Re: [tlug] Doesn't the Ampersand make commands run in the background?

[Romans Malinovskis <romaninsh@example.com>]

> I dutifully looked up the answer to my question before posting here,  
> but what I read doesn't seem to be the case.
>
> A web site said:
> "The shell has the capacity to run multiple commands at one time,  
> and can run commands in the background using the ampersand (&) after  
> the command."
>
> But on my system, when I try adding an ampersand after a command, I  
> don't get the command prompt back. I have to either wait for wait  
> for the command to finish it's task, or press [ctrl]+C.
>
> Did I miss something? This seems very straight forward, so it's hard  
> to guess at what could be wrong.

If you execute something like this:


app1 ; app2 &

then it might not happen.. You can try

( app1; app2 ) &

also - even if you type ampersand at the end, application is still  
using stdin/stdout (unless it specifically decides to detach those).  
That means you can't run "screen" or "mc" or "vi" in background, they  
would mess up your command line.

there are two tools which can help you. First you can use "screen"  
application. Check it's command line arguments, you can make it detach  
with the child process running and it will be hanging.

other way is to use "nohup". It's a standard tool, but might be  
missing from some distribution. It's idea is to detach stdin/stdout/ 
stderr from your terminal.

Another issue you might run into is - when you exit bash session (for  
example close terminal) child processes running in background will  
loose their terminal. Some (like "tail") don't care about that, while  
others (like vim) will die. Once again - screen and nohup helps.

Last tip - with bash you may run some program, hit Ctrl+Z (which  
suspends application) then type "bg" to resume it at the background.  
Some application will refuse to run in background. You can use "jobs"  
or "fg" to bring task back. You may specify number of task, see bash's  
help (type help jobs) for more info.


There is a good howto on this, which might be a bit too geeky:)
 - http://www.math.ucdavis.edu/~zjohnson/doc/Adv-Bash-Scr-HOWTO/

I hope this helps.

romans