Tuncay Sahin

ICT Engineer | Docent ICT & Trainer

User- and Group Management

Published 19 maart, 2014 | By Tuncay Sahin

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 HOME=/new/path
Change Home Directory for existing users	usermod -m -d /path/to/new/home/dir userNameHere Where -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 HOSTNAME=COMMAND Where, 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.	#visudo Find the line: root ALL=(ALL) ALL Under this line, add: {username} ALL=(ALL) ALL

Posted in ICT Knowledgebase, Linux (RHEL / CentOS)