Using TPM as a source of randomness entropy

Lencois_Maranhenses_7-x256A headless server by definition has no input devices such as a keyboard or a mouse which provides a great deal of external randomness to the system. Thus, on such a server, even if using rotational hard disks, it can be difficult to avoid the depletion of the Linux kernel’s random entropy pool. A simplified view of this situation is if the entropy pool is deemed too low, one of the “dices” which generates random numbers is getting biased.  This is can be even more exacerbate on server hosted in virtual machines, but this article won’t help you in this case.

Update 2015-08-24: the article was updated to provide some more information on TPM and commands adapted to the new systemd-based Ubuntu 15.04 and newer. When marked, use either the classic commands from Ubuntu 14.04 LTS and older or the newer ones.

The level of the kernel entropy pool can be checked with the following command:

$ echo $(cat /proc/sys/kernel/random/entropy_avail)/$(cat /proc/sys/kernel/random/poolsize)

(Note depending of the workload of your server the above result could be considered adequate or not)

What means a depleted entropy pool? It means that any call to /dev/random would be blocking until enough entropy is available. A blocking call is not usually wished, it means the application could be considered frozen until the call is freed. On the other side, calls to /dev/urandom would not be blocking in such situation, but there is a higher risk that the randomness quality of the output decreases. Such a higher risk could mean giving a higher chance for an attacker to predict your next dice roll. This could be exploitable or not and it is hard to tell, at least for me. Therefore, I tend to try avoiding having a depleted entropy pool especially for certain workload.

There are several mechanism to provide randomness sources to the entropy pool. The haveged daemon uses some CPU clock timers variation to achieve that, but it is highly dependant of the CPU being used. Other approaches are using sound cards, etc. And finally there are hardware random number generators (RNG). In my previous article, I talked briefly about the hardware RNG from the Raspberry Pi. In this article, I will present another hardware RNG which is available in many computers and servers: Trusted Platform Module (TPM).


I found the name somewhat marketing, and I’m not even sure we should trust it that much. But we will activate it only to provide a new source of entropy and nothing more. I would advise to use other source of entropy as well. Anyway, if interested the following paragraphs are describing how to achieve this, and if you decide to implement them, be reminded that I give no warranty that it will work for you nor that it won’t break things. I can only guarantee you that it worked on my machine running Ubuntu 14.04.2 LTS.

Let’s install the necessary tools and deactivate the main services (the tools launch a daemon which we don’t want to use as we will use rngd to get and verify the randomness of the TPM RNG before feeding the entropy pool).

Ubuntu 14.04 LTS

$ sudo apt install tpm-tools
$ sudo update-rc.d trousers disable
$ sudo service trousers stop

Ubuntu 15.04 and newer

$ sudo apt install tpm-tools
$ sudo systemctl stop trousers.service
$ sudo systemctl disable trousers.service

Then, you will need to go into the BIOS/EFI settings of your computer/server and activate TPM, and possibly clear the ownership of the TPM if it happened to be owned by someone else. Of course, don’t do that if it is not your computer.

I found out that my particular BIOS option only allow clearing from the BIOS settings. Trying to do so from the OS results in the following:

$ sudo tpm_clear --force
Tspi_TPM_ClearOwner failed: 0x0000002d - layer=tpm, code=002d (45), Bad physical presence value

I also found out that my particular BIOS when clearing the ownership, deletes also the Endorsement Key (EK). When I was trying to take ownership of the TPM device (see further) I was getting the following error:

$ sudo tpm_takeownership
Tspi_TPM_TakeOwnership failed: 0x00000023 - layer=tpm, code=0023 (35), No EK

So I had to do an extra step, to generate a new EK:

$ sudo tpm_createek

After having creating a new EK, I was able to successfully take ownership of the TPM device.

$ sudo tpm_takeownership
Enter owner password:
Confirm password:
Enter SRK password:
Confirm password:
tpm_takeownership succeeded

Once all this is done, we are ready to load the TPM RNG kernel module and launch the user space tool that will use this source to feed the Linux kernel entropy pool. The user space tool are the rng-tools suite (with the rngd daemon).

