Unable to connect Nvidia Sync to DGX Spark: unsupported DSA key size 768

Accelerated Computing DGX Spark / GB10 User Forum DGX Spark / GB10
1

When trying to add the DGX Spark to NVidia Sync, I am getting the error:

Unexpected Error, ssh: unsupported DSA key size 768

I can use SSH to log into the Spark without any issues. I am using a Mac (most recent MacOS).

Any ideas what to try next?

Detailed logs from the Sync log file:

{“level”:“info”,“time”:“2025-10-17T19:46:56.441Z”,“source”:“cli”,“message”:[“executeCLICommand”,“create”,[“ssh://user1@192.168.10.13”,“–password-stdin”]]}
{“level”:“info”,“time”:“2025-10-17T19:46:56.443Z”,“source”:“cli”,“message”:[“cliPath: “/Applications/NVIDIA Sync.app/Contents/Resources/bin/nvsync-arm64”, create args: ssh://user1@192.168.10.13,–password-stdin, [command, …stringArgs]: create,ssh://user1@192.168.10.13,–password-stdin”]}
{“level”:“info”,“time”:“2025-10-17T19:46:56.444Z”,“source”:“async-spawn”,“message”:[“spawnProcess: “/Applications/NVIDIA Sync.app/Contents/Resources/bin/nvsync-arm64” args: create,ssh://user1@192.168.10.13,–password-stdin “]}
{“level”:“info”,“time”:“2025-10-17T19:46:56.489Z”,“source”:“async-spawn”,“message”:[”“/Applications/NVIDIA Sync.app/Contents/Resources/bin/nvsync-arm64””,[“create”,“ssh://user1@192.168.10.13”,“–password-stdin”],“Process exited with code 1”]}
{“level”:“error”,“time”:“2025-10-17T19:46:56.489Z”,“source”:“async-spawn”,“message”:[“asyncSpawn: “/Applications/NVIDIA Sync.app/Contents/Resources/bin/nvsync-arm64” args: create,ssh://user1@192.168.10.13,–password-stdin error”]}
{“level”:“info”,“time”:“2025-10-17T19:46:56.490Z”,“source”:“cli”,“message”:[“create args: ssh://user1@192.168.10.13,–password-stdin, result: {\n “heading”: “Unexpected Error”,\n “details”: “ssh: unsupported DSA key size 768”\n}\n”]}

(swapped my actual username and IP for generic values)

2

Hi, thanks for reaching out. We are investigating this issue and will reach back out with more info

3

Hi jullrich1

Can you provide the full nvsync.log. You can attach it to this topic or message me directly

4

sent to you directly. Thanks for investigating!

5

found a solution: Moving my entire ~/.ssh directory worked. NVIDIA Sync created a new ~/.ssh directory with a new config file.

FWIW: Removing the config file was not sufficient. I also tried moving just the keys and it didn’t help. But will investigate a bit more.

6

new error after moving the files back, and including the “include” line created by NVidia Sync in my config file:

Unexpected Error

daemon not running: socket /Users/jullrich/Library/Application Support/NVIDIA/Sync/session/10.5.2.21.socket doesn’t exist

7

Hi,

DSA authentication is unsupported for both the Spark and NV Sync and should not be used.

The situation is a little confusing now, are you using the Sync CLI directly? We see what look like invalid flags being used in the log files. (-debug and -verbose)

I think you should try uninstalling NV Sync and removing all of your config changes and reinstall after from a clean base.

8

I finally was able to figure it out. My “known_hosts” file had two old entries for “ssh-dss” host keys. I would have expected these to be ignored. These entries used hostnames/IP addresses completely unrelated to the Spark. So I would have expected them to be ignored, and while I have not used the systems they refer to in years, they never caused issues before.

@aniculescu I will send you a direct message with the full keys so you can reproduce and maybe fix that before it causes issues for someone else :)

9

Thank you for figuring this out. We will look into it.

11

hey @jullrich1 - thanks for the information in this thread. Just confirming that we found the same thing (some old entry in the known hosts file can cause an unexpected parsing issue). We’ll be able to apply a fix to ignore this and similar issues in a future update.

1 Like
12

I am having the same problem, but it is saying unsupported DSA key size 512.

I removed all records in known hosts for this box, but it still gets the same error.

13

@hagelk you didn’t specify your host OS, if Windows delete the files in C:\Users\$USER\AppData\Local\NVIDIA Corporation\Sync\config> and restart Sync setup.

14

I’m on Mac OS 26.1

15

I was on Mac OS 26, and removing ~/.ssh/known_hosts did it for me. (back it up… if this fixes the issue you can then copy the “good” keys to a new known_hosts file)