Apart from eating it, I mean

- Using kdesu 4.9.5 and konsole 4.9.5
- If, under konsole, I launch whatever_binary, the content of whatever_binary's standard error is correctly printed.
- If, I launch kdesu whatever_binary then, konsole displays miscellaneous traces from kdesu but whatever_binary's stderr content is no longer displayed.

How can I get it back ?

Can you try passing the "-t" argument to kdesu?

I don't think you can

supposedly the gtk command gksu, if available, will work

I don't understand why this works and I'm pretty sure in days of old it did not, if you can open a root tab in Konsole and you'll see output. not sure this would be considered good practices though.

bcooksley wrote:Can you try passing the "-t" argument to kdesu?

Thanks bcooksley. That fits for purpose.

google01103 wrote:I don't understand why this works and I'm pretty sure in days of old it did not

That is because a child process inherits the stdin / stdout / stderr from its parent.
- su forks an interactive shell (stdin=keyboard / stdout = stderr = console) and then the commands you type are children of that shell. => unless you specifically redirect them, those file descriptors will be kept for the commands you type.
- With kdesu whatever_command, things appear a little more complicated. From what I can observe :
kdesu starts forking su kdesu_stub which in turns forks kdesu_stub which in turn forks whatever_command.
I suspect the stderr / stdout are closed by one of these cascaded children unless the t parameter is given.

Nevermind. Thank you all for your contributions.

Not a problem.
You may also want to check the other arguments supported by "kdesu", by checking it's help: "kdesu --help".