Category Archives: Mobile

Manually update firmware on Nexus devices

The release of Android 6.0.1 had me excited because it enables LTE band 12 for my phone, the Nexus 5X, which currently uses T-mobile. Band 12 is in the 700mhz range which should greatly increase speed and coverage. I’m too impatient to wait for the OTA!

This tutorial will walk you through how to manually backup, unlock, flash, re-lock, and restore a Google Nexus 5X, but the procedure is pretty much the same for any Nexus device.

First, obtain two necessary Android development tools: adb and fastboot. Do not use your distribution’s versions of these tools – they are likely out of date. Instead, download the Android SDK directly from Google by going here and scrolling to the bottom of the page. Java is required for the sdk to install – install it if you haven’t already. Thanks to this site for explaining how to only obtain platform-tools.

sudo apt-get install openjdk-7-jre
tar zxvf android-sdk_r24.4.1-linux.tgz
android-sdk-linux/tools/android update sdk --no-ui --filter 1,platform-tools

Once you have platform-tools you need to add them to your PATH to make scripts run adb successfully (thanks to this site for the information). When you run the command below make sure to update /path/to/… to the folder where you extracted the android-sdk.

echo "export PATH=$PATH{}:/path/to/android-sdk/tools:/path/to/android/platform-tools" >> ~/.bashrc
source ~/.bashrc

Next, obtain the latest firmware for your device from the google developers site. Extract it somewhere you will remember for later.

Now, enable USB debugging on your phone if you haven’t already (thanks to this site for the info.) To do this, go to Settings / About phone, scroll to the bottom and press on the build number 7 times. Press back and go to developer options, and enable USB debugging and enable OEM unlocking. Then plug in your phone to the computer with adb installed and run this command (thanks to xda for the information)

adb backup -apk -shared -all -f <backup_filename>

Confirm the on-screen prompt on your phone. Make sure you specify a password for encryption. The above command should backup everything, but in my case it did not backup files in the flash partition (downloads, pictures, etc). Make sure you manually copy any important files from your phone before you proceed.

My first attempt at the above command didn’t work for me. I received the error message:

adb: unable to connect for backup

When I ran adb devices it showed this:

List of devices attached 
00c739918fbf4e2a offline

It turns out I had an old version of adb installed. Make sure you download Google’s official SDK instead of relying on your distribution’s version.

Once the backup is complete, you then need to reboot your phone into fastboot mode:

adb reboot bootloader

Wait for the reboot, then run the following command. Warning: this command will wipe your device. Make sure you have a reliable backup and confirm the message on your phone screen.

fastboot oem unlock

Now, navigate to the directory where you extracted your latest firmware and execute the flash-all script:

cd bullhead-mmb29k

After some time your phone will reboot into your shiny new updated OS. Skip everything setup-wise. Re-enable developer mode and android debugging, and then re-lock your bootloader:

adb reboot bootloader
fastboot oem lock

Lastly, we need to restore everything from the backup we made and re-lock the bootloader for security. Once again skip everything setup-wise on the phone, re-enable developer mode and android debugging, and then restore your stuff:

adb restore <filename>

Don’t forget to manually copy back any flash files you manually backed up earlier.

The very last (optional) step is to go into developer options settings and disable OEM unlocking.


Use a freedompop phone for OOB management

I’ve been wanting to have an out of band (OOB) way to manage my home servers for some time now. Why OOB? Sometimes the regular band fails you, like when the internet connection goes down or when I remote into my firewall and fat finger a setting causing the WAN link to go down. Everything is still up, I just can’t get to it remotely. I then have to drive home to fix it all like a luser. This is especially difficult if I’m out of town.

Enter Freedompop. Freedompop is as Sprint MVNO that offers data-only 4g access for cheap – in this case, completely free if you stay under 500 MB of data a month. I got a freedompop phone so my wife could play Ingress before the iOS client came out. Once the iOS Ingress client was released, the freedompop phone began collecting dust.

Note that this would all be a lot simpler if I just did things the “proper” way, such as purchasing a freedompop access point or paying for a tethering plan.. but what’s the fun in that? My solution is quite convoluted and silly – it uses all three types of SSH tunnels –  but it works.. and it was fun!


  • Local, out of band server: An old laptop with a broken screen running Xubuntu 14.04
    • Ethernet cable attached to my local network
  • Remote, regularly banded SSH server: My parents’ dd-wrt powered router (any remote ssh server you have access to will do.)
  • Phone: Sprint Samsung Galaxy S3 activated on the Freedompop network
    • Attached to the out of band server via USB


  • openssh-server: Install this on your out of band server so you can SSH into it
    • ssh-keygen: used to generate RSA private/public key pair to allow for passwordless SSH logins
  • screen: Allows programs to keep running even if SSH is disconnected (optional)
  • autossh: Monitors the state of your ssh connection and will continually attempt to re-connect if the connection is lost, effectively creating a persistent tunnel.
  • tsocks: Allows you to tunnel all traffic for a specified command through a SOCKS proxy
  • Android SSH Server (I use SSH server by Icecold apps.) This is an SSH server for android devices, no root required.


