[Bug 1755863] Re: netbooting the bionic live CD over NFS goes straight to maintenance mode :

[thh]

Based on in-depth analysis, I found the cause of the error：

“Apr 03 12:59:15 ubuntu systemd[1]: Failed to set up mount unit: Device
or resource busy”

call tree on systemd mount.c & unit.c:
 mount_dispatch_io
  -> mount_load_proc_self_mountinfo
     -> mount_setup_unit
         -> mount_setup_existing_unit 
             -> mount_add_extras
                 -> unit_set_default_slice:
                      -> unit_set_slice:
                         if (unit_active_state(u) != UNIT_INACTIVE)
                              return -EBUSY;  

"unit_set_slice" return EBUSY always, because of nfsroot always active
state in netbooting,

"mount_dispatch_io" give up updating mount state when
"mount_load_proc_self_mountinfo" return the error.

finally, all systemd mount service failed and then goto emergency shell.

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Title:
  netbooting the bionic live CD over NFS goes straight to maintenance
  mode :

Status in casper package in Ubuntu:
  Confirmed
Status in systemd package in Ubuntu:
  Confirmed

Bug description:
  netbooting the bionic live CD[1] over NFS goes straight to maintenance
  mode :

  [1] http://cdimage.ubuntu.com/daily-live/current/

  # casper.log
  Begin: Adding live session user... ... dbus-daemon[568]: [session uid=999 pid=568] Activating service name='org.gtk.vfs.Daemon' requested by ':1.0' (uid=999 pid=569 comm="" label="unconfined")
  dbus-daemon[568]: [session uid=999 pid=568] Successfully activated service 'org.gtk.vfs.Daemon'
  dbus-daemon[568]: [session uid=999 pid=568] Activating service name='org.gtk.vfs.Metadata' requested by ':1.0' (uid=999 pid=569 comm="" label="unconfined")
  fuse: device not found, try 'modprobe fuse' first
  dbus-daemon[568]: [session uid=999 pid=568] Successfully activated service 'org.gtk.vfs.Metadata'

  (gvfsd-metadata:580): GUdev-CRITICAL **: 16:28:56.270:
  g_udev_device_has_property: assertion 'G_UDEV_IS_DEVICE (device)'
  failed

  (gvfsd-metadata:580): GUdev-CRITICAL **: 16:28:56.270: g_udev_device_has_property: assertion 'G_UDEV_IS_DEVICE (device)' failed
  A connection to the bus can't be made
  done.
  Begin: Setting up init... ... done.

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