我有一个使用创建的相当标准的初始 ramdisk mkinitcpio。我使用的是 Arch GNU/Linux。
不久前，我被扔到了一个救援外壳中，并在/bin虚拟磁盘中四处查看，看看有什么可用的。由于某种原因，有很多实用程序似乎无关紧要（想想这样的事情ping- 为什么你想要在救援环境中使用它？）。
alex@alexs-arch-imac:/tmp$ mkdir initramfs
alex@alexs-arch-imac:/tmp$ cd initramfs
alex@alexs-arch-imac:/tmp/initramfs$ cp /boot/initramfs-linux.img .
alex@alexs-arch-imac:/tmp/initramfs$ cat initramfs-linux.img | unlzma - >
initramfs-linux # needed because unlzma complains that it doesn't recognize the .img extension
alex@alexs-arch-imac:/tmp/initramfs$ cpio -iV < initramfs-linux
.............................................................................................................................................................................................................................................................................................................................................................
24225 blocks
alex@alexs-arch-imac:/tmp/initramfs$ ls
bin buildconfig config dev etc hooks init init_functions initramfs-linux initramfs-linux.img lib lib64 new_root proc run sbin shutdown sys tmp usr VERSION
alex@alexs-arch-imac:/tmp/initramfs$ ls -l bin
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 bin -> usr/bin
alex@alexs-arch-imac:/tmp/initramfs$ ls bin
[ blkid chown cttyhack dirname egrep free hexdump ip iptunnel less ls mkfifo mount nslookup ping6 readlink route sha1sum stat tac touch uniq yes
[[ busybox chroot cut dmesg env getopt ifconfig ipaddr kbd_mode ln lsblk mknod mountpoint openvt poweroff reboot sed sha256sum strings tail true uptime
ash cat clear dd dmsetup expr grep init iplink kill loadfont lsmod mktemp mv pgrep printf rm seq sha512sum switch_root telnet udevadm vi
awk chgrp cp depmod du false halt insmod iproute killall loadkmap md5sum modinfo nc pidof ps rmdir setfont sleep sync test umount wc
basename chmod cryptsetup df echo findmnt head install iprule kmod losetup mkdir modprobe netstat ping pwd rmmod sh sort systemd-tmpfiles tftp uname wget
alex@alexs-arch-imac:/tmp/initramfs$
请注意，该图像具有最奇怪的公用事业。只要看看它，我就明白了，，，wget……为什么这些会在这里？pingtelnetsha1sum
这是我的输出/etc/mkinitcpio.conf。图像是使用 生成的mkinitcpio -p linux。
# vim:set ft=sh
# MODULES
# The following modules are loaded before any boot hooks are
# run. Advanced users may wish to specify all system modules
# in this array. For instance:
# MODULES="piix ide_disk reiserfs"
MODULES=""
# BINARIES
# This setting includes any additional binaries a given user may
# wish into the CPIO image. This is run last, so it may be used to
# override the actual binaries included by a given hook
# BINARIES are dependency parsed, so you may safely ignore libraries
BINARIES=""
# FILES
# This setting is similar to BINARIES above, however, files are added
# as-is and are not parsed in any way. This is useful for config files.
FILES=""