My strategy uses a system of tunnels through the intertubes to accomplish what I want.

  1. Install the OS, openssh-server, autossh, and tsocks on your OOB server, then disconnect it from the internet while keeping it on your local network (I manually configured the IP to not have a default gateway.)
  2. Install an ssh server on your phone
  3. Tether your phone to the computer via USB
  4. Create a dynamic SOCKS proxy tunnel between the OOB server and your phone (Freedompop appears to block internet traffic through USB tethers unless you have a tethering plan, so I had to get creative.)
  5. Configure tsocks on your OOB server to point to the socks proxy established in step 4
  6. Use autossh in conjuction with tsocks to initiate a reverse tunnel between your OOB server and the remote SSH server over the 4G connection from your freedompop phone
  7. (From some other network) SSH into your remote SSH server and create a local tunnel pointing to the remote tunnel created in step 6.
  8. SSH into your locally created tunnel, and… profit?

Adventure, here we come.

Create private / public keys

First, since we’re going to be creating a persistent tunnel, passwordless login is required. We do this by generating an RSA private/public key pair. Create the key pair on your server as per these instructions:

cd ~/.ssh
ssh-keygen -t rsa

Generating public/private rsa key pair.
Enter file in which to save the key (/home/nicholas/.ssh/id_rsa): oob
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in oob.
Your public key has been saved in

Copy the public key generated ( in my case) to your phone.

Configure phone SSH server

Create an SSH server on your phone. Configure the user you created to use the public key generated above. Once that’s configured, start the ssh server on the phone, plug the phone into USB cable and plug the other end into server, and activate USB tethering in Android settings.

On the OOB server, find out IP address of tether by issuing the route command. Look for the gateway on the usb0 interface.

Destination Gateway Genmask Flags Metric Ref Use Iface
default UG 0 0 0 usb0

In my case the gateway IP is

Configure OOB server

Initiate an autossh connection to the usb0 gateway, creating a dynamic (socks) proxy in the process.

autossh -l nicholas -i ~/.ssh/oob -p 34097 -D9999

Argument breakdown:

  • -l  username to log in as
  • -i keyfile to use (passwordless login, optional but recommended)
  • -p port to ssh to. This will be random and told to you by the android ssh server on the phone.
  • -D port for your dynamic (socks) proxy to bind to. This can be anything of your choosing.

The phone <-> OOB server tunnel is now established. This tunnel will be used to provide 4G internet access to your server.

Next, configure tsocks to use our newly created tunnel. The options we want to modify are Local Networks, server, and server_port.

sudo vi /etc/tsocks.conf

local =
server =
server_port = 9999

You can now use the 4G internet if you prepend tsocks in front of the program you want to use the internet.

Update 07/01/2015 I discovered my off site router changes SSH host keys every reboot. This was causing SSH to fail due to host key mismatches. Disable strict SSH host key checking per this post to get around this:

vi ~/.ssh/config

Host *
    StrictHostKeyChecking no

Update 08/04/2015

I found an even better way than the one above to avoid SSH key changing errors. Simply add the following options to your ssh command:

-o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null

That takes care of changing ssh keys for good. Thanks to this site for the info.

Establish tunnel with external server

Now that we have 4g internet we can use autossh to call out to an external SSH server (my parent’s router in my case.) This time we will be initiating a reverse tunnel. It will cause the remote server to listen on a specified port and tunnel all traffic on that port through the SSH tunnel to your local server. Note that you will have to copy your public key generated earlier to this remote host as well.

tsocks autossh <remote server IP/DNS> -p <remote port> -l<remote user> -i <remote keyfile> -R5448:localhost:22

The local <-> remote server tunnel is now established. The remote port to listen on (-R argument)  can be anything of your choosing. Remember what port you used for the last step.

Automating connections

Since the SSH connections are interactive I’ve found it easier to run these commands via screen as I outline in this post. To have these tunnels form automatically on startup we will have to make a quick and dirty upstart script as detailed here and further clarified here.

vi /etc/init/tunnel.conf
author "Your name goes here - optional"
description "What your daemon does shortly - optional"

start on started dbus
stop on stopping dbus

# console output # if you want daemon to spit its output to console... ick
# respawn # it will respawn if crashed/killed

 screen -dm bash -c "autossh -l nicholas -i /home/nicholas/.ssh/oob -p34097 -D9999"
 sleep 5
 screen -dm bash -c "tsocks autossh -l root -p 443 -i /home/nicholas/.ssh/oob -R5448:localhost:22"
end script
sudo initctl reload-configuration

Accessing your server out of band

Now that we have a tunnel established between our local and remote servers, we can access our local server through the remote server. On the remote server:

ssh localhost -p5448

The -p command of ssh specifies which port to connect to. Since we have a reverse tunnel listening on port 5448, the server will take the ssh connection you’ve initiated and send it through the intertubes to your OOB server over its 4G connection.

