I tried to reboot a computer running Ubuntu 20.04 (Linux 5.15.0-67-generic #74~20.04.1-Ubuntu), but it keeps outputting error or warning messages on the black screen and does not shut down. What should I do? Is it good to press the power button for 5 seconds and force it turn off? Or, will it cause any inconsistency in the disk?

The shutdown message started to deviate from the usual one around the following point.

[ *** ] A stop job is running for /data (11s / 1min 32s)
[756977.526939] RIP: 0010:release_pages+0x278/0x4e0
[756977.527758] Code: b8 49 8d 7f 50 e8 ......
[756977.528654] RSP: 0018:ffff......
[756977.529559] RAX: dead000000000122 RBX: 0000......
[ OK ] Unmounted /data
[ OK ] Reached target Unmount All Filesystems.
[ OK ] Stopped File System Check on /dev/disk/by-label/......
[ OK ] Removed slice system-systemd\x2dfsck.slice.
[ OK ] Stopped target Local File Systems (Pre).
       Stopping Monitoring of LVM2 mirrors, snapshots, etc. using dmeventd or progress polling...
[ OK ] Stopped Create Static Device Nodes in /dev.
[ OK ] Stopped Create System Users.
[ OK ] Stopped Remount Root and Kernel File Systems.
[ OK ] Stopped Monitoring of LVM2 mirrors, snapshots etc. using dmeventd or progress polling...
[ OK ] Reached target Shutdown.
[ OK ] Reached target Final Step.
[ OK ] Finished Reboot.
[ OK ] Reached target Reboot.
[756977.819522] systemd-shutdown[1]: Syncing filesystems and block devices.
[757007.823383] systemd-shutdown[1]: Syncing filesystems and block devices - timeed out, issuing SIGKILL to PID 382289.
[757007.827668] systemd-shutdown[1]: Sending SIGTERM to remaining processes...
[757007.831640] systemd-journald[377]: Received SIGTERM from PID 1 (systemd-shutdow).
[757017.831895] systemd-shutdown[1]: Waiting for process: (sd-sync)
[757097.831617] systemd-shutdown[1]: Sending SIGKILL to remaining remaining processes...
[757097.842836] systemd-shutdown[1]: Sending SIGKILL to PID 382289 ((sd-sync)).
[757107.844080] systemd-shutdown[1]: Waiting for process: (sd-sync)
[757187.849840] systemd-shutdown[1]: Unmounting file systems.
[757187.854008] [382290]: Remounting '/' read-only in with options 'errors=remount-ro'.
[757188.790620] EXT4-fs (dm-1): re-mounted. Opts: errors=remount-ro. Quota mode:none.

Here ...... means that I omitted the rest of the line, and two vertical :s means that several lines were omitted.

The screen continued running. It is currently repeating to emit chucks of message similar (but slightly changing) as following:

[762469.371157] rcu: INFO: rcu_sched detected stalls on CPUs/tasks:
[762469.371816] rcu: $0-...0: (130 GPs behind) idle=689/1/0x4000000000000000 softirq=7399238/7399238 fqs=650925
[762469.372457] $(detected by 2, t=1320148 jiffies, g=23438573, q=695)
[762469.373098] Sending NMI from CPU 2 to CPUs 0:
[762469.373730] NMI backtrace for cpu 0
[762469.373731] CPU: 0 PID: 382290 Comm: (sd-remount) Tainted: G    B D    OE    5.15.0-67-generic #74~20.04.1-Ubuntu
[762469.373732] Hardware name: LENOVO ........
[762469.373733] RIP: 0010:native_queued_spin_lock_slowpath+0x79/0x230
[762469.373734] Code: 7c f0 0f ba 2b 08 0f ......
[762469.373735] RSP: 0018:ffff........
[762469.373736] RAX: 00000000......
[762469.373743] Call Trace:
[762469.373743]  <TASK>
[762469.373744]  _raw_spin_lock_irqsave+0x3b/0x50
[762469.373745]  lock_page_lruvec_irqsave+0x62/0x90
[762469.373747]  release_pages+0x264/0x4e0
[762469.373749]  __pagevec_release+0x30/0x70
[762469.373750]  __invalidate_mapping_pages+0x201/0x270
[762469.373752]  ? __wait_for_common+0xf7/0x160
[762469.373756]  invalidate_mapping_pages+0x10/0x20
[762469.373757]  invalidate_bdev+0x5b/0x60
[762469.373759]  reconfigure_super+0x12d/0x240
[762469.373761]  path_mount+0x969/0xa70
[762469.373762]  ? putname+0x57/0x70
[762469.373764]  do_mount+0x80/0xa0
[762469.373766]  __x64_sys_mount+0x8b/0xe0
[762469.373768]  do_syscall_64+0x59/0xc0
[762469.373769]  entry_SYSCALL_64_after_hwframe+0x61/0xcb
[762469.373770] RIP: 0033:0x7f07bc......
[762469.373771] Code: 48 8b 0d 15 c2 0c 00 ......
[762469.373772] RSP: 002b:00007ffd......
[762469.373773] RAX: ffffffff......
[762469.373777]  </TASK>
  • 2
    When a shutdown hangs I poweroff. I've been doing that for years and years and as a home user I have never had a problem. Working a production server with many connections you have more to think about but as a home user just go ahead and pull the plug. Mar 18, 2023 at 3:38

1 Answer 1


I remembered there were those Magic SysRq keys. While holding down both Left-Alt and SysRq (Prt Scn) keys, I pressed R, E, I, S, U, and B one by one.

I saw a message like

This SysRq key is disabled.

or something like that for R, E, and I. Then, different messages appeared for S, U, and B. After B, the computer rebooted.

After the reboot, the computer operates normally at least for the time being. I still don't know what the error was. I would be glad if someone could post a proper answer.


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