GNU bug report logs - #76998
Guix Home leaves user shepherd on logout, starts new instance on login

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Ludovic Courtès <ludo <at> gnu.org>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#76998: closed (Guix Home leaves user shepherd on logout,
 starts new instance on login)
Date: Sat, 14 Jun 2025 21:28:03 +0000

[Message part 1 (text/plain, inline)]

Your message dated Sat, 14 Jun 2025 23:26:53 +0200
with message-id <871prm3tgi.fsf_-_ <at> gnu.org>
and subject line Re: bug#76998: Guix Home leaves user shepherd on logout, starts new instance on login
has caused the debbugs.gnu.org bug report #76998,
regarding Guix Home leaves user shepherd on logout, starts new instance on login
to be marked as done.

(If you believe you have received this mail in error, please contact
help-debbugs <at> gnu.org.)


-- 
76998: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=76998
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: dannym <at> friendly-machines.com
To: Bug Guix <bug-guix <at> gnu.org>
Subject: user shepherd stays around with some zombies
Date: Thu, 13 Mar 2025 20:10:36 +0100

Steps to reproduce:

1. Log into the console using your regular user
2. Log into GUI using your regular user
3. Log out of GUI
4. Switch to logged-in console
5. Run "px --tree" there
6. Observe the following:

shepherd(1)
  accounts-daemon(1110)
  avahi-daemon:(2443)
    avahi-daemon:(2446)
  bluetoothd(1026)
  colord(25587)
  cupsd(2440)
  dbus-daemon(769)
  dnsmasq(1845)
    dnsmasq(1846)
  earlyoom(744)
  elogind(1024)
  gdm(1038)
  guix-daemon(740)
  libvirtd(1023)
  login(26536)
    -bash(6739)
  mcron(747)
  mingetty... (5×)
  ModemManager(1276)
  NetworkManager(1256)
  nginx:(797)
    nginx:(798)
  nscd(2177)
  polkitd(1231)
  postgres(852)
    postgres:... (6×)
  rasdaemon(796)
  rpc.idmapd(2447)
  rpc.mountd(2501)
  rpc.statd(2444)
  rpcbind(2441)
  shepherd(6395) <--- also dannym
    [dbus-daemon](6397)
    [ssh-agent](6444)
    [xdg-permission-](6411)
    wireplumber(6399)
  shepherd(26114) <--- dannym
    dbus-daemon(6881)
    pipewire(6882)
    pipewire-pulse(6883)
    ssh-agent(6880)
    wireplumber(6888)
    xdg-permission-store(7259)
  udevd(330)
  upowerd(1025)
  virtlogd(742)
  wpa_supplicant(1045)

Those "[...]" with brackets mean that these processes were not reaped 
(so is defunct).

What the hell?

$ guix describe
Generation 194	Mar 13 2025 19:11:33	(current)
  guix 678b3dd
    repository URL: https://git.savannah.gnu.org/git/guix.git
    branch: master
    commit: 678b3dddfe442e643fe5cff7730d4f9690c3e2c2

[Message part 3 (message/rfc822, inline)]

From: Ludovic Courtès <ludo <at> gnu.org>
To: Danny Milosavljevic <dannym <at> friendly-machines.com>
Cc: 74912 <at> debbugs.gnu.org, 76998 <at> debbugs.gnu.org, Tomas Volf <~@wolfsden.cz>,
 76998-done <at> debbugs.gnu.org, Jake <jforst.mailman <at> gmail.com>,
 Daniel Littlewood <dan <at> danielittlewood.xyz>
Subject: Re: bug#76998: Guix Home leaves user shepherd on logout, starts new
 instance on login
Date: Sat, 14 Jun 2025 23:26:53 +0200

Hi Danny,

Danny Milosavljevic <dannym <at> friendly-machines.com> writes:

> It's good that the "is a shepherd already running" check is back in
> shepherd.  It was in shepherd years ago, then got removed without
> explanation, then now it's back again (now in a very convoluted but
> safer way).  This shouldn't have been removed in the first place.
> It's EXTREMELY dangerous to have multiple parallel shepherds for the
> same user (automated backup service destroying backups etc).  Please,
> let's not remove it ever again.

If you’re referring to 649a98a6697d358a53eccc45b387e5130278b5ec (8 years
ago), I believe it wasn’t doing just that due to lingering.

(Aside: I think the tone of this paragraph is uncalled for.)

> In any case, what shepherd 1.0.4 does is stop the bleeding, but not fix the problem:
> It prevents two (or 100) user shepherds for the same user from running in parallel.
> It does not stop shepherd when a user closed all their sessions.

Yes.  It just occurred to me that we probably just got it wrong from the
start: ‘XDG_RUNTIME_DIR’ (/run/user/$UID) is specified as having limited
lifetime.  Quoth
<https://specifications.freedesktop.org/basedir-spec/latest/>:

  The lifetime of the directory MUST be bound to the user being logged
  in.  It MUST be created when the user first logs in and if the user
  fully logs out the directory MUST be removed.

So it was probably a bad idea in the first place for shepherd to store
its socket in /run/user/$UID (even more so that this directory doesn’t
exist on systems without elogind/systemd).  GnuPG avoids
$XDG_RUNTIME_DIR for exactly this reason (there’s a comment in
‘homedir.c’).

So, what can we do?

In the Shepherd 1.1, we could default to $XDG_STATE_HOME instead; we
probably shouldn’t change that in 1.0.x.

Any other idea?

Thanks,
Ludo’.

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