Load the kernel module (to load it permanently add tpm_rng as a new line to /etc/modules):

$ sudo modprobe tpm_rng

And then install the user space tool.

$ sudo apt install rng-tools

The default configuration should be good enough. But you can check it by editing the file /etc/default/rng-tools. The default settings for rngd are to not fill more than half of the pool. I don’t advise to set it to higher, unless you really trust blindly those TPM chips. If you have installed the tool, it should already be running but if you modified the default settings then a restart is necessary.

Ubuntu 14.04 LTS

$ sudo service rng-tools restart

Ubuntu 15.04 and newer

$ sudo systemctl restart

Now you can check again the available entropy with the command that I gave at the beginning of this post.

Installing Linux on Raspberry Pi – The Easy Way

As I announced, I got a Raspberry Pi 2 Model B and although I did not get much time to play yet with it, it was just an excuse to get back to programming and a little computer science fun.

Anyway, I’ve installed Raspbian on it and did a few configurations which I think are worthy to share with others. I’m not going to describe a step-by-step to install a Linux distribution on your Pi, I recommend trying NOOBS and check the good documentation from the Raspberry Pi Foundation. With this setup you can choose during the installation process which Linux distribution to install.

That’s what I did as a warm-up and a quick way to get an up-and-running Pi.

Note that the Raspberry Pi 2 has a new CPU (ARMv7) which is not yet fully exploited by most distribution targeted at the Raspberry Pi ecosystem (with the exception of the Linux kernel). There is one exception: Snappy Ubuntu Core but it is yet alpha. However it should be possible to install most standard Linux distribution that are supporting ARMv7 instructions set, however this is an interesting exercise which I did not perform (yet).

Anyway, using the NOOBS installation or any of the images provided for SD Card has several implication in terms of security. Here is what I recommend to do after the first boot.

Changing password and locking root

If you use the Raspbian installation, then you have one user account `pi’. If you haven’t changed the password for this user during installation, then better do it now. Once connected as `pi’ do:

$ passwd

And enter and then confirm the password you want to use.

With Raspbian, the `pi’ user has administrator’s rights. You can call sudo to perform system changes. If you are comfortable with that, then simply lock the root account:

$ sudo passwd -dl root

Or if you simply want to give a password of your own and use root:

$ sudo passwd root

Getting some Entropy

I am preparing a more detail article on this topic, so for now I am only going to give some background and the commands to increase the sources of entropy. Entropy is important, you need sufficient entropy (which your Linux kernel can gather for you) to be able to generate good pseudo-random numbers. Those numbers are used by many cryptographic services, such as generating SSH keys or SSL/TLS certificates.

The problem with embedded devices such as the Raspberry Pi (especially if you run it headless like I do) is that there aren’t many sources of entropy available to the kernel, especially at boot time.

The Raspberry Pi has an integrated hardware random number generator (HW RNG) which Linux can use to feed its entropy pool. The implication of using such HW RNG is debatable and I will discuss it in the coming article. But here is how to activate it.

First of all, load the kernel module (aka driver) for the HW RNG (the Raspberry Pi 2 can use the same kernel module as the Raspberry Pi 1 models). The Linux way of doing it is via modprobe:

$ sudo modprobe bcm2708-rng

If it worked a new device should be now available /dev/hwrng and the following should be visible in the system messages:

$ dmesg | tail -1
[ 133.787336] bcm2708_rng_init=bbafe000

To make the change permanent, on any Linux system you simply load the module in the /etc/modules file by adding a new line with bcm2708_rng (see next command). Or you can use the Raspberry Pi firmware Device Tree (DT) overlays (see below).

