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The computer froze and then I held down Alt+PrtSc and pressed R, E, I, S, U, B, one by one, but it didn't shut down. So I waited for some time and then again held down Alt+PrtSc and pressed R, E, I, S, U, B.

Then it turned to a black screen with a tiny white line on the top left corner. Then I did Alt+PrtSc+REISUB several times, and there was no visible response. I held down the power button and shut it down.

These are the last few lines of log before I powered off the computer:

11:17:53 kernel: sysrq: Keyboard mode set to system default
11:17:53 kernel: sysrq: Keyboard mode set to system default
11:15:38 kernel: sysrq: HELP : loglevel(0-9) reboot(b) crash(c) terminate-all-tasks(e) memory-full-oom-kill(f) kill-all-tasks(i) thaw-filesystems(j) sak(k) show-backtrace-all-active-cpus(l) show-memory-usage(m) nice-all-RT-tasks(n) poweroff(o) show-registers(p) show-all-timers(q) unraw(r) sync(s) show-task-states(t) unmount(u) force-fb(v) show-blocked-tasks(w) dump-ftrace-buffer(z) 
11:15:35 kernel: sysrq: HELP : loglevel(0-9) reboot(b) crash(c) terminate-all-tasks(e) memory-full-oom-kill(f) kill-all-tasks(i) thaw-filesystems(j) sak(k) show-backtrace-all-active-cpus(l) show-memory-usage(m) nice-all-RT-tasks(n) poweroff(o) show-registers(p) show-all-timers(q) unraw(r) sync(s) show-task-states(t) unmount(u) force-fb(v) show-blocked-tasks(w) dump-ftrace-buffer(z) 
11:15:31 kernel: sysrq: HELP : loglevel(0-9) reboot(b) crash(c) terminate-all-tasks(e) memory-full-oom-kill(f) kill-all-tasks(i) thaw-filesystems(j) sak(k) show-backtrace-all-active-cpus(l) show-memory-usage(m) nice-all-RT-tasks(n) poweroff(o) show-registers(p) show-all-timers(q) unraw(r) sync(s) show-task-states(t) unmount(u) force-fb(v) show-blocked-tasks(w) dump-ftrace-buffer(z) 
11:15:26 kernel: sysrq: HELP : loglevel(0-9) reboot(b) crash(c) terminate-all-tasks(e) memory-full-oom-kill(f) kill-all-tasks(i) thaw-filesystems(j) sak(k) show-backtrace-all-active-cpus(l) show-memory-usage(m) nice-all-RT-tasks(n) poweroff(o) show-registers(p) show-all-timers(q) unraw(r) sync(s) show-task-states(t) unmount(u) force-fb(v) show-blocked-tasks(w) dump-ftrace-buffer(z) 
11:15:20 kernel: sysrq: HELP : loglevel(0-9) reboot(b) crash(c) terminate-all-tasks(e) memory-full-oom-kill(f) kill-all-tasks(i) thaw-filesystems(j) sak(k) show-backtrace-all-active-cpus(l) show-memory-usage(m) nice-all-RT-tasks(n) poweroff(o) show-registers(p) show-all-timers(q) unraw(r) sync(s) show-task-states(t) unmount(u) force-fb(v) show-blocked-tasks(w) dump-ftrace-buffer(z) 
11:15:15 kernel: sysrq: HELP : loglevel(0-9) reboot(b) crash(c) terminate-all-tasks(e) memory-full-oom-kill(f) kill-all-tasks(i) thaw-filesystems(j) sak(k) show-backtrace-all-active-cpus(l) show-memory-usage(m) nice-all-RT-tasks(n) poweroff(o) show-registers(p) show-all-timers(q) unraw(r) sync(s) show-task-states(t) unmount(u) force-fb(v) show-blocked-tasks(w) dump-ftrace-buffer(z) 
11:15:00 kernel: sysrq: HELP : loglevel(0-9) reboot(b) crash(c) terminate-all-tasks(e) memory-full-oom-kill(f) kill-all-tasks(i) thaw-filesystems(j) sak(k) show-backtrace-all-active-cpus(l) show-memory-usage(m) nice-all-RT-tasks(n) poweroff(o) show-registers(p) show-all-timers(q) unraw(r) sync(s) show-task-states(t) unmount(u) force-fb(v) show-blocked-tasks(w) dump-ftrace-buffer(z) 
11:14:57 kernel: sysrq: HELP : loglevel(0-9) reboot(b) crash(c) terminate-all-tasks(e) memory-full-oom-kill(f) kill-all-tasks(i) thaw-filesystems(j) sak(k) show-backtrace-all-active-cpus(l) show-memory-usage(m) nice-all-RT-tasks(n) poweroff(o) show-registers(p) show-all-timers(q) unraw(r) sync(s) show-task-states(t) unmount(u) force-fb(v) show-blocked-tasks(w) dump-ftrace-buffer(z) 
11:14:56 kernel: sysrq: HELP : loglevel(0-9) reboot(b) crash(c) terminate-all-tasks(e) memory-full-oom-kill(f) kill-all-tasks(i) thaw-filesystems(j) sak(k) show-backtrace-all-active-cpus(l) show-memory-usage(m) nice-all-RT-tasks(n) poweroff(o) show-registers(p) show-all-timers(q) unraw(r) sync(s) show-task-states(t) unmount(u) force-fb(v) show-blocked-tasks(w) dump-ftrace-buffer(z) 
11:12:05 kernel: ---[ end trace a43d1a9c4ed7a4a1 ]---
11:12:05 kernel: Modules linked in: nls_iso8859_1 snd_hda_codec_hdmi snd_hda_codec_realtek snd_hda_codec_generic ledtrig_audio snd_hda_intel snd_intel_dspcfg snd_intel_sdw_acpi intel_rapl_msr snd_hda_codec snd_hda_core snd_hwdep snd_pcm mei_hdcp intel_rapl_common intel_tcc_cooling x86_pkg_temp_thermal intel_powerclamp coretemp kvm_intel kvm snd_seq_midi snd_seq_midi_event crct10dif_pclmul snd_rawmidi ghash_clmulni_intel aesni_intel crypto_simd cryptd rapl intel_cstate snd_seq snd_seq_device snd_timer i915 gigabyte_wmi wmi_bmof snd efi_pstore drm_kms_helper cec rc_core ee1004 i2c_algo_bit fb_sys_fops syscopyarea joydev input_leds soundcore mei_me sysfillrect sysimgblt mei mac_hid acpi_pad acpi_tad sch_fq_codel msr parport_pc ppdev drm lp parport ip_tables x_tables autofs4 hid_generic usbhid hid crc32_pclmul e1000e i2c_i801 nvme i2c_smbus nvme_core ahci xhci_pci libahci xhci_pci_renesas wmi video
11:12:05 kernel:  </TASK>
11:12:05 kernel: R13: 00007ffd70516ca8 R14: 00007f606a9e6018 R15: 00007ffd70516bb8
11:12:05 kernel: R10: 00007ffd7051d090 R11: 0000000000000293 R12: 0000000000000000
11:12:05 kernel: RBP: 00007ffd70516ca4 R08: 0000000000000000 R09: 0000000000000000

