razzmatazz
You must install .NET to run this application.
When trying to start csharp-ls from the terminal I get the following error:
WARD-LAPTOP-ARCH ~ > csharp-ls 2025-08-30 14:10:12
You must install .NET to run this application.
App: /home/ward/.dotnet/tools/csharp-ls
Architecture: x64
App host version: 9.0.8
.NET location: Not found
Learn more:
https://aka.ms/dotnet/app-launch-failed
Download the .NET runtime:
https://aka.ms/dotnet-core-applaunch?missing_runtime=true&arch=x64&rid=linux-x64&os=arch&apphost_version=9.0.8
Failed to resolve libhostfxr.so [not found]. Error code: 0x80008083
This is a fairly new install of Arch linux, and the first time I'm installing dotnet in general. Have removed and reinstalled dotnet a few times.
Found a number of similar issues - most said adding the DOTNET_ROOT envvar fixed it. I tried a few over more convoluted things as well, to no avail.
WARD-LAPTOP-ARCH ~ > dotnet --info 2025-08-30 14:19:43
.NET SDK:
Version: 9.0.304
Commit: f12f5f689e
Workload version: 9.0.300-manifests.70d87660
MSBuild version: 17.14.16+5d8159c5f
Runtime Environment:
OS Name: arch
OS Version:
OS Platform: Linux
RID: linux-x64
Base Path: /home/ward/.dotnet/sdk/9.0.304/
.NET workloads installed:
There are no installed workloads to display.
Configured to use loose manifests when installing new manifests.
Host:
Version: 9.0.8
Architecture: x64
Commit: aae90fa090
.NET SDKs installed:
9.0.304 [/home/ward/.dotnet/sdk]
.NET runtimes installed:
Microsoft.AspNetCore.App 9.0.8 [/home/ward/.dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.NETCore.App 9.0.8 [/home/ward/.dotnet/shared/Microsoft.NETCore.App]
Other architectures found:
None
Environment variables:
Not set
global.json file:
Not found
Learn more:
https://aka.ms/dotnet/info
Download .NET:
https://aka.ms/dotnet/download
WARD-LAPTOP-ARCH ~ > dotnet tool list --global 2025-08-30 14:20:32
Package Id Version Commands
--------------------------------------
csharp-ls 0.19.0 csharp-ls
WARD-LAPTOP-ARCH ~ > which dotnet 2025-08-30 14:21:02
/home/ward/.dotnet/dotnet
WARD-LAPTOP-ARCH ~ > which csharp-ls 2025-08-30 14:21:56
/home/ward/.dotnet/tools/csharp-ls
WARD-LAPTOP-ARCH ~ > echo $DOTNET_ROOT 2025-08-30 14:21:59
/home/ward/.dotnet
I don't think this is so much a csharp-ls issue but a dotnet issue. As you mentioned, there are loads of issues about this, most notably on the dotnet sdk repo itself. It seems to be the installation path, whenever it's not installed globally for the system but only for the user.
I hit this the other week on a fresh Windows server install, using the dotnet-install.ps1 script to install the runtimes. I had to get the DOTNET_ROOT environment variable to get my services running.
You most likely followed the dotnet-install.sh method. This will only install dotnet for the current user ($HOME/.dotnet). This means that any global tools will use the DOTNET_ROOT env var, or /usr/share/dotnet by default for searching for the runtime.
I managed to replicate your issue on a fresh Arch install, but adding export DOTNET_ROOT=~/.dotnet to the ~/.bashrc did fix this issue. I'm guessing you just didn't export the variable, since that would mean that no subprocess has visibility of it.
I'd suggest just running ./dotnet-install.sh --install-dir /usr/share/dotnet -c STS -v latest to install it globally to avoid any other quirks
I installed the sdk as in https://learn.microsoft.com/nb-no/dotnet/core/install/linux-ubuntu-install?tabs=dotnet9&pivots=os-linux-ubuntu-2404
which puts them in /usr/share/dotnet
then I installed csharp-ls as in this readme with dotnet tool install --global csharp-ls
and I got an error like the above.
I fixed it with
export DOTNET_ROOT=/usr/share/dotnet
(or (setenv "DOTNET_ROOT" "/usr/share/dotnet") in ~/emacs.d/init.el)
Maybe the README should mention that you can set DOTNET_ROOT if it can't find it? Or TROUBLESHOOTING.md
