Mosh (Mobile Shell)

Mosh (mobile shell) is a remote terminal application that allows roaming, supports intermittent connectivity, and provides intelligent local echo. Developed by Keith Winstein and Nelson Minar at MIT in 2012, Mosh addresses the key pain points of traditional SSH for mobile and unreliable network connections. While SSH drops the connection entirely when the client IP changes or connectivity is lost, Mosh maintains the session alive through network transitions (switching from WiFi to cellular, moving between access points, or suspending and resuming a laptop). Key features include: persistent connection (the session stays alive when the network drops and automatically reconnects when connectivity returns, even after hours of disconnection), roaming (the client transparently reconnects to the server when the client IP address changes, without dropping the session), intelligent local echo (Mosh predicts the effect of keystrokes locally, showing them immediately even on high-latency connections, providing a responsive typing experience that feels local), differential screen synchronization (Mosh uses a custom protocol that only transmits the parts of the screen that changed, using the Stardard State Synchronization Protocol, reducing bandwidth usage and providing smooth screen updates), robustness against packet loss (using UDP instead of TCP, Mosh degrades gracefully under packet loss without head-of-line blocking issues that plague SSH), Ctrl-C responsiveness (interrupting a running command works immediately due to the separate signaling channel), SSH for initial authentication (Mosh uses SSH for the initial connection and key exchange, then switches to its own UDP-based protocol), and a server component (mosh-server) that runs on the remote machine.