d'après : http://kernel-handbook.alioth.debian.org/ch-initrd.html

1- Regenerating the initrd

The ramdisk setting mentioned above will only take effect when implemented before the kernel image installation. If the changes are desired after the corresponding linux-image has been installed, the initrd needs to be regenerated. This is achieved by the command

# dpkg-reconfigure linux-image-2.6.14-1-686

where linux-image-2.6.14-1-686 is the name of the kernel package for which the initrd regeneration is requested.

2- Examining the initrd contents

Occasionally it is useful to examine the contents of initrd to diagnose a problem or for educational purposes. The old-style initrds created by /usr/sbin/mkinitrd from initrd-tools package are either cramfs or ext2 filesystem, so they need to be mounted to access their contents. This may be achieved with the commands like

# mkdir -p /mnt/initrd
# mount -t cramfs /boot/initrd.img-2.6.12-1-686 /mnt/initrd -o loop

New style initrds, created by yaird or initramfs-tools are compressed cpio archives, which may be extracted using the command sequence similar to this one:

$ mkdir -p /tmp/initrd
$ cd /tmp/initrd
$ cp /boot/initrd.img-2.6.14-1-686 ./initrd.gz
$ gzip -d initrd.gz
$ cpio -i < initrd

After that the contents of the initrd are going to be unpacked into the /tmp/initrd directory.

3- Ajouter un module manquant a initrd :

Editer le fichier /etc/yaird/Default.cfg, rajouter dans la bonne section le module manquant, puis relancer dpkg-reconfigure linux-image-2.6.15-1-k7
Par exemple, sur ma carte mère, il a fallu mettre :
MODULE via82cxxx
MODULE ide-generic
MODULE ide-disk
sinon pas d'UDMA sur le lecteur de CD-ROM