Après installation d'Ubuntu, pas de Grub boot

Disque /dev/sda: 250.0 Go, 250059350016 octets
255 heads, 63 sectors/track, 30401 cylinders
Units = cylindres of 16065 * 512 = 8225280 bytes
Identifiant disque: 0x2d362d35

Périphérique Amorce    Début         Fin      Blocs    Id  Système
/dev/sda1   *           1       27704   222532348+   7  HPFS/NTFS
/dev/sda2           27705       30401    21663652+   5  Extended
/dev/sda5           27705       30283    20715786   83  Linux
/dev/sda6           30284       30401      947803+  82  Linux swap / Solaris

Disque /dev/sdb: 164.6 Go, 164696555520 octets
255 heads, 63 sectors/track, 20023 cylinders
Units = cylindres of 16065 * 512 = 8225280 bytes
Identifiant disque: 0x352e9dfd

Périphérique Amorce    Début         Fin      Blocs    Id  Système
/dev/sdb1   *           2       20023   160826715    f  W95 Etendu (LBA)
/dev/sdb5               2       20023   160826683+   7  HPFS/NTFS

ubuntu@ubuntu:~$ sudo mkdir /mnt/sda5
mkdir: ne peut créer le répertoire `/mnt/sda5': Le fichier existe
ubuntu@ubuntu:~$ mount /dev/sda5/mnt/sda5
mount: ne peut repérer /dev/sda5/mnt/sda5 dans /etc/fstab ou /etc/mtab
ubuntu@ubuntu:~$ mount /dev/sda5 /mnt/sda5
mount: seul l'usager ROOT peut faire cela

ubuntu@ubuntu:~$ sudo mkdir /mnt/sda5ubuntu
mkdir: ne peut créer le répertoire `/mnt/sda5ubuntu': Le fichier existe
ubuntu@ubuntu:~$ sudo mount /dev/sda5 /mnt/sda5ubuntu
mount: /dev/sda5 est déjà monté ou /mnt/sda5ubuntu est occupé
mount: selon mtab /dev/sda5 est déjà monté sur /mnt/sda5ubuntu
ubuntu@ubuntu:~$ cat /mnt/sda5/boot/grub/menu.lst
cat: /mnt/sda5/boot/grub/menu.lst: Aucun fichier ou dossier de ce type

ubuntu@ubuntu:~$ cat /mnt/sda5ubuntu/boot/grub/menu.lst
# menu.lst - See: grub(8), info grub, update-grub(8)
#            grub-install(8), grub-floppy(8),
#            grub-md5-crypt, /usr/share/doc/grub
#            and /usr/share/doc/grub-doc/.

## default num
# Set the default entry to the entry number NUM. Numbering starts from 0, and
# the entry number 0 is the default if the command is not used.
#
# You can specify 'saved' instead of a number. In this case, the default entry
# is the entry saved with the command 'savedefault'.
# WARNING: If you are using dmraid do not use 'savedefault' or your
# array will desync and will not let you boot your system.
default		0

## timeout sec
# Set a timeout, in SEC seconds, before automatically booting the default entry
# (normally the first entry defined).
timeout		10

## hiddenmenu
# Hides the menu by default (press ESC to see the menu)
#hiddenmenu

# Pretty colours
#color cyan/blue white/blue

## password ['--md5'] passwd
# If used in the first section of a menu file, disable all interactive editing
# control (menu entry editor and command-line)  and entries protected by the
# command 'lock'
# e.g. password topsecret
#      password --md5 $1$gLhU0/$aW78kHK1QfV3P2b2znUoe/
# password topsecret

#
# examples
#
# title		Windows 95/98/NT/2000
# root		(hd0,0)
# makeactive
# chainloader	+1
#
# title		Linux
# root		(hd0,1)
# kernel	/vmlinuz root=/dev/hda2 ro
#

#
# Put static boot stanzas before and/or after AUTOMAGIC KERNEL LIST

### BEGIN AUTOMAGIC KERNELS LIST
## lines between the AUTOMAGIC KERNELS LIST markers will be modified
## by the debian update-grub script except for the default options below

## DO NOT UNCOMMENT THEM, Just edit them to your needs

## ## Start Default Options ##
## default kernel options
## default kernel options for automagic boot options
## If you want special options for specific kernels use kopt_x_y_z
## where x.y.z is kernel version. Minor versions can be omitted.
## e.g. kopt=root=/dev/hda1 ro
##      kopt_2_6_8=root=/dev/hdc1 ro
##      kopt_2_6_8_2_686=root=/dev/hdc2 ro
# kopt=root=UUID=46fd1633-c10f-4132-8786-98836b5c99c1 ro

## Setup crashdump menu entries
## e.g. crashdump=1
# crashdump=0

## default grub root device
## e.g. groot=(hd0,0)
# groot=(hd1,4)

## should update-grub create alternative automagic boot options
## e.g. alternative=true
##      alternative=false
# alternative=true

## should update-grub lock alternative automagic boot options
## e.g. lockalternative=true
##      lockalternative=false
# lockalternative=false

## additional options to use with the default boot option, but not with the
## alternatives
## e.g. defoptions=vga=791 resume=/dev/hda5
# defoptions=quiet splash