# HOOKS
# This is the most important setting in this file. The HOOKS control the
# modules and scripts added to the image, and what happens at boot time.
# Order is important, and it is recommended that you do not change the
# order in which HOOKS are added. Run 'mkinitcpio -H <hook name>' for
# help on a given hook.
# 'base' is _required_ unless you know precisely what you are doing.
# 'udev' is _required_ in order to automatically load modules
# 'filesystems' is _required_ unless you specify your fs modules in MODULES
# Examples:
## This setup specifies all modules in the MODULES setting above.
## No raid, lvm2, or encrypted root is needed.
# HOOKS="base"
#
## This setup will autodetect all modules for your system and should
## work as a sane default
# HOOKS="base udev autodetect block filesystems"
#
## This setup will generate a 'full' image which supports most systems.
## No autodetection is done.
# HOOKS="base udev block filesystems"
#
## This setup assembles a pata mdadm array with an encrypted root FS.
## Note: See 'mkinitcpio -H mdadm' for more information on raid devices.
# HOOKS="base udev block mdadm encrypt filesystems"
#
## This setup loads an lvm2 volume group on a usb device.
# HOOKS="base udev block lvm2 filesystems"
#
## NOTE: If you have /usr on a separate partition, you MUST include the
# usr, fsck and shutdown hooks.
HOOKS="base udev autodetect modconf keyboard block encrypt resume filesystems fsck shutdown"
# COMPRESSION
# Use this to compress the initramfs image. By default, gzip compression
# is used. Use 'cat' to create an uncompressed image.
#COMPRESSION="gzip"
#COMPRESSION="bzip2"
COMPRESSION="lzma"
#COMPRESSION="xz"
#COMPRESSION="lzop"
#COMPRESSION="lz4"
# COMPRESSION_OPTIONS
# Additional options for the compressor
#COMPRESSION_OPTIONS=""
答案1
初始 ramdisk 使用 Busybox 来节省空间。从本质上讲，mv类似的实用程序cp共享许多通用逻辑 - 打开文件描述符、将缓冲区读入内存等。Busybox 基本上将所有通用逻辑放入一个二进制文件中，该二进制文件根据调用的名称改变其行为方式。让我们看一下那个 ramdisk。
alex@alexs-arch-imac:/tmp/initramfs/bin$ ls -l
total 1308
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 [ -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 [[ -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 ash -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 awk -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 basename -> busybox
-rwxr-xr-x 1 alex alex 68840 Mar 24 17:06 blkid
-rwxr-xr-x 1 alex alex 287096 Mar 24 17:06 busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 cat -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 chgrp -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 chmod -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 chown -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 chroot -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 clear -> busybox
-rwxr-xr-x 1 alex alex 130272 Mar 24 17:06 cp
-rwxr-xr-x 1 alex alex 59264 Mar 24 17:06 cryptsetup
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 cttyhack -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 cut -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 dd -> busybox
lrwxrwxrwx 1 alex alex 4 Mar 24 17:06 depmod -> kmod
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 df -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 dirname -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 dmesg -> busybox
-r-xr-xr-x 1 alex alex 92227 Mar 24 17:06 dmsetup
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 du -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 echo -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 egrep -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 env -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 expr -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 false -> busybox
-rwxr-xr-x 1 alex alex 53696 Mar 24 17:06 findmnt
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 free -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 getopt -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 grep -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 halt -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 head -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 hexdump -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 ifconfig -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 init -> busybox
lrwxrwxrwx 1 alex alex 4 Mar 24 17:06 insmod -> kmod
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 install -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 ip -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 ipaddr -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 iplink -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 iproute -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 iprule -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 iptunnel -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 kbd_mode -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 kill -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 killall -> busybox
-rwxr-xr-x 1 alex alex 142424 Mar 24 17:06 kmod
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 less -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 ln -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 loadfont -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 loadkmap -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 losetup -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 ls -> busybox
-rwxr-xr-x 1 alex alex 70192 Mar 24 17:06 lsblk
lrwxrwxrwx 1 alex alex 4 Mar 24 17:06 lsmod -> kmod
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 md5sum -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 mkdir -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 mkfifo -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 mknod -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 mktemp -> busybox
