Ubuntu 20.04 系统的显示器会在 30 分钟后自动关闭。但是，有一次按下某些键盘键后，显示器无法重新打开并显示登录屏幕。
尝试从另一个系统通过 SSH 连接到该机器，但似乎 SSH 服务器不再响应 SSH 请求和 ping。
我们如何找出冻结的原因？
查看/var/log/syslog并查看以下在系统冻结/崩溃时以及手动重启后显示的消息。
Apr 30 14:08:53 x-pc kernel: [144091.494964] audit: type=1400 audit(1619806133.342:99): apparmor="DENIED" operation="open" profile="snap.snap-store.ubuntu-software" name="/var/lib/snapd/hostfs/usr/share/gdm/greeter/applications/gnome-initial-setup.desktop" pid=3610 comm="snap-store" requested_mask="r" denied_mask="r" fsuid=1000 ouid=0
Apr 30 14:08:53 x-pc kernel: [144091.938048] audit: type=1400 audit(1619806133.782:100): apparmor="DENIED" operation="open" profile="snap.snap-store.ubuntu-software" name="/var/lib/snapd/hostfs/usr/share/gdm/greeter/applications/gnome-initial-setup.desktop" pid=3610 comm="snap-store" requested_mask="r" denied_mask="r" fsuid=1000 ouid=0
Apr 30 14:08:54 x-pc kernel: [144092.311141] audit: type=1326 audit(1619806134.158:101): auid=1000 uid=1000 gid=1000 ses=3 subj=snap.snap-store.ubuntu-software pid=3610 comm="snap-store" exe="/snap/snap-store/518/usr/bin/snap-store" sig=0 arch=c000003e syscall=93 compat=0 ip=0x7fa31b27c4e7 code=0x50000
Apr 30 14:08:54 x-pc dbus-daemon[3131]: apparmor="DENIED" operation="dbus_method_call" bus="session" path="/org/gtk/Notifications" interface="org.gtk.Notifications" member="RemoveNotification" mask="send" name="org.gtk.Notifications" pid=3610 label="snap.snap-store.ubuntu-software" peer_pid=3346 peer_label="unconfined"
Apr 30 14:08:54 x-pc dbus-daemon[3131]: apparmor="DENIED" operation="dbus_method_call" bus="session" path="/org/gtk/Notifications" interface="org.gtk.Notifications" member="RemoveNotification" mask="send" name="org.gtk.Notifications" pid=3610 label="snap.snap-store.ubuntu-software" peer_pid=3346 peer_label="unconfined"
Apr 30 14:16:06 x-pc dbus-daemon[3131]: [session uid=1000 pid=3131] Activating via systemd: service name='org.freedesktop.Tracker1' unit='tracker-store.service' requested by ':1.2' (uid=1000 pid=3127 comm="/usr/libexec/tracker-miner-fs " label="unconfined")
Apr 30 14:16:06 x-pc systemd[3119]: Starting Tracker metadata database store and lookup manager...
Apr 30 14:16:07 x-pc dbus-daemon[3131]: [session uid=1000 pid=3131] Successfully activated service 'org.freedesktop.Tracker1'
Apr 30 14:16:07 x-pc systemd[3119]: Started Tracker metadata database store and lookup manager.
Apr 30 14:16:41 x-pc tracker-store[147368]: OK
Apr 30 14:16:41 x-pc systemd[3119]: tracker-store.service: Succeeded.
Apr 30 14:17:02 x-pc CRON[147391]: (root) CMD ( cd / && run-parts --report /etc/cron.hourly)
Apr 30 14:46:58 x-pc systemd-modules-load[537]: Inserted module 'lp'
Apr 30 14:46:58 x-pc systemd-modules-load[537]: Inserted module 'ppdev'
Apr 30 14:46:58 x-pc systemd-modules-load[537]: Inserted module 'parport_pc'
Apr 30 14:46:58 x-pc systemd-sysctl[561]: Not setting net/ipv4/conf/all/promote_secondaries (explicit setting exists).
Apr 30 14:46:58 x-pc systemd-sysctl[561]: Not setting net/ipv4/conf/default/promote_secondaries (explicit setting exists).
Apr 30 14:46:58 x-pc systemd[1]: Starting Flush Journal to Persistent Storage...
Apr 30 14:46:58 x-pc systemd[1]: Started udev Kernel Device Manager.
Apr 30 14:46:58 x-pc systemd[1]: Finished Monitoring of LVM2 mirrors, snapshots etc. using dmeventd or progress polling.
Apr 30 14:46:58 x-pc mtp-probe: checking bus 3, device 3: "/sys/devices/pci0000:00/0000:00:01.2/0000:20:00.0/0000:21:08.0/0000:2a:00.3/usb3/3-5"
Apr 30 14:46:58 x-pc systemd[1]: Reached target Local File Systems (Pre).
Apr 30 14:46:58 x-pc mtp-probe: bus: 3, device: 3 was not an MTP device
Apr 30 14:46:58 x-pc systemd[1]: Mounting Mount unit for canonical-livepatch, revision 97...
Apr 30 14:46:58 x-pc mtp-probe: checking bus 3, device 2: "/sys/devices/pci0000:00/0000:00:01.2/0000:20:00.0/0000:21:08.0/0000:2a:00.3/usb3/3-2"
Apr 30 14:46:58 x-pc systemd[1]: Mounting Mount unit for canonical-livepatch, revision 98...
Apr 30 14:46:58 x-pc systemd[1]: Mounting Mount unit for code, revision 61...
Apr 30 14:46:58 x-pc systemd[1]: Mounting Mount unit for code, revision 62...
Apr 30 14:46:58 x-pc systemd[1]: Mounting Mount unit for core, revision 10908...
Apr 30 14:46:58 x-pc kernel: [ 0.000000] Linux version 5.8.0-50-generic (buildd@lgw01-amd64-030) (gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0, GNU ld (GNU Binutils for Ubuntu) 2.34) #56~20.04.1-Ubuntu SMP Mon Apr 12 21:46:35 UTC 2021 (Ubuntu 5.8.0-50.56~20.04.1-generic 5.8.18)
Apr 30 14:46:58 x-pc kernel: [ 0.000000] Command line: BOOT_IMAGE=/boot/vmlinuz-5.8.0-50-generic root=UUID=8686a110-298e-49e7-8509-15fca1f29b59 ro quiet splash vt.handoff=7
Apr 30 14:46:58 x-pc kernel: [ 0.000000] KERNEL supported cpus:
Apr 30 14:46:58 x-pc systemd[1]: Mounting Mount unit for core, revision 10958...