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Re: dash/bash: exec behaviour change on Buster

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On Wed, Jul 17, 2019 at 04:49:28PM +0900, John Crawley wrote:
> The behaviour of exec seems to have changed from Stretch to Buster -
> whether using bash or "sh" (dash here).
> 
> Simple test, in default bash shell on terminal:
> 
> sh
> # now with dash
> exec x-terminal-emulator
> # close new window
> 
> In Stretch, the launching dash shell is held until the new one is
> closed, then exits and returns to bash.
> In Buster, the launching dash shell dies *immediately* and the bash
> prompt returns, even while the new window is still open.
> 
> If the test is done without switching to sh, the change between
> stretch and buster is similar, but the launching terminal is
> destroyed, the difference being in whether that's immediate or after
> closing the new one.
> 
> Was this a bug in Stretch? I haven't been able to find any references to it.
> 
> As it happens, I was using that behaviour in a script, but I'll hold
> that question for a bit...

Perhaps it's your interpretation of what you see what you've to
question.

What 'exec' does is it substitutes the program the current process is
running for another one.

So once you run 'exec x-terminal-emulator', your sh "is no more",
in the sense that the process which was executing /bin/sh is now
executing "whatever x-terminal-emulator" is. Same PID, though [1].

If what you observe changes (I'd describe what I understood from
your description as "before, the command line was blocked as
long as "x-terminal-emulator" ran, nowadays the command prompt
returns right away and the "x-terminal-emulator" keeps running
"in the background"), that most probably is due to a change
in behaviour of "x-terminal-emulator".

Note that "x-terminal-emulator" isn't really a single program,
but an "alternatives" thing, pointing to whatever terminal
emulator you've declared as your favourite.

Try

  update-alternatives --display x-terminal-emulator

to get an idea of what's going on.

Cheers
-- tomás

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Thread

dash/bash: exec behaviour change on Buster John Crawley <john@bunsenlabs.org> - 2019-07-17 09:50 +0200
  Re: dash/bash: exec behaviour change on Buster <tomas@tuxteam.de> - 2019-07-17 10:20 +0200
    Re: dash/bash: exec behaviour change on Buster "Thomas Schmitt" <scdbackup@gmx.net> - 2019-07-17 10:40 +0200
      Re: dash/bash: exec behaviour change on Buster John Crawley <john@bunsenlabs.org> - 2019-07-18 03:40 +0200
        Re: terminal window returns prompt (was: dash/bash: exec behaviour  change on Buster) John Crawley <john@bunsenlabs.org> - 2019-07-18 05:40 +0200
        Re: dash/bash: exec behaviour change on Buster Richard Hector <richard@walnut.gen.nz> - 2019-07-18 08:00 +0200
          Re: dash/bash: exec behaviour change on Buster John Crawley <john@bunsenlabs.org> - 2019-07-18 09:50 +0200

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