Editing grub for multiple OSes
 

I also found a problem for my multiple installation of linux distros.When I checked on the first distros when I boot up the system,I found out that some distros are gone or cannot be found in the list during booting.what should i do?

I moved this to a new thread---it was not related to the one in which it was posted.

First, you need to confirm which installation has the active configuration file (/boot/grub/menu.lst). If nothing else, look at all of them and find the one that matches what you see when you boot up.

Then, simply edit the file to add what you need.

If you have a system working--and then install another distro--there are a minimum of two options for installing/configuring grub:

1. Let the new system install GRUB and then edit the new config file

2. Do NOT install GRUB with the new system. Edit the original config file as required.

For what it's worth I like option 2 in this situation. If you have something that works in place, (IMHO) it's best to leave it in place unless you have a good reason for doing otherwise.

1. Start your LINUX which created the last grub.
2. Mount all other partitions.
3. Look for each /boot/grub/menu.lst of the partitions at the file-explorer.
4. Copy and paste the {title unix-distro-superspecial, kernel :superkernel 0.1.23-45, evtl intrd if it is there ,evtl safedefault, evtl boot} lines (two to five in general) completely into an editor like Geany, kate or gedit that has opened the actual running /boot/grub/menu.lst with an empty line after each last entry.
5. Save the this now modified /boot/grub/menu.lst under its name.
6. Close the editor.
7. U(n)mount all not running partitions.
8. Reboot.
9. The title-rows will show up at the boot-menu.
10. If kernel panic occurs try to 'e' edit the lines at grub-start-menu.
11. Try the commands there; especially the TAB-key is very useful.
12. One of the most interesting commands is 'find'.
13. The Linux have often different kernel-appendings and names for the partitions. Some use 'disk by uuid' and others simple '/dev/hda1' (hda2,hda3 a.s.o.).
14. You can learn a lot by reading and writing down to a piece of paper. Syntax is unfortunately very important and disk by uuid can lead to several written rows.

I believe if you have one or both of the two distros using grub2 and the others with grub legacy then you may want to consider chainloading with grub legacy. If you are talking about grub2 I will leave you with this tutorial.

grub2

Grub is only capable to mount filesystems that are written within a script or are installed binairies at /boot.
If you also installed these OS on their default fs then it is probably possible that grub does not know to read these. If the existing grub was installed on ext3 then it is much likely that grub does not read BSD fs like ufs. There are so many Unix fs like xfs, jfs and reiserfs.