The Grub Bootloader is a bootloader package from the GNU Project.
GRUB (short for GRand Unified Bootloader).
GRUB is the reference implementation of the Free Software Foundation’s Multiboot Specification, which provides a user the choice to boot one of multiple operating systems installed on a computer or select a specific kernel configuration available on a particular operating system’s partitions.
Grub version 1 ( known as Grub Legacy) is no longer under development and is being phased out. The GNU GRUB developers have switched their focus to GRUB 2, a complete rewrite with goals including making GRUB cleaner, more robust, more portable and more powerful.
In Pisi Linux works Grub 2
It gives for Grub much configuration Tools such as example YaST2 on SUSE/openSUSE distributions and Anaconda on Fedora/RHEL distributions. StartUp-Manager and GRUB Customizer are graphical configuration editor for Debian-based distributions of GRUB.
For GRUB 2 there are KDE Control Modules, in Pisi Linux 1.2 is it the grub2-editor, you found it in Menu>Settings>System Settings>Start up and Shutdown, in Pisi Linux 2.0 there is no graphical Grub-Editor at the Moment.
In the operating system selection menu GRUB accepts a couple of commands:
By pressing e, it is possible to edit parameters for the selected operating system before the operating system is started. Typically, this is used to change kernel parameters for a Linux system. The reason for doing this in GRUB (i.e. not editing the parameters in an already booted system) can be an emergency case: the system has failed to boot. Using the kernel parameters line it is possible, among other things, to specify a module to be disabled (blacklisted) for the kernel. This could be required if the specific kernel module is broken and thus prevents boot-up. For example, to blacklist the kernel module nvidia-current, append modprobe.blacklist=nvidia-current at the end of the kernel parameters.
By pressing c, the user enters the GRUB command line. The GRUB command line is not a regular Linux shell, like e.g. bash, and accepts only certain GRUB-specific commands, documented by various Linux distributions.
Once boot options have been selected, GRUB loads the selected kernel into memory and passes control to the kernel. Alternatively, GRUB can pass control of the boot process to another boot loader, using chain loading. This is the method used to load operating systems such as Microsoft Windows, that do not support the Multiboot Specification or are not supported directly by GRUB.
If the usage of dm-crypt is intended, the contents of /boot, i.e. /boot/grub, the Linux kernel and initramfs respectively initrd need to be on a distinct non-encrypted partition, because the logic to handle encrypted partitions resides inside the Linux kernel.
When you installed a new System and you do it with the default Settings Grub takes all Times the MBR Section ( /dev/sda) as Boot Section.
When a computer is turned on, the computer’s BIOS finds the configured primary bootable device (usually the computer’s hard disk) and loads and executes the initial bootstrap program from the master boot record (MBR). The MBR is the first sector of the hard disk, with zero as its offset (sectors counting starts at zero). For a long time, the size of a sector has been 512 bytes, but since 2009 there are hard disks available with a sector size of 4096 bytes, called Advanced Format disks. As of October 2013, such hard disks are still accessed in 512-byte sectors, by utilizing the 512e emulation.
When you now has install as example Linux Mint with default settings, so has Grub in Linux Mint write to /dev/sda, install you now a other Distribution too such as Pisi Linux and you install it with default Settings so overwrite Grub the entry from Linux Mint.
Note: Each Time when you install a other System and you take the default Settings the last System would be overwritten each Time the MBR
What can you do now when one of this System’s detect not the other it is simple:
You have Pisi Linux as default System and you installed Linux Mint too, and Linux Mint is not detect go in Pisi Linux and open a Terminal (Menu>System>Konsole) and write there:
sudo pisi it –rei grub2
sudo grub2-mkconfig -o /boot/grub2/grub.cfg
to update Grub in Pisi Linux
have you installed Linux Mint as first and Pisi Linux as last, and Linux Mint detects not Pisi Linux, open in Linux Mint a Terminal
for reinstall from Grub in Linux Mint to the MBR write
sudo grub-install /dev/sda
and after it
The Entries from Grub in Pisi Linux found you in /boot/grub2.
Warning: Change nothing in this Directory it can break your System when you not know what you are doing
Source for Information about Grub: Grub Wikipedia