Grub is very smart but not as smart as you want believe.
It has 38 commands (see below)
You can easily achieve you goal *without reinstalling, swapping out disks
or entering rescue mode to fix things.
"DD" is nearly always available!
However no matter how badly a system gets hosed, there is nearly always
/sbin that stays intact.
Also /etc/fstab & a few other files of paramount importance are often intact
to allow a minimal system to be run.
..... then you have "dd" to copy partions here & there.
The 3 Run levels of : emergency , 1 , S often are available when you
can't boot the system to higher run levels.
If ALL the above fails .....
appending " init=/bin/bash "
to the kernel grub line will often work. (albeit in read only) you can fix
that by "/sbin/mount -o remount,rw /"
note the full path is probably required.
Then DD will be available " /sbin/dd"
If you have an exact image of a partiton elswhere just clobber the partion
you have booted to.
Of course you must be certain of what partition you are on. ( having an
erronous entry in fstab may fool you at this point... in which case
"/sbin/df" will tell you lies.
The gotcha points are that /boot/grub/grub.conf entries must coincide
with /etc/fstab.
Three variations work with these files
1 "device" names as a naming convention
2 "label" names as a naming convention
3 "UUID" strings as a naming convention
... again .... grub.conf & fstab must coincide
Hope this helps
Roger
Grub commands .......... no dd or cp etc
1 blocklist FILE
2 boot
3 cat FILE
4 chainloader [--force] FILE
5 clear
6 color NORMAL [HIGHLIGHT]
7 configfile FILE
8 device DRIVE DEVICE
9 displayapm
10 displaymem
11 find FILENAME
12 geometry DRIVE [CYLINDER HEAD SECTOR [
13 halt [--no-apm]
14 help [--all] [PATTERN ...]
15 hide PARTITION
16 initrd FILE [ARG ...]
17 kernel [--no-mem-option] [--type=TYPE]
18 makeactive
19 map TO_DRIVE FROM_DRIVE
20 md5crypt
21 module FILE [ARG ...]
22 modulenounzip FILE [ARG ...]
23 pager [FLAG]
24 partnew PART TYPE START LEN
25 parttype PART TYPE
26 quit
27 reboot
28 root [DEVICE [HDBIAS]]
29 rootnoverify [DEVICE [HDBIAS]]
30 serial [--unit=UNIT] [--port=PORT] [--
31 setkey [TO_KEY FROM_KEY]
32 setup [--prefix=DIR] [--stage2=STAGE2_
33 terminal [--dumb] [--no-echo] [--no-ed
34 terminfo [--name=NAME --cursor-address
35 testvbe MODE
36 unhide PARTITION
37 uppermem KBYTES
38 vbeprobe [MODE]
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