Save Bash Output to A File – Automatically

I often have a need to save the output a bash file to another file, e.g., log file. I know I could use redirection “>” or “tee”. But I would have to type it from command line. This post talk about doing it from within the script itself.

Google search does not yield much meaningful results. To save the hassle for me and potentially others. Here is the straight no-BS code.


readonly file="output"
exec 1> >(tee $file)
exec 2>&1

Experience of Donation With Cardano

I just made a donation of 15 ADA to Cardano Forest project. I like share my experience and some thoughts.

The process is relative simple:

  • View the project page on web browser,
  • Click the donate button and copy the receiver address
  • Then switch to Yoroi wallet app on the phone
  • Click “Send” button, paste the receiver address, enter 15 ADA and click “continue” finish the sending.

First, this is really just a payment use case, which in theory it should not be too much different from, say, a PayPal-enabled transaction. However, there are 3 important differences.

  • No intermediary party needed. It is just one address paying another address. No platform company like PayPal or banks needed to facilitate the transaction.
  • No personal information exchange. None of email, name, or phone number get exchanged.
  • NFT token to ensure tracking of your donation to the true beneficiary. You will get a NFT token for every tree planted. Each ADA will plant 1 tree. People can still make flaws here, but the whole process is definitely more transparent and more trackable.

You can find out more at their web site. It is a good cause, and I encourage everyone to donate, not only for the cool and new experience, but also for its cause.

A few wishes that would make the experience even better.

  • I wish there is a “pay” button from the donation web page which triggers Yoroi mobile app directly. This is more of Android/iOS issue.
  • I wish the receive address and related qr code can embed the ADA amount, and perhaps even a short memo.
  • I wish Yoroi mobile app can scan a QR code from a picture, which is useful when you have the mobile phone for both web viewing and QR code scanning.

Please consider staking with us @ MYADA pool

Increase Root Volume Size for AWS EC2 Linux Instances

It turns out it is extremely simple to increase volume size for AWS EC2 Linux instances. In this article we use Ubuntu 20.04 as an example to show how it works in simple 3 steps, without restarting the instance.

  1. Increase volume size – Go to AWS console; find the volume used for the instance as the root device; Choose “Modify volume” action item; increase the size to the desired number
  2. Log into the AWS machine, type “lsblk” to verify the root device size has been increase. Also confirm that the partition size remains the same as before.
  3. Expand partition size to fill up the drive. For example, if root device is /dev/xvda and root partition is the first partition, you would run “sudo growpart /dev/xvda 1”. Run “lsblk” again to verify partition size.
  4. Resize filesystem to use the new space. For the previous example, one would run “sudo resize2fs /dev/xvda1”. Run “df -h /” to verify.

Viola! You are done!

Install Full Ubuntu on Portable USB Drive


My goal is to install fully updateable Ubuntu 20.04 onto a USB stick, so that I can boot it up with any Intel-based PC’s or laptops. However, due to what I considered a bug in Ubuntu, this is actually harder than it should be. So I wrote down this blog in the hope it might help others, as well as my future self, in the similar shoes.

Note that the objective is different from so-called LiveUSB ubuntu with persistency, where Ubuntu OS itself will remain as a static ISO image and updates are added on-top in a separate persistent partition. My goal is to install a standard Ubuntu OS on a USB disk, which can be updated and upgraded just like normal PC case, except that a) it is on a portable USB drive or disk and b) it is portable across different PC’s. I suppose this setup gives longer life span of the installation, which potentially allows you to even upgrade your OS later.

In the following steps, I will also show an optional feature which creates an encrypted home directory.

Assumptions and Prerequisites

  • You need Intel x86_64 PC
    • We assume it support UEFI and GPT partitions which are standards for all recent ones
  • A USB drive that holds Ubuntu ISO image for installation, a.k.a. the installation media drive. This needs to have 4GB minimum size.
  • A second USB drive or disk that will hold installed Ubuntu OS, a.k.a. the installation target drive. This one needs 16GB minimum size

Step 1 – flash Ubuntu ISO image to the installation media drive

I will not repeat the process here. Please refer to many pages below.

