When to run "update-grub" ?

https://www.wilderssecurity.com/showpost.php?p=1464528&postcount=32

I asked this in the above post but am still not sure whether to run 'update-grub'
after editing the menu.lst by adding another debian (Ubuntu) as chainloader
to the existing Ubuntu menu.lst.
I have a strong feeling that it should not be done....
If so under what conditions would one run 'update-grub' ?
Also is it better to share existing swap partition or have a separate one for
each distro ? They would be on separate drives.

Regards

 

Why should you run update-grub? GRUB is dynamic unlike LILO, so no need to do that. That would only be important if you want to use another OS stage1 than the one you currently use, which is unnecessary.

As to swap, I used to use and use a single swap on my triple boot ans linux-only dual boot systems. Unless you need to copy raw binary data off swap ...

Mrk