One day ago, I started upgrading my Ubuntu 16.04 to 18.04, after I see the update from website. The most diffrience betwen 16.04 and 18.04 is that the 18.04 use GNOME desktop rather than Unity. I had heard that the GNOME desktop is better than Unity, so I tried 18.04 for the new desktop. Unfortunately, after I upgraded my OS, I found that the GNOME desktop wasjust so uncomfortable. And after one hour I gone back to 16.04:(, and content of this article is about the problems I met while reinstalling the OS.

I installed the 16.04 OS just the same as what I done before: burned the IOS to USB, started the computer, and do what the OS suggested to do.

Soft Lockup

The first thing I met was what called soft lockup, like below

 watchdog: BUG: soft lockup cpu#0 stuck for 23s.

emmm, it was quite depressed, but fortunately I found the solutions on ubuntu forums. The problem can be solved add grub boot option as below.

When you stay at the GRUB menu(you maybe need to press and hold the left shift key right after starting the system if you only has one OS.). Then Hightlight the kernel you want to use and press the e key, thus you should able to see and edit the commands associated with the hightlighted kernel you do before. Go down to the line starting with linux and add the parameter nomodeset to its end. Now press Ctrl + x to boot in the specific config. And remember it just work temporarily, you should configure the /etc/default/grub file as same as what you do before, finally run sudo update-grub to permanently update GRUB’s configuration.

So in conclusion, what you need to do is add nomodeset to kernel boot configure.

PCIe Bus Error

After I solved the problem above, finally I was led to a NEW PROBLEM:( The PCIe Bus error actually appeared before the soft lockup, it was solved by askubuntu, just add pci=noaer to the kernel boot config, which I explained at soft lockup.

Finally I could use my Ubuntu again. But what the parameter, like pci=nomsi really mean?, or “just work” is fine? Thanks the internet a lot, I found an post about this, here are some summary.

  1. nomodeset, may be the most common one, which is needed for some graphics cards that otherwise boot into a black screen or corrupted splash. The newest kernels have moved the video mode setting into the kernel. So all the programming of hardware specific clock rates and registers on the video card happen in the kernel rather than in the X driver when the X server starts. This make it possible to have high resolution nice looking splash(boot) screens and flicker free transitions from boot splash to login screen. Unfortunately, on some cards this doesn’t work properly and you end up with a black screen(or soft lockup above). Adding the parameter instructs the kernel to not load video drivers and use BIOS modes instead until X is loaded. Note that this option is sometions needed for nVidia cards when using the default “nouveau” drivers. Installing proprietary nvidia drivers ususlly makes this option no longer necessary, so it may not be needed to make this option permanet, just for one boot until you installed the nvidia drivers.

  2. pci=, the argument can be used to change the behaviour of PCI bus device problem and device behaviour.

Ubuntu and Windows Time Difference

Operating systems store and retrieve the time in the hardware clock located on your motherland so that it can keep track of the time even when the system does not have power. Most operating system(Linux, Unix, MacOS) store the time on the hardware clock as UTC by default, though some system(notably Microsoft Windows) store the time on the hardware clock as the “local” time. This causes problems in a dual boot system if both system view the hardware clock differently.

The advantage of having the hardware clock as UTC is that you don’t need to change the hardware clock when moving bewteen timezones or when Daylight Savings Time(DST) begins or ends as UTC does not have DST or timezone offsets. And changing Linux to use local time is easier and more reliable than changing Windows to use UTC.

  1. Make Linux use ’local’ time, pre-Ubuntu 15.04 systems, you should edit /etc/default/rcS and add or change the following section UTC=no, while Ubuntu 15.04 and above you should run timedatectl set-local-rtc 1 --adjust-system-clock in terminal since the Ubuntu use timedatectl to manage time after 15.04.

  2. Make Windows use UTC, for windows 10 you can create a *.reg(on the desktop) with the following content and double-click it to import it to registry:

    Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\TimeZoneInformation]
 "RealTimeIsUniversal"=dword:00000001