Frozen terminal
What “Frozen terminal” usually means
When PuTTY reports Frozen terminal, 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 window still exists but does not accept input or update output—may be network stall, host overload, flow control, or a remote process stuck.
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.
- Cursor idle; typing does nothing visible.
- Reconnecting may work while the old window stays wedged.
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.
- Remote process blocking on tty.
- SSH connection dead without GUI noticing yet.
- Local window hung drawing huge paste buffers.
- Serial-like flow control oddities in terminal settings (less common on SSH).
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.
- Try Enter and Ctrl+C; wait a few seconds for overloaded hosts.
- Open a second session to the same host to see if the server is alive.
- Avoid pasting megabytes into the terminal in one shot.
- Check keepalive and network stability.
- Review Terminal → features if breaks/special keys misbehave.
- Close and reopen rather than force-killing mid-password prompts blindly.
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
Check load averages, disk waits, and stuck controlling processes. Operator education on using tmux reduces pain from laptop sleep.
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.