Howto manage user and groups

creating users

UID definitions:

UID 0 is reserve for the root user only
UID 1-999 is used for system users
UID 1000 and up are normal users

you can change this definitions on this file:

cat /etc/login.defs | grep GID

add user and create home folder:

useradd -m student

specify user shell when creating the user:

useradd -m -s /bin/bash student

specify another location for user home folder:

useradd -m -d /opt/student student

specify default group name or group id:

useradd -m -g student 

specify userid:

useradd -m -u 1000 student

create user and add this user to different groups:

useradd -m -g student -G video,docker,sound,lp student

assign password to user:

passwd student

manage groups

add group:

groupadd vidalinux

to create a group with specific group id:

groupadd -g 1010 vidalinux

add user to group:

gpasswd -a student vidalinux

add user to more than one group:

usermod -aG wheel,video,sound,lp student

list all groups and filter the result with grep:

getent group | grep vidalinux

delete a group:

groupdel vidalinux

usermod

add a comment for a user:

usermod -c "course student user" student

to change the login shell of a user:

usermod -s /sbin/nologin username

change the home directory of a user:

usermod -d /opt/student student

change user login name:

usermod -l newuser currenuser
usermod -l student1 student

Locking a user account:

usermod -L username

Unlock a user account:

usermod -U username

change the user id of a user

usermod -u 4000 student

Add user to group:

usermod -aG groupname username

Modify username to expire at specific date:

usermod -L -e 2019-10-05 user03