$ sudo bash -c 'echo bcm2708_rng >> /etc/modules'

Now install the rng-tools (the service should be automatically activated and started, default configuration is fine, but you can tweak/amend it in /etc/default/rng-tools)

$ sudo apt-get install rng-tools

After awhile you can check the level of entropy in your pool and some stats on the rng-tools service:

$ echo $(cat /proc/sys/kernel/random/entropy_avail)/$(cat /proc/sys/kernel/random/poolsize)                                 
$ sudo pkill -USR1 rngd; tail -15 /var/log/syslog
rngd[7231]: stats: bits received from HRNG source: 100064
rngd[7231]: stats: bits sent to kernel pool: 40512
rngd[7231]: stats: entropy added to kernel pool: 40512
rngd[7231]: stats: FIPS 140-2 successes: 5
rngd[7231]: stats: FIPS 140-2 failures: 0
rngd[7231]: stats: FIPS 140-2(2001-10-10) Monobit: 0
rngd[7231]: stats: FIPS 140-2(2001-10-10) Poker: 0
rngd[7231]: stats: FIPS 140-2(2001-10-10) Runs: 0
rngd[7231]: stats: FIPS 140-2(2001-10-10) Long run: 0
rngd[7231]: stats: FIPS 140-2(2001-10-10) Continuous run: 0
rngd[7231]: stats: HRNG source speed: (min=824.382; avg=1022.108; max=1126.435)Kibits/s
rngd[7231]: stats: FIPS tests speed: (min=6.459; avg=8.161; max=9.872)Mibits/s
rngd[7231]: stats: Lowest ready-buffers level: 2
rngd[7231]: stats: Entropy starvations: 0
rngd[7231]: stats: Time spent starving for entropy: (min=0; avg=0.000; max=0)us

Securing SSH – the basic

I run my Pi headless for the moment. So after the first boot, I went into the advanced configuration of the raspi-config and activated SSH daemon. I’m not here going to describe how to properly secure the SSHd daemon, which can be a topic for a future article. I’m only going to focus on one topic which is SSH host keys.

SSH host keys are the means for a user connecting to a remote server to verify the authenticity of the server. That the sort of message you see the first time you connect to an SSH server:

$ ssh pi@raspberrypi
The authenticity of host 'raspberrypi (' can't be established.
ECDSA key fingerprint is 42:3d:4f:b7:0b:4b:62:11:47:28:cc:86:76:0c:ac:24.
Are you sure you want to continue connecting (yes/no)?

If an attacker tries to spoof your SSH server, on connection you will get this message:

$ ssh pi@raspberrypi
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that a host key has just been changed.
The fingerprint for the ECDSA key sent by the remote host is
Please contact your system administrator.
Add correct host key in /home/pithagore/.ssh/known_hosts to get rid of this message.
Offending ECDSA key in /home/pithagore/.ssh/known_hosts:3
  remove with: ssh-keygen -f "/home/pithagore/.ssh/known_hosts" -R raspberrypi
ECDSA host key for raspberrypi has changed and you have requested strict checking.
Host key verification failed.

So this is all good, but the problem with these host keys is that you cannot really trust the one installed by default. They could be the same as the one from the image you downloaded and flashed on your SD Card, and so would be similar to all other persons installing the same image. Another problem is that they could have been generated at a point in the installation where not enough entropy was gathered by the kernel to be able to provide non-predictable random numbers. Therefore someone could use this to generate new host keys that would match the one on your Raspberry Pi.

Now that in the earlier chapter we added good source to feed the entropy pool, we can regenerate better host keys. First get rid off the previous ones:

$ sudo rm /etc/ssh/ssh_host_*key{,.pub}

Then generate new ones with one of the 3 possibilities:

  • Automatic configuration using dpkg
$ sudo dpkg-reconfigure openssh-server 
Creating SSH2 RSA key; this may take some time ...
Creating SSH2 ECDSA key; this may take some time ...
Restarting OpenBSD Secure Shell server: sshd.
  • Automatic configuration using ssh-keygen
$ sudo ssh-keygen -A
$ sudo service ssh restart
  • Manual configuration
$ sudo ssh-keygen -t rsa -b 4096 -N "" -f /etc/ssh/ssh_host_rsa_key
$ sudo ssh-keygen -t ecdsa -b 521 -N "" -f /etc/ssh/ssh_host_ecdsa_key
$ sudo service ssh restart

Now if you want to print the fingerprint of any of your host keys to make sure of the authenticity of the server you are connecting to (should only be needed the first time your client connects to your server):

$ ssh-keygen -l -f


Gnome 3 on Ubuntu LTS

This mini how-to is to install Gnome on Ubuntu 14.04 LTS. Of course the best approach would have been to install Ubuntu Gnome in the first place. But if you didn’t (like me) and have Unity as desktop and would like Gnome (or just give it a try), check the rest of this article.

