Difference between revisions of "Allow a program to continue after logoff"

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=== xpra ===
 
=== xpra ===
Xpra, which is available in AUR (as xpra-winswitch), allows you to start X programs and leave them running after disconnecting to reconnect again at a later time. It is possible to start X programs on a remote machine, connect to the machine over ssh, disconnect and reconnect again while the programs continue running.
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Xpra allows you to start X programs and leave them running after disconnecting to reconnect again at a later time. It is possible to start X programs on a remote machine, connect to the machine over ssh, disconnect and reconnect again while the programs continue running.
  
 
Read the [[Xpra]] article for more information.
 
Read the [[Xpra]] article for more information.

Revision as of 07:46, 11 September 2013

Tango-edit-clear.pngThis article or section needs language, wiki syntax or style improvements.Tango-edit-clear.png

Reason: please use the first argument of the template to provide a brief explanation. (Discuss in Talk:Allow a program to continue after logoff#)

Have you ever had the need to leave a program running after you have logged off?

This article will show you how to easily achieve this goal. The things you need to do differ depending on if you are trying to keep a console application running (e.g. mutt, centerICQ) or a X application running (e.g. gaim, graveman). I have created a section for each scenario.

Console applications

Tango-view-fullscreen.pngThis article or section needs expansion.Tango-view-fullscreen.png

Reason: Needs expansion with regard to systemd and its KillUserProcesses option. (Discuss in Talk:Allow a program to continue after logoff#)

You can use a terminal multiplexer to create a session and launch some program inside it. Then you can detach from the session and leave it running in background. When you reattach later (even after logout), you will find the session in the state you left it.

Popular terminal multiplexers are screen and tmux.

X applications

X move

Tango-edit-cut.pngThis section is being considered for removal.Tango-edit-cut.png

Reason: The xmove project seems dead (since 2008, see [1]). (Discuss in Talk:Allow a program to continue after logoff#)

To detach an X application you need xmove. Like screen, xmove has some similar capabilities. Read the manpage for more info.

Install it with pacman:

$ pacman -S xmove

xmove is a pseudo server X. It is pseudo since it does not actually do the work of a server, but instead it speaks with an existing X server.

Open a terminal and start xmove with

$ /usr/bin/xmove -server :0 -port 9 &

Do not forget the &, this will start xmove in the background. It will continue working until explicitly killed with kill -TERM `pidof xmove`.

Now, xmove is working as X server in port :9 speaking with the X server in port :0. Zero is usually the port of the first X server, however if you know your X server is somewhere else change the line accordingly.

If more than one user needs to use xmove at the same time, every user needs to starts his copy of xmove in a different port. If xhost allows it, the server can be shared.

Let me explain how to detach with a little example: we want to start ktorrent' and let it continue seeding after log off.

$ export DISPLAY=:9
$ nohup ktorrent &
$ exit

of if you like it compact

$ env DISPLAY=:9 nohup ktorrent & exit

ktorrent will start, lets start the downloading of the .torrent we need. After a while we want log off without interrupting ktorrent's work. Lets start an other terminal:

$ export DISPLAY=:9
$ xmovectrl -list
4      ktorrent        :0
$ xmovectrl -move -suspend 4

xmovectrl controls the xmove server, the command -list gives a list of the attached applications. The first column gives an id of the window. The same id used by the -mode command.

The command -move moves the window from a X server to an other. Putting -suspend will make the window appear nowhere while letting the program continue working.

nohup may be unnecessary; many X applications ignore the hang up signal by default. To test an application start it from a terminal putting & at the end of the line, close the terminal. If the X application continues nohup is not necessary.

To restore the window and work with the application again you need to start a terminal, set the DISPLAY variable and move the window back to :0. In our example:

$ export DISPLAY=:9
$ xmovectrl -list
4    ktorrent    suspended
$ xmovectrl -move :0 4

The ktorrent window will be restored even after log off.

If you use xmove often you may like the idea of making an alias of xmovectrl so you do not need to set DISPLAY every time. To do that add to your ~/.bashrc (or other shell initializing file):

alias xmovectrl='env DISPLAY=:9 xmovectrl'

This alias will set DISPLAY for you every time you call xmovectrl.

xmove X server has less capabilities than the usual server. Some applications will not work well, or not work at all. Make some tests before using it with vital applications!

Secondary X server

xmove project seems dead, many applications do not work inside the xmove pseudo server. So an other solution is using a secondary real X server.

With your favourite editor make a script with this content, use chmod to make it executable (chmod a+x scriptname.sh).

#!/bin/sh

if [ $# -eq 0 ] ; then # check to see if arguments are given (color depth)
    a=24        # default color depth
else
    a=$1        # use given argument
fi

if [ $a -ne 8 -a $a -ne 16 -a $a -ne 24 ] ; then
    echo "Invalid color depth. Use 8, 16, or 24."
    exit 1
fi

for display in 0 1 2 3 4 5 ; do
    if [ ! -f "/tmp/.X$display-lock" ] ; then
        exec startx -- :$display -depth $a -quiet
        exit 0
    fi
done

echo "No displays available."
exit 1

executing this little script will start a new X server. Then you can simply start your application and lock the server with xlock -mode blank (you need the xlockmore package for using xlock.)

Do not start your application in the first X server. If it is not already started, start the first and start a second one. Use the second one for your applications.

This is important because some features, like AGP mode, works only on one X server and other users of the computer will be annoyed if those feature will be lacking because you started a X server for your own purposes. So just use the second, the first will be full featured for everyone who need.

xpra

Xpra allows you to start X programs and leave them running after disconnecting to reconnect again at a later time. It is possible to start X programs on a remote machine, connect to the machine over ssh, disconnect and reconnect again while the programs continue running.

Read the Xpra article for more information.

Conclusion

Detaching programs is very useful in shared systems, you can easily leave the machine to someone else while your programs continue to run. At the moment, however, it is still easier to do this with console applications. Since in the Linux world almost every task has its console the only application it is a good idea use it with screen. In the above example using transmission and screen is actually easier than ktorrent and xmove.