Getting mosh server running on macOS Catalina

mosh-macos.md

Running into this error message when trying to run a mosh server on macOS Catalina? The steps below should solve the problem which is most likely either a $PATH and/or firewall issues.

command not found: mosh-server
Connection to X.X.X.X closed.
/usr/local/bin/mosh: Did not find mosh server startup message. (Have you installed mosh on your server?)

1. Install Mosh

$ brew install mosh

2. Update path to include mosh-server

zsh

$ echo "export PATH=$PATH:/usr/local/bin" >> ~/.zshenv

bash

$ echo "export PATH=$PATH:/usr/local/bin" >> ~/.bashrc

3. Update the firewall

# Turn the firewall off
$ sudo /usr/libexec/ApplicationFirewall/socketfilterfw --setglobalstate off

# Enable the firewall rules (make sure you are using your actual path)
$ sudo /usr/libexec/ApplicationFirewall/socketfilterfw --add /usr/local/bin/mosh-server

# Unblock the app
$ sudo /usr/libexec/ApplicationFirewall/socketfilterfw --unblockapp /usr/local/bin/mosh-server

# Turn the firewall back on
$ sudo /usr/libexec/ApplicationFirewall/socketfilterfw --setglobalstate on

4. Now try connecting using the mosh client

$ mosh [email protected]

Just got mosh-server running on a Mac via SSH using this little snippet. Thanks!

Just an addition if the above does not work (had the same issue while trying to connect from iPad to iMac (Ventura)):

If you installed mosh via brew, the binaries are usually located in '/usr/local/Cellar/mosh/...' and only links created in '/usr/local/bin'. For the macOS Firewall to allow connections, you have to give permissions to the binary and not the symlink. So just add '/usr/local/Cellar/mosh/.../mosh-server' for incoming connections. - Worked for me.

@Boggnogg this last part made it working. Thanks!

Just an addition if the above does not work (had the same issue while trying to connect from iPad to iMac (Ventura)):

If you installed mosh via brew, the binaries are usually located in '/usr/local/Cellar/mosh/...' and only links created in '/usr/local/bin'. For the macOS Firewall to allow connections, you have to give permissions to the binary and not the symlink. So just add '/usr/local/Cellar/mosh/.../mosh-server' for incoming connections. - Worked for me.

That fixed it here too. Thanks!

Just an addition if the above does not work (had the same issue while trying to connect from iPad to iMac (Ventura)):

If you installed mosh via brew, the binaries are usually located in '/usr/local/Cellar/mosh/...' and only links created in '/usr/local/bin'. For the macOS Firewall to allow connections, you have to give permissions to the binary and not the symlink. So just add '/usr/local/Cellar/mosh/.../mosh-server' for incoming connections. - Worked for me.

Hello, would this mean that every time I upgrade MOSH through Homebrew I need to run socketfilterfw?

you can run this to handle wherever you installed mosh (brew, whatever)

# Turn the firewall off
$ sudo /usr/libexec/ApplicationFirewall/socketfilterfw --setglobalstate off

# Enable the firewall rules (make sure you are using your actual path)
$ sudo /usr/libexec/ApplicationFirewall/socketfilterfw --add $(which mosh-server)

# Unblock the app
$ sudo /usr/libexec/ApplicationFirewall/socketfilterfw --unblockapp $(which mosh-server)

# Turn the firewall back on
$ sudo /usr/libexec/ApplicationFirewall/socketfilterfw --setglobalstate on

brew install mosh
MOSH_BIN=$(which mosh-server)
MOSH_BINDIR=$(dirname $MOSH_BIN)
echo "export PATH=$PATH:$MOSH_BINDIR" >> ~/.zshenv
sudo /usr/libexec/ApplicationFirewall/socketfilterfw --setglobalstate off
sudo /usr/libexec/ApplicationFirewall/socketfilterfw --add $MOSH_BIN
sudo /usr/libexec/ApplicationFirewall/socketfilterfw --unblockapp $MOSH_BIN
sudo /usr/libexec/ApplicationFirewall/socketfilterfw --setglobalstate on