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. -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1755863 Title: netbooting the bionic live CD over NFS goes straight to maintenance mode : To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/casper/+bug/1755863/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs