Managing Users and Groups in Linux

This tutorial describes How to Managing Users and Groups in Linux





The most important part of system administration is configuring and managing users and groups. This article describes how to manage users and groups.

User Administration in Linux

When we create a new user in linux, following process are taking place.

* User informations stored in /etc/passwd
* Encrypted password information stored in /etc/shadow
* Creating a home directory under /home/username
* Creating a mail box in /var/spool/mail/username

/etc/passwd

Let's begin with /etc/passwd file,


/etc/passwd file stores user account information. /etc/passwd is a text file, which contains username,password,user id,group id,user id information,login shell, separated with colon (:) .




# vim /etc/passwd




Note:

For root user entry in /etc/passwd file will be like this :-  root:x:0:0:root:/root:/bin/bash

To deactivate a user's login, change login shell parameter /bin/bash  to /sbin/nologin

/etc/shadow

/etc/shadow file stores encrypted password information. Each line of this file contains 9 fields, separated by colons (“:”), in the following order:





# vim /etc/shadow

/etc/group

It stores group information. It defines the groups to which users belong. Each line of this file contains 4 fields, separated by colons (“:”), in the following order:




# vim /etc/group

Commands

Create new user

# useradd alleria

Update user password

# passwd alleria

Change home directory of a user at the time of useradd

# useradd -d /admincool pugna





Switch a user

# su - pugna

Delete user

# userdel -r alleria

Create a group

# groupadd group1

Delete a group

# groupdel group1

Add a new user to a group

# useradd -g group1 alleria

Print groups of a user

# groups alleria

Specify secondary group

# useradd -G group2 pudge



# groups pudge





Modify an existing user using usermod command

# usermod -g group2 alleria



# groups alleria

Assign multiple groups to a user

# usermod -G group1,group2,group3,group4,group5 alleria



# groups alleria

Specify shell at the time of user creation

# usermod -s /bin/nologin alleria