Mosh: The Mobile Shell — SSH That Stays Connected

TL;DR — Quick Summary

Mosh is a replacement for SSH that stays connected through network changes, Wi-Fi switching, and high latency. It uses UDP and shows local echo instantly.

Mosh keeps your remote sessions alive. Switch networks, close your laptop, ride through high latency — Mosh reconnects automatically and shows instant local echo.

Installation

# Install on BOTH client and server
# macOS
brew install mosh

# Ubuntu/Debian
sudo apt install mosh

# Arch Linux
sudo pacman -S mosh

# Open UDP ports 60000-61000 on server firewall
sudo ufw allow 60000:61000/udp

Usage

# Basic connection (replaces ssh)
mosh user@server

# Custom SSH port
mosh --ssh='ssh -p 2222' user@server

# Custom SSH port 443 (corporate firewalls)
mosh --ssh='ssh -p 443' user@server

# Specify mosh-server path
mosh --server=/usr/local/bin/mosh-server user@server

# Use with tmux/zellij (best combo)
mosh user@server -- tmux attach -t main

Comparison

Feature	Mosh	SSH	Eternal Terminal
Protocol	UDP	TCP	TCP
Survives roaming	Yes	No	Yes
Local echo	Yes	No	No
Port forwarding	No	Yes	Yes
File transfer	No	Yes (scp)	No
Encryption	AES-128	Various	AES

Summary

Mosh keeps terminal sessions alive through network changes and sleep
UDP-based protocol survives Wi-Fi switching, cellular roaming, high latency
Instant local echo — no waiting for server round-trip
Uses SSH for authentication — your keys and config work automatically
Best combined with tmux or Zellij for persistent sessions

Guide & Instructions

Estimated Time: 5m

Tools Needed:

Mosh
Terminal

Install Mosh

Install on both client and server: brew install mosh, apt install mosh, or pacman -S mosh.

Connect

Run mosh user@server instead of ssh user@server.

Use with SSH key

Mosh uses SSH for auth, so your SSH keys work automatically.

Test roaming

Switch Wi-Fi networks or close laptop lid — Mosh reconnects automatically.

Custom SSH port

Use mosh --ssh='ssh -p 2222' user@server for non-standard SSH ports.

Frequently Asked Questions

What is Mosh?

Mosh (Mobile Shell) is a remote terminal that replaces SSH for interactive use. It uses UDP instead of TCP, so it survives network changes (Wi-Fi to cellular), sleep/wake, and high-latency connections without disconnecting.

How is Mosh different from SSH?

SSH uses TCP — if the network hiccups, the connection dies. Mosh uses UDP with its own protocol, so it automatically reconnects after network changes. It also shows instant local echo before the server responds.

Does Mosh replace SSH?

Mosh uses SSH for initial authentication, then switches to its own UDP protocol. You still need SSH access to the server. For non-interactive tasks (scp, port forwarding), use SSH directly.

Is Mosh secure?

Yes, Mosh uses AES-128-GCM encryption for all traffic. The initial authentication goes through SSH. Mosh never stores data on disk.