smux: SSH with auto reconnect & tmux, a mosh replacement

Mosh was a great idea, but the lack of IPv6 is enough of a nuisance that I've come up with a suitable alternative that's working great for me now.

This approach uses autossh + tmux. The benefits are:

• IPv6 support
• Uses ssh_config, therefore you can use ProxyCommand transparently
• Auto launches a tmux session, or reconnects to a running one
• Reconnects to the host if you lose your connection

The only real feature mosh adds that is not addressed here is the low-latency feedback.

Getting this going on OSX:

• Install autossh. I use MacPorts: sudo port install autossh

• Create the new smux script

  #!/bin/sh
  if [ "X$1" = "X" ]; then
      echo "usage: `basename $0` <host>"
      exit 1
  fi
  
  if [ "X$SSH_AUTH_SOCK" = "X" ]; then
          eval `ssh-agent -s`
          ssh-add $HOME/.ssh/id_rsa
  fi
  
  AUTOSSH_POLL=20
  AUTOSSH_PORT=$(awk 'BEGIN { srand(); do r = rand()*32000; while ( r < 20000 ); printf("%d\n",r)  }' < /dev/null)
  #AUTOSSH_GATETIME=30
  #AUTOSSH_LOGFILE=$HOST.log
  #AUTOSSH_DEBUG=yes
  #AUTOSSH_PATH=/usr/local/bin/ssh
  export AUTOSSH_POLL AUTOSSH_LOGFILE AUTOSSH_DEBUG AUTOSSH_PATH AUTOSSH_GATETIME AUTOSSH_PORT
  
  # -t is the ssh option to force a pseudo terminal (pty)
  autossh -t $@ "tmux attach-session"

• Make the new smux script executable:

  chmod 755 /path/to/smux

- On the server make sure you have the following line in your /etc/tmux.conf. This will ensure tmux will start a new session if one doesn't already exist.

new-session -s main

• Connect to your server with

  smux your.serv.er

• Test the auto reconnect by disabling your network then re-enabling it, or switching from wire to wifi, etc.