Difference between pages "Bg, fg and jobs" and "Find out where configuration changes are stored"

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imported>ThorstenStaerk
 
 
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bg, fg and jobs are [[process]] related [[commands]] that belong together. bg stands for background and fg stands for foreground.
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Whenever I set up a computer, I start konsole and change its settings. I choose Settings -> Configure Current Profile -> Tabs -> "Show 'New Tab' and 'Close Tab' buttons in tab bar". Today I wanted to write a script to do this configuration change for me. The most important question is - where is this setting being saved?
  
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= Concept =
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I could find this out using the command
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When you start a [[program]] under Linux, by default the command runs in the foreground. This means the console is reserved for in- and output to and from this program. You do not get a prompt while the program is running. Here is an example for this showing the program xclock being called by the command
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strace -ffe open konsole
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  xclock
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[[strace]] is a cool [[command]] that shows you every syscall invoked by a program (in the above case konsole). When called with the -e open argument, it will only show the open syscalls. This gives you a powerful tool into your hands: A monitor which files are read and/or modified by a program. The output will read like this:
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[pid 29951] open("/etc/localtime", O_RDONLY) = 3
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[pid 29951] open("/etc/kde4rc", O_RDONLY|O_CLOEXEC) = 3
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  [pid 29951] open("/root/.kde4/share/config/kdeglobals", O_RDONLY|O_CLOEXEC) = 3
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The -ff argument is needed so strace still follows spawning processes; for more information, read [http://man-wiki.net/index.php/1:strace strace's man page].
  
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[[File:Snapshot-fg-xclock.png]]
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So I did [[open a console]], entered
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strace -ffe open konsole
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A konsole window popped up and I chose Settings -> Configure Current Profile -> Tabs -> "Show 'New Tab' and 'Close Tab' buttons in tab bar". When I clicked on "Apply", I found a line saying
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[pid 29951] open("/root/.kde4/share/apps/konsole/Shell.profile", O_RDONLY|O_CLOEXEC) = 16
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And I could verify my changes go to /root/.kde4/share/apps/konsole/Shell.profile:
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# [[cat]] /root/.kde4/share/apps/konsole/Shell.profile
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[...]
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ShowNewAndCloseTabButtons=false
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[...]
  
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This program runs in the foreground, the console is reserved for its in- and output. To run the same program in the background, start it with the ampersand ("&") after the program name:
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[[Category:Geeky]]
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xclock &
 
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[[File:Snapshot-bg-xclock.png]]
 
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In this case you can continue to call further [[commands]] on the console.
 
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= Hints =
 
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Maybe you have started a program without the & behind it, and now you want to use console to issue further commands. In this case stop the program using CTRL_Z:
 
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tweedleburg:~ # xclock
 
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^Z
 
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[1]+  Stopped                xclock
 
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List it using the command jobs
 
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tweedleburg:~ # jobs
 
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[1]+  Stopped                xclock
 
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And send it to the background using the command bg
 
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tweedleburg:~ # bg
 
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[1]+ xclock &
 
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tweedleburg:~ #
 
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Now it will be as if you had called the command with the & behind it. You will be able to use console for issueing further commands.
 
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= See also =
 
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* [[disown]]
 

Revision as of 09:33, 22 December 2011

Whenever I set up a computer, I start konsole and change its settings. I choose Settings -> Configure Current Profile -> Tabs -> "Show 'New Tab' and 'Close Tab' buttons in tab bar". Today I wanted to write a script to do this configuration change for me. The most important question is - where is this setting being saved?

I could find this out using the command 

strace -ffe open konsole

strace is a cool command that shows you every syscall invoked by a program (in the above case konsole). When called with the -e open argument, it will only show the open syscalls. This gives you a powerful tool into your hands: A monitor which files are read and/or modified by a program. The output will read like this: 

[pid 29951] open("/etc/localtime", O_RDONLY) = 3
[pid 29951] open("/etc/kde4rc", O_RDONLY|O_CLOEXEC) = 3
[pid 29951] open("/root/.kde4/share/config/kdeglobals", O_RDONLY|O_CLOEXEC) = 3

The -ff argument is needed so strace still follows spawning processes; for more information, read strace's man page.

So I did open a console, entered 

strace -ffe open konsole

A konsole window popped up and I chose Settings -> Configure Current Profile -> Tabs -> "Show 'New Tab' and 'Close Tab' buttons in tab bar". When I clicked on "Apply", I found a line saying 

[pid 29951] open("/root/.kde4/share/apps/konsole/Shell.profile", O_RDONLY|O_CLOEXEC) = 16

And I could verify my changes go to /root/.kde4/share/apps/konsole/Shell.profile: 

# cat /root/.kde4/share/apps/konsole/Shell.profile 
[...]
ShowNewAndCloseTabButtons=false
[...]
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