# Troubleshooting

In case of an error, you might find an answer of how to deal it here.

## Building SerenityOS

### CMake fails to configure the build because it's outdated

Ensure your CMake version is >= 3.16 with `cmake --version`. If your system doesn't provide a suitable
version of CMake, you can download a binary release from the [CMake website](https://cmake.org/download).

### QEMU is missing or is outdated

Ensure your [QEMU](https://www.qemu.org/) version is >= 5 with `qemu-system-i386 -version`. Otherwise,
install it. You can also build it using the `Toolchain/BuildQemu.sh` script.

### GCC is missing or is outdated

Ensure your gcc version is >= 10 with `gcc --version`. Otherwise, install it. If your gcc binary is not
called `gcc` you have to specify the names of your C and C++ compiler when you run cmake, e.g.
`cmake ../.. -GNinja -DCMAKE_C_COMPILER=gcc-11 -DCMAKE_CXX_COMPILER=g++-11`.

## Running SerenityOS

### The VM is really slow

On Linux, QEMU is significantly faster if it's able to use KVM. The run script will automatically enable KVM
if `/dev/kvm` exists and is readable+writable by the current user. On Windows, ensure that you have
WHPX acceleration enabled.

### Boot fails with "Error: Kernel Image too big for memory slot. Halting!"

This means the kernel is too large again. Contact us on the discord server or open a GitHub Issue about it.
You might want to revert latest changes in tree to see if that solves the problem temporarily.

### Boot fails with "Your computer does not support long mode (64-bit mode). Halting!"

Either your machine (if you try to boot on bare metal) is very old, thus it's not supporting x86_64
extensions, or you try to use VirtualBox without using a x64 virtualization mode or you try to use
`qemu-system-i386` which doesn't support x86_64 extensions too.

### Boot fails with "Your computer does not support PAE. Halting!"

- If booting on bare metal, your CPU is too old to boot Serenity.
- If you're using VirtualBox, you need to enable PAE/NX. Check the instructions [here.](VirtualBox.md)
- If you're using QEMU, the [CPU model configuration](https://qemu-project.gitlab.io/qemu/system/qemu-cpu-models.html) is not exposing PAE.