diff --git a/opt/backup-fs b/opt/backup-fs
index 88dbd3b..ddfe13e 100644
--- a/opt/backup-fs
+++ b/opt/backup-fs
@@ -27,14 +27,40 @@ function yesno {
   done
 }
 
-#TODO: remove
-bash -i < $TTY_OR_CONSOLE
+# cutting off the leading slash allows us to just ignore empty lines below
+readarray -t MOUNT_LIST <<< "$(findmnt --output TARGET --noheadings --raw | sed -e 's|^/||' | sort)"
+# always ignore /tmp and the package cache
+EXCLUDE_LIST=("tmp" "var/cache/xbps")
+
+for I in ${!MOUNT_LIST[@]}; do
+  if [ ! -z "${MOUNT_LIST[$I]}" ]; then
+    FOUND=0
+    for J in ${!EXCLUDE_LIST[@]}; do
+      if grep "${EXCLUDE_LIST[$J]}" > /dev/null <<< "${MOUNT_LIST[$I]}"; then
+        FOUND=1
+        break
+      fi
+    done
+    # if no parent dir of ${MOUNT_LIST[$I]} is found in $EXCLUDE_LIST
+    if [ $FOUND -eq 0 ]; then
+      EXCLUDE_LIST+=("${MOUNT_LIST[$I]}")
+    fi
+  fi
+done
+
+touch /run/void-usb/backup-fs-excludes
+touch /run/void-usb/backup-fs-pseudo
+for I in ${!EXCLUDE_LIST[@]}; do
+  echo "/${EXCLUDE_LIST[$I]}" >> /run/void-usb/backup-fs-excludes
+  FILE_PERMS="$(stat -c '%a %u %g' "${EXCLUDE_LIST[$I]}")"
+  echo "\"/${EXCLUDE_LIST[$I]}\" d $FILE_PERMS" >> /run/void-usb/backup-fs-pseudo
+done
 
 #TODO: refuse to run if system is running
 
-#TODO: add a way to tell the system whether to back up before shutting down
+#TODO: add a way to force backing up without asking (for example a file in /run/void-usb)
 
-#TODO: colors
+#TODO: colors (bright white / light gray for readability)
 echo "Back up system changes to disk?
 
 This only affects things outside the /home directory.
@@ -43,9 +69,7 @@ Backing up the system will take some time.
 
 if yesno; then
   echo "Backing up..."
-  #TODO: fiddle with squashfs parameters to find optimal settings
-  #TODO: exclude /tmp
-  mksquashfs / /run/void-usb/container/new_squashfs.img -b 1M -comp xz -one-file-system -progress -noappend -e /var/cache/xbps
+  mksquashfs / /run/void-usb/container/new_squashfs.img -b 1M -comp xz -progress -noappend -pf /run/void-usb/backup-fs-pseudo -ef /run/void-usb/backup-fs-excludes
   #TODO: check if enough disk space
   # yes -> create new image next to old image
   # no  -> create new image in RAM