Despite the log shows "Keyboard mode set to system default", the computer didn't shut down, even after I had waited for several minutes. How do I make REISUB work?

OS is Ubuntu 20.04.3 LTS.

edit: These are the entries of syslog at about the time the freeze happened.

11:12:01 kernel: RAX: feff8d06657e1cc0 RBX: ffffe01c08836000 RCX: 0000000000000007
11:12:01 kernel: RSP: 0018:ffffaf8f8127bac0 EFLAGS: 00010202
11:12:01 kernel: Code: 3d 3d 01 48 29 c8 41 8b 48 20 89 c6 48 0f af f1 41 0f b6 48 24 48 c1 ee 20 29 f0 d3 e8 41 0f b6 48 25 01 f0 d3 e8 48 8d 04 c2 <4c> 8b 20 4d 85 e4 0f 84 af 00 00 00 48 c7 00 00 00 00 00 41 8b 70
11:12:01 kernel: RIP: 0010:memcg_slab_free_hook+0x70/0x230
11:12:01 kernel: Hardware name: Gigabyte Technology Co., Ltd. B365 M AORUS ELITE/B365 M AORUS ELITE-CF, BIOS F2 08/13/2019
11:12:01 kernel: CPU: 0 PID: 1949 Comm: Socket Thread Not tainted 5.13.0-37-generic #42~20.04.1-Ubuntu
11:12:01 kernel: general protection fault, probably for non-canonical address 0xfeff8d06657e1cc0: 0000 [#1] SMP PTI




