June 15, 2017

xxd reverse with an offset

When using xxd to reverse a hex dump file, if you hexdump file has a non-0 offset like this:

bc000000: 01 02 03 04 05 06 07 08  ........

You would need to use the "-s offset" option of the xxd. However, there is a bug in the code that makes this options only works as the FIRST option. Otherwise, it wouldn't work.

You want to do this:

xxd -s -0xbc000000 -r -g 1 test.dump test.bin

Basically the xxd is hardcoded to look for the offset at argv[2].

Another alternative:

May 17, 2017

ios command line console log viewing

use "idevice_id --list" to list the UUIDs.
use "deviceconsole" to actually view the logs
deviceconsole -u <UUID>

May 16, 2017

unbrick TPLINK Archer C7 V2 (2017-05 from Amazon)

I bricked my Archer C7 v2 with bad configuration.

TFTP boot didn't work for me. It turned out that the product id doesn't match.

Had to connect to console.

1. The pinout is as follows. The warning on this page (https://wiki.openwrt.org/toh/tp-link/tl-wdr7500#tftp_recovery_de-bricking) itself is wrong.

2. I used the Openwrt Snapshot image. I tried the official image from TPLink website but that didn't work. I didn't try the "cut" process described in the above link.

3. The command is as follows

type "tpl" really fast at boot time to stop the autoboot

tftpboot 0x81000000 [name of your firmware file].bin
erase 0x9f020000 +f80000
cp.b 0x81000000 0x9f020000 0xf80000

That's it.

May 11, 2017

socket buffer size

To find the current socket buffer size:

getsockopt(fdsocket,SOL_SOCKET,SO_RCVBUF,(void *)&n, &m);

getsockopt(fdsocket,SOL_SOCKET,SO_SNDBUF,(void *)&n, &m);

To find out more, do "man getsockopt"

To find the current bytes in the socket's buffer:

To find out more, do "man ioctl"

May 8, 2017

FreeBSD recompile kernel


untar this to /usr/src

Go to the kernel source directory which contains the configurations.
cd /usr/src/sys/amd64/conf
Create a folder named kernel in the home directory of root user i.e. /root.
mkdir /root/kernels

config -x /root/kernels/MYKERNEL

The above command generates the current configuration of the kernel

Now you can add the options you want to change.

Create a soft link in the /usr/src/sys/amd64/conf named “MYKERNEL” which links to /root/kernels/MYKERNEL file.

ln -s /root/kernels/MYKERNEL

Goto the folder created above.
cd /root/kernels/

To build a file which contains all available options, run the following commands.
cd /usr/src/sys/amd64/conf
make LINT
Goto the main source folder.
cd /usr/src
Build and Install the new kernel with reference from the file “MYKERNEL”.
make buildkernel KERNCONF=MYKERNEL
make installkernel KERNCONF=MYKERNEL
Now reboot the machine to boot into the new kernel you just created now.

use "uname -a" and "sysctl -a" to check

Enable multi routing table in the kernel:

FreeBSD dump current kernel config

config -x /boot/kernel/kernel

May 2, 2017

Adding swap to your VM

sudo fallocate -l 1G /swapfile
sudo chmod 600 /swapfile
sudo mkswap /swapfile
sudo swapon /swapfile
sudo swapon --show
echo '/swapfile none swap sw 0 0' | sudo tee -a /etc/fstab

April 4, 2017

seafiles upload error

The solution:
I needed to go into the webui system admin -> settings and change FILE_SERVER_ROOT to be seafile.example.com/seafhttp as per the local help text.