[Qt-interest] unable to run application in background

[Thiago Macieira]

Em Quinta-feira 19. Novembro 2009, às 05.50.33, linux newbie escreveu:
> Hi,
> 
> I tested some of the example application in our ARM based embedded
> platform and it is working, but when I tried to run it in the
> "background"(by adding '&' at the end of command), system freezes.
> 
> When I gave the following command
> ./Qt_test -qws &
> system freezes.
> 
> Our console is running at ttyS0(serial port) and when I gave 'ps'
> command, it shows the
> 891 root     18536  T    ./Qt_test -qws
> 
> It seems that Qt process is terminated and I couldnt kill that process
> using kill command.
> 
> Can anyone share their thoughts in this regard?

T means "sTopped", meaning the application was stopped by an external reason. 
It happens when the application is being traced (another reason for T), such 
as by strace or gdb, or when it has been stopped by a signal.

The signals that can stop an app are SIGSTOP (cannot be caught), SIGTTOU and 
SIGTTIN, indicating the application tried to do output to the terminal or do 
input.

For example:
$ emacs -nw &
[1] 27704
$
[1]  + suspended (tty output)  emacs -nw
$ ps 27704
  PID TTY      STAT   TIME COMMAND
27704 pts/9    TN     0:00 emacs -nw

As you can see, an application tried to use the terminal exclusively, but 
since it was in the background, it couldn't. It got suspended until I move it 
to the foreground.

-- 
Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org
  Senior Product Manager - Nokia, Qt Development Frameworks
      PGP/GPG: 0x6EF45358; fingerprint:
      E067 918B B660 DBD1 105C  966C 33F5 F005 6EF4 5358
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