Step 2 – Prepare the partition table on the target drive

  • Insert installation media drive into PC.
  • Interrupt normal booting sequence and choose the media USB drive as the boot device
    • Different PC have different process to do this. On Lenovo PC, one has to press ENTER on bootup, and then press F12 to select boot device
  • Select “Try Ubuntu” when presented the option
  • Insert target USB drive
    • Identify which drive is target USB drive by examining the output “lsblk”
    • In most case if you follow the instructions exactly, it would be “/dev/sdb”
  • Once Ubuntu is up and running, start a terminal and type “sudo gparted /dev/sdb” (replace “/dev/sdb” with the right usb device you have for the target USB drive)
    • create GPT partition table
      • click “Device”/”Create Partition Table …”
      • select “gpt” as partition table type
      • See Pic #1 below
    • create 100MB fat32 partition as ESP partition
      • Click “Partition”/”New”;
      • Enter “100MB” as size and select “FAT32” as file type
      • See Pic #2 below
    • set “esp”, “boot” attributes to the new ESP partition
      • Apply changes to actually crate the partition
      • Select the ESP partition and then select “Partition”/”Manage Flags”
      • In the pop-up window, select “esp” and “boot” flag
      • See pic #3 below
    • create an ext4 partition that takes the rest of space for root partition
      • See pic #4 below
    • (optional) if you like to have encrypted home partition, create an ext4 root partition with size of 10GB or more, and leave the rest free space open for encrypted home petition later.
      • Pic #5 shows the partition table at this step.
Pic #5 – after create ESP and root partitions

Step 3 – Install Ubuntu

Once we finish the above step, quit gparted and we are ready to install Ubuntu into the target USB drive.

  • click “install ubuntu” icon on the desk to to start installation
    • select “something else” in partition page. See Pic #6 below.
    • select the ESP partition on the target USB drive as the “ESP” partition. See Pic #7 below.
    • select root partition and mount as “/”. See Pic #8 below.
    • (optional) Create encrypted physical volume
      • Select the free space left during creating partitions
      • Click “+” to create a new partition/volume
      • select “encrypted physical partition”.
      • See Pic #9 below.
    • wait for a while, select “/dev/mapper/sdb3_crypt” as “/home”. See Pic #10 below
    • Finish installation.

Step 4 – Fix EFI on target USB drive

At this point you might get an illusion everything is working, because if you reboot the PC you will be able to select either Ubuntu or Windows to boot up, and they all work. However, there are 2 very serious problems

  • If you boot into BIOS and select the USB disk as boot device, it won’t work.
  • Even worse, your PC is likely not able to boot up Windows either if you remove the target USB disk.

The reason for these problems is that, despite we told Ubuntu installer to install Ubuntu on the USB disk, which implies it should use the ESP partition on target USB disk, it still uses the ESP partition on PC built-in disk, and thus screws up EFI partition on PC and leave an empty EFI on target USB disk. See more details at this very old bug report.

So the first thing we need to do is to install Ubuntu loader into USB ESP partition and install grub into USB disk

  • Reboot into BIOS firmware and select “ubuntu” as the boot target
  • switch EFI mount
    • Type “lsblk” to verify that ESP partition on PC built-in drive is mounted
    • umount it, “sudo umount /boot/efi”
    • mount the right one, ” sudo mount /dev/sda1 /boot/efi”
  • install grub boot on USB EFI partition
    • “sudo modprobe efivars”
    • “grub-install -d /usr/lib/grub/x86_64-efi –efi-directory=/boot/efi/ –removable /dev/sda”
    • Note “–removable” flag is important in the above command as it allows USB to boot on any Intel-based PCs
  • Reboot into BIOS firmware and select target USB as boot device. It should work now.
    • You can try the USB disk on other PCs, and it should work as well.

At this point, /etc/fstab is probably mounting PC EFI partition to /boot/efi, which is wrong and will break when you boot the target USB from another PC. You can either delete the /boot/efi line in /etc/fstab, or replace the UUID with the one for EFI partition on target USB. You can find out the UUID with “blkid” command (e.g., blkid /dev/sda1)

Step 5 – Restore PC boot loader

Now let us fix PC does not boot up problem (if you encounter this)

  • Boot up the PC into BIOS and select the newly made Ubuntu USB drive as boot device. This will boot into Ubuntu.
  • Open a terminal
  • Remove Ubuntu from PC EFI partition, and PC will boot up windows again
    • Mount host EFI partition as /mnt, “sudo mount /dev/nvme01n1p1 /mnt”
    • “cd /mnt/EFI/”
    • “sudo rm -rf ubuntu”
  • NOTE 1: If your PC is already installed with another Ubuntu system, the bootloader entry “ubuntu” will collide with each other and the previous Ubuntu will not be able to boot. You can follow this guide to restore booting the previous Ubuntu system.
  • NOTE 2: Annoyingly, if your PC is already installed with another Ubuntu system, each time you boot up with the USB target disk Ubuntu, it will modify the bootloader entry and cause previously installed Ubuntu unable to boot. It is possible to rename previous Ubuntu bootloader in some tricky way so that both can live peacefully. That probably warrant another blog.

