在MacOS上无法在`/ dev / fd`上调用`ioutil.ReadDir`

First, let's remember that /dev/fd is special. Its contents are different for every process (since they reflect the file descriptors of that process), so it doesn't really mean anything that ls can list it because its contents will be different for ls and your program.

Anyway, here's a slightly updated version of your program where instead of letting ioutil do things behind our back, we do it ourselves to see what's going on:

package main

import (
        "fmt"
        "time"
        "os"
        "log"
)

func main() {
        d, err := os.Open("/dev/fd")
        if err != nil {
                log.Fatal(err)
        }
        names, err := d.Readdirnames(0)
        if err != nil {
                log.Fatal(err)
        }
        for _, n := range names {
                n = "/dev/fd/" + n
                fmt.Printf("file: %s
", n)
                _, err := os.Lstat(n)
                if err != nil {
                        fmt.Printf("lstat error: %s - %v
", n, err)
                }
        }

        time.Sleep(time.Second * 200)
}

And then when run it gives me:

file: /dev/fd/0
file: /dev/fd/1
file: /dev/fd/2
file: /dev/fd/3
file: /dev/fd/4
lstat error: /dev/fd/4 - lstat /dev/fd/4: bad file descriptor

So this is indeed the same problem. I added the sleep at the end so that the process doesn't die so that we can debug which file descriptors it has. In another terminal:

$ lsof -p 7861
COMMAND  PID USER   FD     TYPE     DEVICE SIZE/OFF       NODE NAME
foo     7861  art  cwd      DIR        1,4     2272     731702 /Users/art/src/go/src
foo     7861  art  txt      REG        1,4  1450576 8591078117 /private/var/folders/m7/d614cd9x61s0l3thb7cf3rkh0000gn/T/go-build268777304/command-line-arguments/_obj/exe/foo
foo     7861  art  txt      REG        1,4   837248 8590944844 /usr/lib/dyld
foo     7861  art    0u     CHR       16,4   0t8129        645 /dev/ttys004
foo     7861  art    1u     CHR       16,4   0t8129        645 /dev/ttys004
foo     7861  art    2u     CHR       16,4   0t8129        645 /dev/ttys004
foo     7861  art    3r     DIR 37,7153808        0        316 /dev/fd
foo     7861  art    4u  KQUEUE                                count=0, state=0x8

We can see that fd 4 is a KQUEUE. Kqueue file descriptors are used for managing events on OSX, similar to epoll on Linux if you know that mechanism.

It appears that OSX does not allow stat on kqueue file descriptors in /dev/fd which we can verify with:

$ cat > foo.c
#include <sys/types.h>
#include <sys/event.h>
#include <sys/stat.h>
#include <stdio.h>
#include <err.h>

int
main(int argc, char **argv)
{
    int fd = kqueue();
    char path[16];
    struct stat st;

    snprintf(path, sizeof(path), "/dev/fd/%d", fd);
    if (lstat(path, &st) == -1)
        err(1, "lstat");
    return 0;
}
$ cc -o foo foo.c && ./foo
foo: lstat: Bad file descriptor
$

Go programs on OSX need a kqueue to handle various events (not exactly sure which, but probably signals, timers and various file events).

You have four options here: don't stat, ignore the error, don't touch /dev/fd because it's weird, convince Apple that this is a bug.