Mac Terminal User Switching: su, sudo & Fast User Commands

Introduction

For system administrators, developers, and power users, knowing how to switch users on a Mac using Terminal commands offers flexibility that the graphical interface cannot match. You can run commands as another user without logging in, switch to a different user’s shell environment, or even launch the graphical login window from the command line.

This guide covers the three main Terminal commands for user switching: su for switching to another user’s shell, sudo for running individual commands as another user, and launchctl for triggering the graphical Fast User Switching mechanism. For the standard graphical switching methods, see our how to switch users on a Mac guide . For the keyboard shortcuts that pair well with Terminal use, our Mac user switching shortcuts guide covers those.

Switching to Another User’s Shell with su

The su command (substitute user) switches your Terminal session to another user account. To switch to a user named “jessica”:

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su jessica

You will be prompted for Jessica’s password. After entering it correctly, your Terminal prompt changes to indicate you are now operating as that user. To return to your own account, type exit.

To switch to the root superuser account, use su with no username. You will need the root password, which is usually disabled by default on macOS. For security, it’s better to use sudo for individual commands rather than enabling the root account.

Running Individual Commands as Another User with sudo

The sudo command is safer and more controlled than su. Instead of switching your entire shell session, you run just one command as another user. For example, to view a file that only another user can read:

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sudo -u jessica cat /Users/jessica/Documents/private.txt

The -u jessica specifies which user to run the command as. Without the -u flag, sudo runs the command as root. Most administrative tasks (like installing software) use sudo directly, but for multi‑user administration, the -u flag is essential.

Triggering Fast User Switching from the Terminal

You can switch users on a Mac from the Terminal to the graphical login window using the launchctl command. This is useful for scripting, remote administration, or when the menu bar is unavailable:

First, find the user ID of the account you want to switch to. Open Terminal and type:

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dscl . -list /Users UniqueID | grep jessica

This returns a number like 501. Then use that ID with launchctl:

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sudo launchctl asuser 501 /usr/bin/open -n /System/Library/CoreServices/loginwindow.app

This command triggers the graphical login screen, simulating a Fast User Switch. Your current session remains active in the background. To switch back to your original account, either use the login window manually or repeat the command with your own user ID.

How to Find a User’s ID

To see all user accounts and their IDs on your Mac, run:

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dscl . -list /Users UniqueID

You’ll see a list like:

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jessica         501
alex            502
guest           201

Ignore system accounts like _spotlight, _mdnsresponder, etc. The user accounts you created will have IDs starting at 501.

Scripting User Switches

The launchctl command can be placed in a shell script to automate user switching. For example, you could create a script that switches to a specific user at a scheduled time:

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#!/bin/bash
# Switch to user jessica
UID=$(dscl . -list /Users UniqueID | grep jessica | awk '{print $2}')
sudo launchctl asuser $UID /usr/bin/open -n /System/Library/CoreServices/loginwindow.app

Save this as switch-users.sh, make it executable (chmod +x switch-users.sh), and run it from Terminal. This is powerful for shared workstations that need to rotate between users automatically.

Security Considerations

When using Mac Terminal user switching, keep these security tips in mind:

sudo commands are logged in /var/log/system.log and can be audited.
Avoid enabling the root account. Use sudo instead.
Never hardcode passwords in scripts. Use secure password prompts or SSH keys where possible.
Regularly review which users have sudo privileges by checking the /etc/sudoers file.

Frequently Asked Questions

What’s the difference between su and sudo?
su opens an interactive shell as another user until you type exit. sudo runs a single command as another user and then returns to your original shell.

Can I switch users via Terminal over SSH?
Yes. After connecting via SSH, use the launchctl command to switch users on the graphical display, or use su/sudo for command‑line tasks.

Does launchctl work on all Mac models?
Yes, on both Apple Silicon and Intel Macs. It requires Fast User Switching to be enabled in System Settings.