Advanced screen topics

Finding lost screens

Once you start a screen session you need to remember which lxplus node it is running on. If you forget to note that down you can use the following little snippet to find any screen sessions running on lxplus nodes:

for i in $(seq -f "%04g" 1 500); do
 ssh -o ConnectTimeout=10 -o PreferredAuthentications=gssapi-with-mic,gssapi -o GSSAPIAuthentication=yes -o StrictHostKeyChecking=no -o LogLevel=quiet lxplus$ "(screen -list | head -1 | grep -q 'There is a screen on') && hostname && screen -list"

This will connect to the first 500 lxplus nodes in turn, checking if a screen session is running and if yes prints the hostname and output of screen -list.

Using tabs in screen

Screen supports some features beyond detaching a session. A very useful feature is different sessions in tab pages, all within a single instance of screen. In order to maximise the usefulness of this feature, you need to set the screen status bar. The simplest way to do this is by appending the following line to the file ~/.screenrc (create it if it doesn’t already exist):

# Status lines
hardstatus off
hardstatus alwayslastline
hardstatus string '%{= BG}%{.g}[ %{.G}%H %{.g}][ %{= Bw}%?%-Lw%?%{Yr}%{.k}%n*%f%? %t%?%?(%u)%?%{.r}%{Bw}%?%+Lw%? %{.g}%=][%{.W} %Y-%m-%d %c %{.g}]'

Note that this has predefined colours and layout that you can easily change yourself, see eg. this detailed discussion.

The following commands should help you get started using multiple tabs in a screen window. Note that ^a stands for Ctrl-a in this list.

  • Create a new tab: ^a c

  • Switch to tab number #: ^a # (where # is a digit)

  • Switch to the last visited tab: ^a ^a

  • Close a tab: log out of the shell with ^d

  • Kill a tab: ^a k (only use if normal logout through ^d doesn’t work because a process has crashed)

  • Change a tab’s name: ^a A

As one last note, you may find it easier if the tab numbers start with 1, rather than 0. To accomplish this, append the following lines to the aforementioned file ~/.screenrc:

# Start with window 1 (instead of 0)
bind c screen 1
bind ^c screen 1
bind 0 select 10
screen 1