Bug 2118593

This bug was initially created as a copy of Bug #2053273

I am copying this bug because: 
If we're doing this in RHEL-8, we need to do it in RHEL-9 as well to avoid a regression in behavior.


Description of problem:

Client would like to request a backport of the upstream commit to address the issue detailed here.  

Description/details copied from:
https://github.com/systemd/systemd/issues/22058

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System V compatibility shutdown/reboot/halt commands (ie via /usr/sbin/{shutdown,reboot}) do not exhibit the same behavior as a systemctl {reboot,halt} when run as root.

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Most notable is that inhibitors appear to be skipped and a PrepareForShutdown DBus signal is not emitted when immediate action via /usr/sbin/{reboot,shutdown,halt,poweroff} are executed.

This behavior changes when using /usr/sbin/shutdown in a scheduled manner - i.e. /usr/sbin/shutdown -r +1 . In this case, delay inhibitors are honored and the DBus signal goes out, giving an inconsistent behavior in shutdown, reboot and poweroff operations between systemctl and the System V compatibility commands.

Example Test Case
Install required python depedencies:
~~~
apt install libdbus-1-dev libglib2.0-dev python3-gi pip
pip3 install dbus-python
Use the following sample script:

#!/usr/bin/python3

import time, os, sys
import dbus
from gi.repository import GLib
from dbus.mainloop.glib import DBusGMainLoop

def handle_shutdown(*args):
    # Note: Default maximum inhibit delay time is 5 seconds.
    # This can be raised in /etc/systemd/login.conf by
    # setting InhibitDelayMaxSec .
    print("Inhibit the shutdown for 30 seconds...")
    time.sleep(30)
    print("Letting go of inhibit lock")
    os.close(inhibitor_fd)

DBusGMainLoop(set_as_default=True)
bus = dbus.SystemBus()

login = bus.get_object("org.freedesktop.login1", "/org/freedesktop/login1")
manager = dbus.Interface(login, dbus_interface='org.freedesktop.login1.Manager')
inhibitor = manager.Inhibit("shutdown", "Shutdown Handler", "Handle events on shutdown notification", "delay")

inhibitor_fd = inhibitor.take()

bus.add_signal_receiver(handle_shutdown, dbus_interface="org.freedesktop.login1.Manager", signal_name="PrepareForShutdown")

loop = GLib.MainLoop()
loop.run()
~~~

Run the above script.

As root, issue a systemctl reboot command. The inhibitor is honored, the PrepareForShutdown signal is sent and the inhibitor actions the signal.

Repeat the test, this time issuing a /usr/sbin/reboot or /usr/sbin/halt command. The inhibitor will not be triggered and the system will immediately go down.

Again repeat the test, running /usr/sbin/shutdown -r +1 . After one minute, the inhibitor will be honored, the PrepareForShutdown signal is sent and the inhibitor actions the signal.

Expected behavior:

~~~
root@image:~# ./inhibitor.py &
[1] 64
root@image:~# systemctl reboot
Inhibit the shutdown for 30 seconds...
root@image:~# 
         Stopping Session 262 of User root...
[  OK  ] Removed slice Slice /system/getty.
[  OK  ] Removed slice Slice /system/modprobe.
[  OK  ] Stopped target Graphical Interface.
[  OK  ] Stopped target Multi-User System.
[  OK  ] Stopped target Login Prompts.
[  OK  ] Stopped target Host and Network Name Lookups.
[....]
~~~
Describe the solution you'd like:

Legacy shutdown, halt and poweroff commands should be able to take advantage of the inhibitors, as well as the PepareForShutdown signal, even when run as root - as they are for systemctl reboot/halt commands.

This looks to be due to logind_reboot() not being called in halt_main() if the reboot was executed by root.

systemd/src/systemctl/systemctl-compat-halt.c
~~~
Lines 156 to 175 in 3989bdc

         if (geteuid() != 0) { 
                 if (arg_dry_run || arg_force > 0) { 
                         (void) must_be_root(); 
                         return -EPERM; 
                 } 
  
                 /* Try logind if we are a normal user and no special mode applies. Maybe polkit allows us to 
                  * shutdown the machine. */ 
                 if (IN_SET(arg_action, ACTION_POWEROFF, ACTION_REBOOT, ACTION_KEXEC, ACTION_HALT)) { 
                         r = logind_reboot(arg_action); 
                         if (r >= 0) 
                                 return r; 
                         if (IN_SET(r, -EOPNOTSUPP, -EINPROGRESS)) 
                                 /* Requested operation is not supported on the local system or already in 
                                  * progress */ 
                                 return r; 
  
                         /* on all other errors, try low-level operation */ 
                 } 
         } 
~~~

Bypassing the check and calling logind_reboot() yields the expected behavior.


Additional info:

Patch commit:
https://github.com/systemd/systemd/commit/adefc8789b63225662e50ceaa282f9553b5c64eb