Linux Screen Tutorial for ssh

Since the projects for this group are using linux machines through remote connections, I thought it might be useful to give a brief tutorial on a tool called screen that is available on Linux. Screen can be used as a way to manage a shell connection and allow the connection to persist through network problems allowing you to resume work where you left off. For instance, if you name a screen session gpgpusim when working from your desktop at home, you can then connect to the same screen session using that name on your laptop during a group meeting in the engineering building. You can also leave a long running script active and connect to it when you feel like it at any time. Screen has many more features than the ones I will cover in this post, but I thought it might be useful to give a brief introduction. If you want more information than I provide here, there is a lot more information available on the internet.

The first thing to do when you log in for the first time to work on something is to start a screen session. I recommend the following command because it will start the session with a name:

screen -S gpgpusim

This will create a screen session and give it the name "gpgpusim" allowing you to refer to it by that name in the future. If you accidentally started screen without the name, I believe you can name your session with the following while screen is running:

Control-a A

This means to hold the Control key and press the 'a' key then to press a capital 'A' (shift-a). Control-a is the magic combination that starts essentially all interactions with screen. For example, you can create a new window (screen's term for a new terminal within the session) by using Control-a c and you can switch between the first 10 windows with Control-a # where # is a number between 0 and 9 corresponding to the window you want to switch to. When you want to leave a session running but log out of the ssh connection, you can use the following to detatch the session:

Control-a d

When you want to reattach to a session that has previously been detached, you can use the following command where gpgpusim is the name of the session to reattach to:

screen -R gpgpusim

If you don't know whether the previous terminal detached, you can add the -d option to force it to detach. Alternatively, you can have multiple terminal connected to the same session by using the -x option instead of -d -R. If you use the -r option instead, it will reatach to whichever session you were last attached to instead of having to provide a session name.

An advanced setting that some people may want to change is switching the default Control-a behavior to something else. To change it to Control-z you can use the following command:

echo "escape ^Zz" > ~/.screenrc

which can also be undone by editing your ~/.screenrc file.

For more help on screen you can type Control-a ? within screen, or you can type man screen for the manual page.