Fix SSH attach control socket path length#4013
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Problem
dstack attachcan fail with OpenSSHControlPath too longbefore it connects.How to reproduce
Run attach with a long
~/.dstackpath and a long run name. Example from the failing case:/Users/dstack/.dstack/server/data/endpoint_agent_runs/.../home/.dstack/ssh/qwen36-27b-existing-auth-e2e-2-1.control.sockThat path was over the Unix socket path limit, so OpenSSH rejected it.
Why it happens
dstack attachused:~/.dstack/ssh/<run-name>.control.sockThat path includes the user home/dstack directory and the run name. In endpoint-agent or other nested environments, it can easily exceed OpenSSH's Unix-domain socket path limit.
Fix
On POSIX, use a short runtime socket path:
/tmp/dstack-ssh-<uid>/<hash>.sockKeep the old path only as fallback when
/tmpcannot be used and the old path is still short enough.Why this fix
The socket is runtime state, not SSH config or key material, so it does not need to live under
~/.dstack/ssh./tmp/dstack-ssh-<uid>/<hash>.sockkeeps the path short and stable. The per-user directory is checked for owner, permissions, and symlinks before use.AI Assistance: Used Codex.