You run long processes over SSH, perhaps over the WAN, and when you get disconnected you lose a lot of work. Or perhaps you started a long job from work, but need to go home and be able to check on the job later; you could run your process using nohup, but then you won’t be able to reattach to it when your connection comes back or you get home.

Install and use GNU screen.

Using screen is very simple. Type screen or screen -a. The -a option includes all of screen’s capabilities even at the expense of some redraw (thus bandwidth) efficiency. Honestly, we use -a but have never noticed a difference.

When you do this, it will look like nothing happened, but you are now running inside a screen. echo $SHLVL should return a number greater than one if this worked (see also :L$SHLVL in Customizing Your Prompt). To test it, do an ls -la, then kill your terminal (do not exit cleanly, as you will exit screen as well). Log back into the machine and type screen -r to reconnect to screen. If that doesn’t put you back where you left off, try screen -d -r. If that doesn’t work, try ps auwx | grep [s]creen to see if screen is still running, and then try man screen for troubleshooting information—but it should just work. If you run into problems with that ps command on a system other than Linux, see Finding Out Whether a Process Is Running.

Starting screen with something like the following will make it easier to figure out what session to reattach to later if necessary: screen -aS "$(whoami).$(date' +%Y-%m-%d_%H:%M:%S%z')“. See the run_screen script in Getting Started with a Custom Configuration.

To exit out of screen and your session, keep typing exit until all the sessions are gone. You can also type Ctrl-A Ctrl- or Ctrl-A :quit to exit screen itself (assuming you haven’t changed the default meta-key of Ctrl-A yet).

According to the screen web site:

What that means is you can have more than one session in a single SSH terminal (think DeskView on i286/386). But it also allows you to SSH into a machine, start a process, disconnect your terminal and go home, then reconnect and pick up—not where you left off, but where the process has continued to. And it allows multiple people to share a single session for training, troubleshooting, or collaboration (see Sharing a Single bash Session).

# Sample settings for ~/.screenrc
# Change the C-a default to C-n (use C-n n to send literal ^N)
 escape ^Nn

# Yes annoying audible bell, please
vbell off

# detach on hangup
autodetach on

# make the shell in every window a login shell
shell -$SHELL