tinyramfs/init

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#!/bin/sh
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#
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# Tiny init
#
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# https://www.shellcheck.net/wiki/SC2154
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# shellcheck disable=2154
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print()
{
printf "%b %s\n" "${2:-"\033[1;37m>>\033[m"}" "$1"
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}
panic()
{
print "${1:-unexpected error occurred}" \
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"\033[1;31m!!\033[m"
sh
} >&2
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resolve_device()
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{
count=0; device="$1"
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case "${device%%=*}" in
UUID) device="/dev/disk/by-uuid/${device#*=}" ;;
LABEL) device="/dev/disk/by-label/${device#*=}" ;;
PARTUUID) device="/dev/disk/by-partuuid/${device#*=}" ;;
/dev/*) ;;
*) return 0 ;;
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esac
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# Race condition may occur if device manager is not yet initialized device.
# To fix this, we simply waiting until device is available. If device
# didn't appear in specified time, we panic.
while :; do
if [ -b "$device" ]; then
return 0
elif [ "$((count += 1))" = "${rootdelay:=30}" ]; then
break
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else
sleep 1
fi
done
panic "failed to lookup partition"
}
run_hook()
{
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type="$1"
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# Run hooks if any exist.
#
# https://www.shellcheck.net/wiki/SC1090
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# shellcheck disable=1090
for hook in $hooks; do
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[ -f "/usr/share/tinyramfs/hooks/${hook}/${hook}.${type}" ] || continue
. "/usr/share/tinyramfs/hooks/${hook}/${hook}.${type}"
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done
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}
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prepare_environment()
{
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# https://www.shellcheck.net/wiki/SC1091
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# shellcheck disable=1091
. /etc/tinyramfs/config
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export \
PATH=/bin TERM=linux SHELL=/bin/sh \
LANG=C LC_ALL=C PS1="# " HOME=/root
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mount -t proc -o nosuid,noexec,nodev proc /proc
mount -t sysfs -o nosuid,noexec,nodev sys /sys
mount -t tmpfs -o nosuid,nodev,mode=0755 run /run
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mount -t devtmpfs -o nosuid,noexec,mode=0755 dev /dev
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ln -s /proc/self/fd /dev/fd
ln -s fd/0 /dev/stdin
ln -s fd/1 /dev/stdout
ln -s fd/2 /dev/stderr
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}
parse_cmdline()
{
read -r cmdline < /proc/cmdline
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for line in $cmdline; do case "$line" in
rootfstype=*) root_type="${line#*=}" ;;
rootflags=*) root_opts="${line#*=}" ;;
debug=1) set -x ;;
ro | rw) rorw="-o $line" ;;
--*) init_args="${cmdline#*-- }"; break ;;
*=*) command export "$line" ;;
*) command export "${line}=1" ;;
esac 2> /dev/null || :; done
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}
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mount_root()
{
[ "$break" = root ] && { print "break before mount_root()"; sh; }
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resolve_device "$root"
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# https://www.shellcheck.net/wiki/SC2086
# shellcheck disable=2086
mount \
${rorw:--o ro}${root_opts:+,$root_opts} ${root_type:+-t $root_type} \
-- "$device" /mnt/root || panic "failed to mount root"
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}
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boot_system()
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{
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[ "$break" = boot ] && { print "break before boot_system()"; sh; }
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for dir in run dev sys proc; do
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mount -o move "$dir" "/mnt/root/${dir}"
done
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# POSIX 'exec' has no '-c' flag to execute command with empty environment.
# Using 'env -i' instead to prevent leaking exported variables.
#
# Some implementations of 'switch_root' doesn't conform to POSIX utility
# guidelines and doesn't support '--'. This means that we can't guarantee
# safety of init_args.
# shellcheck disable=2086
exec \
env -i TERM=linux PATH=/bin:/sbin:/usr/bin:/usr/sbin \
switch_root /mnt/root "${init-/sbin/init}" $init_args ||
panic "failed to boot system"
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}
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# Exit if command fails and disable globbing.
set -ef
# Run emergency shell if init unexpectedly exiting due to error.
trap panic EXIT
# TODO display fancy colored status info
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prepare_environment
parse_cmdline
run_hook init
mount_root
run_hook init.late
boot_system