USB flash in failsafe

Installing and Using OpenWrt
1

Hi,

I have an D-Link DIR-505 that is very practical because it is very small. The problem is the size of the flash (only 4 MB).
So I'm using it with a small pen drive, but with 4 GB.
The first thing I do after the basic configuration is install the USB packages, install, format the USB flash drive, copy the /overlay to it and change fstab.
So now, when rebooting I have a big /overlay to install more packages.

The problem is when making a wrong configuration and the router is no more accessible (ports open but no answer; only pinging). In this case it is needed to boot in failsafe mode.

The question is: how to load the USB flash drive manualy the have access to the valid /overlay?
Right after having access to console in failsafe mode, I execute mount_root to have access to /overlay. But this is not "my" USB overlay but the "DIR-505" overlay. Besides that, there is no sda device in /dev. How to mount them manualy?
The "block info" command shows only 2 /dev/mtdblock7 and /dev/mtdblock8 (squashfs and jffs2), no /dev/sda1.

I tried a lot without success. Can anyone help me?

Thanks in advance.

carliedu
SP-Brazil

2

DIR-505 has 8MB flash.
Why do you think it has only 4MB?

3

The "best" would be to build your "ROM" image with the USB drivers, file system drivers, and mounting tools.

The other approach would be to install them onto the flash-based overlay, mount that, load the drivers, then mount the USB stick. That's roughly how the "extroot" configuration works.

4

You are right. I don't know where I found this information. Probably on TOH on Openwrt because I only look there for this type of information.
Now I looked there again and it shows 8 MB. Can be that it was corrected.
Thanks for your comment.

5

Hi Tmomas,
I found why I think it has only 4MB flash.
Right after installing a fresh firmware (Version 18.06.0), with terminal I get the following:

root@D505:~# df -h
Filesystem                Size      Used Available Use% Mounted on
/dev/root                 2.5M      2.5M         0 100% /rom
tmpfs                    29.5M    604.0K     28.9M   2% /tmp
/dev/mtdblock8            3.9M    300.0K      3.6M   7% /overlay
overlayfs:/overlay        3.9M    300.0K      3.6M   7% /
tmpfs                   512.0K         0    512.0K   0% /dev

So, I convinced that TOH is wrong.

Can you check yours again, please?

Best,
carliedu

6

Looks like 2.5 MB for the ROM, 4 MB for the overlay, then the rest perhaps for the boot loader and the like = 8 MB total flash

1 Like
7

Unlikely.

Compare your output of cat /proc/mtd with https://openwrt.org/toh/d-link/dir-505#flash_layout

8

Hi tmomas and jeff.
Both your comments were very important.
-tmomas: I convinced you wrong about TOH. TOH is right. DIR-505 has 8 MB flash size.
-jeff: You showed me an information that was new for me and so I'm convinced that DIR-505 has 8 MB flash size.

Flash memory is mtd formated and holds other partitions besides /overlay.
The command cat /proc/mtd shows the partioning. On DIR-505 it is:

root@(none):~# cat /proc/mtd
dev:    size   erasesize  name
mtd0: 00010000 00010000 "u-boot"
mtd1: 00010000 00010000 "art"
mtd2: 00010000 00010000 "mac"
mtd3: 00010000 00010000 "nvram"
mtd4: 00040000 00010000 "language"
mtd5: 00780000 00010000 "firmware"
mtd6: 0014da84 00010000 "kernel"
mtd7: 0063257c 00010000 "rootfs"
mtd8: 003f0000 00010000 "rootfs_data"

I will continue to study about and try to understand how to gain access to the /overlay on USB-device.

Thanks for now.

Best,
carliedu

9

Just wonder if anyone working to bring this little gem to ath79 dts too.....

10

You're certainly welcome to port it yourself as I don't see it on master on ath79.

There isn't a lot of appetite to spend time on devices nearly a decade old that have little hope of running what most people consider a minimal OpenWrt install (both flash and RAM both). Suitable replacements with at least 16/128 are available starting at under US$20.