Clone a Website Behind Login with WinHTTrack

I have an very old Fedora server that stopped active running almost 10 years ago. I need to backup its data for archive and physically dispose it.

It used to run wiki site based on moinmoin. If I just back its static files plus database files, chances are I will never be able to re-active those wiki pages and see them again. So I thought a better idea is to clone the web pages and turn them into static local web site, which I can still access easily.

It turns the journey is more complicated than expected. It took me more than a couple of hours to finally nail it down. So I figure it is worth a post here.

The Software

A quick search shows HTTrack seems to be best software for this job. It has a GUI version for Linux, called WebHTTrack. It also has a windows version called WinHTTrack. During my fiddling around, I ended up using WinHTTrack. In retrospect, the method used here should also work for WebHTTrack.

The Challenge

WinHTTrack is generally user friendly. The biggest problem is moin wiki requires a user login to view the content.

The cookie capture method (“Add URL” followed with “Capture URL”) does not work for moin wiki. Only first page works. Later pages still returns “You are not allowed to view this page”

The Solution

Step 1 – prepare cookies.txt file

  • Install and launch firefox browser
  • Install cookies.txt extension
  • Log into the web site and start browsing
  • Click on “cookies.txt” extension and export cookies.txt for the current site.
  • Also note the firefox user agend
    • Clock on top-right “settings” icon
    • Then click on “Help”/”Troubleshooting Information”
    • Note the “User Agent” string. We will use it later.

Step 2 – run WinHTTrack once

  • Start WinHTTrack and set up the project normally without worrying about login
    • Specifically, you don’t need to use “Add URL” button to do anything special. Just type in the URL in the text input area.
  • Click on “Finish” to start downloading
    • It will warn the site seems empty. That is expected.

Step 3 – copy over the cookies.txt

  • Copy the exported cookies.txt file to the top level directory of the local clone.
    • For example, if HTTrack working directory is “%USER%\Documents\httrack-websites” and your project name is “erick-wiki”, then the destination directory is “%USER%\Documents\httrack-websites\erick-wiki”

Step 4 – run it again with proper options

A few options had to be set properly

  • Click on “Set options …” and a new pop-up window shows up
  • On “Spider” tab, set “Spider” to “no robots.txt rules”
  • On “Browser ID” tab, set “Browser Identity” to the “User Agent” of Firefox browser noted in step 1
  • On “Scan Rules” tab, click on “Exclude links”, another pop-up windows shows up
    • Here you can exclude the files you like to clone
    • Most importantly, you need to exclude the “logout” URL. Otherwise cookies.txt will be updated/deleted and you will note be able to continue cloning
      • In my case, the URL will end with “?action=logout”. So I set “criterion” to “Links containing:”, and set “String” to “action=logout”
  • (Optional) On “Experts Only” tab, change “Travel mode” to “can go both up and down”
  • (Optional) On “Flow control”, set “number of connections” to higher number for faster cloning. Note: your website may have surge limit as Moinmoin does, in which case you will need to turn off this feature on the web server in order to increase bandwidth.
  • Once all set, click on “Next” and “Finish” to start cloning.

That is it!

Build, Flash and Un-Flash AOSP Image on Pixel Phones

In this post we will go through a full cycle of building a custom AOSP image, flashing it on a Pixel phone, and then restoring to original stock image. We will use Pixel 4 (codenamed as “flame”) as the device example. We will walk through in a succinct manner without detailed explanations.

Prepare the Device

  • Note the Android build number
    • Click “Settings”/”About Phone”.
    • In my case it is “QQ3A.200805.001”
  • Enable developer options
    • click on “Build Number” row 7 times to enable developer options
  • Enable “OEM unlocking”
    • Toggle “Settings”/”System”/”Advanced”/”Developer Options”/”OEM unlocking”

Build AOSP Image

Prepare the host

My host is Ubuntu 20.04. Generally we are following this guide from Google. Below is a quick gist.

sudo apt-get install git-core gnupg flex bison build-essential zip curl zlib1g-dev gcc-multilib g++-multilib libc6-dev-i386 lib32ncurses5-dev x11proto-core-dev libx11-dev lib32z1-dev libgl1-mesa-dev libxml2-utils xsltproc unzip fontconfig
sudo apt install python2    #repo needs python
sudo usermod -aG plugdev $LOGNAME
apt-get install android-sdk-platform-tools-common   # install udev rules and adb

Download AOSP source

Generally we are following this guide from Google. Below are some specific steps.

