Editor build won't run on server – cannot connect to Package Manager

I'm trying to run Unity in "headless" mode (using xvfb) on a Linux server (Ubuntu 18.04.4). I've manually activated the editor (using .alf/.ulf files), but now when I try to run the build command, I get an error that it can't connect to the package manager. Here's the console output:

Code (CSharp):

1. [LicensingClient] ERROR Failed to connect to local IPC
2. [Licensing::Module] Failed to connect to channel: LicenseClient-nick
3. [Licensing::Module] Successfully launched the LicensingClient
4. [Licensing::Module] Successfully connected to LicensingClient on channel: LicenseClient-nick
5. [SignatureVerifier] Application signature verification not supported on this platform.
6. [Licensing::Module] Successfully launched and connected to LicensingClient
7. Entitlement-based licensing initiated
8. [LicensingClient] Licenses Updated successfully in LicensingClient
9.  
10. LICENSE SYSTEM [20201126 15:59:24] Next license update check is after 2020-11-27T14:50:31
11.  
12. [Licensing::Module] Serial number assigned to: "SB-XYZ"\n[Package Manager] Server::Start -- Port 50602 was selected
13.  
14. COMMAND LINE ARGUMENTS:
15. /unity/editors/folder/2019.4.0/Editor/Unity
16. -nographics
17. -quit
18. -batchmode
19. -executeMethod=BuildProcess.BuildMethod
20. /my/project/folder
21. Using Asset Import Pipeline V2.
22. DisplayProgressbar: Unity Package Manager
23. Rebuilding Library because the metadata folder could not be found!
24. Adding genesis user token [Package Manager] Server::CheckExitCode -- Server stopped with exit code `9`
25. [Package Manager] PackageManager Server::Start -- Process restart attempt #2
26.  
27. [Package Manager] Server::Start -- Port 43639 was selected
28. [Package Manager] Done resolving packages in 3.49s seconds
29. Failed to resolve packages: Cannot connect to Unity Package Manager local server. No packages loaded.
30.  
31. A re-import of the project may be required to fix the issue or a manual modification of /home/nick/gvh-main/Packages/manifest.json file.

I've tried setting

UNITY_NOPROXY=localhost

, but that doesn't seem to have changed anything.

Is there any reason the Package Manager would be unreachable, and how can I fix that to continue with the project build?

 

@nickfourtimes, I have been working on doing builds with Unity in Docker and haven't had connectivity issues. However, I'm using 2020/2021.

There are some key differences, but none that deal with connectivity. The primary difference is that you don't need xvfb in 2020+ because the -nographics option now works correctly.