Background program stopped because of tty output

[zharr]

Hello,
I am trying to get my program constantly running for an embedded application and face some problems.
I'll try to split this in hopes this circumvents the current server issues (another poster did this successfully)
 - Yeah no chance, I'll try attaching my post as txt until I can post it

[zharr]

Here's my intended post as a txt

[Rich]

Hi zharr

So testing sudo ./program 2>&1 >> output.log & reveals the problem:

Does it work any better like this:

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sudo ./program >> output.log 2>&1 &

[gadget42]

worked through your attachment and the server didn't like the tabs(using spacebar worked though)...

Hello,
I am trying to get my program constantly running for an embedded application and face some problems.

I add my program to bootlocal:

Code: [Select]

while :
              do
                      ./program 2>&1 >> output.log
                      sleep 5s
              done
However this does not work - the program is always stopped.

Executing sudo ./program 2>&1 >> output.log in the shell works.

This is in bootlocal, which itself is a background script.

So testing sudo ./program 2>&1 >> output.log & reveals the problem:

[1]+  Stopped (tty output)       sudo ./program 2>&1 1>>output.log

Looking this up implies it's stopped because it has tty output, but is a background process which should not write to stdout.

Now I wonder:
a) How am I writing to stdout? I am explicitly trying to write to a log file.
b) How can I disable this behaviour? A similar question suggests to use stty -tostop but this has no effect.
c) Is there any better/recommended way to create a constantly running, logging-enabled service in tinyCore?

Thanks for any help!

also the

Code: [Select]

[tt] ... [/tt] stuff didn't work(and is depreciated as per https://developer.mozilla.org/en-US/docs/Web/HTML/Element/tt)

[zharr]

Hi zharr

So testing sudo ./program 2>&1 >> output.log & reveals the problem:

Does it work any better like this:

Code: [Select]

sudo ./program >> output.log 2>&1 &

Sorry for the late reply, got sick.
No, same result unfortunately.

[zharr]

Interestingly, normal commands that take a while end with another code printed in the console, but always Done(1), e.g. this after about 3 seconds, and these two commands work as expected:

Code: [Select]

find *.conf / >> output.log  & prints stderr, and stdout to file

Code: [Select]

find *.conf / 2>> output.log  & prints stdout, and stderr to file
So writing to tty as a background process is probably not the issue I face, maybe it has something to do with my program after all

[zharr]

Alright, was my program, namely the following:

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tcgetattr(STDIN_FILENO, &terminalSettings);
struct termios termSet = terminalSettings;
atexit([]{ // Reset at exit
    tcsetattr(STDIN_FILENO, TCSAFLUSH, &terminalSettings);
});
termSet.c_lflag &= ~ECHO;
termSet.c_lflag &= ~ICANON;
termSet.c_cc[VMIN] = 0;
termSet.c_cc[VTIME] = 0;
tcsetattr(STDIN_FILENO, TCSAFLUSH, &termSet);which I set up at some point to correctly receive input in the terminal as well as over SSH.
Though there is one other part later that also triggers the same, so I'll have to search more tomorrow.

[zharr]

Aand the other trigger was a

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read(STDIN_FILENO, &cin, 1) to get input.
Of course for background not relevant, still annoying that I have to add a switch to the program for background execution. Maybe there is a way to detect it?

[Rich]

Hi zharr

... Maybe there is a way to detect it?

I think you can use  isatty()  for that:
https://man7.org/linux/man-pages/man3/isatty.3.html

Wrapping something like this around your TTY code should fix it:

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#include <unistd.h>

if(isatty(STDIN_FILENO))
{
    // Place code requiring a TTY here.
}
That should also work if the program gets switched back and forth (foreground, background, foreground, ...) while
it is running.

[zharr]

Thank you very much, will do that!