screen¶

Set up GNU `screen` for long running processes¶

screen is a simple way to start a process on the research servers that you want to keep running even aver you are logged out of the session.

Configuring Screen¶

Before we start, lets add as simple configuration file that vastly improves the screen programs behavior.

Create a file in your home directory called .screenrc:

touch ~/.screenrc

Paste in the following settings using your preferred $EDITOR

  # Source: https://gist.github.com/bcomnes/6689991/download
  # Sets the screen to use login shells
  shell -$SHELL

  # To reload .screenr Press Ctrl - a : source ~/.screenrc

  # Turn of startup message
  startup_message off

  # This helps prevent the screen from doing funny things.
  defflow off
  defnonblock on

  # Enable 256-color mode when screen is started with TERM=xterm-256color
  # Taken from: http://frexx.de/xterm-256-notes/
  # I took it from: http://www.robmeerman.co.uk/unix/256colours
  #
  # Note that TERM != "xterm-256color" within a screen window. Rather it is
  # "screen" or "screen-bce"
  #
  # terminfo and termcap for nice 256 color terminal
  # allow bold colors - necessary for some reason
  attrcolor b ".I"
  # tell screen how to set colors. AB = background, AF=foreground
  termcapinfo xterm-256color 'Co#256:AB=\E[48;5;%dm:AF=\E[38;5;%dm'

  # Sets the status bar
  caption string "%?%F%{= Bk}%? %C%A %D %d-%m-%Y %{= kB} %t%= %?%F%{= Bk}%:%{=  wk}%? %n "
  hardstatus alwayslastline
  hardstatus string '%{= kG}[ %{G}%H %{g}][%= %{= kw}%?%-Lw%?%{r}(%{W}%n* %f%t%?(%u)%?%{r})%{w}%?%+Lw%?%?%= %{g}][%{B} %d/%m %{W}%c %{g}]'

Download screenrc

This changes some subtle behavior and turns on a status bar making screen a little bit easier to wrap your head around. It also turns off the annoying startup message.

Using Screen¶

Here is a quick walkthrough of how to use screen. To start using screen, run:

> screen

This opens a new screen session. Type some commands into the window such as listing files (ls) or changing directory (cd ..).

Now we can disconnect from this screen and have it continue to run in the background. screen uses keyboard shortcuts where you press two keys at once, let go, then press the next key to actually issue the command. First press the two keys at the same time:

Ctl-a

Let go, then press:

This should disconnect you from your screen session and take you back to where you were before you launch screen. You can have multiple screen sessions running at the same time (and have even more screen windows per screen session if you really want!).

Note

In the future, this kind of keyboard shortcut will be referred to as Ctl-a d

Reconnecting to screen¶

To reconnect to screen, we can type screen -ls similar to list the running screen sessions. (Similar to how ls will list the files in the current directory).

> screen -ls
There is a screen on:
 19250.pts-8.rocks (Detached)
1 Socket in /var/run/screen/S-bcomnes.

This lists the running screen sessions. Each session has a number associated with it. To reconnect to a particular screen session type:

screen -r 19250

where 19250 is the number associated with the screen session you want to connect to.

To end a screen session, reconnect to it, and just exit out of all the processes running and then end the session by typing:

exit

There are lots of cool screen features. Here is a quick rundown of screen window management:

Ctl-a c: Create a window in the current screen session
Ctl-a n: Go to the next window in the current screen session
Ctl-a d: Disconnect from current screen session.