OpenWRT and Bare Metal BackUps: Difference between revisions

The "Backing Up" or BackUp Process is the first part of cloning a system too.  So why not just use something like an external drive bay to clone the disk / SSD to another drive?  Because that involves removing the drive.  The end objective is to be able to do a live, bare metal cloning process.

In syntax examples, devices are assumed to be in /dev.

Copy the Root Partition (second partition on a 'stock' / 'standard' OpenWRT x86 installation):

*if: Input File (or Device)

...and finally, DD seems to be a Zero Based utility, similar to how Disks (and other items like Intel SATA Ports, etc.) are numbered starting from Zero ( 0 ).  So setting skip=511 will skip sectors 0 through 511, for a total of 512 sectors.

Real quick, here's what's going on with a typical Router based installation of OpenWRT that is stored on Flash Memory Storage.

How is it done? Using the Overlay / Union Mount capabilities of Linux. Sorry, not here to explain that fully, hence the above links.

Ideally (since LVM isn't typically available to do "Volume Shadow Copies"), one would boot to an alternative OS, use DD to clone the /overlay "Partition" / "Device". Easy with an x86_64 based install of OpenWRT, but also very possible with a Router based on Flash Memory Storage too. For the Router scenario, again ideally, if the /overlay "Partition" / "Device" is on an external USB Flash Drive (as it should be if a router has a USB 3.0 port), just pop it into a "Linux Box" (virtual or otherwise) for backing up. It can also be done "live" without much chance of something being modified during the cloning process.

<nowiki>*</nowiki>If you haven't spotted it yet, but you've been asking, "Where is that file that OpenWRT mounts a Directory named /overlay as a LOOP Device?" Answer: There is no file. It is simply a sector on the Disk / SSD Drive to the end of it. And you might ask, "But won't it be overwritten?" Answer: Nope, because everything before it is considered ROM (as in no write), so it won't expand. And yes that means the entire disk drive (well, at least the OpenWRT partitions) is considered a File that breaks down into a ROM Section and an /overlay Section.

mount -t f2fs /dev/loop1 /mnt/loop1

losetup -fP WhatEverImageName.img (To see mounted "Devices": losetup -a), (f = File Name to configure as a Loop Device, P = Scan Partition Size, a = Show All Loop Devices, b = sector size)

Loop Device: <nowiki>https://en.wikipedia.org/wiki/Loop_device</nowiki>

mount -t squashfs /dev/loop7 /mnt/squash

Keep in mind this only works with IMG Files created from Partitions. If an entire disk drive is imaged, the above method won't work. However...

If an entire disk is imaged with DD, then a "map" of it can be viewed with CFDISK: cfdisk /dev/WhatEverLoopDevice (Example: cfdisk /dev/loop5) (Remember, use losetup -a to see "Devices")

With the above information garnered from CFDISK, then mount individual Partitions: mount -t WhatEverFileSystem (squashfs, ext4, ntfs-3g, etc.) /dev/WhatEverLoopDevice /mnt/WhatEverMountPoint: mount -t squashfs /dev/loop6p2 /mnt/Loop6/p2 (Also: losetup -d /dev/WhatEverLoopDevice will delete the loop device)

Bad news. The delete command doesn't always work. After issuing the command on a legitimate Loop Device, and with no errors, the Loop Device will persist. Checking it with LOSETUP -a shows it is still there. Accessing it with CFDISK or MOUNT still works. Oh, well. Windows solution time. Reboot.

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OpenWRT specifically mentions GRUB 2 in their documentation.  But the way it works on an x86_64 EXT4 installation of OpenWRT would convince anyone that it is Legacy GRUB (except for the GNU GRUB  version 2.02 heading at the top of the screen).  The way it is configured via /etc/grub/grub.cfg would also convince anyone that Legacy GRUB was being used.  So, the conclusion is that GRUB 2.02 is indeed being used, but since it is backwards compatible, it is in 'Legacy Mode'.

How can the entire OpenWRT installation be backed up in a fashion similar to Acronis products, Clonezilla, etc.?

The first answer is that there is no built in facility to do that. Dang! Why not? Well, first of all, OpenWRT is intended to be installed on small router devices where this type of backup (Disk / Drive Imaging, Bare Metal BackUp, etc.) just isn't a thing. Second, and largely because of something mentioned in the first item, is that a program like that can't be crammed into a small enough space to fit on small router device.

What about Baquacil, err, wait, that's a pool chemical. Bactine! No, that's the antiseptic. RESTIC! Yup, that's the utility for backing up in OpenWRT (the only one)

Wah! But what if I want to do it anyway because... Well, because I want to

Clonezilla? Yup, great, but one issue. One has to boot from the Clonezilla CD / DVD / USB Flash Drive / ISO to do it. Router off, Clonezilla on.

Again; WAH! I want to do it with the Router still fully functional, IE from within OpenWRT.

Perfect! Except for one thing: Files might change right in the middle of a backup (because it takes a long time). Remember DD has no capability or concept of "Volume Shadow Copy" (Note: RESTIC doesn't have the capability, but it does have the concept of it, however that would require converting the entire OpenWRT install over to an LVM based Disk / SSD / Whatever 'Layout'.)

Ideally, the only solution would seem to be something like Acronis for Linux (or some other commercial product). Or something like RUBackUp and / or FSArchiver. The latter requiring the above noted conversion of OpenWRT over to an LVM based Disk / SSD / FlashDrive system. That's a lot of work. The best option would be making DD aware of Volume Snapshots and doing it that way. Ongoing work with this experiment will be to attempt changing the disk layout to include an LVM volume that allows for "Volume Shadow Copy" (Volume Snapshot, etc., IE, the Linux equivalent of that Windows feature) and using DD for a Bare Metal BackUp!

Please remember, none of this is rant is intended to be disrespectful to the OpenWRT, RESTIC, or anyone else that might have felt slighted. It is simply a colorful way of noting how in the software world, once someone is given something, the inevitable question and desire of 'What else can it do?" comes up. That's what this is about