OverlayFS

OverlayFS

OverlayFS is used when booting from internal flash as a way to edit, create and install files without modifying the core root file system. We use a squashfs partition for the rootfs and a jffs2 partition for storage as an overlayfs. An overlayfs is layered on top of the rootfs. Any file created or edited is saved to the overlayfs but appears as if it's in the rootfs. The default openwrt-zipit configuration uses the jffs partition as the overlayfs. You can also use a SD Card as an overlayfs by creating a new config file in /etc/overlay.conf.d/. The following example config file exists at /etc/overlay.conf.d/example and can be copied/modified by following it's instructions:

 ### overlayfs configuration example (SD Card) ###
 ### ALL options are REQUIRED ###
 # Files in /etc/overlay.conf.d are read from the
 # jffs partition during boot. conf files should
 # be numbered in the order you wish them to be
 # mounted, lowest number mounted first. The last
 # overlay mounted becomes the upper writable dir.
 # Numbers below 10 need the preceding 0 to be
 # mounted in proper order.
 # ex:
 #       01-mmcblk0p1.conf (mounted first)
 #       10-sda1.conf      (mounted second)
 #       99-mmcblk0p2.conf (mounted last, writable)
 #
 # If a file name "disabled" exists in overlay.conf.d
 # then only the jffs will be mounted as overlay
 
 # Overlay device (default mmblk0p1, do not add
 # preceding /dev path)
 #overlaydev=mmcblk0p1
 
 # Overlay filesystem type (default, ext2)
 #fstype=ext2
 
 # Overlay upper directory (default, upper)
 # This is the directory of files on the overlaydev
 # that are overlayed onto root as r/w. Cannot be
 # the device root (ie, /); must be a dir on the
 # device
 #upperdir=upper
 
 # Overlay work directory (default, work)
 # This is a directory on the overlaydev used by
 # the overlayfs filesystem driver. Cannot be a
 # subdir of upperdir
 #workdir=work