Valve says your Nvidia driver files must match exactly or SteamVR hits error 303
If SteamVR on Linux dies with error 303, Valve's answer is to look at your Nvidia driver install before anything else. Replying on its SteamVR-for-Linux tracker on September 30 at 23:26 UTC, Valve wrote that "the NVIDIA proprietary driver requires that the driver's running kernel module, 32 bit userspace libraries, and 64 bit userspace libraries are all installed and exactly the same version to work properly".
The SteamVR dashboard as Valve published it with the 2.17 release, with Half-Life: Alyx at the front of the library. Image: Valve
In the report that prompted it, they were not. Valve told the owner their install was "missing 32 bit userspace libraries", and that this was "forcing Steam to fallthrough to llvmpipe (mesa's faster CPU renderer) to run at all". Valve added that Vulkan was broken on the system in general. A VR runtime has nothing to work with in that state.
A half-installed driver does not look like a driver problem
The desktop still comes up, Steam still opens, and nothing announces that the graphics card has quietly dropped out of the picture and a CPU renderer has taken over. What the owner saw was a VR error code and no compositor logs, which reads like a SteamVR fault.
The bug report, "303 Error when launching game, no compositor logs", was opened on September 30 at 23:12 UTC. Valve's reply came about 14 minutes later and pointed at the diagnostics rather than at SteamVR. After moving to a 610 driver, the owner reported that the diagnostics stopped saying llvmpipe. By October 1 at 02:38 UTC SteamVR was booting into Half-Life: Alyx and then hanging on a Mongoose timeout, so nothing about the thread is finished.
What Valve has and has not committed to
This is a diagnosis in a tracker reply, not a support article. Valve named the requirement, named the symptom and named the component doing the work instead of the GPU, and that is the whole of it. There is no patch, no SteamVR check that warns you when the three pieces of a driver install disagree, and no statement that one is planned. The report is still open.
Valve frames the rule as a property of Nvidia's proprietary driver rather than of SteamVR, and the Vulkan breakage it described was system-wide rather than something confined to VR. The driver branch numbers in this case come from the owner's own testing rather than from Valve, so the part to hold on to is the requirement Valve stated, not any particular release.
It is also one report. Issue 977 has a single reporter, and Valve's statement about the driver is general rather than a count of anything. This is a useful thing to check, not evidence of a wave of broken installs.
Not the same as the 580 branch problem
Valve has separately confirmed that Nvidia's 580 driver branch breaks Steam Link VR on Linux, which is a different issue with a different cause. A mismatched install can be present alongside it, and the two will produce different symptoms.
For anyone whose PC VR stopped working after a driver update or a distribution upgrade, that single sentence from Valve is the cheapest thing to rule out. If the kernel module, the 32-bit libraries and the 64-bit libraries are not all on the same version, Valve's position is that the driver is not expected to work properly at all.