lrwxrwxrwx 1 alex alex 4 Mar 24 17:06 modinfo -> kmod
lrwxrwxrwx 1 alex alex 4 Mar 24 17:06 modprobe -> kmod
-rwsr-xr-x 1 alex alex 40168 Mar 24 17:06 mount
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 mountpoint -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 mv -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 nc -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 netstat -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 nslookup -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 openvt -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 pgrep -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 pidof -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 ping -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 ping6 -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 poweroff -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 printf -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 ps -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 pwd -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 readlink -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 reboot -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 rm -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 rmdir -> busybox
lrwxrwxrwx 1 alex alex 4 Mar 24 17:06 rmmod -> kmod
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 route -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 sed -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 seq -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 setfont -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 sh -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 sha1sum -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 sha256sum -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 sha512sum -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 sleep -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 sort -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 stat -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 strings -> busybox
-rwxr-xr-x 1 alex alex 14816 Mar 24 17:06 switch_root
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 sync -> busybox
-rwxr-xr-x 1 alex alex 63992 Mar 24 17:06 systemd-tmpfiles
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 tac -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 tail -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 telnet -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 test -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 tftp -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 touch -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 true -> busybox
-rwxr-xr-x 1 alex alex 264696 Mar 24 17:06 udevadm
-rwsr-xr-x 1 alex alex 27616 Mar 24 17:06 umount
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 uname -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 uniq -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 uptime -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 vi -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 wc -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 wget -> busybox
lrwxrwxrwx 1 alex alex 7 Mar 24 17:06 yes -> busybox
alex@alexs-arch-imac:/tmp/initramfs/bin$
正如您所看到的，该图像中的几乎每个二进制文件都链接到 Busybox。
alex@alexs-arch-imac:/tmp/initramfs/bin$ ls -l | grep --invert-match busybox -
total 1308
-rwxr-xr-x 1 alex alex 68840 Mar 24 17:06 blkid
-rwxr-xr-x 1 alex alex 130272 Mar 24 17:06 cp
-rwxr-xr-x 1 alex alex 59264 Mar 24 17:06 cryptsetup
lrwxrwxrwx 1 alex alex 4 Mar 24 17:06 depmod -> kmod
-r-xr-xr-x 1 alex alex 92227 Mar 24 17:06 dmsetup
-rwxr-xr-x 1 alex alex 53696 Mar 24 17:06 findmnt
lrwxrwxrwx 1 alex alex 4 Mar 24 17:06 insmod -> kmod
-rwxr-xr-x 1 alex alex 142424 Mar 24 17:06 kmod
-rwxr-xr-x 1 alex alex 70192 Mar 24 17:06 lsblk
lrwxrwxrwx 1 alex alex 4 Mar 24 17:06 lsmod -> kmod
lrwxrwxrwx 1 alex alex 4 Mar 24 17:06 modinfo -> kmod
lrwxrwxrwx 1 alex alex 4 Mar 24 17:06 modprobe -> kmod
-rwsr-xr-x 1 alex alex 40168 Mar 24 17:06 mount
lrwxrwxrwx 1 alex alex 4 Mar 24 17:06 rmmod -> kmod
-rwxr-xr-x 1 alex alex 14816 Mar 24 17:06 switch_root
-rwxr-xr-x 1 alex alex 63992 Mar 24 17:06 systemd-tmpfiles
-rwxr-xr-x 1 alex alex 264696 Mar 24 17:06 udevadm
-rwsr-xr-x 1 alex alex 27616 Mar 24 17:06 umount
alex@alexs-arch-imac:/tmp/initramfs/bin$ ls | wc -l # total number of files
116
alex@alexs-arch-imac:/tmp/initramfs/bin$ ls -l | grep --invert-match busybox - | grep --invert-match kmod | wc -l # number of real binaries minus two (busybox and kmod)
12
镜像中有 116 个文件，但其中只有 14 个实际上是二进制文件。其余的都是 或kmod的符号链接busybox。
所以：之所以有这么多随机实用程序，是因为您不妨将它们放在那里。符号链接不占用任何空间，即使您删除它们，该功能也会保留在 Busybox 二进制文件中，占用空间。由于没有真正的理由删除所有链接，因此打包者不会这样做。
这里还有另一个需要考虑的问题：为什么不简单地从 Busybox 二进制文件中删除网络功能呢？正如@Gilles 提到的，有是在合法（如果不常见）的情况下，您需要在 initcpio 中建立网络。因此，打包者有两个选择：一是按照他们现在的做法并默认包含所有内容，二是将网络功能拆分为自己的mkinitcpio钩子。前者非常简单（你基本上什么都不做）并且成本非常非常小，而第二个则非常复杂（再次感谢@Gilles 指出了这一点）并且收益确实不足以重要。因此，打包者采取了聪明的方法，不对网络进行任何操作。
答案2
虽然这不是一个非常常见的设置，但某些安装只有一些非常小的本地存储，或者实际上根本没有，并通过以下方式检索包括内核在内的启动代码TFTP。然后内核通过网络挂载其根文件系统，例如：网络文件系统。对于此类系统，可能需要基本的网络工具来定位和挂载根文件系统。
初始 ramdisk 包含与挂载根文件系统所需功能相对应的内核模块，忙碌盒实用程序套件，以及更多实用程序。 initramfs 是根据您系统的需要组装的mkinitcpio（这取决于发行版，例如基于 Debian 的发行版使用类似的程序姆基尼特拉姆夫斯）。每个驱动程序都存储在单独的文件中，因此可以将 initramfs 中的内核模块缩减为仅系统所需的模块（但代价是使系统在不同硬件上无法启动）。 BusyBox 包含在一个二进制文件中，其中包含编译时选择的所有功能，因此缩减它需要重新编译它。除非您正在构建具有静态设置和有限空间的嵌入式设备，否则不值得这么复杂。
答案3
简短的回答，这是一个保留busybox。您需要从启动恢复环境进行网络访问的可能性很低。赔率是偶数降低你甚至会有一个可用的网络驱动程序——发行版内核没有内置它们，并且它们不会出现在 initrd 中，除非你把它们放在那里。