参考链接
initrd.img的作用
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用于在启动时临时挂载根文件系统
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加载关键驱动
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切换到真正的根文件系统
initrd.img所处的位置
bash
ls -lh /boot/initrd.img-*
可以看到有多个initrd.img文件
查看当前内核版本确定使用的initrd.img文件
bash
uname -r
解压initrd.img
1. 查看压缩方式
bash
file /boot/initrd.img-$(uname -r)-
gzip compressed data→ 压缩的CPIO归档 -
ASCII cpio archive→ 未压缩的CPIO归档。 -
Linux rev 1.0 ext2 filesystem data→ 旧式RAM磁盘映像
压缩方式为未压缩的cpio归档
2. 解压
bash
cd /boot
sudo mkdir temp_initrd
cd temp_initrd
sudo cpio -idmv < /initrd.img-$(uname -r)
此时你会发现这并不是实际的initrd.img文件:(
因为Debian系统使用了另一套方式（initramfs-tools）来管理initrd.img文件
bash
sudo unmkinitramfs /boot/initrd.img-$(uname -r) /boot/temp_initrd使用这条命令才能正确地解压
之后打开文件夹，目录如下
bash
/tmp/initrd/
├── main/ # 主 initramfs 内容（包含 init 脚本和核心文件）
│ ├── bin
│ ├── dev
│ ├── etc
│ ├── init # 初始化脚本
│ ├── lib
│ └── ...
└── early/ # 早期加载的微码文件（如 CPU 微码更新）
└── kernel/x86/microcode/AuthenticAMD.bin查看initrd.img内部的执行命令
initrd.img内部执行操作由init脚本决定
使用cat命令打开init脚本后可以看到内部操作
bash
cat /boot/temp_initrd/main/init
bash
#!/bin/sh
# Default PATH differs between shells, and is not automatically exported
# by klibc dash. Make it consistent.
export PATH=/sbin:/usr/sbin:/bin:/usr/bin
[ -d /dev ] || mkdir -m 0755 /dev
[ -d /root ] || mkdir -m 0700 /root
[ -d /sys ] || mkdir /sys
[ -d /proc ] || mkdir /proc
[ -d /tmp ] || mkdir /tmp
mkdir -p /var/lock
mount -t sysfs -o nodev,noexec,nosuid sysfs /sys
mount -t proc -o nodev,noexec,nosuid proc /proc
# shellcheck disable=SC2013
for x in $(cat /proc/cmdline); do
case $x in
initramfs.clear)
clear
;;
quiet)
quiet=y
;;
esac
done
if [ "$quiet" != "y" ]; then
quiet=n
echo "Loading, please wait..."
fi
export quiet
# Note that this only becomes /dev on the real filesystem if udev's scripts
# are used; which they will be, but it's worth pointing out
mount -t devtmpfs -o nosuid,mode=0755 udev /dev
# Prepare the /dev directory
[ ! -h /dev/fd ] && ln -s /proc/self/fd /dev/fd
[ ! -h /dev/stdin ] && ln -s /proc/self/fd/0 /dev/stdin
[ ! -h /dev/stdout ] && ln -s /proc/self/fd/1 /dev/stdout
[ ! -h /dev/stderr ] && ln -s /proc/self/fd/2 /dev/stderr
mkdir /dev/pts
mount -t devpts -o noexec,nosuid,gid=5,mode=0620 devpts /dev/pts || true
# Export the dpkg architecture
export DPKG_ARCH=
. /conf/arch.conf
# Set modprobe env
export MODPROBE_OPTIONS="-qb"
# Export relevant variables
export ROOT=
export ROOTDELAY=
export ROOTFLAGS=
export ROOTFSTYPE=
export IP=
export DEVICE=
export BOOT=
export BOOTIF=
export UBIMTD=
export break=
export init=/sbin/init
export readonly=y
export rootmnt=/root
export debug=
export panic=
export blacklist=
export resume=
export resume_offset=
export noresume=
export drop_caps=
export fastboot=n
export forcefsck=n
export fsckfix=
# Bring in the main config
. /conf/initramfs.conf
for conf in conf/conf.d/*; do
[ -f "${conf}" ] && . "${conf}"
done
. /scripts/functions
# Parse command line options
# shellcheck disable=SC2013
for x in $(cat /proc/cmdline); do
case $x in
init=*)
init=${x#init=}
;;
root=*)
ROOT=${x#root=}
if [ -z "${BOOT}" ] && [ "$ROOT" = "/dev/nfs" ]; then
BOOT=nfs
fi
;;
rootflags=*)
ROOTFLAGS="-o ${x#rootflags=}"
;;
rootfstype=*)
ROOTFSTYPE="${x#rootfstype=}"
;;
rootdelay=*)
ROOTDELAY="${x#rootdelay=}"
case ${ROOTDELAY} in
*[![:digit:].]*)
ROOTDELAY=
;;
esac
;;
nfsroot=*)
# shellcheck disable=SC2034
NFSROOT="${x#nfsroot=}"
;;
initramfs.runsize=*)
RUNSIZE="${x#initramfs.runsize=}"
;;
ip=*)
IP="${x#ip=}"
;;
boot=*)
BOOT=${x#boot=}
;;
ubi.mtd=*)
UBIMTD=${x#ubi.mtd=}
;;
resume=*)
RESUME="${x#resume=}"
;;
resume_offset=*)
resume_offset="${x#resume_offset=}"
;;
noresume)
noresume=y
;;
drop_capabilities=*)
drop_caps="-d ${x#drop_capabilities=}"
;;
panic=*)
panic="${x#panic=}"
;;
ro)
readonly=y
;;
rw)
readonly=n
;;
debug)
debug=y
quiet=n
if [ -n "${netconsole}" ]; then
log_output=/dev/kmsg
else
log_output=/run/initramfs/initramfs.debug
fi
set -x
;;
debug=*)
debug=y
quiet=n
set -x
;;
break=*)
break=${x#break=}
;;
break)
break=premount
;;
blacklist=*)
blacklist=${x#blacklist=}
;;
netconsole=*)
netconsole=${x#netconsole=}
[ "$debug" = "y" ] && log_output=/dev/kmsg
;;
BOOTIF=*)
BOOTIF=${x#BOOTIF=}
;;
fastboot|fsck.mode=skip)
fastboot=y
;;
forcefsck|fsck.mode=force)
forcefsck=y
;;
fsckfix|fsck.repair=yes)
fsckfix=y
;;
fsck.repair=no)
fsckfix=n
;;
