Use Mosh

Mosh sessions run over UDP and survive network changes and short outages: after a drop, the session goes on without logging in again. In Sternway a host’s switch for it is called Mosh-compatible session.

Sternway does not ship Mosh’s own programs. It logs in over SSH, starts mosh-server new on the host, and then runs the mosh-client installed on your computer for the session itself.

Install mosh-client

System	Command
Debian, Ubuntu	sudo apt install mosh
Fedora, RHEL	sudo dnf install mosh
Arch	sudo pacman -S mosh

The host needs mosh-server too (the same package there). Windows has no native Mosh client, so Mosh sessions are not available in the Windows app; use SSH, or the Linux app under WSL.

Turn it on for a host

1. Open the host’s editor and open Advanced.
2. Under Mosh, turn on Mosh-compatible session.
3. Optionally set the Mosh server command (for a mosh-server outside the host’s PATH) and a Mosh UDP port range that the host’s firewall lets through.
4. Save and connect.

Mosh needs UDP between your computer and the host, on the port range mosh-server picks (60000 to 61000 unless you set one). If SSH works but the Mosh session never starts, a firewall or NAT is usually blocking that range.

Limits

• No jump hosts or proxies. Mosh speaks UDP straight to the host, so a host that has jump hosts or a proxy and Mosh on does not connect: the attempt stops with an error naming this. Turn Mosh off for such a host.
• No fallback. If mosh-client is not on your PATH, connecting fails with “mosh-client not found” and the install commands; it does not fall back to SSH. The desktop app has no setting for a mosh-client elsewhere.
• Not in session logs. Mosh sessions are not written to session logs (they can still be recorded, see Record and play back sessions).
• Not on the phone. The phone app cannot run Mosh. A host with Mosh on opens over plain SSH there, and the setting syncs unchanged. On the phone, tmux keeps your work instead.
• After a very long outage, Mosh’s own client may have given up; connect again.