Tuncay Sahin

ICT Engineer | Docent ICT & Trainer

This document describes the basic commands for User- and Group Management.

User Management

View existing users

cat /etc/passwd

Check if an user exist

grep {username} /etc/passwd

User passwords and password expiry information is stored in:

cat /etc/shadow

Create a new user

adduser {username}

Setup password for a user

passwd {username}

Remove User Account

userdel {username}

Remove the user’s home directory

userdel -r {username}

Rename user name

usermod -l new_user_name old_user_name

Change user’s ID

usermod -u UID username

Change User’s Home Directory

Change Home Directory for new users
The default home directory for new users is defined by HOME variable in /etc/default/useradd

vi /etc/default/useradd
#Replace “HOME=/home” with

Change Home Directory for existing users

usermod -m -d /path/to/new/home/dir userNameHere

-d : Path to new home directory.

-m : Moves contents of the current home directory to the new home directory.

Group Management

User group information is stored in

cat /etc/group

Add a new user to primary group

useradd -g {group-name} {username}

Add a new user to secondary group

useradd -G {group-name} {username}

Find out users group identity

id -ng {user-name}
id -nG {user-name}

Add an existing user to secondary group

usermod -a -G {group-name} {username}

Change users primary group

usermod -g {group-name} {username}

Check if a group exists)

grep {groupname} /etc/group

Add a group

groupadd {groupname}

Delete a group

groupdel {groupname}

View users’ group membeship

id {username}

Add user to multiple groups

useradd -G {group1},{group2},{group3} {username}

Remove user from a group by entering the groups to be preserved. If the user is currently a member of a group which is not listed, the user will be removed from the group.

usermod -G {group1-to be preserved,group2,group3} {user-name}

Change file/folder owner/group

Change files ownership to a user

chown {username} {file or folder}

Change files ownership to a user on files and directories recursively

chown -R {username} /var/www/html

Change files ownership to a group

chgrp {groupname} {file or folder}

To setup a file readable/executable by everyone and writable by the owner only

chmod 755 {file or folder}

change permissions for all files and directories within a directory

chmod -R 755 directory-name/

Delegate Permissions

Edit sudo config file

vi /etc/sudoers

or run #visudo

If you run the command vi /etc/sudoers
Sudoers file is read-only!
To save and quit the sudoers file.

press esc
type :w !sudo tee %
type q!

Append rights



  • USER: Name of normal user
  • HOSTNAME: Where command is allowed to run. It is the hostname of the system where this rule applies. sudo is designed so you can use one sudoers file on all of your systems. This space allows you to set per-host rules.
  • COMMAND: A simple filename allows the user to run the command with any arguments he/she wishes. However, you may also specify command line arguments (including wildcards). Alternately, you can specify “” to indicate that the command may only be run without command line arguments.
Allow a user to sudo, sudo allows a user to temporarily take on the role as root.


Find the line:

root    ALL=(ALL)       ALL

Under this line, add:

{username}       ALL=(ALL)           ALL


Meer informatie

Voor meer informatie of voor een persoonlijk adviesgesprek kunt u altijd vrijblijvend contact met mij opnemen.