esac
done
# Default to BOOT=local if no boot script defined.
if [ -z "${BOOT}" ]; then
BOOT=local
fi
if [ -n "${noresume}" ] || [ "$RESUME" = none ]; then
noresume=y
else
resume=${RESUME:-}
fi
mount -t tmpfs -o "nodev,noexec,nosuid,size=${RUNSIZE:-10%},mode=0755" tmpfs /run
mkdir -m 0700 /run/initramfs
if [ -n "$log_output" ]; then
exec >"$log_output" 2>&1
unset log_output
fi
maybe_break top
# Don't do log messages here to avoid confusing graphical boots
run_scripts /scripts/init-top
maybe_break modules
[ "$quiet" != "y" ] && log_begin_msg "Loading essential drivers"
[ -n "${netconsole}" ] && /sbin/modprobe netconsole netconsole="${netconsole}"
load_modules
[ "$quiet" != "y" ] && log_end_msg
starttime="$(_uptime)"
starttime=$((starttime + 1)) # round up
export starttime
if [ "$ROOTDELAY" ]; then
sleep "$ROOTDELAY"
fi
maybe_break premount
[ "$quiet" != "y" ] && log_begin_msg "Running /scripts/init-premount"
run_scripts /scripts/init-premount
[ "$quiet" != "y" ] && log_end_msg
maybe_break mount
log_begin_msg "Mounting root file system"
# Always load local and nfs (since these might be needed for /etc or
# /usr, irrespective of the boot script used to mount the rootfs).
. /scripts/local
. /scripts/nfs
. "/scripts/${BOOT}"
parse_numeric "${ROOT}"
maybe_break mountroot
mount_top
mount_premount
mountroot
log_end_msg
if read_fstab_entry /usr; then
log_begin_msg "Mounting /usr file system"
mountfs /usr
log_end_msg
fi
# Mount cleanup
mount_bottom
nfs_bottom
local_bottom
maybe_break bottom
[ "$quiet" != "y" ] && log_begin_msg "Running /scripts/init-bottom"
# We expect udev's init-bottom script to move /dev to ${rootmnt}/dev
run_scripts /scripts/init-bottom
[ "$quiet" != "y" ] && log_end_msg
# Move /run to the root
mount -n -o move /run ${rootmnt}/run
validate_init() {
run-init -n "${rootmnt}" "${1}"
}
# Check init is really there
if ! validate_init "$init"; then
echo "Target filesystem doesn't have requested ${init}."
init=
for inittest in /sbin/init /etc/init /bin/init /bin/sh; do
if validate_init "${inittest}"; then
init="$inittest"
break
fi
done
fi
# No init on rootmount
if ! validate_init "${init}" ; then
panic "No init found. Try passing init= bootarg."
fi
maybe_break init
# don't leak too much of env - some init(8) don't clear it
# (keep init, rootmnt, drop_caps)
unset debug
unset MODPROBE_OPTIONS
unset DPKG_ARCH
unset ROOTFLAGS
unset ROOTFSTYPE
unset ROOTDELAY
unset ROOT
unset IP
unset BOOT
unset BOOTIF
unset DEVICE
unset UBIMTD
unset blacklist
unset break
unset noresume
unset panic
unset quiet
unset readonly
unset resume
unset resume_offset
unset noresume
unset fastboot
unset forcefsck
unset fsckfix
unset starttime
# Move virtual filesystems over to the real filesystem
mount -n -o move /sys ${rootmnt}/sys
mount -n -o move /proc ${rootmnt}/proc
# Chain to real filesystem
# shellcheck disable=SC2086,SC2094
exec run-init ${drop_caps} "${rootmnt}" "${init}" "$@" <"${rootmnt}/dev/console" >"${rootmnt}/dev/console" 2>&1
echo "Something went badly wrong in the initramfs."
panic "Please file a bug on initramfs-tools."