Note and disclaimer: Gnome3 will be available alongside Unity. So you can always switch back and forth between the two without troubles. However, a word of caution, as usual with system modifications, make sure you have backups available and working before proceeding. I make no guarantee that the following will work for you. I’m only stated it worked for me.

Installing Gnome Shell (aka Gnome3)

Installing the “core” Gnome 3 is rather easy. You need to have the Universe repository activated and then:

$ sudo apt update; sudo apt upgrade
$ sudo apt install gnome-shell

During installation of gnome-shell, you will be prompted to choose between GDM (the default Gnome Display Manager) and LightDM (an alternative Ubuntu is using by default). The main functions of these DM, from an end user perspective, is that they provide a graphical login where you can choose the user (and type a password) and choose the desktop environment to use once logged in. In addition these DM can offer things such as autologin. There is no wrong answer here. You can stick with LightDM (it is the one installed by default on UBuntu, and that’s the option I chose) or switch to GDM. In both cases, you need to choose for the session if you wish to use Gnome or Unity desktop environment.

Now you can log out and log in again (choosing Gnome for the session).

Installing some missing default Gnome Apps

This is entirely optional. If you have seen Gnome3 release notes, you will be looking for a few extra applications that are not installed by default by Ubuntu and that are available in the Universe repository. Example applications: Gnome Maps, Gnome Weather, etc.

To install them, you can either install the gnome-core package which will install a minimal Gnome applications environment to start with. Or install a complete Gnome applications environment (which includes all of gnome-core) by installing the package gnome. Or finally simply install a few goodies (a subselection of gnome) that is tailored to your needs. Here is a list of goodies that I installed (from Universe Repos):

$ sudo apt install eog-plugins gnome-{backgrounds,boxes,clocks,color-manager} \
  gnome-{dictionary,documents,maps,packagekit,shell-extension-weather} \
  gnome-{system-tools,weather,music,photos} gnote

And a few others from the main repos:

$ sudo apt install gnome-user-share indicator-printers

And with this, you can get a nice Gnome environment with a Ubuntu based OS.

For Ubuntu 14.10 Users

The above instructions works also for Ubuntu 14.10 users.

Too long without programming

I love programming! And because I do it less and less at work, I felt the need to do something about it.

I was looking for a project to help when I read the news about the new Raspberry Pi. And it took me only a couple of days to realise that was it, so I ordered it online and just received it. Raspberry Pi 2 Model BA beautiful little device with enough connectivity and power to have some fun!

I did not have much time yet to play with it, I was able to install Raspbian on it and that’s it. But I’m quite happy about my decision and I’m looking forward for the projects I plan with it (I’m hesitating between creating a weather station together with a small Arduino board as the “sensor”, or perhaps starting with something less ambitious maybe related to home automation).

Click more to see the system information (OS name, memory and CPU information) of that little wonder.

Continue reading “Too long without programming”

Comments blocked on Magical World

Today I took the decision to block all comments on Magical World.

Spammers are currently flooding the blog with spam which are filling up our backend database (it is a small and cheap hosting service). Although all spam are captured by our spam filter, we end up with our hosting service provider blocking SQL insert and update statements. It basically freezes our website.

In the near future I will evaluate a better solution and restore comments. But for the time being, feedback can be provided to us via the contact us page.

How to verify your Synology NAS hard disks

I upgraded my 2 HDD in my Synology NAS to bigger ones. The change and rebuild of the RAID mirror was seemless. But I wanted to verify the health of the filesystems before growing the volumes. Here is how to do it.

Note: I am making the following assumptions, you know what you are doing, you activated SSH on your box and know how to connect as root, you know and understand how your NAS HDD have been configured, you have a wokring backup of your HDD data, you are not afraid of losing your data.

First find out what is the drive name of your volume(s) and also what is the filesystem type:

# mount
/dev/root on / type ext4 (rw,relatime,barrier=0,journal_checksum,data=ordered)
/dev/mapper/vol1-origin on /volume1 type ext4 (usrjquota=aquota.user,,jqfmt=vfsv0,synoacl)
/dev/mapper/vol2-origin on /volume2 type ext4 (usrjquota=aquota.user,,jqfmt=vfsv0,synoacl)

In my case, I have created 2 volumes on top of my mirror. The device on which these volumes are stored are /dev/mapper/vol1-origin and vol2-origin, they are both ext4 filesystems. But you probably do not have such a setup and only have one volume on top of your RAID array and your device might simply be /dev/md[x].

The fact that my devices were in /dev/mapper hinted me that they might be a LVM layer somewhere. So I executed the following command (harmless):

# lvs
LV                    VG   Attr   LSize    Origin Snap%  Move Log Copy%  Convert
syno_vg_reserved_area vg1  -wi-a-   12.00M
volume_1              vg1  -wi-ao    1.00T
volume_2              vg1  -wi-ao    1.00T

So my 2 volumes are LVM logical volumes. Now that I have this information, I can do the following to verify the filesystems’ health. First of all, shutting down most services and unmounting the filesystems:

# syno_poweroff_task

Now if you did not have LVM but rather a /dev/md[x] device, you can simply do (if you have an ext2/ext3/ext4 filesystem only, and replace the ‘x’ by the correct number):

# e2fsck -pvf /dev/mdx

But if like me you have LVM, then you will need a few extra steps. The ‘syno_power_off’ has probably deactivated the LVM logical volumes, to be sure check the “LV Status” given by the next command (harmless, not the complete output is here given):

# lvdisplay
--- Logical volume ---
LV Name                /dev/vg1/volume_1
VG Name                vg1
LV UUID                <UUID>
LV Write Access        read/write
LV Status              NOT available
LV Size                1.00 TB

As you can see the logical volume is not available. We need to make it available so that the link to the logical volume is accessible:

# lvm lvchange -ay vg1/volume_1
# lvdisplay
--- Logical volume ---
LV Name                /dev/vg1/volume_1
VG Name                vg1
LV UUID                <UUID>
LV Write Access        read/write
LV Status              available
# open                 0
LV Size                1.00 TB

The status has changed now to “available”, so we can proceed with the filesystem verification:

# e2fsck -pvf /dev/vg1/volume_1

To finish this, you need to remount and restart all the stopped services. I do not know a specific Synology command to do that, so I simply rebooted the machine:

# shutdown -r now

What is PSS memory?

Measuring and understanding how a process is using the primary memory (aka RAM) is complex because Operating System have been optimising primary memory use to save space or optimise run time (memory map, virtual memory, kernel same page merging, etc.). Therefore most tasks managers are reporting several metrics to inform about memory usage, and even their own help page are sometimes reporting a wrong definition for a metric. So I am always learning new things about what actually all those metrics are measuring. Today’s is PSS:

Linux’s PSS (Proportional Set Size) metric. This is the amount of RAM actually mapped into the process, but weighted by the amount it is shared across processes. So if there is a 4K page of RAM mapped in to two processes, its PSS amount for each process would be 2K. The nice thing about using PSS is that you can add up this value across all processes to determine the actual total RAM use. – Android Developer Blog, Understanding How Your App Uses RAM

OS X unstability, Mavericks is just unfinished!

I am really really disapointed by Apple, and for more than just one reason. Here below is my list of  growing concerns with the company and especially how they molest OS X.

First of, when I have a stable running system, the last thing I want to hear is that there is availability of an upgraded OS version which, on top of providing new features, is correcting several security flaws which won’t be corrected on the current stable OS release!!!

Imagine a world where Microsoft would have stopped providing security updates to Windows XP the day Vista was out, even if it had been for free, would you have done the upgrade right away? No! You want to wait that the new OS gets stable enough (in Vista’s case that meant waiting for Windows 7) before you upgrade.

Well bad luck, Apple decided last October to provide OS X 10.9 (a.k.a Mavericks) to everyone without providing further supports (at least in terms of security updates) to previous OS X versions. Giving this upgrade for free was just the sweet juice to cover the bitter poison taste.

I analysed the vulnerabilities in our current OS X version and decided that I could wait for OS X 10.9.1 before upgrading, hoping that Apple would also see that stopping security updates on previous OS X versions was plain stupid. This did not happen and shortly after OS X 10.9.1 was published I did the jump and upgraded.

The upgrade was bug free, but not the use of OS X since then. For the past month we have been struggling with the following problems:

  • Impossibly slow to switch users (my wife and me are sharing the same and unique MacBook, so we do use quite often this feature)…
  • …when it does not simply hang in the process of switching!
  • The screen, mouse and keyboard freezes randomly, often this is related to the insertion of the Thunderbolt network adapter, other times it is out of the blue.
    Note: sometimes pulling out the Thunderbolt plug unfreezes the Mac, sometimes not.
  • Mail App crashes often or the geometry of the window keeps on changing to the weirdest form. I simply stopped using it.
  • Launchpad should support keyboard input to quickly filter the list of application, so that typing “Con” would propose you “Contacts”, “Console”, etc.. But since Mavericks this handy feature does not work everyday.
  • WiFi needs router reboot to get IP address after the computer was asleep. It is a bug from iOS that has been carefully ported to OS X. Now I can also enjoy router reboot because I just want to use the WiFi! Yeah!
  • App Store updates which get lost: I got notified that I had 1 possible updates, I fired up the App Store app and clicked on Update. I saw that Evernote had an update but then the computer froze. I waited 5 min after which I shutted down and restarted. The App Store shows no update to perform (even after search for them) but looking for Evernote shows that it can be updated! That’s a reliable update mechanism!

Giving upgrade for free is no excuse for the unstability and little testing that this OS X Mavericks has received. Take the example of Ubuntu and their Long Term Support release, that is serious work done and they also provide their upgrades for free!

So I really despise Apple for bragging so much about the 200 new features coming along with OS X Mavericks. Well I have seen a myriad of bugs, if they count as new features then yes they probably are not far from the 200 ones. But apart from an application which provides maps (where is the web version of it, I don’t want an app for that!), another one for reading books (like a MacBook is the most handy reading machine, sure!!) there are close to no visible features to the end-users. Ho yeah I forgot tags, like I am going to tag the 1 TiB of data I own just because I can!!!

Really Apple, stop wasting so much of your developers time into just providing what looks like a new skin for iOS 7+ and invest some valuable effort into bringing back OS X to the stable and professional OS it was!

Addendum – 2014-02-05: Today I tried to rate the OS X 10.9.1 application in the Mac App Store, my rate was one star, I clicked on it but got the following message “To rate this app, you must have purchased it from the Mac App Store”?!? Well it is true that I did not “buy” OS X 10.8, it was bundled with the laptop. So I only upgraded it to the “free” version from the Mac App Store using the Mac App Store.You can't give negative feedback ;-) So I did not technically buy it, true, but I own it! You can see a screenshot on the right-end side.

How to revert phone encryption on Android

How to revert your Smartphone encryption, credit: image based on Oxygen Icons
Smartphone Encryption Reverted

I am a recent owner of a smartphone (since August 2013), it is a relatively old one, a Samsung Galaxy S (GT-I9000), but it is still a usable and cool computer-in-a-pocket/phone.

Samsung dropped support for the phone a long time ago, but other projects picked-up and you can install various Android distributions on it. I am running CyanogenMod 10.2 (Android 4.3) and it works great.

I would anyway have done so even if Samsung would have continued support ;-) but that could be a story for another post and another day.

Encryption has slowed down the phone

However, one month ago I decided to encrypt the phone, this was a good idea (and I would recommend anyone to use encryption on a device as mobile as phones) but it turned out to slow down excessively everything on the phone up to the point that I was barely using it. Even calling or answering the phone was a pain.

I was decided to revert the encryption without losing too much of the data/settings of the phone. Here is how I did it.

Note: the following steps worked for me, it does not necessary means it will work for anyone. I cannot be held responsible if by using this shared experience you lose any data.

Approach to revert the phone encryption

The approach is to do a full backup, restore to phone to “factory” settings (restoring the installed OS without encryption or any settings) and applying back the backup.

This approach should work on any Android version. But the instructions here are given for Android 4.x release, and for some steps are specific to CyanogenMod 10.1 and above and/or Samsung Galaxy S. If you have a different phone or Android, you will have to find the specifics by yourself (when there will be specific instructions, I will mention it either with CM10 for CyanogenMod 10.x or with SGS for Samsung Galaxy S).


As mentioned in the previous chapter, these instructions could work for other phones and Android versions, but I mention here only my own setup, the one on which I successfully went through these steps.

My environment:

  • A Samsung Galaxy S (GT-I9000) phone with CyanogenMod 10.2 installed;
  • A computer (OS X 10.9) with ADT installed (version 20131030);
    • Please make sure to install the ADT Bundle to be able to use adb.
  • A micro-USB cable to connect your phone to your computer.

Backup your data

For the backup, I have used adb (Android Debug Bridge) and I have used the recovery mode to reset to factory the phone. The rest of this section contains the various steps to do the backup.

Activate the adb daemon on the phone (CM10)

This steps depends on your Android flavour, please refer to your Android phone manufacturer documentation or community project. The instructions in this section apply to CyanogenMod 10.x.

When using CyanogenMod 10.2, you need to activate the Developer Options. This is done by taping 7 times the build number field in the About section of your phone Settings. You now have a new section in your Settings dubbed Developer Options.

Authorise to gain root access via adb
Authorise to gain root access via adb

Under Developer Options you can tick ON USB debugging which will activate the adb daemon once you connect your phone to a computer.

You need to also be able to give root access via adb in order to perform a full backup (that is my assumption). This is done by selecting ADB only or Apps and ADB in the Root access option under Developer Options (see screenshot).

Now plug your phone to your computer, your phone should ask for a USB debugging authorisation from the connected computer. You should authorise that.

You have now your phone ready to receive commands from your computer using adb.

Backup the phone using adb

The instructions in this section will be given for Unix/Linux/OS X. They work the same way for Windows, but the file path names will be different (e.g. ‘\’ instead of ‘/’, and so on). I am not going to give here Windows instruction. I assume that if you were able to install CyanogenMod on your phone, you can “translate” the below instruction for your platform. If you need assistance on Windows, you can use this excellent answer by Ryan Conrad.

Under Unix/Linux/OS X simply open up a Terminal. And go to where adb was installed. I assume below that you unpack ADT in your Desktop folder:

cd ~/Desktop/adt-bundle*/sdk/platform-tools

Now run the following command which will create a backup in your Desktop folder. This backup will include all applications and their data, all shared data (e.g. sdcard content) and full system backup.

./adb backup -apk -shared -all -f ~/Desktop/$(date +%F)-android-backup.abkp

Once you typed in this command, your device will ask you to confirm the operation and provide a password to encrypt the backup. I have used the same password as for the phone encryption, but I guess any password should work. Carefully remember the password because you will need it when restoring.

After you authorised the backup, it will take a while before it is completed (it took about 20 minutes for me).

Sadly, and this is a risk you will have to take, I know of no way to test the generated backup. After the completion of the above procedure, I simply checked the size of the file and verified that it could reasonably (even with some compression) contains my phone data. If you know better, let me know and I will update this section.

Reset to factory

Now come the part where you take some risk. In order to revert the encryption on the phone, we need to reset it to factory settings, which includes wiping out all your data. If the previous backup did not work or if your backup gets corrupted, your data might be lost once this step is performed. It is a good time to make a copy of the generated backup somewhere safe in case something goes wrong.

ClockWorkMod Recovery menu
ClockWorkMod Recovery menu (copyright Makvana @TheUnlockr)

First unplug your phone’s USB cable from the computer (this is optional I believe, but I think it is safer) and shutdown the phone. Once switched off, start your phone in recovery mode (e.g. on Galaxy S this is Volume Up + Home + Power). I assume you know how to use the recovery menu, without which you could not have installed your CyanogenMod version. But as a quick reminder, Volume Up/Down correspond to Arrow Up/Down and the Home button corresponds to Select.

Once in recovery mode, select the item wipe data/factory reset and proceed. This will delete all data on your phone, you have been warned. You will be asked to confirm and you should do so.

