[SOLVED] How do I ask nohup not to redirect stderr to stdout if it is detached from terminal?

How do I ask nohup not to redirect stderr to stdout if it is detached from terminal?

This question looks naive but I can't find the answer after half an hour of intensive searching. Basically I do not want stderr messages to sneak into my result file.

$nohup ./a.out | gzip -c > result.txt.gz 2>log.txt &
nohup: ignoring input and redirecting stderr to stdout
$zcat result.txt.gz
this is stderr output.
this is stdout output.

The a.out file was compiled from the following test.c by "cc test.c",

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
int main(int argc, char *argv[])
{
    fprintf(stderr, "this is stderr output.\n");
    fprintf(stdout, "this is stdout output.\n");
    return 0;
}

But I do not want stderr message to be in the result file result.txt.gz. It should be in log.txt but that file is empty. Thank you!

Solution

That error redirection actually applies to the gzip command, not /.a.out. What you're looking for is ./a.out 2> log.txt | gzip -c > result.txt.gz.