Linux 上的 initramfs 存档可以由一系列串联的、gzip 压缩的 cpio 文件组成。
给定这样一个档案，如何提取全部嵌入式档案，而不是第一个？
以下是一个模式示例，虽然它似乎有工作的潜力，但仅提取第一个存档：
while gunzip -c | cpio -i; do :; done <input.cgz
我也尝试过来自 dracut 的skipcpio 助手将文件指针移过第一个 cpio 图像，但以下结果会导致发送到 cpio 的损坏流（不在输入中的正确位置）：
# this isn't ideal -- presumably would need to rerun with an extra skipcpio in the pipeline
# ...until all files in the archive have been reached.
gunzip -c <input.cgz | skipcpio /dev/stdin | cpio -i
答案1
/usr/lib/dracut/skipcpio $your-initrd-img | zcat | cpio -id --no-absolute-file-names
要不然
/usr/lib/dracut/skipcpio $your-img | gunzip -c | cpio -id
（在 FreeBSD 中，cpio 没有 --no-absolute-file-names 选项）
这个小程序skipcpio是 dracut 包的一部分。但您甚至可以在 FreeBSD 下下载代码 (skipcpio.c) 并编译它。
提取 dracut 创建的 initrd 映像时需要这个，至少在 RedHat 支持的发行版（例如 Fedora）下是这样。它将一个名为“early_cpio”的文件放入映像中，因此以以前已知的正常方式提取 initramfs 将不起作用。
答案2
gunzip 只需要运行一次（消耗所有输入），而 cpio 应为每个嵌入式存档运行一次，如下所示：
gunzip -c <input.cgz | while cpio -i; do :; done
答案3
您可以手动执行此操作dd skip=。在我的 Ubuntu 20.04 上，我可以使用以下命令查看第一部分（偏移 0 块）
# dd if=/boot/initrd.img-5.4.0-45-generic skip=0 | file -
/dev/stdin: ASCII cpio archive (SVR4 with no CRC)
然后查看内容
# dd if=/boot/initrd.img-5.4.0-45-generic skip=0 | cpio -it
.
kernel
kernel/x86
kernel/x86/microcode
kernel/x86/microcode/AuthenticAMD.bin
62 blocks
第二部分更远 62 个街区
# dd if=/boot/initrd.img-5.4.0-45-generic skip=62 | file -
/dev/stdin: ASCII cpio archive (SVR4 with no CRC)
再次只是一个简单的 cpio 存档，但这次更大
# dd if=/boot/initrd.img-5.4.0-45-generic skip=62 | cpio -it
kernel
kernel/x86
kernel/x86/microcode
kernel/x86/microcode/.enuineIntel.align.0123456789abc
kernel/x86/microcode/GenuineIntel.bin
5868 blocks
现在将5868 + 62块跳过到 initramfs 中
# dd if=/boot/initrd.img-5.4.0-45-generic skip=5930 | file -
/dev/stdin: LZ4 compressed data (v0.1-v0.9)
这次是压缩流，所以
# dd if=/boot/initrd.img-5.4.0-45-generic skip=5930 | lz4cat | file -
/dev/stdin: ASCII cpio archive (SVR4 with no CRC)
我们再次找到了下一个（也是最终的）cpio 存档
# dd if=/boot/initrd.img-5.4.0-45-generic skip=5930 | lz4cat | cpio -it
... lots of output
usr/share/plymouth/themes/spinner/watermark.png
usr/share/plymouth/ubuntu-logo.png
var
var/cache
var/cache/fontconfig
var/cache/fontconfig/383ee5b3-5437-4bdc-87f6-cf314658a7c0-le64.cache-7
var/cache/fontconfig/575cffd4-ae01-4067-914f-7545fe566c1b-le64.cache-7
var/cache/fontconfig/CACHEDIR.TAG
var/cache/fontconfig/c467a813-186f-476e-880a-3770402989a9-le64.cache-7
var/cache/fontconfig/d912fc4e-f5b6-456d-a86d-e4c3ccbbefe9-le64.cache-7
var/lib
var/lib/dhcp
450460 blocks
尽管如此，这仅在第一个流未压缩的情况下才有效。否则，cpio 不会将大小报告到 initramfs 中，而是报告未压缩部分的大小。
答案4
安装了软件包amd64-microcode/intel-microcode软件包的 Debian 似乎使用了某种混乱的未压缩cpio存档，其中包含 CPU 微代码，后跟包含实际 initrd 内容的gzip压缩存档。cpio我能够提取它的唯一方法是使用binwalk( apt install binwalk)，它都可以正确列出结构：
binwalk /path/to/initrd
示例输出：
host ~ # binwalk /boot/initrd.img-5.10.0-15-amd64
DECIMAL HEXADECIMAL DESCRIPTION
--------------------------------------------------------------------------------
0 0x0 ASCII cpio archive (SVR4 with no CRC), file name: "kernel", file name length: "0x00000007", file size: "0x00000000"
120 0x78 ASCII cpio archive (SVR4 with no CRC), file name: "kernel/x86", file name length: "0x0000000B", file size: "0x00000000"
244 0xF4 ASCII cpio archive (SVR4 with no CRC), file name: "kernel/x86/microcode", file name length: "0x00000015", file size: "0x00000000"
