Most Linux systems actually offer multiple boot options. The most common dual-boot configuration allows you to boot either Linux or Microsoft Windows. And in fact, most modern Linux distributions automatically detect a pre-existing Windows operating system during the installation process. The Windows partition is left alone, and the installation program adds a stanza to the bootloader to facilitate booting into Windows.
You don't have to have a second operating system to have a dual boot. If you've installed new kernels from an RPM or DEB package, it has set up alternate kernel selections in GRUB or LILO. Alternatively, if you installed a new kernel from a tarball, you need to know how to configure a new kernel selection in your bootloader.
In this annoyance, I'll show you the basics of configuring a dual boot for multiple Linux kernels, as well as a configuring a dual boot on GRUB and LILO for Linux and Microsoft Windows. This annoyance provides fundamental bootloader basics for the one that follows.
If you have just configured a new Linux kernel, you'll want to be able to boot both the old and the new kernel. At least until you've completely tested the new kernel, you need access to the old one just in case something goes wrong.
If you install (not upgrade) a Linux kernel from a modern RPM or DEB package, the process automatically adds the new kernel to your current bootloader. If you're using a distribution with one ...