Fixing Slow Git SSH Pull Speeds | Generated by AI

Home 2026.05

Here’s the full breakdown of the investigation and fix.

Problem

Git pull on Qwen2.5-Coder was downloading at 81 KiB/s through SSH (git@github.com:QwenLM/Qwen2.5-Coder.git), pulling 2976 objects (~30 MB).

Investigation Steps

Step 1: Check git remote and proxy config

git -C /Users/lzwjava/projects/Qwen2.5-Coder remote -v
# → git@github.com:QwenLM/Qwen2.5-Coder.git (SSH)

git config --global --list | grep -iE 'proxy|http'
# → http.proxy=127.0.0.1:7890
# → https.proxy=127.0.0.1:7890

The HTTP proxy (7890) is configured for git, but the remote uses SSH — so git’s http.proxy doesn’t apply. SSH has its own proxy path.

Step 2: Check SSH config

cat ~/.ssh/config

Found the key line:

Host !192.168.*.*
    ProxyCommand ncat --proxy localhost:7891 --proxy-type socks5 %h %p

This means all non-local SSH connections (including GitHub) go through ncat → SOCKS5 proxy at localhost:7891. This is the SSH data path, separate from git’s HTTP proxy.

Step 3: Check what’s running on the proxy ports

lsof -i :7890 -sTCP:LISTEN
lsof -i :7891 -sTCP:LISTEN

Both ports are served by mihomo-da (PID 86998) — that’s mihomo (Clash Meta), your local proxy. Port 7890 = HTTP proxy, port 7891 = SOCKS5 proxy. Both are healthy.

Step 4: Test proxy speed directly

curl -x socks5h://localhost:7891 -o /dev/null -w "speed: %{speed_download}\n" https://github.com
# → ~1 MB/s — proxy is fast

curl -x http://127.0.0.1:7890 -o /dev/null -w "speed: %{speed_download}\n" https://github.com
# → ~980 KB/s — also fast

Conclusion: The proxy itself is not the bottleneck. Both HTTP and SOCKS5 routes are fast for HTTPS traffic.

Step 5: Test SSH auth speed

time ssh -T git@github.com
# → 3.6 seconds, authenticated successfully

SSH handshake is fine. The slowness is in the data transfer phase after auth, not the connection setup.

Step 6: Identify the bottleneck

The chain is: git fetch → SSH → ncat → SOCKS5 proxy (7891) → mihomo → internet.

ncat (from nmap 7.98) is the weak link. It’s designed as a network utility, not a high-throughput SSH tunnel proxy. For small packets (auth, handshake) it’s fine. For sustained large transfers (git packfiles), it adds significant overhead — the 81 KiB/s vs 1 MB/s difference.

Compare: HTTPS goes through git → libcurl → HTTP proxy (7890) → mihomo → internet. No ncat in the chain. libcurl is optimized for bulk transfers.

Step 7: Test HTTPS fetch

GIT_TRACE=1 git -C /Users/lzwjava/projects/Qwen2.5-Coder fetch --depth=1
# → 413 objects in ~77 seconds, completed successfully

Timestamps from the trace:

14:01:45.303  index-pack started (receiving data)
14:03:02.436  index-pack done

~77 seconds for 413 objects. The original SSH pull was fetching 2976 objects — that would have taken ~10+ minutes at 81 KiB/s.

What Was Done

Switched all 5 Qwen repos from SSH to HTTPS:

Qwen2-Audio:    git@github.com → https://github.com/QwenLM/Qwen2-Audio.git
Qwen2.5-Coder:  git@github.com → https://github.com/QwenLM/Qwen2.5-Coder.git
Qwen2.5-Math:   git@github.com → https://github.com/QwenLM/Qwen2.5-Math.git
Qwen2.5-VL:     git@github.com → https://github.com/QwenLM/Qwen2.5-VL.git
Qwen3:          already HTTPS (no change)

Command used:

git -C /path/to/repo remote set-url origin https://github.com/QwenLM/RepoName.git

Auth works automatically because git-credential-manager is configured.

Key Takeaways

  1. SSH proxy ≠ HTTP proxy in git. http.proxy only affects HTTPS remotes. SSH remotes use ~/.ssh/config ProxyCommand.
  2. ncat is slow for bulk SSH tunneling. Fine for small exchanges, terrible for large packfile transfers. If you ever need SSH through a proxy, connect (from brew install connect) or nc -X 5 -x localhost:7891 are faster alternatives.
  3. For large repos (model weights, datasets), prefer HTTPS when you have a fast HTTP proxy. The libcurl path is optimized for bulk data; SSH through SOCKS5 adds overhead.
  4. Diagnostic commands to remember:
    • lsof -i :PORT -sTCP:LISTEN — what’s listening
    • curl -x socks5h://localhost:PORT -o /dev/null -w "%{speed_download}" URL — test proxy speed
    • GIT_TRACE=1 git fetch — see exactly where git spends time
    • git config --global --list | grep proxy — check proxy config
Back Donate