376 0x178 ASCII cpio archive (SVR4 with no CRC), file name: "kernel/x86/microcode/.enuineIntel.align.0123456789abc", file name length: "0x00000036", file size: "0x00000000"
540 0x21C ASCII cpio archive (SVR4 with no CRC), file name: "kernel/x86/microcode/GenuineIntel.bin", file name length: "0x00000026", file size: "0x00455C00"
4546224 0x455EB0 ASCII cpio archive (SVR4 with no CRC), file name: "TRAILER!!!", file name length: "0x0000000B", file size: "0x00000000"
4546560 0x456000 gzip compressed data, has original file name: "mkinitramfs-MAIN_dTZaRk", from Unix, last modified: 2022-06-14 14:02:57
37332712 0x239A6E8 MySQL ISAM compressed data file Version 9
并提取单独的部分：
binwalk -e /path/to/initrd
示例输出：
host ~ # binwalk -e /boot/initrd.img-5.10.0-15-amd64
DECIMAL HEXADECIMAL DESCRIPTION
--------------------------------------------------------------------------------
0 0x0 ASCII cpio archive (SVR4 with no CRC), file name: "kernel", file name length: "0x00000007", file size: "0x00000000"
120 0x78 ASCII cpio archive (SVR4 with no CRC), file name: "kernel/x86", file name length: "0x0000000B", file size: "0x00000000"
244 0xF4 ASCII cpio archive (SVR4 with no CRC), file name: "kernel/x86/microcode", file name length: "0x00000015", file size: "0x00000000"
376 0x178 ASCII cpio archive (SVR4 with no CRC), file name: "kernel/x86/microcode/.enuineIntel.align.0123456789abc", file name length: "0x00000036", file size: "0x00000000"
540 0x21C ASCII cpio archive (SVR4 with no CRC), file name: "kernel/x86/microcode/GenuineIntel.bin", file name length: "0x00000026", file size: "0x00455C00"
4546224 0x455EB0 ASCII cpio archive (SVR4 with no CRC), file name: "TRAILER!!!", file name length: "0x0000000B", file size: "0x00000000"
4546560 0x456000 gzip compressed data, has original file name: "mkinitramfs-MAIN_dTZaRk", from Unix, last modified: 2022-06-14 14:02:57
37332712 0x239A6E8 MySQL ISAM compressed data file Version 9
这将为您提供单独文件中的单独部分，现在您终于可以提取正确的cpio存档：
host ~ # ls -l _initrd.img-5.10.0-15-amd64.extracted
insgesamt 187M
drwxr-xr-x 3 root root 4,0K 14. Jun 17:53 cpio-root/
-rw-r--r-- 1 root root 114M 14. Jun 17:53 mkinitramfs-MAIN_dTZaRk
-rw-r--r-- 1 root root 39M 14. Jun 17:53 0.cpio
-rw-r--r-- 1 root root 35M 14. Jun 17:53 mkinitramfs-MAIN_dTZaRk.gz
host ~/_initrd.img-5.10.0-15-amd64.extracted # mkdir extracted
host ~/_initrd.img-5.10.0-15-amd64.extracted # cd extracted
host ~/_initrd.img-5.10.0-15-amd64.extracted/extracted # cat ../mkinitramfs-MAIN_dTZaRk | cpio -idmv --no-absolute-filenames
[...]
host ~/_initrd.img-5.10.0-15-amd64.extracted/extracted # ll
insgesamt 28K
lrwxrwxrwx 1 root root 7 14. Jun 17:55 bin -> usr/bin/
drwxr-xr-x 3 root root 4,0K 14. Jun 17:55 conf/
drwxr-xr-x 7 root root 4,0K 14. Jun 17:55 etc/
lrwxrwxrwx 1 root root 7 14. Jun 17:55 lib -> usr/lib/
lrwxrwxrwx 1 root root 9 14. Jun 17:55 lib32 -> usr/lib32/
lrwxrwxrwx 1 root root 9 14. Jun 17:55 lib64 -> usr/lib64/
lrwxrwxrwx 1 root root 10 14. Jun 17:55 libx32 -> usr/libx32/
drwxr-xr-x 2 root root 4,0K 14. Jun 16:02 run/
lrwxrwxrwx 1 root root 8 14. Jun 17:55 sbin -> usr/sbin/
drwxr-xr-x 8 root root 4,0K 14. Jun 17:55 scripts/
drwxr-xr-x 8 root root 4,0K 14. Jun 17:55 usr/
-rwxr-xr-x 1 root root 6,2K 14. Jan 2021 init*