Mar 26 10:45:19  gnome-shell[1517]: cr_parser_new_from_buf: assertion 'a_buf && a_len' failed
Mar 26 10:45:19  gnome-shell[1517]: cr_declaration_parse_list_from_buf: assertion 'parser' failed
Mar 26 10:45:19  gnome-shell[1517]: cr_parser_new_from_buf: assertion 'a_buf && a_len' failed
Mar 26 10:45:19  gnome-shell[1517]: cr_declaration_parse_list_from_buf: assertion 'parser' failed
Mar 26 10:45:19  gnome-shell[1517]: cr_parser_new_from_buf: assertion 'a_buf && a_len' failed
Mar 26 10:45:19  gnome-shell[1517]: cr_declaration_parse_list_from_buf: assertion 'parser' failed
Mar 26 10:45:19  gnome-shell[1517]: g_dbus_connection_emit_signal: assertion 'G_IS_DBUS_CONNECTION (connection)' failed
Mar 26 10:45:19  gnome-shell[1517]: cr_parser_new_from_buf: assertion 'a_buf && a_len' failed
Mar 26 10:45:19  gnome-shell[1517]: cr_declaration_parse_list_from_buf: assertion 'parser' failed
Mar 26 11:03:49  dbus-daemon[646]: [system] Activating via systemd: service name='net.reactivated.Fprint' unit='fprintd.service' requested by ':1.81' (uid=1000 pid=1517 comm="/usr/bin/gnome-shell " label="unconfined")
Mar 26 11:03:49  systemd[1]: Starting Fingerprint Authentication Daemon...
Mar 26 11:03:49  dbus-daemon[646]: [system] Successfully activated service 'net.reactivated.Fprint'
Mar 26 11:03:49  systemd[1]: Started Fingerprint Authentication Daemon.
Mar 26 11:03:59  gnome-shell[1517]: cr_parser_new_from_buf: assertion 'a_buf && a_len' failed
Mar 26 11:03:59  gnome-shell[1517]: cr_declaration_parse_list_from_buf: assertion 'parser' failed
Mar 26 11:03:59  NetworkManager[649]: <info>  [1648263839.2005] agent-manager: agent[7cccc8467972acfa,:1.81/org.gnome.Shell.NetworkAgent/1000]: agent registered
Mar 26 11:03:59  dbus-daemon[1311]: [session uid=1000 pid=1311] Activating service name='org.freedesktop.FileManager1' requested by ':1.43' (uid=1000 pid=1517 comm="/usr/bin/gnome-shell " label="unconfined")
Mar 26 11:03:59  gnome-shell[1517]: cr_parser_new_from_buf: assertion 'a_buf && a_len' failed
Mar 26 11:03:59  gnome-shell[1517]: cr_declaration_parse_list_from_buf: assertion 'parser' failed
Mar 26 11:03:59  dbus-daemon[1311]: [session uid=1000 pid=1311] Activating service name='org.gnome.Nautilus' requested by ':1.43' (uid=1000 pid=1517 comm="/usr/bin/gnome-shell " label="unconfined")
Mar 26 11:03:59  gnome-shell[1517]: cr_parser_new_from_buf: assertion 'a_buf && a_len' failed
Mar 26 11:03:59  gnome-shell[1517]: cr_declaration_parse_list_from_buf: assertion 'parser' failed
Mar 26 11:03:59  gnome-shell[1517]: Window manager warning: Overwriting existing binding of keysym 31 with keysym 31 (keycode a).
Mar 26 11:03:59  gnome-shell[1517]: Window manager warning: Overwriting existing binding of keysym 32 with keysym 32 (keycode b).
Mar 26 11:03:59  gnome-shell[1517]: Window manager warning: Overwriting existing binding of keysym 38 with keysym 38 (keycode 11).
Mar 26 11:03:59  gnome-shell[1517]: Window manager warning: Overwriting existing binding of keysym 39 with keysym 39 (keycode 12).
Mar 26 11:03:59  gnome-shell[1517]: Window manager warning: Overwriting existing binding of keysym 33 with keysym 33 (keycode c).
Mar 26 11:03:59  gnome-shell[1517]: Window manager warning: Overwriting existing binding of keysym 34 with keysym 34 (keycode d).
Mar 26 11:03:59  gnome-shell[1517]: Window manager warning: Overwriting existing binding of keysym 35 with keysym 35 (keycode e).
Mar 26 11:03:59  gnome-shell[1517]: Window manager warning: Overwriting existing binding of keysym 36 with keysym 36 (keycode f).
Mar 26 11:03:59  gnome-shell[1517]: Window manager warning: Overwriting existing binding of keysym 37 with keysym 37 (keycode 10).