## should update-grub lock old automagic boot options
## e.g. lockold=false
##      lockold=true
# lockold=false

## Xen hypervisor options to use with the default Xen boot option
# xenhopt=

## Xen Linux kernel options to use with the default Xen boot option
# xenkopt=console=tty0

## altoption boot targets option
## multiple altoptions lines are allowed
## e.g. altoptions=(extra menu suffix) extra boot options
##      altoptions=(recovery) single
# altoptions=(recovery mode) single

## controls how many kernels should be put into the menu.lst
## only counts the first occurence of a kernel, not the
## alternative kernel options
## e.g. howmany=all
##      howmany=7
# howmany=all

## should update-grub create memtest86 boot option
## e.g. memtest86=true
##      memtest86=false
# memtest86=true

## should update-grub adjust the value of the default booted system
## can be true or false
# updatedefaultentry=false

## should update-grub add savedefault to the default options
## can be true or false
# savedefault=false

## ## End Default Options ##

title		Ubuntu 8.04.1, kernel 2.6.24-19-generic
root		(hd1,4)
kernel		/boot/vmlinuz-2.6.24-19-generic root=UUID=46fd1633-c10f-4132-8786-98836b5c99c1 ro quiet splash
initrd		/boot/initrd.img-2.6.24-19-generic
quiet

title		Ubuntu 8.04.1, kernel 2.6.24-19-generic (recovery mode)
root		(hd1,4)
kernel		/boot/vmlinuz-2.6.24-19-generic root=UUID=46fd1633-c10f-4132-8786-98836b5c99c1 ro single
initrd		/boot/initrd.img-2.6.24-19-generic

title		Ubuntu 8.04.1, memtest86+
root		(hd1,4)
kernel		/boot/memtest86+.bin
quiet

### END DEBIAN AUTOMAGIC KERNELS LIST

# This is a divider, added to separate the menu items below from the Debian
# ones.
title		Other operating systems:
root


# This entry automatically added by the Debian installer for a non-linux OS
# on /dev/sdb1
title		Microsoft Windows XP Professionnel
root		(hd1,0)
savedefault
makeactive
map		(hd0) (hd1)
map		(hd1) (hd0)
chainloader	+1

ubuntu@ubuntu:~$ ls -l /mnt/sda5ubuntu
total 88
drwxr-xr-x   2 root root  4096 2009-01-10 20:29 bin
drwxr-xr-x   3 root root  4096 2009-01-10 20:28 boot
lrwxrwxrwx   1 root root    11 2009-01-10 19:18 cdrom -> media/cdrom
drwxr-xr-x   4 root root  4096 2008-07-02 10:26 dev
drwxr-xr-x 120 root root  4096 2009-01-10 20:29 etc
drwxr-xr-x   3 root root  4096 2009-01-10 19:27 home
drwxr-xr-x   2 root root  4096 2008-07-02 10:16 initrd
lrwxrwxrwx   1 root root    33 2009-01-10 20:28 initrd.img -> boot/initrd.img-2.6.24-19-generic
drwxr-xr-x  16 root root  4096 2009-01-10 20:29 lib
drwx------   2 root root 16384 2009-01-10 19:18 lost+found
drwxr-xr-x   4 root root  4096 2008-07-02 10:16 media
drwxr-xr-x   2 root root  4096 2008-04-15 05:53 mnt
drwxr-xr-x   2 root root  4096 2008-07-02 10:16 opt
drwxr-xr-x   2 root root  4096 2008-04-15 05:53 proc
drwxr-xr-x   3 root root  4096 2009-01-10 20:28 root
drwxr-xr-x   2 root root  4096 2009-01-10 20:29 sbin
drwxr-xr-x   2 root root  4096 2008-07-02 10:16 srv
drwxr-xr-x   2 root root  4096 2008-04-19 05:05 sys
drwxrwxrwt   2 root root  4096 2009-01-10 20:28 tmp
drwxr-xr-x  11 root root  4096 2008-07-02 10:18 usr
drwxr-xr-x  15 root root  4096 2008-07-02 10:34 var
lrwxrwxrwx   1 root root    30 2009-01-10 20:28 vmlinuz -> boot/vmlinuz-2.6.24-19-generic

ubuntu@ubuntu:~$ sudo chroot /mnt/sda5ubuntu
root@ubuntu:/# sudo grub-install /dev/sda
sudo: unable to resolve host ubuntu
/dev/sda: Not found or not a block device.

ubuntu@ubuntu:~$ cat /mnt/sda5ubuntu/etc/hosts
127.0.0.1	localhost
127.0.1.1	xxx-desktop

# The following lines are desirable for IPv6 capable hosts
::1     ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
ff02::3 ip6-allhosts

ubuntu@ubuntu:~$ sudo gedit /etc/hosts
ubuntu@ubuntu:~$ sudo chroot /mnt/sda5ubuntu
chroot: ne peut changer le répertoire racine vers /mnt/sda5ubuntu: Aucun fichier ou dossier de ce type
ubuntu@ubuntu:~$ sudo grub-install /dev/sda
Could not find device for /boot: Not found or not a block device.