# Installing next to Windows or Linux

> Share a disk: your other system keeps its files, gets smaller, and you pick one at start. What to do first, and what to do when the installer refuses.

Source: https://wolos.org/manual/dual-boot

## What it is

**Install Alongside** puts WolOS on the same disk as Windows or another Linux. It makes the other system's partition smaller (you drag a slider to split the room), adds WolOS's partitions in the freed space, and leaves every file of the other system where it was. At start you choose which system to run.

It is like moving a bookshelf to make room for a second one: nothing on the first shelf is thrown away, it just stands a little closer together.

## Why

Sharing a disk is risky when a tool guesses. WolOS reads the disk first (which systems are on it, whether Windows is hibernated or uses BitLocker), shows exactly what changes in the summary, and refuses the cases where shrinking could damage files. The plan names the partitions it may touch; if anything else moves, the install stops.

## How

### Before you start

1. **Back up what matters.** As with any change to a disk, back up first. The installer says so on the Alongside page.
2. **Shut Windows down fully.** A Windows that is hibernated or was shut down with *Fast Startup* is refused, so its files cannot be damaged. In Windows turn off Fast Startup, choose **Shut down** (not Restart), then start the stick.
3. **Know your BitLocker state.** The installer cannot shrink a BitLocker-protected partition ("BitLocker protects Windows here"). Turn BitLocker off in Windows for that partition, then try again. If Windows keeps BitLocker on and Secure Boot changes, Windows asks once for its recovery key (see below).
4. **macOS is not shrunk by the installer.** Make room with Disk Utility in macOS, then start the installer again.

### In the installer

1. **Choose the disk, then Install Alongside.**
   You see "Nothing changes until the last step." on the method page, with **Install Alongside Windows** at the top, then "Drag to choose how much room each system gets." The page names each system found on the disk.

   ![How to Install: Install Alongside Windows (Keeps what's there) ticked, Replace a Partition, Erase Disk and Manual.](/img/manual/installer-method-1280.png)
2. **Drag the slider** to split the room. The other system only gets smaller; its files stay.
   If a partition cannot be shrunk, the page says why in one sentence (see the table below).

   ![The Share the Disk page: a bar shows how much room Windows and WolOS each get, and a slider moves the line between them.](/img/manual/installer-alongside.png)
3. **Continue** through encryption, Secure Boot, account and modules as in [Installing WolOS](/manual/install).
   If Windows uses BitLocker and its computer trusts only Windows at start, you see "Change One Startup Setting First" with the steps, and the warning that Windows will ask once for its recovery key.

   ![Change One Startup Setting First: this computer's Secure Boot only trusts Windows; allow third-party certificates after installing; Windows uses BitLocker, so it asks once for its recovery key; Back, Restart and Install Anyway.](/img/manual/installer-secure-boot-bitlocker-1280.png)
4. **Read the summary.**
   You see "Nothing has changed yet. This is exactly what will happen." It lists what is kept, what is shrunk and what is created. If Windows stays with BitLocker and Secure Boot is on, it also tells you about the BitLocker recovery key.

   ![Ready to Install next to Windows: shrink Windows from 600 GB to 392 GB, add 1 GB for startup files and 215 GB for WolOS (encrypted), keep the other Linux as it is, how to start Windows, and the warning to back up first.](/img/manual/installer-summary-windows-1280.png)
5. **Click Install**, wait, and read the last page.
   You see how to start the other system, for example "To start Windows, open your computer's startup menu while it starts, often with F12, F9 or Esc."

   ![WolOS Is Installed: click Restart, remove the USB stick when the screen goes dark, and to start Windows open the computer's startup menu with F12, F9 or Esc.](/img/manual/installer-done-windows-1280.png)

### Replacing one partition instead

**Replace a Partition** on the method page erases one partition you choose and gives it to WolOS; every other partition and its files stay. Use it when you already made room, or to replace an old Linux.

![Replace a Partition: a Windows partition of 600 GB and a Linux partition of 200 GB, the Linux one ticked. Only the ticked partition is erased; the rest of the disk stays.](/img/manual/installer-replace-1280.png)

If the disk already holds an earlier WolOS, you can install again over it: the old WolOS's startup files are cleared first and the rest of the disk stays.

### Choosing a system at start

- When another system stays on the disk, WolOS's boot menu waits a moment so you can choose.
- When WolOS gets its own startup partition next to Windows', the WolOS menu lists WolOS only, because it cannot reach the other partition. Start Windows from your computer's startup menu, which you open while the computer starts, often with **F12**, **F9** or **Esc**. The installer's last page says the same, with the other system's name.
- Another system's boot manager can start WolOS too. Most find it on their own. How to add WolOS to one that does not is in the [Reference](/reference/boot).

### The clock

WolOS keeps the clock in **local time** when Windows stays, as Windows does, so neither system shows the wrong time after the other has run.

### Secure Boot and BitLocker

Secure Boot changes can make Windows ask once for its BitLocker recovery key. When Windows stays with BitLocker on, the Secure Boot page and the Summary tell you before it happens:

- Have the key ready; it is saved at `account.microsoft.com/devices/recoverykey`.
- To avoid the prompt on a computer in Setup Mode, restore the factory Secure Boot keys in the startup settings first; WolOS then uses a one-time key screen instead.
- On a computer whose Secure Boot trusts only Windows, suspend BitLocker in Windows before you change the startup setting.
- Or leave Secure Boot off in the installer; Windows' keys are then untouched. You can turn it on later ([Secure Boot](/manual/secure-boot)).

## A worked example

Alice has Windows on a 600 GB disk and wants to try WolOS without losing it. In Windows she turns off Fast Startup and shuts down fully. She starts the stick, chooses **Install Alongside Windows**, drags the slider until WolOS has 215 GB and reads the summary: Windows shrinks from 600 GB to 392 GB and keeps every file. After the restart she presses **F12** to choose a system. Windows opens as before, and WolOS opens when she picks it.

## If something goes wrong

| What you see | What to do |
|---|---|
| "This disk is empty, so there's nothing to install alongside" | Use Erase Disk. A disk with an older kind of layout (not GPT, the layout every recent computer uses) can only be erased too. |
| "Windows didn't shut down fully" | Turn off Fast Startup in Windows, shut down fully, try again. |
| "BitLocker protects Windows here" | Turn BitLocker off in Windows, then try again. |
| "{partition} can't get that small" | Choose a larger size for that partition (give WolOS less). |
| "There isn't enough room for that" | Delete or shrink a partition first, or give WolOS less. |
| "Another system starts from that partition, so it can't be erased" (Manual) | Do not erase Windows' startup partition: keep it as it is, or add a new startup partition of 1 GB for WolOS. |
| After the install Windows is not in the menu | Start it from the firmware's startup menu (F12, F9 or Esc). |
| Windows asks for a BitLocker recovery key | Enter it from `account.microsoft.com/devices/recoverykey`. It asks once. |
| WolOS does not appear at all | Open the firmware's startup menu and pick the WolOS entry; see [Recovery](/manual/recovery). |