Golang Getrlimit returns the different value from ulimit-CodePudding

I tried to use Golang to get current "open fd" limit with the Getrlimit function, here is my code:

package main

import (
    "fmt"
    "syscall"
)

func main() {
    lim := syscall.Rlimit{}

    err := syscall.Getrlimit(syscall.RLIMIT_NOFILE, &lim)
    if err != nil {
        panic(err)
    }
    fmt.Println("soft:", lim.Cur)
    fmt.Println("hard:", lim.Max)
}

Run this will print:

$ go run main.go
soft: 1048576
hard: 1048576

Here you can see the soft number is "1048576", however, the ulimit -Sn prints it as "1024". I also tried this with C code:

#include <sys/resource.h>
#include <stdio.h>

int main() {
    struct rlimit rlim;
    if (getrlimit(RLIMIT_NOFILE, &rlim) == -1) {
        return -1;
    }
    printf("soft: %lld \n", (long long) rlim.rlim_cur);
    printf("hard: %lld \n", (long long) rlim.rlim_max);
    return 0;
}

Compile and run it will also print:

soft: 1024
hard: 1048576

So the number Golang printed out for the "rlim_max" (hard) is correct, but "rlim_cur" (soft) is incorrect, it's supposed to be "1024"? As you can see both the C code and ulimit -Sn command printed "1024".

Here is my testing environment:

Operating system: Ubuntu 22.04 LTS x86_64
Golang 1.19.1 for amd64

I am wondering if anyone experienced the same problem and why it happened like this? Thank you!

CodePudding user response：

This is per design since 1.19, see https://github.com/golang/go/issues/46279 for the whole discussion.