How to fix MBR for Windows

Problem

I had installed Windows 10 successfully. While messing around with my other Linux partitions, a partition delete went awry and on booting I was dropped into a GRUB rescue prompt. What I wanted was the Master Boot Record to be restored to boot into Windows 10.

Solution

  • On another computer, I downloaded a Windows 10 ISO and created a bootable Windows recovery USB disk as described here.

  • I booted with this USB disk, chose Troubleshoot -> Advanced Options -> Command Prompt.

  • At the command prompt, type these commands:

$ bootrec /rebuildbcd
$ bootrec /fixmbr
$ bootrec /fixboot
$ exit

After restarting I was able to boot into Windows 10.

Missing parameter error on boot from Ubuntu startup disk

Problem

I made a startup USB flash drive for Ubuntu 15.04 using Startup Disk Creator as described here. I booted a computer using this flash drive and the boot process threw this error:

Missing parameter in configuration file. Keyword: path
gfxboot.c32: not a COM32R image
boot:

(This error happens even if the drive is created using UNetBootIn as described here. It happens with Ubuntu 14.10 too.)

Solution

Type help at the boot prompt. It will show a menu of options. Hit Enter here and Ubuntu will boot up as it should have.

How to analyze boot process using Bootchart

Chart generated by Bootchart
Chart generated by Bootchart

Bootchart is a tool that can be used to visualize and analyze the boot process. It is a shell script that is run by the kernel in the background. It analyzes all the information and renders a chart that makes it easy to understand the CPU, disk and services that run at boot. This can be useful to understand your system or find bottlenecks that might be making your system to boot slowly.

Installing Bootchart is easy:

$ sudo apt install bootchart

That is it! It will automatically run every time the system is booted up. The chart it generates is stored in /var/log/bootchart as a PNG file.

Tried with: Bootchart 0.90.2 and Ubuntu 14.04