os.Mkdir and os.MkdirAll set wrong permission bits

[snamber]

Please answer these questions before submitting your issue. Thanks!

1. What version of Go are you using (go version)?
   go version go1.6 linux/amd64
2. What operating system and processor architecture are you using (go env)?
   GOARCH="amd64"
   GOBIN=""
   GOEXE=""
   GOHOSTARCH="amd64"
   GOHOSTOS="linux"
   GOOS="linux"
   GOPATH="/home/user/golang"
   GORACE=""
   GOROOT="/usr/local/go"
   GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
   GO15VENDOREXPERIMENT="1"
   CC="gcc"
   GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0"
   CXX="g++"
   CGO_ENABLED="1"
3. What did you do?

I created a directory using os.Mkdir("foo", 0007) and got a folder with permissions ------r-x instead of ------rwx.

This behavior could not be repeated on play.golang.org.
However this program can be used to recreate similar behavior:

package main

import (
    "fmt"
    "os"
)

func main() {
    fmt.Println(os.Mkdir("foo", 0007))
    fmt.Println(os.Mkdir("bar", 0007))
    os.Chmod("bar", 0007)

    infoFoo, _ := os.Stat("foo")
    infoBar, _ := os.Stat("bar")

    fmt.Println(infoFoo.Mode())
    fmt.Println(infoBar.Mode())
}

1. What did you expect to see?

I expected the folders foo and bar to both have permissions ------rwx

1. What did you see instead?

Folder foo was created with permissions ------r-x.
os.Chmod was setting the permissions correctly, so bar ends up with permissions ------rwx

This is the output of the program above:

<nil>
<nil>
d------r-x
d------rwx

[cmarcelo]

@sn-amber it seems umask is being applied when creating the file. It filter the permissions when creating a file.

You can check the umask value by running umask in a terminal and also change it before running your program to verify, e.g. calling umask 0 before running your test should make Mkdir work as you expect.

[cmarcelo]

You can also set the umask for the process using syscall.Umask.

[ianlancetaylor]

Closing, because umask is a standard Unix feature that affects programs in all languages.

[arvenil]

What would you think about adding this information to documentation? That permissions might be affected by Umask and that you can set it with syscall.Umask?

[ianlancetaylor]

I don't think the Go documentation is the place to discuss details of how the Unix operating system works. If we go down that path we'll wind up documenting things like how the setgid bit of the directory affects file ownership, and the relationship between the effective user ID and file ownership, and I just don't think we should go there. There are many text books and web pages that explain how Unix works.

That said, I could imagine documenting some of these characteristics in a Unix-specific section of the package docs, if somebody wants to work on that. I don't know what others would think of that, though.

[ianlancetaylor]

I should add that this is a discussion to have on the golang-dev mailing list, not on this closed issue.