Boot from Debian install media. Use rescue mode. Mount Debian partition when prompted. Run os-prober and update-grub then exit. Machine should reboot into Debian.
On Wed, Aug 5, 2020 at 1:28 PM Long Wind <longwi...@yahoo.com> wrote: > Thank Greg! > but chroot dance is new to me, it doesn't seem easy > it involves many steps (commands) > a small error will lead to failure > > i install centos just for fun > i can install lubuntu at sda3 and it can boot buster > > > > > On Wednesday, August 5, 2020, 8:15:14 PM GMT+8, Greg Wooledge < > wool...@eeg.ccf.org> wrote: > > > On Wed, Aug 05, 2020 at 12:04:48AM +0000, Long Wind wrote: > > > i have win7 at sda1 and buster at sda2i install centos 6 at sda3, it can > boot win7, can't see busteri mean i can't boot buster now > > is there some rescue image that can be written to bootable usb disk? > > or do you know how to config centos 6 boot loader?is buster's boot code > installed at sda2 by default? > > > I'm going to assume you're using Legacy/MBR booting, because I don't know > enough about UEFI to answer this question in that universe. > > If you're trying to multi-boot several different Linuxes from one > hard drive, the first thing you have to do is make a decision. You > must choose which Linux will be in control of the boot loader. > > Let's say you choose Debian. (If you choose something else, stop > reading now, and go ask the other OS's mailing list for help.) > > First step, then, will be to boot into Debian successfully. For this, > you'll probably need to boot into whatever Linux you *can* boot, whether > that's the CentOS on the hard drive, or a rescue CD, or whatever. > > Once you're booted into *a* Linux, then you can do the chroot dance > to mount the Debian file system(s) underneath that. > > According to the IRC bot factoid, that dance goes something like > this: > > Mount your root filesystem with "mount -t ext2 /dev/whatever /target" > and make /dev, /proc and /sys usable with "mount --rbind --make-rslave > /dev /target/dev ; mount -t proc none /target/proc ; mount -t sysfs none > /target/sys". You can then chroot into the system with "chroot /target". > > There may be other dances that will also work. > > Once you're chrooted into Debian running under some sort of Linux > kernel, first make sure the os-prober package is installed. Then you can > write Debian's GRUB into the master boot recor, by running grub-install. > > After doing grub-install, you should have GRUB in the hard drive's > master boot record and it should be configured to read the menu in > Debian's version of the /boot directory. > > In order to make the Debian GRUB menu point to all of the operating > systems on your hard drive, make sure os-prober is installed (yes, I > know, I already said it; I'm saying it again). Then run update-grub. > > Exit out of the chroot, unmount it, and reboot. You should get Debian's > GRUB menu, and you should be able to boot into Debian, at the very > least. > > If the Debian GRUB menu doesn't contain all of the operating systems > that you think it should contain, then you'll have to poke around in > the update-grub and os-prober internals and figure out what's wrong. > > Once you get everything working, you'll need to remember that you have > chosen to make Debian the controller of the boot loader. Every time > you make a kernel change to any of the *other* Linuxes on your hard > drive, you'll need to boot into Debian, and run update-grub, to pick > up the changes in the other Linuxes. > > >
