coreutils-who: not returning any useful output

[psmode]

Maintainer: @httpstorm and Jo-Philipp Wich jo@mein.io
Environment: (x86, 64, OpenWrt v 22.03.05)

Description:
coreutils-who v9.0-2 appears to be non-functional in my environment. Executing the command who by itself or with "-a" returns no output at all. Adding -H or -Hl will return the column headings, but no data beyond that. -q returns a blank line, then "# users=0"

[httpstorm]

@psmode
I reproduced the behaviour you described on the following versions of coreutils-who: 9.3-1 9.2-1 9.1-1 9.0-2 9.0-1 8.32-6. I am not able to go back in time before version 8.32-6 using simple git revert.
Platforms tested: x64 and WRT3200ACM. OpenWrt SNAPSHOT r22888-86adc89390.

coreutils-who-9.3 on macOS Ventura 13.4.1 (c) (22F770820d) works fine, except for -Hl which prints only the title row.
coreutils-who-8.32 on Ubuntu 22.04.2 LTS kernel 5.15.0-76 works fine.

Did any previous version of coreutils-who work in the past on OpenWRT?
Try contacting the coreutils team. coreutils at gnu . org

[psmode]

Unfortunately, I cannot say which, if any, prior versions worked.

I will reach out to the team via email referencing this thread

[httpstorm]

Just a thought, might be completely wrong, but I wonder whether the kernel we build offers all necessary features for who to work? One more thing to consider: the exit code is 0 (success):

who && echo success || echo fail
success

[psmode]

I believe that the problem is not so much with who, but rather with the fact that I do not have a /var/run/utmp file being populated for who to read. This seems to be an issue on a number of platforms.

So now the question becomes, it it possible/desirable to have the /var/run/utmp populated by the kernel for who to read? (without recompiling from source)

[httpstorm]

I tried copying utmp from Ubuntu and macOS, makes no difference. Though I believe that file should be created by the system or kernel to represent the currently logged on users. And since the Linux kernel in OpenWRT is very tiny, you would need to find and add the proper components to make it work. Hence rebuild should be needed.

[M95D]

I belive this is not a bug. It's something OpenWrt just doesn't have.

w, who and users take data from /var/run/utmp. That file is updated using functions from libc (musl or glibc). Musl doesn't support utmp (read their FAQ). Even if built with glibc instead of musl, Dropbear and Busybox login, getty and tftpd don't write utmp data in the default OpenWrt build configuration. To support utmp, you have to build your own OpenWrt firmware from sources.

Details here: openwrt/openwrt#15417

PS: Kernel has nothing to do with it.