• In case you not want to build you own firmware, there is a separate howto for that: install extroot later on
• An alternative to ExtRoot could be to make opkg install new packages somewhere else: See Installation.destinations
• Another one to hack the bootloader and make him boot from external device directly. See dockstar
• And yet another one to use kexec

1. OpenWrt Buildroot – Installation
2. OpenWrt Buildroot – Usage

Assuming you just started # make menuconfig and are in the build system.

The package block-extroot won't even be displayed unless you have selected a block device package in Kernel Modules. Specifically you must have either ide-core (and any other required IDE drivers), or usb-storage (and the USB host controller, such as usb-ohci), or the mmc package (and any required modules for an SD/MMC device).

You must also select the block-mount package from Base system.

As of r26314 block-extroot has been merged with block-mount. That means that once you select block-mount the scripts for extroot mounting are installed. block-mount can be used even if you have not selected a block device package, but if you want extroot behaviour you must still install the drivers (block device package) for the external root device as well as the filesystem you want to use (e.g. fat or ext4)

If you want the filesystem to be run through a filesystem check/repair before mounting, you must also include the appropriate fsck package (.e.g. e2fsprogs which contains e2fsck for ext2/3/4 filesystems), however you are not required to have an fsck program.

You will also need the kernel modules for the filesystem format you want to use on your root filesystem. Don't forget the nls-base kernel module, if you system requires it, however neither of these are a dependency of the block-extroot package.

If you intend to partition and/or format the filesystem on a live system, so that you can use an external storage device, you will the packages required to do that in the image, or available to opkg as well.

NOTE At this time block-extroot does not activate until there is a valid configuration. If you are using a squashfs based filesystem it will never boot into your external rootfs on the first boot. With other filesystem types, or an upgrade of a squashfs filesystem, if there is a valid configuration in the firmware image (i.e. by placing a ./files/etc/config/fstab in your OpenWRT root directory), then it will be used on the first (and subsequent boots).

You will also need to make sure your rootfs is empty, or contains only valid files from the system you are upgrading.

see extroot.prerequisites for information on how to prepare the filesystem.

e.g. make from the root directory of your OpenWRT tree.

e.g. sysupgrade imagefile

1. Partition your device (if not already partitioned as you desire)
2. Format the device (partition) if not already formatted
3. Copy everything from /jffs (if on a squashfs and you want the current configuration and settings to be copied to the new rootfs) to the new root device (partition)
4. Edit /etc/config/fstab (as described in fstab. Also see extroot.examples for configuration examples)

You should now be in the rootfs on your external storage device.

See extroot.system.upgrade for information on updating your extroot image. Note that for revisions before OpenWrt 10.03.1-rc4 'Backfire' you will always have to build your own image because extroot must be included in the image. After that the appropriate packages are allowed be added to the jffs2 after flashing instead of being required in the image (e.g. packages from the same snapshot as your kernel and jffs2/squashfs).

With extroot you will be able to easily upgrade your packages, but not be able to perform kernel update, since the kernel remains on the device flash on a read-only partition.

opkg upgrade

will not do anything anyway, since with opkg you have to name the package you want to upgrade. So to upgrade all your installed packages, you could do

opkg upgrade $(opkg list-upgradable)

DO NOT DO THAT! Since the kernel is on read-only flash partition, and all the kernel modules are on your external device, the modules will be updated, but the kernel not. You will end up with not matching kernel <> kernel-modules and your installation will not survive a reboot. To avoid that, you have to exclude all kernel-modules from being updated, for example so:

opkg upgrade $(opkg list-upgradable | awk '($1 !~ "^kmod|Multiple") {print $1}')

Since Trunk r23173 (Backfire r23206) the kernel and kmod packages are flagged as hold. The opkg upgrade command won't attempt to update them anymore.