script-dump/lxc/remap-uid-and-gid-for-lv

#!/bin/sh
# Remap all files uid/gid to a new range
#
# This is an inferior version of `fuidshift` from the `lxd-tools` Debian package, as it only handles uid/gid and
# doesn't handle ACLs and thus journalctl's files and by that hinders updating systemd inside the container. It's also
# quite slow.

usage () {
	echo "remap-uid-and-gid <container-name> [<target-lv>]"
	printf "\nIf <target-lv> is not given it is computed from a default value with the given container name\n"
	exit 1
}

CONTAINER_NAME="${1}"
if [ "${CONTAINER_NAME}" = "" ]; then
	usage
fi

TARGET_LV="${2}"
if [ "${TARGET_LV}" = "" ]; then
	GUESSED_LV="/dev/mapper/daffy--vg-lxc--${CONTAINER_NAME}"
	if [ -e "${GUESSED_LV}" ]; then
		TARGET_LV="${GUESSED_LV}"
	fi
fi
if [ "${TARGET_LV}" = "" ]; then
	usage
fi

if mount | grep -qF " on /mnt"; then
	echo "Mountpoint /mnt is already in use."
	exit 1
fi

mount "${TARGET_LV}" /mnt
cd /mnt

ROOT_USER_ID=$(get-lxc-idmap-config u $CONTAINER_NAME | cut -d ' ' -f 5)
ROOT_GROUP_ID=$(get-lxc-idmap-config g $CONTAINER_NAME | cut -d ' ' -f 5)

printf "uid: %s gid: %s\n" $ROOT_USER_ID $ROOT_GROUP_ID

# We ignore links here, because they might not point to a valid location and would make our program fail. They are also
# owned by whoever mounted the filesystem it seems, so don't need a chown.
# Funny enough, the above statement is not true. I see symlinks in the container that are not owned by a valid user
# inside the container ...
# chown
#       -h, --no-dereference
#              affect  symbolic links instead of any referenced file (useful only on systems
#              that can change the ownership of a symlink)
#
#       --from=CURRENT_OWNER:CURRENT_GROUP
#              change the owner and/or group of each file only if its current  owner  and/or
#              group  match  those  specified  here.  Either may be omitted, in which case a
#              match is not required for the omitted attribute
#
find . -xdev -printf "%U %G %p\n" | \
	while read F; do
		U=$(echo $F | cut -d ' ' -f 1)
		if [ ${U} -lt ${ROOT_USER_ID} ] || [ ${U} -gt $(( ${ROOT_USER_ID} + 65535 )) ]; then
			NEW_U=$(( ${U} + ${ROOT_USER_ID} ))
		else
			NEW_U=${U}
		fi

		G=$(echo $F | cut -d ' ' -f 2)
		if [ ${G} -lt ${ROOT_GROUP_ID} ] || [ ${G} -gt $(( ${ROOT_GROUP_ID} + 65535 )) ]; then
			NEW_G=$(( ${G} + ${ROOT_GROUP_ID} ))
		else
			NEW_G=${G}
		fi

		if [ "${U}" = "${NEW_U}" ] && [ "${G}" = "${NEW_G}" ]; then
			continue
		fi

		P=$(echo $F | cut -d ' ' -f 3-)
		printf "chown --no-dereference %s:%s %s\n" ${NEW_U} ${NEW_G} "${P}"
		# chown --no-dereference ${NEW_U}:${NEW_G} "${P}"
	done

cd /
umount /mnt