name1},{group_name2} {user_name}

[CENTOS] [Linux] User / group command summary