Fix mosh server on macOS

fix_mosh_server.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>Label</key>
    <string>com.example.my_script</string>
    <key>ProgramArguments</key>
    <array>
        <string>/Users/ericswpark/fix_mosh_server.sh</string>
    </array>
    <key>RunAtLoad</key>
    <true/>
    <key>UserName</key>
    <string>root</string>
</dict>
</plist>

fix_mosh_server.sh

#!/bin/bash

# Thanks to @anhdle14 for the original script
# Find it here: https://github.com/mobile-shell/mosh/issues/1074#issuecomment-978832126

#!/bin/bash
fix_mosh_server() {
  local fw='/usr/libexec/ApplicationFirewall/socketfilterfw'
  local mosh_sym
  mosh_sym="$(which mosh-server)"
  local mosh_abs
  mosh_abs="$(greadlink -f "$mosh_sym")"

  # Turn off firewall temporarily
  sudo "$fw" --setglobalstate off

  # Add symlinked location to firewall
  sudo "$fw" --add "$mosh_sym"
  sudo "$fw" --unblockapp "$mosh_sym"

  # Add symlinked location to firewall
  sudo "$fw" --add "$mosh_abs"
  sudo "$fw" --unblockapp "$mosh_abs"

  # Re-enable firewall
  sudo "$fw" --setglobalstate on
}

fix_mosh_server

fix_mosh_server_readme.md

Fix mosh server on macOS

Why?

The macOS firewall has a bug where it will block connections that you explicitly allowed for a given program, if said program is added as a symlink.

If you are getting Nothing received from port XXXXX when connecting to your Mac via mosh, this solution is for you!

Setup

The fix_mosh_server.sh script goes in your user directory.

The fix_mosh_server.plist file goes in /Library/LaunchDaemons/. Once created, give it the proper permissions:

sudo chown root:wheel /Library/LaunchDaemons/fix_mosh_server.plist
sudo chmod 644 /Library/LaunchDaemons/fix_mosh_server.plist

Then load it:

sudo launchctl load /Library/LaunchDaemons/fix_mosh_server.plist