提取连接的 cpio 档案

Question

Linux 上的 initramfs 档案可以由一系列串联的、gzipped cpio 文件组成。

给定这样的档案，如何提取所有嵌入的档案，而不是仅提取第一个？

下面是一个模式的例子，虽然它看起来有可能工作，但只提取第一个存档：

while gunzip -c | cpio -i; do :; done <input.cgz

---

我还尝试了dracut的skipcpio 帮助程序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（不在输入中的正确点）：

# 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

Answer 1

gunzip 只需要运行一次（消耗所有输入），而 cpio 应该为每个嵌入的存档运行一次，如下所示：

gunzip -c <input.cgz | while cpio -i; do :; done

Answer 2

/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如果是dracut包的一部分。但是你可以下载代码（skipcpio.c）并在 FreeBSD 下编译它。

在提取 dracut 创建的 initrd 映像时，至少在 RedHat 驱动的发行版（如 Fedora）下，您需要使用它。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。

Answer 3

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*