SSH ProxyCommand Fails with Command Not Found

connect: command not found means SSH could not launch its ProxyCommand helper locally. There is no proxy handshake to repair yet. The name may refer to a separate executable, not a shell builtin or OpenSSH subcommand.

1. Find the selected command. Inspect the effective SSH configuration for the same destination alias and account. Host sections, included files and command-line options may select a different ProxyCommand from the file you edited.
2. Locate its executable. Compare the launching environment's PATH with the interactive terminal where the helper works. An absolute path to the intended existing program removes that ambiguity.
3. Match the helper implementation. Do not substitute any binary named nc. OpenBSD netcat uses -X connect for HTTP CONNECT and -X 5 for SOCKS5; other variants may lack those options or the proxy's authentication support.

After the helper launches, follow the next failure in order: connection to proxy, proxy negotiation, destination connection, then SSH authentication. A failure at one stage does not establish a problem at the later ones.

ProxyJump requires an SSH jump host. It can replace this arrangement only when that service is available; an HTTP proxy does not become an SSH login endpoint because the setting changed.