How can I get stdio output when running application as root?

Question

I'm trying to run my application as root because I need to access low level hardware on my computer.

When I run the command:

./application_name

...it works, except gives an error that it needs root. However, when I run this:

sudo ./application_name

...I get no terminal ouput.

I've tested that every time that I run an executable on Linux as root, it doesn't print anything to terminal. How can I fix this?

Edit: somewhat of a test case provided (mobile so can't type out much):

sudo g++ test.cpp -o executable
sudo chmod +x executable

This works on Debian:

./executable

This doesn't:

sudo ./executable

test.cpp:

#include <iostream>

int main() {
  std::cout << "Hello World!";
}

Close voters: why is this off topic but this on topic? Both are about executing code: stackoverflow.com/questions/817060/… — Anonymous Penguin
– Anonymous Penguin, Commented Dec 27, 2014 at 1:22
That question is five years old and was posted at a time when the posting guidelines were quite different. The existence of a very old question does not mean it is OK to post a similar one. — Captain Obvlious
– Captain Obvlious, Commented Dec 27, 2014 at 1:36
Apparently that's how the application behaves. Some applications just don't produce output (/bin/true, for example). We know nothing at all about the application, so we can't help you figure out why it's not producing any output. Try sudo echo hello; it should print hello. — Keith Thompson
– Keith Thompson, Commented Dec 27, 2014 at 1:36
@CaptainObvlious some other related ones: stackoverflow.com/questions/15080835/… stackoverflow.com/questions/10467031/at-command-is-not-executed stackoverflow.com/questions/9812145/… stackoverflow.com/questions/14625580/… and they aren't closed. — Anonymous Penguin
– Anonymous Penguin, Commented Dec 27, 2014 at 1:50
Note that you don't terminate the output with a newline. Adding << endl or including a newline in the string to be printed would improve the chances of the output being printed. That doesn't really explain the difference between root and non-root behaviour. — Jonathan Leffler
– Jonathan Leffler, Commented Dec 27, 2014 at 5:36

23ars · Accepted Answer · 2014-12-27 10:05:42Z

1

That behavior is really strange. Root permissions for that application should have no effect on std output. For example, I made a simple test, a "hello world" that I ran as root on Debian OS and I had output in terminal.

A simple test to convince yourself that you should have the output, is to make a redirect to a file. For example sudo ./executable > output.txt and you'll see that everything should be OK.

Note that it should be strange if you don't have output from a simple "hello world".

answered Dec 27, 2014 at 10:05

23ars

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