overlayfs example

Author: cirosantilli

docker/README.md

@@ -202,7 +202,9 @@ Only works for new containers: <https://stackoverflow.com/questions/28302178/how
 
 ### GUI apps
 
-https://stackoverflow.com/questions/16296753/can-you-run-gui-apps-in-a-docker-container
+Easiest method: https://stackoverflow.com/questions/31446661/build-a-full-ubuntu-desktop-docker-image/51122106#51122106
+
+More manual method: https://stackoverflow.com/questions/16296753/can-you-run-gui-apps-in-a-docker-container
 
     sudo docker run --net=host
 

overlay.sh

@@ -0,0 +1,47 @@
+#!/usr/bin/env bash
+set -eux
+
+# Global setup.
+top=overlay.tmp
+rm -rf "$top"
+mkdir -p "$top"
+cd "$top"
+
+# Create the filesystems.
+mkdir lower
+mkdir upper
+mkdir overlay
+dd if=/dev/zero of=lower.ext4 bs=1024 count=102400
+dd if=/dev/zero of=upper.ext4 bs=1024 count=102400
+mkfs -t ext4 lower.ext4
+mkfs -t ext4 upper.ext4
+sudo mount lower.ext4 lower
+sudo mount upper.ext4 upper
+sudo chown "$USER:$USER" lower
+sudo chown "$USER:$USER" upper
+printf 'lower-content' > lower/lower-file
+# upper and work must be on the same filesystem.
+mkdir upper/upper
+mkdir upper/work
+printf 'upper-content' > upper/upper/upper-file
+# Work must be empty.
+# echo 'work-content' >> upper/work/work-file
+
+# Make the lower readonly to show that that is possible:
+# writes actually end up on the upper filesystem.
+sudo mount -o remount,ro lower.ext4 lower
+
+# Create the mount.
+sudo mount \
+  -t overlay \
+  -o lowerdir=lower,upperdir=upper/upper,workdir=upper/work \
+  none \
+  overlay \
+;
+printf 'overlay-content' > overlay/overlay-file
+ls lower upper/upper upper/work overlay
+
+# Cleanup.
+sudo umount overlay
+sudo umount upper
+sudo umount lower

overlayfs.md

@@ -1,30 +1,6 @@
 # OverlayFS
 
+<https://askubuntu.com/questions/109413/how-do-i-use-overlayfs/1075564#1075564>
 <https://askubuntu.com/questions/699565/example-overlayfs-usage>
 
-Basic:
-
-    mkdir -p lower upper work overlay
-    sudo mount -t overlay -o lowerdir=lower,upperdir=upper,workdir=work none overlay
-    touch lower/a upper/b overlay/c
-    ls lower upper overlay
-    sudo umount overlay
-
-Outcome:
-
-    lower:
-    a
-
-    overlay:
-    a  b  c
-
-    upper:
-    b  c
-
-Preparing to override root:
-
-    mkdir -p lower lower/upper lower/work overlay
-    sudo mount -t overlay -o lowerdir=lower,upperdir=lower/upper,workdir=lower/work none lower
-    touch lower/a lower/upper/b
-    ls lower lower/upper
-    sudo umount overlay
+[overlayfs.sh](overlayfs.sh)