I sometimes have long running processes that I want to kick off before going home, so I create a SSH session to the server to start the process, but then I want to close my laptop and go home and later, after dinner, I want to check on the process that I started before leaving work. How can I do that with SSH? My understanding is that if you break your SSH connection you will also break your login session on the server, therefore killing the long running process.
nohup to make your process ignore the hangup signal:
$ nohup long-running-process & $ exit
You want to be using GNU Screen. It is super awesome!
ssh email@example.com screen #start a screen session run-a-long-process
CTRL+a , d to detatch from your screen session
exit #disconnect from the server, while run-a-long-process continues
When you come back to your laptop:
ssh firstname.lastname@example.org screen -r #resume the screen session
Then check out the progress of your long-running process!
screen is a very comprehensive tool, and can do a lot more than what I've described. While in a screen session, try ctrl+a,? to learn a few common commands. Probably the most common are:
- CTRL+a , c to create a new window
- CTRL+a , n to switch to the next window in your screen session
- CTRL+a , p to switch to the previous window in your screen session
- if you log in from a bunch of different systems, you may have accidentally left yourself attached to an active screen session on a different computer. for that reason, I always resume with
screen -d -rto ensure that if another shell is attached to my screen session, it will be detached before I resume it on my current system.
If you haven't planned ahead and setup
screen, etc. just do the following:
If your process is running in the background: goto #3, else:
Ctrl-Zto suspend foreground process. This will report the job # of the suspended process, for example:
+ Stopped processName
processNameto the background with
bg %1(using whatever the job # is following the
%). This will resume
processNamein the background.
disown PID. Use the
-hflag if you want to maintain ownership until you terminate your current shell.
What you want to use is screen or even better a user-friendly wrapper around screen called byobu.
byobu is a wrapper that allows to easily open new screens with a simple function key instead of key combination from ctrl-a. It also shows a status line with all the open virtual terminals which can be named.
Another nice feature is the fact that all your screen can stay up while your ssh connection is disconnected. You just connect again via ssh and call byobu and everything is like before.
At last some screenshots of byobu.
It might be worth noting that
ssh -t lala screen -rxU moo will attach to the moo session on host lala
ssh -t lala screen -S moo will create the moo session on host lala
ssh -t lala screen -S moo quux will create the moo session on host lala and run the program quux, quitting the session on completion.
Old question, strange still nobody advised tmux, which acts as a wrapper for n consoles and keep them open until needed. This allows more control, beside a number of functions tmux has. It's easy to manage it, you just execute tmux, which brings you in its shell, start your looong job, then press ctrl+b followed by d (detach) (
ctrl+b is the "ok google" of tmux, and
d is the command to close without exit from the shell). This actually works if you just close, for example, putty. After dinner, when you connect again, you can reopen tmux with
tmux attach to see your screen exactly as you left. Something I love is splitting pane:
ctrl+b and then press
". To change from one pane to another,
ctrl+b and then press the up/down arrow.
You can find a good guide here: Keep Your SSH Session Running when You Disconnect
sudo apt-get install screen
Now you can start a new screen session by just typing screen at the command line. You’ll be shown some information about screen. Hit enter, and you’ll be at a normal prompt.
To disconnect (but leave the session running) Hit Ctrl + A and then Ctrl + D in immediate succession. You will see the message [detached]
To reconnect to an already running session
To reconnect to an existing session, or create a new one if none exists
screen -D -r
To create a new window inside of a running screen session Hit Ctrl + A and then C in immediate succession. You will see a new prompt.
To switch from one screen window to another Hit Ctrl + A and then Ctrl + A in immediate succession.
To list open screen windows Hit Ctrl + A and then W in immediate succession
I use NX NoMachine, which is free for me because it's only me. Essentially, it runs an X session on the server which you can connect to and disconnect from over and over. The X session keeps running when you're not connected. Connections can be made from anywhere. You can choose between floating windows or a single window containing a whole desktop (eg a complete Gnome desktop). The client (which you would run on your laptop) can be run on Linux, MacOS, Solaris or Microsoft Windows. In the latter case if you choose floating windows they appear individually on the Windows Taskbar.
I use my Windows XP laptop (which I need for certain Windows-specific hardware I have) as a front end for my two Linux servers using NX Nomachine. I can even print to the printer attached to my Windows laptop from Linux.