0. list users
# cat /etc/passwd
# cut -f1 -d: /etc/passwd
1. add user
# useradd -d /home/fish fish
creates new user(account) “fish”
option “-d” is for the directory where the user is created.
2. set password
# passwd fish
type password 2 times.
3. check information of user
# cat /etc/passwd | grep username
user:01:x:501:100:username:/home/username:/bin/bash
2nd column “x” : password (encoded)
3rd column “501” : UID
4th column “100” : GID
5th column “username” : explanation of account (option -c)
6th column “/home/username” : home directory of account
7th column “/bin/bash” : login shell
4. delete account
# userdel username : delete only account “username” without deleting directory and files
# userdel -r username : delete all include directory and files
5. intercepting login
change password value on “/etc/passwd” from (x) to *.
or
change shell information from “/bin/bash” to “/bin/false” on “/etc/passwd”.
<Group setting>
1. create group (addgroup)
# addgroup group_name
ex) addgroup giant
1.1. option: group ID
# addgroup -g id
ex) addgroup -g 1003
1.1.1. check group and ID
# cat /etc/group | grep giant
can see this message “giant:x:1003” <- group name: password:group id
2. add users to group (usermod)
form) usermod -a -G group user
ex) usermod -a -G giant human
2.0.1. add user to group by specific UID and GID
ex) useradd -u 511 -g 556 username
2.1. check group
# groups group_name
3. change group name
# groupmod -n new_name old_name
# groupmod -g NEWGID GROUP
ex) groupmod -g 555 mygroup (change instantly)
4. change password / management users
4.1. change group password
# gpasswd group_name
4.2. users
# gpasswd option user_name group_name
options:
-A user_name group_name : appoint the user as manager
-a user_name group_name : add the user as users of the group
-d user_name group_name : exclude the user from the group
5. delete group
groupdel group_name