Socket is not connected
What “Socket is not connected” usually means
When PuTTY reports Socket is not connected, the client has already attempted a network or protocol step and failed before a normal interactive shell is available. This guide explains what the message usually means on Windows clients, which local settings to verify first, and when the problem is almost certainly on the server, firewall, or DNS path rather than inside the PuTTY GUI.
The GUI attempted an operation on a socket that is no longer connected—often a follow-on error after an earlier drop, or a race during cancel/reconnect.
Independent resource: Putty.info is educational only and is not affiliated with the official PuTTY project. Compare symptoms against the official documentation for your installed version.
Symptoms you will see
Operators usually notice this failure in one of a few repeatable ways. Capture the exact dialog text, the hostname and port from the Session panel, and whether the failure happens before or after a username prompt—those details decide which checklist below applies.
- Error after an already-failing session or rapid Open/Cancel cycles.
- Automation with Plink may surface related socket errors when stdin handling is wrong.
Likely causes ranked by frequency
Several independent conditions can produce the same client-facing wording. Work from the outside in: reachability first, protocol selection second, authentication third. Changing key files will not fix a TCP refusal, and opening a wider firewall will not fix a rejected public key.
- Using a session object after disconnect.
- Proxy misconfiguration leaving half-open state.
- Local firewall killing the socket underneath PuTTY.
Step-by-step client checks
Use this ordered checklist on a workstation you control. Prefer saved sessions so Host Name, Port, and Connection type stay consistent while you isolate one variable at a time.
- Close the window fully and open a fresh session rather than repeatedly clicking Open.
- Clear Connection → Proxy settings if you do not need a proxy.
- Verify basic TCP connectivity first with a simpler saved session.
- Update the client; extremely old builds have rougher error recovery.
- For Plink scripts, ensure you are not closing stdin unexpectedly for interactive auth.
- Check whether another process is forcing interface changes mid-connect.
Do not paste private keys, passphrases, or production passwords into Putty.info tools or contact forms. Diagnose locally with PuTTY, Plink, PSCP, or PSFTP from an official install.
When it is a server or network issue
Usually client-local. If tied to one destination, still collect server logs, but start with workstation network stability.
If TCP connects from another network path but fails from yours, involve the network team with traceroute/path evidence rather than repeatedly regenerating keys. If authentication fails after a banner appears, collect the server sshd logs for the same timestamp and username—client-side retries alone rarely reveal AccountLocked, Match blocks, or AllowUsers denials.