XDG_RUNTIME_DIR is set to non-existent directory on ubuntu-slim runner

[andyn-ff]

Description

Using the new ubuntu-slim runner we found some issues using just, a command runner which for some cases writes a command script to a temporary file. In these cases we get:

error: I/O error in runtime dir `/run/user/1001/just`: Permission denied (os error 13)

At this point, just is trying to write a file to $XDG_RUNTIME_DIR and then execute it

Some testing reveals that /run/user/1001 is inaccessible - see repro steps below. On ubuntu-latest, $XDG_RUNTIME_DIR is set to /run/user/1001, and this is accessible with rwx permission.

We can work around this temporarily by setting XDG_RUNTIME_DIR to ${{ runner.temp }} but this behaviour doesn't seem deliberate and I'd expect it to work out-of-the-box

Platforms affected

• Azure DevOps
• GitHub Actions - Standard Runners
• GitHub Actions - Larger Runners

Runner images affected

• Ubuntu 22.04
• Ubuntu 24.04
• Ubuntu Slim
• macOS 13
• macOS 13 Arm64
• macOS 14
• macOS 14 Arm64
• macOS 15
• macOS 15 Arm64
• macOS 26 Arm64
• Windows Server 2019
• Windows Server 2022
• Windows Server 2025

Image version and build link

Current runner version: '2.329.0'

Is it regression?

No - this is a new image in public preview

Expected behavior

XDG_RUNTIME_DIR should be set similarly to ubuntu-latest. Output of repro steps command on ubuntu-latest runner:

XDG_RUNTIME_DIR is set to: /run/user/1001
Permissions for XDG_RUNTIME_DIR:
drwx------ 4 runner runner 140 Dec  9 13:29 /run/user/1001

Actual behavior

XDG_RUNTIME_DIR is inaccessible. Output of script:

XDG_RUNTIME_DIR is set to: /run/user/1001
XDG_RUNTIME_DIR does not exist or is not set.

Running ls -ld "$XDG_RUNTIME_DIR" returns an error reporting that /run/user/1001 does not exist

Repro steps

Example script to run in a run step on ubuntu-latest:

echo "XDG_RUNTIME_DIR is set to: $XDG_RUNTIME_DIR"
if [ -n "$XDG_RUNTIME_DIR" ] && [ -d "$XDG_RUNTIME_DIR" ]; then
  echo "Permissions for XDG_RUNTIME_DIR:"
  ls -ld "$XDG_RUNTIME_DIR"
else
  echo "XDG_RUNTIME_DIR does not exist or is not set."
fi

[Alexey-Ayupov]

Hello @andyn-ff, we will take a look