If you would rather SSH into your OOB server directly from your laptop instead of through your remote SSH server, you will need to create more tunnels, this time regular local port forwarding tunnels. Why would you possibly want more tunnels? If you want to access things like SSH, VNC or RDP for servers on your network through your OOB tunnel directly to your laptop, it will be necessary to create even more tunnels through the tubes.

First tunnel (to expose the OOB server’s SSH port to your laptop)

ssh <remote server> -L2222:localhost:5448

-L specifies which port your laptop will listen on. The other two parts  specify where your laptop will send traffic it sees on that port (from the perspective of the remote SSH server.)

Second tunnel (to expose ports of servers of your choosing to your laptop as well as give you shell access to your local OOB server) You can add as many -L arguments as you wish, one for each address/port combination you wish to access.

ssh localhost -p2222 -L3333: ... ...


If you’ve made it this far, congratulations. This was an exercise in accessing my home network even if the internet connection goes down. You could bypass half of these tunnels if you set up an openvpn server on your out of band server, but that’s a tutorial for another time.

If you followed this madness you would have the following tunnels through the tubes:

  • SOCKS proxy tunnel from server to phone
  • Remote port forward tunnel from OOB server to remote server
  • Local port forward from remote server to your computer
  • Local port forward(s) from your computer to anything on your local network through the tunnel created above

Restore Verizon Galaxy S4 to factory firmware

My new job has a BYOD policy, which means I can use my personal phone for work use. Before I ascribed to their policy I wanted to make sure my phone was in pristine condition. I wrote earlier about how I rooted and flashed a custom ROM for my phone. This will explain how to un-do all of that and restore it to pristine factory condition.

I got my information from here, which is a great guide on how to do this.  I will mirror the files mentioned there as it’s well known that XDA mirrors come and go.

Here is the rundown:

  1. Download Samsung USB drivers from here and install them.
  2. Download ODIN 3.09 here (alternate)
  3. Download PIT file for the S4 here (alternate)
  4. Download full wipe stock firmware here (make sure you’ve backed up anything important) (alternate)
  5. Unzip everything into a common directory
  6. Run ODIN and flash back to factory
    1. Put your phone in ODIN mode by turning the phone off, then pressing and holding power and volume down at the same time. A message will appear, press volume up to confirm and enter ODIN mode.
    2. Plug your phone into USB and run ODIN on your PC. Make sure the odin log says Added!! If it doesn’t, drivers are not installed properly.
    3. Check AP and then press the AP button to specify the firmware file (wait a minute for md5 verification)
    4. Press the PIT button and select the PIT file downloaded
    5. Press start. It will take about ten minutes.
  7. Profit!


When I first tried to do this I soft bricked my phone. I was very confused because everything seemed to be going fine and then suddenly FAIL

<ID:0/003> sbl1.mbn
<ID:0/003> sbl2.mbn
<ID:0/003> sbl3.mbn
Complete(Write) operation failed.
<OSM> All threads completed. (succeeded 0 / failed 1)
<ID:0/003> Removed!!

I scratched my head for quite some time before I came across came across this post suggesting it’s a bad USB cable / port. Sure enough, I switched out the cable I was using with the official cable the phone came with, and it worked beautifully!

Rooting and flashing Verizon Galaxy S4 VRUFNC5

Below is my experience with rooting and flashing a newer ROM on my Verizon Wireless Samsung Galaxy S4. Thanks to a recently discovered kernel exploit (both scary and awesome) rooting was the easy part. Thanks to the encrypted bootloader on my phone and the KitKat update which made it impenetrable (at least for now) getting a new ROM on the phone was a little more difficult. Thanks to for the informative video guide.

  1. Root the phone with towelroot.
    Simply navigate to the site, click the lambda to download the towelroot APK, then copy to your device and install it.
  2. Install SuperSU from the Google Play store
  3. Install Android Terminal Emulator
  4. Set selinux to permissive mode
    Open terminal editor and type the following:
    setenforce 0
  5. Install busybox
  6. Install Safestrap 3.72 (the ATT version works fine)
  7. Reboot into safestrap and backup the current ROM (optional, but recommended)
  8. Install ROM of choice via Safestrap on the Stock ROM slot (other slots don’t work as of this writing.)
    I chose the hyperdrive ROM
  9. Flash safestrap KitKat module to fix Wireless functionality
  10. Remove “Press and Hold to add items to launcher screen” by dragging a widget from one screen to another