Mar 26 11:04:19  systemd[1]: fprintd.service: Succeeded.
Mar 26 11:04:41  dbus-daemon[1311]: [session uid=1000 pid=1311] Activating service name='org.gnome.ControlCenter.SearchProvider' requested by ':1.43' (uid=1000 pid=1517 comm="/usr/bin/gnome-shell " label="unconfined")
Mar 26 11:04:41  dbus-daemon[1311]: [session uid=1000 pid=1311] Activating service name='org.gnome.Nautilus' requested by ':1.43' (uid=1000 pid=1517 comm="/usr/bin/gnome-shell " label="unconfined")
Mar 26 11:04:41  dbus-daemon[1311]: [session uid=1000 pid=1311] Activating service name='org.gnome.Calculator.SearchProvider' requested by ':1.43' (uid=1000 pid=1517 comm="/usr/bin/gnome-shell " label="unconfined")
Mar 26 11:04:41  dbus-daemon[1311]: [session uid=1000 pid=1311] 
Activating service name='org.gnome.Calendar' requested by ':1.43' (uid=1000 pid=1517 com
m="/usr/bin/gnome-shell " label="unconfined")
Mar 26 11:04:41  dbus-daemon[1311]: [session uid=1000 pid=1311] 
Activating service name='org.gnome.Characters.BackgroundService' requested by ':1.43' (u
id=1000 pid=1517 comm="/usr/bin/gnome-shell " label="unconfined")
Mar 26 11:04:41  dbus-daemon[1311]: [session uid=1000 pid=1311] 
Activating service name='org.gnome.seahorse.Application' requested by ':1.43' (uid=1000 
pid=1517 comm="/usr/bin/gnome-shell " label="unconfined")
Mar 26 11:04:41  dbus-daemon[1311]: [session uid=1000 pid=1311] 
Activating via systemd: service name='org.gnome.Terminal' unit='gnome-terminal-server.se
rvice' requested by ':1.43' (uid=1000 pid=1517 comm="/usr/bin/gnome-shell " label="uncon
fined")
Mar 26 11:04:41  systemd[1300]: Created slice apps.slice.
Mar 26 11:04:41  systemd[1300]: Created slice apps-org.gnome.Ter
minal.slice.
Mar 26 11:04:41  systemd[1300]: Starting GNOME Terminal Server..
.
Mar 26 11:04:41  dbus-daemon[1311]: [session uid=1000 pid=1311] 
Successfully activated service 'org.gnome.ControlCenter.SearchProvider'
Mar 26 11:04:41  dbus-daemon[1311]: [session uid=1000 pid=1311] 
Successfully activated service 'org.gnome.seahorse.Application'
Mar 26 11:04:41  dbus-daemon[646]: [system] Activating via syste
md: service name='org.freedesktop.timedate1' unit='dbus-org.freedesktop.timedate1.servic
e' requested by ':1.184' (uid=1000 pid=5785 comm="/usr/bin/gnome-calendar --gapplication
-service " label="unconfined")
Mar 26 11:04:41  systemd[1]: Starting Time & Date Service...
Mar 26 11:04:41  dbus-daemon[1311]: [session uid=1000 pid=1311] Successfully activated service 'org.gnome.Terminal'
Mar 26 11:04:41  systemd[1300]: Started GNOME Terminal Server.
Mar 26 11:04:41  dbus-daemon[1311]: [session uid=1000 pid=1311] Successfully activated service 'org.gnome.Characters.BackgroundService'
Mar 26 11:04:41  dbus-daemon[646]: [system] Successfully activated service 'org.freedesktop.timedate1'
Mar 26 11:04:41  systemd[1]: Started Time & Date Service.
Mar 26 11:04:41  dbus-daemon[1311]: [session uid=1000 pid=1311] Successfully activated service 'org.gnome.Calendar'
Mar 26 11:04:41  dbus-daemon[1311]: [session uid=1000 pid=1311] Successfully activated service 'org.gnome.Nautilus'
Mar 26 11:04:41  dbus-daemon[1311]: [session uid=1000 pid=1311] Successfully activated service 'org.gnome.Calculator.SearchProvider'
Mar 26 11:04:43  dbus-daemon[1311]: [session uid=1000 pid=1311] Activating service name='org.gnome.gedit' requested by ':1.119' (uid=1000 pid=5780 comm="/usr/bin/nautilus --gapplication-service " label="unconfined")
Mar 26 11:04:43  dbus-daemon[1311]: [session uid=1000 pid=1311] Successfully activated service 'org.gnome.gedit'
