airgap/rootfs/etc/init.d/S20urandom

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#! /bin/sh
#
# Preserve the random seed between reboots. See urandom(4).
#
# Quietly do nothing if /dev/urandom does not exist
[ -c /dev/urandom ] || exit 0
URANDOM_SEED="/var/lib/random-seed"
# shellcheck source=/dev/null
[ -r "/etc/default/urandom" ] && . "/etc/default/urandom"
if pool_bits=$(cat /proc/sys/kernel/random/poolsize 2> /dev/null); then
pool_size=$((pool_bits/8))
else
pool_size=512
fi
init_rng() {
[ -f "$URANDOM_SEED" ] || return 0
printf 'Initializing random number generator: '
dd if="$URANDOM_SEED" bs="$pool_size" of=/dev/urandom count=1 2> /dev/null
status=$?
if [ "$status" -eq 0 ]; then
echo "OK"
else
echo "FAIL"
fi
return "$status"
}
save_random_seed() {
printf 'Saving random seed: '
status=1
if touch "$URANDOM_SEED.new" 2> /dev/null; then
old_umask=$(umask)
umask 077
dd if=/dev/urandom of="$URANDOM_SEED.tmp" bs="$pool_size" count=1 2> /dev/null
cat "$URANDOM_SEED" "$URANDOM_SEED.tmp" 2>/dev/null \
| sha256sum \
| cut -d ' ' -f 1 > "$URANDOM_SEED.new" && \
mv "$URANDOM_SEED.new" "$URANDOM_SEED" && status=0
rm -f "$URANDOM_SEED.tmp"
umask "$old_umask"
if [ "$status" -eq 0 ]; then
echo "OK"
else
echo "FAIL"
fi
else
echo "SKIP (read-only file system detected)"
fi
return "$status"
}
case "$1" in
start|restart|reload)
# Carry a random seed from start-up to start-up
# Load and then save the whole entropy pool
init_rng && save_random_seed;;
stop)
# Carry a random seed from shut-down to start-up
# Save the whole entropy pool
save_random_seed;;
*)
echo "Usage: $0 {start|stop|restart|reload}"
exit 1
esac