Sorry to disappoint you, but it Just Doesn't Work.
On 18/11/18 at 10:18, aitor_czr wrote: > > Hendrik, you can uncompress the content of the initrd.img by the > following way: > > 1) Rename it to initrd.gz and use gunzip: > > # mv initrd.img initrd.gz > # gunzip initrd.gz 1) You assume the initramfs was compressed with gzip. This is the default, but it could be changed in /etc/initramfs-tools/initramfs.conf setting, for instance, COMPRESS=xz. 2) initramfs is actually formed of two cpio archives: a small, uncompressed one that is followed by a compressed one. [alessandro@wkstn05 ~]$ file /boot/initrd.img-4.18.0-0.bpo.1-amd64 /boot/initrd.img-4.18.0-0.bpo.1-amd64: ASCII cpio archive (SVR4 with no CRC) [alessandro@wkstn05 ~]$ mkdir /tmp/initramfs [alessandro@wkstn05 ~]$ cd /tmp/initramfs [alessandro@wkstn05 initramfs]$ cpio -vi < /boot/initrd.img-4.18.0-0.bpo.1-amd64 kernel kernel/x86 kernel/x86/microcode kernel/x86/microcode/.enuineIntel.align.0123456789abc cpio: kernel/x86/microcode/GenuineIntel.bin not created: newer or same age version exists kernel/x86/microcode/GenuineIntel.bin 28 blocks [alessandro@wkstn05 initramfs]$ 28 blocks are 14 KiB, a very small part of the 5,4M initrd.img-4.18.0-0.bpo.1-amd64 file. > 2) After that, you can extract the files using cpio: > > # mkdir tmp > # cd tmp > # cpio -id < ../initrd The rest of the initramfs are in a compressed archive that starts after the 28th block (in my case). To get that archive you have to extract it from the 29th block on: [alessandro@wkstn05 initramfs]$ dd if=/boot/initrd.img-4.18.0-0.bpo.1-amd64 skip=28 of=/tmp/initrd.img-4.18.0-0.bpo.1-amd64.cpio.xz 11012+1 record dentro 11012+1 record fuori 5638392 bytes (5,6 MB, 5,4 MiB) copied, 0,0228946 s, 246 MB/s [alessandro@wkstn05 initramfs]$ file /tmp/initrd.img-4.18.0-0.bpo.1-amd64.cpio.xz /tmp/initrd.img-4.18.0-0.bpo.1-amd64.cpio.xz: XZ compressed data [alessandro@wkstn05 initramfs]$ > > 3) Look at the content (in this case is the initrd.img of > debian-installer): > > # ls > bin conf etc init lib sbin scripts usr Right now I only have: [alessandro@wkstn05 initramfs]$ ls -R .: kernel ./kernel: x86 ./kernel/x86: microcode ./kernel/x86/microcode: GenuineIntel.bin [alessandro@wkstn05 initramfs]$ To extract the rest of the initramfs you decompress the second part of the file and feed it to cpio: [alessandro@wkstn05 initramfs]$ xz -dc /tmp/initrd.img-4.18.0-0.bpo.1-amd64.cpio.xz | cpio -iv [alessandro@wkstn05 initramfs]$ . lib64 lib64/ld-linux-x86-64.so.2 init scripts scripts/init-top scripts/init-top/ORDER scripts/init-top/udev scripts/init-top/blacklist scripts/init-top/keymap scripts/init-top/all_generic_ide scripts/functions scripts/local scripts/nfs scripts/init-bottom scripts/init-bottom/ORDER scripts/init-bottom/udev scripts/local-premount scripts/local-premount/ORDER [...] cpio: bin/busybox linked to bin/cat cpio: bin/busybox linked to bin/cal cpio: bin/busybox linked to bin/bzip2 cpio: bin/busybox linked to bin/bzcat cpio: bin/busybox linked to bin/bunzip2 cpio: bin/busybox linked to bin/basename cpio: bin/busybox linked to bin/awk cpio: bin/busybox linked to bin/ash cpio: bin/busybox linked to bin/ar cpio: bin/busybox linked to bin/[[ cpio: bin/busybox linked to bin/[ bin/busybox bin/udevadm bin/loadkeys bin/cryptroot-unlock bin/kmod 40012 blocks [alessandro@wkstn05 initramfs]$ 40.012 blocks are 20MiB. This works in my Devuan Ascii, but didn't work on a colleague's Ubuntu 18.something. > > 4) Now you can modify the content of the initrd, and generate the new > initrd in the parent directory: > > # find . | cpio --create --format='newc' > ../newinitrd > > Compress it with gzip and rename it to initrd.img > > And ready :) > > Aitor. And I end up with an unbootable system. -- Alessandro Selli <alessandrose...@linux.com> VOIP SIP: dhatarat...@ekiga.net Chiave firma e cifratura PGP/GPG signing and encoding key: BA651E4050DDFC31E17384BABCE7BD1A1B0DF2AE
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