os/user: LookupUser() doesn't find users on macOS when compiled with CGO_ENABLED=0

[jeffreydwalter]

Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

go version go1.9.2 darwin/amd64

Does this issue reproduce with the latest release?

Yes.

What operating system and processor architecture are you using (go env)?

GOARCH="amd64"
GOBIN=""
GOCACHE="/home/jeff_walter/.cache/go-build"
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="freebsd"
GOOS="darwin"
GOPATH="/home/jeff_walter/src/agent"
GORACE=""
GOROOT="/usr/local/go"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/freebsd_amd64"
GCCGO="gccgo"
CC="clang"
CXX="clang++"
CGO_ENABLED="0"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build053729832=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

If I run the following program with sudo I get a different result than I get when I run it as 'someuser' (where 'someuser' is my current logged in user).

package main

import (
    "fmt"
    "os/user"
)

func main() {
    u, err := user.Lookup("someuser")
    if err != nil {
        fmt.Printf("%s", err)
        return
    }

    fmt.Printf("%V", u)
}

What did you expect to see?

$ ./user
&{%!V(string=502) %!V(string=20) %!V(string=someuser) %!V(string=) %!V(string=/Users/someuser)}

What did you see instead?

$ sudo ./user
user: unknown user someuser

[odeke-em]

Hello @jeffreydwalter, I am not sure what you were expecting to see but when running as root, you are a different user entirely so hardcoding the username wouldn't work unless you actually used "root"

Here is an update of your repro that'll get you the information from the environment whether ran as root or as an ordinary user, it uses os.ExpandEnv("$USER")

package main

import (
    "fmt"
    "os"
    "os/user"
)

func main() {
    u, err := user.Lookup(os.ExpandEnv("$USER"))
    if err != nil {
        fmt.Printf("%s", err)
        return
    }

    fmt.Printf("%+v\n", u)
}

Ran as a normal user

e$ go run main.go 
&{Uid:501 Gid:20 Username:emmanuelodeke Name:Emmanuel Odeke HomeDir:/Users/emmanuelodeke}

Ran as root

sudo su && go run main.go
&{Uid:0 Gid:0 Username:root Name:System Administrator HomeDir:/var/root}

Hope this helps.

[jeffreydwalter]

What I'm expecting is to get back the user info for the username I passed in, regardless of which user I'm running as. If that function only returns the current user, then it's misnamed and should probably be something like LookupCurrentUser().

…

On Tue, Mar 13, 2018, 8:30 PM Emmanuel T Odeke ***@***.***> wrote: Hello @jeffreydwalter <https://github.com/jeffreydwalter>, I am not sure what you were expecting to see but when running as root, you are a different user entirely so hardcoding the username wouldn't work unless you actually used "root" Here is an update of your repro that'll get you the information from the environment whether ran as root or as an ordinary user, it uses os.ExpandEnv("$USER") package main import ( "fmt" "os" "os/user" ) func main() { u, err := user.Lookup(os.ExpandEnv("$USER")) if err != nil { fmt.Printf("%s", err) return } fmt.Printf("%+v\n", u) } Ran as a normal user e$ go run main.go &{Uid:501 Gid:20 Username:emmanuelodeke Name:Emmanuel Odeke HomeDir:/Users/emmanuelodeke} Ran as root sudo su && go run main.go&{Uid:0 Gid:0 Username:root Name:System Administrator HomeDir:/var/root} Hope this helps. — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#24383 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAinBwZLGdqRSvJOBd-rGMEXNS6vkBVCks5teHKwgaJpZM4Sprb3> .

[mattn]

please use user.Current()

https://golang.org/pkg/os/user/#Current

[odeke-em]

What expecting is to get back the user info for the username I passed in,
regardless of which user I'm running as.

Gotcha, sorry @jeffreydwalter, I misunderstood your intention. Okay, re-running your original repro but searching for "emmanuelodeke" my user, even as root gives me the correct output

&{%!V(string=501) %!V(string=20) %!V(string=emmanuelodeke) %!V(string=Emmanuel Odeke) %!V(string=/Users/emmanuelodeke)}

or with %V fixed to %+v

sh-3.2# go run main.go 
&user.User{Uid:"501", Gid:"20", Username:"emmanuelodeke", Name:"Emmanuel Odeke", HomeDir:"/Users/emmanuelodeke"}

[odeke-em]

And vice versa, searching for root as my ordinary user gives me the correct output

[jeffreydwalter]

Thanks @odeke-em,

Are you running on macOS? Did you run as root?

[jeffreydwalter]

Interesting... I wonder if it has to do with the underscore in my username?

[jeffreydwalter]

@odeke-em, so there must be something with my user. If I lookup root, everything works as it does for you.

$ ./user 
&{%!V(string=0) %!V(string=0) %!V(string=root) %!V(string=System Administrator) %!V(string=/var/root)}
🍺  [585] jeff_walter@T2000:~/Code
$ sudo ./user 
&{%!V(string=0) %!V(string=0) %!V(string=root) %!V(string=) %!V(string=/Users/jeff_walter)}
🍺  [586] jeff_walter@T2000:~/Code

[jeffreydwalter]

I tried creating a new user, same issue as my existing user. :/

[odeke-em]

@jeffreydwalter interesting, no dice in a new shell? How about with other users on there? Without underscores either?

[jeffreydwalter]

@odeke-em no dice... :/ I downloaded iTerm and still no luck. The only things I haven't tried are to log out or reboot.

I created a user without underscores, named user, same stuff:

$ ./user user
Current user: &{502 20 jeff_walter  /Users/jeff_walter}
Looking up username: user
user: unknown user user

$ sudo ./user user
Current user: &{0 0 root  /Users/jeff_walter}
Looking up username: user
user: unknown user user

$ sudo su - user
T2000:~ user$ ./user user
Current user: &{503 20 user  /Users/user}
Looking up username: user
&{503 20 user  /Users/user}T2000:~ user$ exit
logout

$ sudo su -
T2000:~ root# /Users/user/user user
Current user: &{0 0 root  /var/root}
Looking up username: user

This is really baffling to me... :)

[crvv]

There are two implementations of user.Lookup.

1. Parse /etc/passwd
2. Use getpwnam_r in libc

I can't find my normal user in /etc/passwd on macOS, but root is in it.
With export CGO_ENABLED=0, I can reproduce this bug.

[odeke-em]

@crvv on mine with CGO_ENABLED=0 or with CGO_ENABLED=1, I get the same results: it works for me.

/cc @kevinburke @ianlancetaylor @bradfitz

[agnivade]

I am on linux/amd64 (Ubuntu 16.04). Unable to reproduce. With both CGO_ENABLED=0 and CGO_ENABLED=1.