I switched from an Ubuntu to the CentOS yesterday. But it seems I have messed my installation somehow, since OS will only start correctly if the USB with the installation is plugged in.
I've downloaded a live DVD CentOS 6 from the public repository, and using it with unetbotin created USB installation. That USB was used to install CentOS.
During the installation, (only 1 ) hard disk was mounted under /sdb and USB installation was mounted under /sda. I "think" I selected to boot from the /sdb.
sudo fdisk -l
Disk /dev/sdb: 1000.2 GB, 1000204886016 bytes 249 heads, 62 sectors/track, 126540 cylinders Units = cylinders of 15438 * 512 = 7904256 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x671e6467 Device Boot Start End Blocks Id System /dev/sdb1 1 26533 204800000 7 HPFS/NTFS /dev/sdb2 26533 28557 15624193 5 Extended /dev/sdb4 * 28569 126540 756238336 83 Linux /dev/sdb5 26533 28557 15624192 82 Linux swap / Solaris Disk /dev/sda: 8086 MB, 8086618112 bytes 37 heads, 13 sectors/track, 32836 cylinders Units = cylinders of 481 * 512 = 246272 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x90909090 Device Boot Start End Blocks Id System /dev/sda1 * 5 32837 7896064 b W95 FAT32
if the USB stick is not connected to the machine, the boot screen will show up ( with both new installation of the CentOS and old Windows installation). But after I select either of them, after few seconds the machine will reboot. If the USB is connected, the same or similar boot screen shows up I OS starts normally.
I've tried to reinstall GRUB using
grub-install using /dev/sdb and /dev/sda options, but I wasn't able to make progress.
Also, I don't understand purpose and content of the
(hd0) /dev/sda (hd1) /dev/sdb
I tried removing /dev/sda from the device.map, which also doesn't help.
grub.conf from /boot/grub/
# grub.conf generated by anaconda # # Note that you do not have to rerun grub after making changes to this file # NOTICE: You do not have a /boot partition. This means that # all kernel and initrd paths are relative to /, eg. # root (hd1,3) # kernel /boot/vmlinuz-version ro root=/dev/sdb4 # initrd /boot/initrd-[generic-]version.img #boot=/dev/sda default=0 timeout=5 splashimage=(hd1,3)/boot/grub/splash.xpm.gz hiddenmenu title CentOS (2.6.32-220.2.1.el6.x86_64) root (hd1,3) kernel /boot/vmlinuz-2.6.32-220.2.1.el6.x86_64 ro root=UUID=6cbcc55f-3342-4e85-a4c2-8355e73962f2 rd_NO_LUKS LANG=en_US.UTF-8 KEYBOARDTYPE=pc KEYTABLE=croat rd_NO_MD quiet SYSFONT=latarcyrheb-sun16 rhgb crashkernel=128M rd_NO_LVM rd_NO_DM initrd /boot/initramfs-2.6.32-220.2.1.el6.x86_64.img title CentOS (2.6.32-220.el6.x86_64) root (hd1,3) kernel /boot/vmlinuz-2.6.32-220.el6.x86_64 ro root=UUID=6cbcc55f-3342-4e85-a4c2-8355e73962f2 rd_NO_LUKS LANG=en_US.UTF-8 KEYBOARDTYPE=pc KEYTABLE=croat rd_NO_MD quiet SYSFONT=latarcyrheb-sun16 rhgb crashkernel=128M rd_NO_LVM rd_NO_DM initrd /boot/initramfs-2.6.32-220.el6.x86_64.img title Other rootnoverify (hd1,0) chainloader +1
EDIT: more information
by deleting "quiet" and "rhgb" from the grub.conf I was able to see the error message : No devices found .