The short answer
- To open a second instance of an app, run
open -n -a "App Name"in Terminal. - That second instance uses the same data as the first, so it’s usually signed in to the same account. Some apps won’t run twice at all.
- For a second account in Chrome or another Chromium-based browser, start it with
--user-data-dirpointing at a folder of its own, or simply use a browser profile. - For a second account in any app, the free option that always works is a second macOS user, but you only see one user at a time.
Why macOS opens only one copy of an app
When you click an app in the Dock or in Finder and it’s already running, macOS brings the running copy to the front instead of starting another one. Most Mac apps are built to run once per user.
An app keeps everything that makes it “yours” in your user Library: settings in ~/Library/Preferences, data and sign-in sessions in ~/Library/Application Support, caches in ~/Library/Caches, and sometimes passwords and tokens in your keychain. Sandboxed apps, including those from the Mac App Store, keep theirs in ~/Library/Containers. A second copy of the app running as the same user finds exactly the same folders, which is why it comes up signed in as the same person.
Method 1: open -n in Terminal
The built-in open command can start a new instance of an app even when one is already running:
- Open Terminal (in Applications › Utilities).
- Type the command below, replacing App Name with the app’s name as it appears in your Applications folder, without
.app, and press Return.
open -n -a "App Name"-a tells open which application to launch, and -n opens a new instance of it even if one is already running. Both are documented in man open. You can try it safely with Calculator: open -n -a Calculator puts a second Calculator in the Dock.
Where open -n breaks
- Same data, same account. Both copies run as you and read the same settings and data folders. There’s no option to point the second copy at a different account.
- The copies can trip over each other. Two instances writing the same settings and databases at once can lose changes or leave data in a bad state, because the app never expected to share them.
- Some apps won’t run twice. Apps built to allow a single instance bring the first copy forward or quit straight away.
- Nothing tells them apart. Both copies have the same name and the same icon in the Dock and in the app switcher.
- It doesn’t stick. You run the command again every time you want the second copy.
Method 2: --user-data-dir for Chrome and other Chromium browsers
Chromium-based browsers such as Google Chrome, Microsoft Edge and Brave keep everything about you, from cookies and sign-ins to extensions and history, in one user data folder. The --user-data-dir switch starts an instance that uses a different folder, which behaves like a brand-new browser you can sign in to with another account:
open -na "Google Chrome" --args --user-data-dir="$HOME/Chrome Second"--args passes everything after it to the app instead of to open. Use the same folder every time to come back to the same session; a new folder starts from scratch.
If the second account is in Chrome itself, you rarely need the flag: Chrome profiles give each Google account its own cookies, history and extensions, with no Terminal. See Chrome profiles vs MacDualSpace for when profiles are enough.
Many desktop apps, such as Slack, Discord and Visual Studio Code, are built on Electron, which is based on Chromium. VS Code documents its own --user-data-dir option for running separate instances. Whether any other Electron app honors the flag depends on the app, so only experiment with one whose data you can afford to lose.
Where --user-data-dir breaks
- Only some apps understand it. Chromium browsers do; native Mac apps and many others ignore it.
- Terminal every time, or a script or shortcut that you write and keep working yourself.
- Look-alike copies. Both instances still share one name and one icon.
Method 3: a second macOS user
Every user account on a Mac has its own home folder, Library and keychain. Log in as a second user and every app starts fresh, ready for a different account. It’s built in, free, and works with every app, including ones that tie your sign-in to your Apple Account.
- In System Settings, open Users & Groups and add a new user.
- Log in to that user once and sign in to the app with your second account.
- Turn on fast user switching (in the Control Center settings) to switch between users from the menu bar without logging out.
Where a second user breaks
- One user on screen at a time. The other user’s apps keep running in the background, but you can’t put the two accounts side by side.
- Every switch asks for a password (or Touch ID) and takes a moment.
- Everything else is separate too. Your files, Dock, browser data and app settings aren’t there, so you set the second user up from scratch.
- Both sessions use memory while both users are logged in.
For a closer look, see a second macOS user vs MacDualSpace.
What about a virtual machine?
A virtualization app such as Parallels Desktop or UTM can run a whole second copy of macOS in a window. That isolates everything and lets you see both accounts at once, but it needs many gigabytes of disk and a large share of your memory, a full macOS install with its own setup and updates, and apps inside it don’t feel like part of your Mac. It’s a lot of machinery for a second sign-in.
All the methods compared
| Method | A different account per copy | Both on screen | Works with | Setup |
|---|---|---|---|---|
open -n | No, the copies share one set of data | Yes | Apps that allow a second instance | A Terminal command each time |
--user-data-dir | Yes | Yes | Chromium browsers, some Electron apps | A Terminal command each time |
| Second macOS user | Yes | No, one user at a time | Every app | A new user, set up from scratch |
| Virtual machine | Yes | Yes, inside the VM window | Apps that run in the VM | A full macOS install |
| MacDualSpace | Yes, each copy has its own data folder | Yes | Most apps; not Apple’s own apps or iPad apps | Drop the app on MacDualSpace (not released yet) |
Where MacDualSpace fits
MacDualSpace does what open -n can’t. It makes a separate copy of an app, which it calls a Space, with its own data folder for cookies, cache, settings and sessions. Each copy can sign in to a different account and stay signed in, right next to the original. Your original app and its data are never changed.
- Clone in a few clicks. Drop an app onto MacDualSpace, or choose Clone in the menu bar while it’s open, then give the copy a name and a color.
- Tell copies apart. Each one wears its Space’s color and letter on the Dock icon and in the title bar, and notifications say which Space they came from.
- Switch in one key. Jump between copies with ⌥⌘1, ⌥⌘2 and so on, or from the menu bar.
- Terminal tools too. Command-line tools like Claude Code and Codex get a separate config folder in every Space.
A few apps can’t be cloned: Apple’s own apps, iPhone and iPad apps, and iPad apps rebuilt for the Mac, like WhatsApp from the App Store. Use their web version in a Chrome or Arc Space instead, or a second macOS user.
MacDualSpace isn’t released yet. The plan is two Spaces free and a one-time $29 Pro for unlimited Spaces. Read the FAQ or see how it works.