Mar 26 11:04:48  dbus-daemon[1311]: [session uid=1000 pid=1311] Activating via systemd: service name='org.freedesktop.Tracker1' unit='tracker-store.service' requested by ':1.2' (uid=1000 pid=1308 comm="/usr/libexec/tracker-miner-fs " label="unconfined")
Mar 26 11:04:48  systemd[1300]: Starting Tracker metadata database store and lookup manager...
Mar 26 11:04:48  dbus-daemon[1311]: [session uid=1000 pid=1311] Successfully activated service 'org.freedesktop.Tracker1'
Mar 26 11:04:48  systemd[1300]: Started Tracker metadata database store and lookup manager.
Mar 26 11:04:48  dbus-daemon[1311]: [session uid=1000 pid=1311] Activating via systemd: service name='org.freedesktop.Tracker1.Miner.Extract' unit='tracker-extract.service' requested by ':1.2' (uid=1000 pid=1308 comm="/usr/libexec/tracker-miner-fs " label="unconfined")
Mar 26 11:04:48  systemd[1300]: Starting Tracker metadata extractor...
Mar 26 11:04:48  tracker-extract[5882]: Set scheduler policy to SCHED_IDLE
Mar 26 11:04:48  tracker-extract[5882]: Setting priority nice level to 19
Mar 26 11:04:48  dbus-daemon[1311]: [session uid=1000 pid=1311] Successfully activated service 'org.freedesktop.Tracker1.Miner.Extract'
Mar 26 11:04:48  systemd[1300]: Started Tracker metadata extractor.
Mar 26 11:04:51  systemd[1300]: gnome-terminal-server.service: Succeeded.
Mar 26 11:04:58  systemd[1300]: tracker-extract.service: Succeeded.
Mar 26 11:05:11  systemd[1]: systemd-timedated.service: Succeeded.
Mar 26 11:05:18  tracker-store[5873]: OK
Mar 26 11:05:18  systemd[1300]: tracker-store.service: Succeeded.
Mar 26 11:05:19  rtkit-daemon[831]: Supervising 6 threads of 5 processes of 1 users.
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  • If the kernel panic'ed SysRQ commands no longer work. This might have happened for you. Mar 26, 2022 at 10:43
  • I added the logs at the freeze to the post. If the kernel panic'ed, what should I have done to safely shut down? What might be the cause of the freeze?
    – istakanvd
    Mar 26, 2022 at 16:04
  • Weird.. it almost looks like the kernel thinks that you are hitting some oddball key that does not have a meaning to magic sysrq so it is printing the help message telling you what the valid keys are. Like your keyboard is sending bad scan codes.
    – psusi
    Apr 1, 2022 at 15:08
  • I did hit some random keys out of frustration, but I also did hit the right REISUB in right order. These 6 keys, along with PrtSc and Alt, function normally, so it's likely not keyboard malfunction.
    – istakanvd
    Apr 1, 2022 at 15:21
  • Magic-sysrq works on my computer when it's not frozen, but doesn't work when it freezes. How do I know if this is a hardware problem, or kernel bug, or something else?
    – istakanvd
    Apr 10, 2022 at 9:06

1 Answer 1

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Some distributions block certain system request commands because they can (potentially) be exploited by someone with physical access to your keyboard. If you issue the command sysctl kernel.sysrq in a terminal and get any numeric answer except for “1” then this is the case on your system. Ubuntu 18.04, for example, returns “176” — which means that the ‘e’ and ‘i’ commands are blocked. If you want to restore full access to system request commands, use sudo to edit the file /etc/sysctl.conf and uncomment the line that reads #kernel.sysrq=1. It will take effect the next time you boot.

https://tp69.blog/2019/04/23/recovering-from-a-freeze-in-linux/

1
  • The command "sysctl kernel.sysrq" shows kernel.sysrq = 1. I probably enabled sysrq commands when similar freezes occurred last year.
    – istakanvd
    Mar 26, 2022 at 7:13

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