How to Switch Users in Ubuntu: A Comprehensive Guide

Linux is a multi-user operating system that allows multiple user accounts to log in and access the system simultaneously without affecting others‘ sessions. As an administrator or power user of Ubuntu, understanding the various methods to switch between users is critical.

This comprehensive guide will cover best practices, security implications, and step-by-step instructions for switching users in Ubuntu locally and remotely using the command line and graphical interfaces.

Why Switch Users in Ubuntu?

There are several reasons you may want to switch between different user accounts within an Ubuntu session:

• Isolation – Switching users can isolate sessions without terminating running processes. This allows you to safely test applications or configuration changes.
• Privilege separation – Accessing privileged accounts like root only when necessary improves security and reduces risk. Use su or sudo to switch temporarily.
• Multiple users – On shared systems, switching users allows individualized settings and accessibility for each team member or family member.
• Remote access – Access GUI sessions remotely via SSH when direct console interaction is not available.

According to recent surveys, over 90% of cloud infrastructure and web servers leverage some form of Linux. Ubuntu has one of the largest user bases globally. Managing multi-user access securely is critical for administrators of these systems.

Comparison of Switch User Methods

There are three primary methods available to switch users within Ubuntu, each better suited to particular use cases:

Method	Graphical	Preserves Session	Secure	Use Case
Logout/Login	Yes	No	Depends	Switching primary user temporarily
su/sudo	No	Yes	Configurable	Elevating privileges for commands
SSH	No	Yes	Yes	Remote access or isolating sessions

Next we will explore these methods and best practices for utilization in more depth.

Using Graphical Switch User

If running Ubuntu desktop with the GNOME or KDE graphical environment, you can leverage the built-in "Switch User" option:

1. Click the user icon/profile picture in the upper right corner
2. Select "Switch Account"
3. Choose an available user and enter the account password

This will logout your active GUI session and terminate running graphical programs. However, any background services, command line processes, SSH connections, etc. started by the original user will continue unaffected.

The primary use case for graphical switch user is to change the primary desktop identity. For example, if a shared family computer is being handed off from a parent to child.

Security consideration – Using the graphical login prompt exposes credentials visually if physically monitored. Ensure no shoulder surfing is possible in public spaces with this method.

su and sudo Commands

The su (switch user) and sudo (superuser do) commands allow changing the active user or elevating privileges directly in a terminal session.

For example, to switch to the user bob:

su - bob

You will be prompted for bob‘s account password. This starts a new shell session as bob without terminating the current processes that were running.

Alternatively, you can switch users temporarily for a single command using -c:

su - bob -c ‘cat /var/log/syslog‘

This is useful for privilege separation – only accessing sensitive accounts like root when absolutely necessary.

Best practices include:

• Use sudo over su where possible – it offers more granular control and typically leverages the user‘s own password for authorization.
• Configure PAM and sudoers policies to restrict the commands each account can run. Never share the root password directly.
• Preserve environments where possible with su -p to avoid disrupting running processes.

Proper sudo policies and access controls are crucial for limiting damage from credential compromise. According to research from Duo Labs, up to 30% of breaches involve some form of unauthorized privilege escalation.

Remote Graphical Access with SSH

In many scenarios, using the local console to switch users may not be possible. SSH allows connecting remotely and can also facilitate user switching:

ssh username@localhost

This will initiate an SSH connection to the localhost and prompt for the username‘s login password over the encrypted connection, rather than exposing it visually at the console.

Additionally,SSH X11 forwarding can enable remotely running graphical applications from the Ubuntu desktop session:

/etc/ssh/sshd_config:

X11Forwarding yes

SSH command:

ssh -X username@host

Now GUI programs can be launched which display securely over SSH. This allows remote user switching while accessing the desktop environment.

Security consideration – For public facing systems, be cautious enabling full X11 forwarding, as this expands the remote attack surface. Limit remote access to specific trusted IP addresses or leverage SSH jump hosts if access is required.

Managing Multiple Sessions with PAM

By default, Ubuntu only allows a single graphical X session to be running for each user. This helps avoid conflicts between simultaneously running desktop programs.

However, in some cases allowing multiple simultaneous GUI logins for the same user can be beneficial – for example accessing the desktop from multiple devices like laptop + mobile.

The Pluggable Authentication Modules (PAM) system controls session management policies on Ubuntu. To enable multiple sessions, edit /etc/pam.d/gdm-autologin and /etc/pam.d/gdm-password to include this line:

session required pam_systemd.so

Now an unlimited number of connections will be allowed until system resources are exhausted. Keep in mind that running too many sessions can destabilize the desktop and performance may suffer.

Troubleshooting Issues Switching Users

In some cases, you may encounter issues when trying to switch users that prevent accessing the new account:

• Failed or incorrect authentication – Ensure the account password was entered correctly. Check /var/log/auth.log for denial reasons.
• No available sessions – Reaching session limits set by PAM will block new logins until old sessions exit.
• SSH connection failures – Validate SSH daemon is running and configured properly. Ping remote host to check for networking problems.
• Desktop fails to load – A resource intensive session may hang or crash the window manager. Switch to a TTY and kill off any GUIs using high CPU/RAM.
• Detached processes persist between users – Some daemons may continue running after switching accounts. Stop via command line or use isolation methods.

Added debugging and auditing around user switching enabled by default in Ubuntu. Consult authentication logs when issues occur during the transition process.

Conclusion

Ubuntu offers flexible options to transition between different user accounts seamlessly while maintaining running sessions using su, sudo, SSH, the graphical login manager and PAM.

Familiarity with the various switch user techniques enables administrators to improve security through privilege separation, facilitate remote work, isolate incompatible applications, and support multiple desktop users efficiently.

Implementing best practices around access controls and logging provides accountability around any privilege escalation or user transitions. Be sure to manage policies and permissions wisely!

I hope this guide gives Ubuntu power users and IT professionals the knowledge needed to switch user contexts smoothly. Let me know if you have any other questions!