You have now a non encrypted phone freshly cleaned. We will need to restore your data. So please reboot the phone by selecting reboot system now.

Restore your data

After the reboot (it can take awhile, like a couple of minutes), you will be prompt to connect to your CyanogenMod and Google accounts. I do not have the former but do use the latter. So I skip the first step (which was registering the CM account) but proceeded with setting up my Google account.

Note: I am using Google 2-step verification and I did not remember my application password that I set-up for my Android phone. So I went to Google’s Account Security Settings on my computer and generated a new application password and revoking the previous one.

During the setup of my Google account I explicitly asked Google to restore my phone (I did use the phone built-in Google backup). After the setup, I waited that Google’s restore was over. Not much is restored by this feature, so I guess it is possible to skip this step, YMMV.

Now it is time to restore the full backup. You will need to reactivate the adb daemon, please refer to the above chapter. And once again the following instructions are given only for Unix/Linux/OS X and you will need a Terminal.

cd ~/Desktop/adt-bundle*/sdk/platform-tools
./adb restore ~/Desktop/$(date +%F)-android-backup.abkp
Android request confirmation to restore (image courtesy of Ryan Conrad)
Android request confirmation to restore (image courtesy of Ryan Conrad)

Note: if you were doing this late at night and have done the backup before midnight and are doing now the restore after midnight, you will need to remove “$(date +%F)” and replace it by yesterday’s date. ;-)

The restoration process will prompt a confirmation on your phone and ask you to enter the same password you used when you created the backup. Hopefully you remember it and can proceed.

The restoration is quite slower than the backup, and after 20 minutes I went to bed. So I do not know how long it took exactly. The app Google Play crashed several time during the restoration which did not seem to affect the process.

Once the restoration was completed, I rebooted the phone just to be safe.


Do not yet delete the full backup on your computer, keep it for awhile just in case.

But you should definitively restore the Developer Options to their original settings:

  • Root access: Apps only
  • USB debugging: OFF (unticked)

And switch OFF the Developer Options all together. You can unplug your phone from your computer and delete ADT bundle from it too (though I would keep it as long as the full backup file).

What worked and What didn’t

With my own experience, everything was restored but some applications authentication, no was data loss. So the approached was a success IMHO.

Some applications lost the authentication, I simply either had to request sign-in and it auto-magically found the account information again (e.g. Firefox Sync) or to request sign-in and fill in my login and password again.

Regarding specifically Google’s 2-step verification and the Google’s Authenticator app, the configuration of this application was not restored, but via Google Account’s Security I was able to set it up again in no time, which has invalidated the previous configuration at the same time. So perfect restoration with this extra step.


My phone is now unecrypted, which is sad, but on the other hand I can use it again. It is now reasonably fast again that I can use applications and browse the web on the go. CyanogenMod 10.2 is a great update, the phone feels more responsive and as definitively more battery life (recharging it every 48h instead of every 36h).

The State of Retina Displays

Since almost a year, I own a retina display device. This type of screen has been so much praised by reviewer that I fell for it. So I got a 15″ Retina MacBook Pro. The screen is indeed beautiful but next time, I will save on the retina display premium cost and buy instead a good external screen.

On a retina screen optimised applications look gorgeous, but I am not a pixel junky and applications can look beautiful too on a non-retina screen. However most non optimised apps look dreadful and pixelated, and they are still loads of them. In addition, little application make really use of the extra amount of pixels, so it just looks slicker for fonts but does not really make use of the extra space.

The money saved by buying a non-retina notebook can be used to buy an external display, and with a small addition a 27″ WQHD screen which is not retina but offers an incredible space to work, I got one at work and I love it, better than a retina display.

So if you need to choose, don’t get the retina and get an extra external screen for that price! You will be more productive.

Corollary: don’t follow the advice of these guys here at CNET. An ultrabook/Air device is meant to have a lot of battery life, so a manufacturer that delivers a good screen with incredible battery (10 hours and more) is doing the right choice. And if that means no retina and no touch screen, then be it. We can wait another couple of years to enjoy this little amusement while keeping sustained battery use.