Monday, November 23, 2015

Optimizing Server Interaction with Screen and Friends

Since becoming part of industry, I've come to see the advantage of doing my work on a remote machine (a DevServer). Now historically, I had been this Linux nut, who loved using tiling window managers. My workflow has been launch a handful of terminals to begin working and launch more as needed. This was a rather mundane setup that just worked. Unfortunately, it just doesn't work in industry. I encountered several challenges:

  • Launching a terminal connects me only to my machine
  • Cannot work locally (challenges through the roof to make this even possible)
  • Accessing the server requires SSH, SSH requires the use of two factor auth (no auto login)
  • Long-lived sessions with SSH are impossible, it cannot withstand a computer suspend and rarely even a momentary loss of network connectivity

So the question became how can I reproduce, if not create an enhanced version of, my previous environment with minimal effort?

  • Find the simplest terminal emulator (st)
    • For better colors, add the solarized patch
    • I tried a few other patches, but they didn't seem to work on my system
  • Use screen locally
    • A keyboard only way to access scrollback buffer (content that was printed out that no longer fits on the screen)
    • Make the local screen respond to easier to access keys: Alt-a instead of Ctrl-a
    • Quicker access to my screen windows I'm looking for (windowlist -b) and make this easier Alt-a ' (instead of Alt-a ")
  • Rename the terminal and screen window with the PWD and command executing inside (fun stuff with PROMPT_COMMAND)
  • Use screen remotely
    • Always ssh into a long-lived state
    • Restart that state automatically, in case I manually close it out or the machine is rebooted
    • No need to SSH in for each additional window, just create new windows in the current screen session
  • Use mosh
  • No need to deal with SSH flakiness -- automatic connection reestablishment after lossy network usage or suspend / resume
  • Mosh can be flaky off of our corporate network -- I can switch to SSH and resume my screen session there

The only thing really missing is that I would love to be able to create multiple distinct views of my remote screen session without multiple SSH sessions. Think of it this way, if I have 3 windows open on a remote screen session. I can only view one of them at a time unless I ssh in again and attach to that same session. Ideally, I could move the multiplexing locally, alas, I couldn't figure a clean way of moving the screen unix domain socket locally and have that local screen connect to it.

Now it is time for the useful code bits.

My .screenrc:

vbell off
startup_message off
autodetach on
defscrollback 100000
shelltitle '$ |/home/davidiw bash'
#hardstatus string "%h"
#caption always "%{= kw} %-w%{= wk}%n*%t%{-}%+w%{= kw} %=%d %M %0c %{g}%H%{-}"
#hardstatus alwayslastline

escape ^Aa
register S ^A
bindkey "^[a" process S # On the remote machine, i set this to "^[s", so I don't have to type Alt-a a
bind "\'" windowlist -b
bind "\"" select

Append this to .bashrc to get nice names for screen and xterm title's and to start screen with the default session (home):

function make_title {
  if [[ $BASH_COMMAND == 'trap "make_title" DEBUG' ]]; then
    cmd="bash"
  else
    cmd=$BASH_COMMAND
  fi
  echo -ne "\033]0;$PWD $cmd\007"
  echo -ne "\033k$PWD $cmd\033\\"
}

term=$TERM

case $term in
  *screen*)
    ;&
  *term*)
    export TERM="xterm-256color"
    export PROMPT_COMMAND='trap "make_title" DEBUG'
    ;;
esac

case $term in
  *term*)
    exec /bin/bash -c "screen -AUx home || screen -AUS home"
    ;;
esac

Future work:

  • Shared local vim buffer
  • Shared remote vim buffer
  • A git repository to make reproduction easy
  • Fix for mosh to not break on non-corp networks
  • Clickable URLs in the Terminal

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