mosh login not showing in `w` output (Ubuntu 24.04)

[cross-cisco]

I have multiple similarly configured servers. Two running Ubuntu 24.04 are showing no users in w output when I log in with mosh, but do show my login when I log in with ssh directly.

A server running RHEL 8.10, however, does show an entry when I'm logged in via mosh. The version of mosh on all systems is 1.40.

== RHEL 8.10 ==

cross@client-mac-host ~> ssh linux-server1.cisco.com w
 13:41:40 up 3 days, 22:57,  0 users,  load average: 0.00, 0.26, 2.68
USER     TTY      FROM             LOGIN@   IDLE   JCPU   PCPU WHAT
cross@client-mac-host ~> ssh linux-server1.cisco.com  
cross@linux-server1 ~ ❯ w
 13:42:17 up 3 days, 22:57,  1 user,  load average: 0.24, 0.29, 2.58
USER     TTY      FROM             LOGIN@   IDLE   JCPU   PCPU WHAT
cross    pts/2    2001:420:20c0::2 13:41    0.00s  0.19s  0.01s w
cross@linux-server1 ~ ❯ ^D
cross@client-mac-host ~> mosh --family=prefer-inet6 linux-server1.cisco.com
cross@linux-server1 ~ ❯ w
 13:43:07 up 3 days, 22:58,  1 user,  load average: 0.30, 0.29, 2.46
USER     TTY      FROM             LOGIN@   IDLE   JCPU   PCPU WHAT
cross    pts/3    2001:420:20c0::2 13:43    0.00s  0.16s  0.01s w
cross@linux-server1 ~ ❯ 

== Ubuntu 24.04 ==

cross@client-mac-host ~> ssh linux-server3.cisco.com w
 13:50:05 up 20 days, 20:30,  4 users,  load average: 0.25, 0.13, 0.10
USER     TTY      FROM             LOGIN@   IDLE   JCPU   PCPU  WHAT
cross            2001:420:20c0::2 13:50   29:29m  0.00s  0.02s sshd: cross [priv]
cross@client-mac-host ~> ssh linux-server3.cisco.com  
Welcome to Ubuntu 24.04.1 LTS (GNU/Linux 6.8.0-51-generic x86_64)
cross@linux-server3 ~ ❯ w
 13:51:45 up 20 days, 20:31,  4 users,  load average: 0.30, 0.17, 0.11
USER     TTY      FROM             LOGIN@   IDLE   JCPU   PCPU  WHAT
cross            2001:420:20c0::2 13:51   29:30m  0.00s  0.02s sshd: cross [p
cross@linux-server3 ~ ❯ ^D
cross@client-mac-host ~> mosh --family=prefer-inet6 linux-server3.cisco.com
cross@linux-server3 ~ ❯ w
 13:52:28 up 20 days, 20:32,  4 users,  load average: 0.27, 0.18, 0.11
USER     TTY      FROM             LOGIN@   IDLE   JCPU   PCPU  WHAT
cross@linux-server3 ~ ❯ who | grep 2025-01-13
cross   pts/7        2025-01-13 13:52 (2001:420:20c0::2830 via mosh [2314904])
cross@linux-server3 ~ ❯ date
Mon Jan 13 13:53:07 EST 2025
cross@linux-server3 ~ ❯ ^D

I notice also that the effect of "w" as an inline command ssh'd over is different, but while that may be related to a solution, it's not a problem I'm worried about.

[achernya]

How did you install mosh? Did you compile from source? Install a package?

[cross-cisco]

In all cases installed from a package. On the ubuntu servers, it is 1.4.0-1ubuntu3
mosh/noble,now 1.4.0-1ubuntu3 amd64 [installed]

[achernya]

On Ubuntu the package should be built with utempter support which writes to wtmp. Is there something preventing the utempter helper from working (like apparmor?)

[cross-cisco]

I'm not sure how to check that. I see that I have libutempter0 package installed, as well as apparmor & libapparmor1 packages. Is there a way to ask utempter if something is interrupting it?

[cross-cisco]

Checking in on this. So, I don't see any reference to problems with utempter. mosh-server is dynamically linked with it, and I see nothing mentioning "utempter" in any of my log files other than the usage errors when I tried to run the binary by hand. :-)
So I don't think anything is wrong, but I need more info to know how to check.

I see the mosh login in "who" output, just not "w", so I think it's more complicated than simply entries in utmp or wtmp.

Again, I note that if I log in with ssh directly I see:

> w
 11:13:09 up 39 days, 17:53,  9 users,  load average: 4.93, 5.90, 10.42
USER     TTY      FROM             LOGIN@   IDLE   JCPU   PCPU  WHAT
otheruser         AA.BBB.CCC.DD    Wed04   19:14m  0.00s  0.01s sshd: otheruser 
cross2            2000:HHH:JJJJ::S 11:12   19:14m  0.00s  0.02s sshd: cross2 [p
> who | grep -v tmux
cross2   pts/15       2025-02-01 11:12 (2000:HHH:JJJJ::SS)

But when logging in with mosh:

❯ w
 11:18:48 up 39 days, 17:58,  9 users,  load average: 2.72, 3.76, 8.07
USER     TTY      FROM             LOGIN@   IDLE   JCPU   PCPU  WHAT
otheruser         AA.BBB.CCC.DD    Wed04   19:20m  0.00s  0.01s sshd: otheruser 
❯ who | grep -v tmux
cross2   pts/16       2025-02-01 11:18 (2000:HHH:JJJJ::SS via mosh [2244365])
❯