Thanks for reporting.

Do you know (or can you check) what was the behavior in Go 1.11 or older versions? In other words, is this a recent regression, or has it always behaved like that?

@dmitshur, I got the same behavior as above with go1.11, all the way down to go1.2.2. So all the go versions are like this.

I believe you'll see the same behavior from a C program; i.e. that's POSIX.

Thank you for confirming this is not a recent regression, that's very helpful.

This issue is under the Go1.14 milestone, so we can investigate it during the upcoming development cycle.

Yeah, a similar c program does this same behavior, which seems a little weird... I guess this is not a issue with Go. Thanks for the help! Close when ready 👍

Closing as per #33605 (comment) and thanks @WestleyK for the report, @dmitshur for the triage and @networkimprov for catching that an equivalent C program produces the same result.

For the record here is the equivalent C program

#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#include <sys/errno.h>
#include <stdio.h>

int main() {
    int fd = open("foo.txt", O_CREAT|O_TRUNC|O_WRONLY, 0777);
    if (fd < 0) {
        fprintf(stderr, "opening file: %s\n", strerror(errno));
        return -1;
    }
    close(fd);
    return 0;
}

and when run, here are the results:

$ gcc main.c -o main
$ ls -lrth
total 32
-rw-r--r--  1 emmanuelodeke  staff   315B 13 Aug 00:18 main.c
-rwxr-xr-x  1 emmanuelodeke  staff   8.5K 13 Aug 00:19 main
$ ./main 
$ ls -lrth
total 32
-rw-r--r--  1 emmanuelodeke  staff   315B 13 Aug 00:18 main.c
-rwxr-xr-x  1 emmanuelodeke  staff   8.5K 13 Aug 00:19 main
-rwxr-xr-x  1 emmanuelodeke  staff     0B 13 Aug 00:19 foo.txt
$ ./main 
$ ls -lrth
total 32
-rw-r--r--  1 emmanuelodeke  staff   315B 13 Aug 00:18 main.c
-rwxr-xr-x  1 emmanuelodeke  staff   8.5K 13 Aug 00:19 main
-rwxr-xr-x  1 emmanuelodeke  staff     0B 13 Aug 00:20 foo.txt
$ chmod 0777 foo.txt # Now trying with chmod and this should change the permissions
$ ls -lrth
total 32
-rw-r--r--  1 emmanuelodeke  staff   315B 13 Aug 00:18 main.c
-rwxr-xr-x  1 emmanuelodeke  staff   8.5K 13 Aug 00:19 main
-rwxrwxrwx  1 emmanuelodeke  staff     0B 13 Aug 00:20 foo.txt