Managing users and groups in Ubuntu: The ultimate guide

Introduction

Ubuntu, like any other multi-user operating system, implements a system of file permissions and ownership as part of its security protocol. Managing users and groups in Ubuntu is crucial for setting up a system’s access rights and ensuring the appropriate segregation of rights. Whether you are an Ubuntu novice or an experienced administrator, knowing how to effectively manage users and groups is key to maintaining a secure system.

This guide will give you an in-depth understanding of user and group management in Ubuntu, taking you through various commands and tools that could be used, illustrated by multiple examples.

Understanding Users and Groups

In Ubuntu, each user has a username and a numeric user ID (UID). Similarly, groups contain zero or more users and are identified by both group names and group IDs (GIDs). When a user creates a file, it is owned by that user and their primary group.

Listing Users and Groups

To list all the users on your system, you can use the following command:

cut -d: -f1 /etc/passwd

To list all the groups, you can use:

cut -d: -f1 /etc/group

Adding Users

To add a new user to your system, use the adduser command:

sudo adduser newusername

After running this command, you will be prompted to set a password and optional user information. An associated group will automatically be created for the new user.

Modifying Users

To change the details of an existing user, such as their username, you can use the usermod command:

sudo usermod -l newusername oldusername

To add a user to a supplementary group, you can use:

sudo usermod -aG groupname username

Deleting Users

To remove a user from your system, the deluser command is used:

sudo deluser username

If you also wish to remove their home directory and mail spool, use the --remove-home option:

sudo deluser --remove-home username

Working with Groups

Similar to users, you can add, modify and delete groups with groupadd, groupmod, and groupdel commands.

Creating Groups:

sudo groupadd groupname

Modifying Groups:

sudo groupmod -n newgroupname oldgroupname

Deleting Groups:

sudo groupdel groupname

Managing Group Membership

To add a user to a group, you can use:

sudo adduser username groupname

To view the groups a user is a part of, type:

groups username

Or, to see the numeric user and group IDs, use the id command:

id username

Advanced Management

Managing Passwords

Passwords can be changed using passwd. To change another user’s password, you need superuser privileges:

sudo passwd username

User Login Information

To display the last login information for all users, you can use:

lastlog

Changing File Ownership and Permissions

To change the owner of a file, use:

sudo chown username filename

To change the group of a file, use:

sudo chgrp groupname filename

Modifying permissions can be done with the chmod command. For instance, to give the owner of a file execute permission:

chmod u+x filename

Conclusion

In conclusion, managing users and groups in Ubuntu involves a series of straightforward practices that ensure a robust security protocol is maintained. By mastering these commands, you pave the way for a system that is well organized, with clear-cut boundaries for user responsibilities and access.