Mosh⚓︎

Mosh (mobile shell) is a remote terminal application that replaces SSH for interactive sessions. It stays connected through network changes, roaming, and intermittent connectivity, and provides local echo for low-latency typing.

Installation⚓︎

sudo pacman -S mosh

Mosh also requires the server binary on the remote host:

# On the remote Arch/CachyOS machine
sudo pacman -S mosh

Firewall⚓︎

Mosh uses UDP ports 60000–61000. Open them on the remote host:

ufwfirewalldnftables

sudo ufw allow 60000:61000/udp

sudo firewall-cmd --permanent --add-port=60000-61000/udp
sudo firewall-cmd --reload

# Add to your nftables ruleset
sudo nft add rule inet filter input udp dport 60000-61000 accept

Usage⚓︎

# Basic connection (uses SSH for key exchange, then switches to UDP)
mosh user@hostname

# Use a specific SSH key
mosh --ssh="ssh -i ~/.ssh/id_ed25519" user@hostname

# Specify a remote port for SSH
mosh --ssh="ssh -p 2222" user@hostname

Mosh will automatically use your ~/.ssh/config aliases, so existing SSH host aliases like mosh myserver work out of the box.

Pair it with tmux

Mosh has no scrollback. Attach to a tmux session on the remote host so you get scrollback, and the session survives if Mosh drops:

mosh myserver -- tmux new -A -s main

Troubleshooting⚓︎

Missing shared library (`libabsl_*.so`)⚓︎

mosh-client: error while loading shared libraries: libabsl_log_internal_check_op.so.2605.0.0: cannot open shared object file: No such file or directory

Cause: Mosh links against Abseil (abseil-cpp), whose .so version encodes the release date (e.g. 2605 = May 2026). If mosh was built against a newer abseil-cpp than what is installed, the library is missing.

Fix: Update abseil-cpp (and all packages) with a full system upgrade:

sudo pacman -Syu

Partial upgrades on Arch/CachyOS are unsupported and cause exactly this kind of ABI mismatch.

Server not found⚓︎

If you get bash: mosh-server: command not found on the remote, install mosh there too:

sudo pacman -S mosh   # Arch/CachyOS
sudo apt install mosh # Debian/Ubuntu
sudo dnf install mosh # Fedora