Only modify files in startup when they aren't mounted

docker/rootfs/etc/s6-overlay/s6-rc.d/prepare/50-ipv6.sh

@@ -8,6 +8,10 @@ set -e
 
 log_info 'IPv6 ...'
 
+is_mounted() {
+	awk -v p="$1" '$5 == p { found=1 } END { exit !found }' /proc/self/mountinfo
+}
+
 process_folder () {
 	FILES=$(find "$1" -type f -name "*.conf")
 	SED_REGEX=
@@ -26,7 +30,10 @@ process_folder () {
 	do
 		echo "- ${FILE}"
 		TMPFILE="${FILE}.tmp"
-		if sed -E "$SED_REGEX" "$FILE" > "$TMPFILE" && [ -s "$TMPFILE" ]; then
+
+		if is_mounted "${FILE}"; then
+			echo "WARNING: skipping ${FILE} — mounted file" >&2
+		elif sed -E "$SED_REGEX" "$FILE" > "$TMPFILE" && [ -s "$TMPFILE" ]; then
 			mv "$TMPFILE" "$FILE"
 		else
 			echo "WARNING: skipping ${FILE} — sed produced empty output" >&2