  • Find exact branch/tag that matches device current build.
    • Go to the Android build tag page
    • Search for the build number noted at the previous step
    • Find corresponding AOSP tag. In my case, it is “android-10.0.0_r41”
  • Check out this branch
mkdir android-10.0.0_r41-shallow
cd android-10.0.0_r41-shallow
repo init --depth=1 -u -b android-10.0.0_r41
repo sync  --force-sync --no-clone-bundle --no-tags -j$(nproc)

Fetch Proprietary Binaries

  • Go to Google proprietary binary page
  • Find the section corresponding to your device (Pixel 4 in my case) and the build number (“QQ3A.200805.001”)
  • Download tarballs from Google and Qualcomm
  • Untar them under the root directory of AOSP source tree
cd ~/work/android/android-10.0.0_r41-shallow
tar xzf ~/Downloads/google_devices-flame-qq3a.200805.001-a7a5499d.tgz
tar xzf ~/Downloads/qcom-flame-rp1a.200720.009-1157dde5.tgz

Build images

source build/
lunch aosp_flame-userdebug

Note “flame” is the codename for Pixel 4. If you have a different device, you should use a different target. See Pixel factory image page for device codenames.

Command ‘m’ starts the build process, which can take very long. My laptop has AMD Ryzen™ 7 Pro 4750U Processor (1.70 GHz, up to 4.10 GHz Max Boost, 8 Cores, 16 Threads, 8 MB Cache) and has a fast NVME SSD disk. It takes about 2.5 hours to finish the build.

Flash AOSP Built Image

  • On the phone, enable OEM unlocking and USB debugging
    • Toggle “Settings”/”System”/”Advanced”/”Developer options”/”USB debugging”
    • Toggle “Settings”/”System”/”Advanced”/”Developer options”/”OEM unlocking”
  • On the PC in the same terminal where you just build the AOSP image
adb devices             # it should show the phone device attached over ADB
adb reboot bootloader   # reboot to fastboot
fastboot devices        # it should show the phone device attached over ADB
fastboot flashing unlock
fastboot flashall -w

During “fastboot flashing unlock” step, you need to following instruction on the screen, press up/down volume button to select “unlock bootloader”, and press power button to commit.

If things go smoothly, phone will reboot a couple of times and eventually boots into the freshly built AOSP image with root access.

Restore to Stock ROM Image

After you played enough with the AOSP image, you may want to return to the original retail state. Google has made it easy recently.

  • Open Chrome browser and go to “”
  • Allow browser to connect to the device
  • Go to Pixel 4 factory image page and find the desired build number to flash
    • Just for fun, I’m selecting Android 11, build number RQ1A.210205.004.
  • Select “Wipe device” and “Lock bootloader”
  • Click “Confirm” to start the process.

What If Things Go Wrong?

Things can go wrong when phone does not boot up anymore. It can be due to build AOSP build, or something due to mismatch between AOSP image and baseban/firmware version (BTW, this is the reason why this guide asks you to download the same version of AOSP that matches existing build).

cd flame-qq3a.200805.001/
fastboot devices   # make sure phone is connected

(Bonus) How to Add a System Privileged App

Before Android 10, you simply re-mount /system as rw and push apk into /system/priv-app/

adb root
adb shell remount -orw,remount /system
adb push my-app.apk /system/priv-app
adb reboot    # to complete the app installation

Since Android 10, /system is mounted as root and cannot be re-mounted as rw. Instead you will need to use “adb remount” to enable overlay FS for any modification.

adb root
adb remount     # if this is first time, "adb reboot" to disable verity first
adb push my-app.apk /system/priv-app
adb reboot      # to complete the app installation

Often times you need to assign PivilegedOrSystem level permissions to system apps (which is why you want to install system app at the first place). Starting from Android 8.1, you will need to explicitly whitelist these permissions in system xml files.

For example, to give READ_PRIVILEGED_PHONE_STATE permission to a testing app, net.junsun.idattestation, you need to create the following file on phone, /etc/permissions/priv-app/privapp-permissions-idattestation.xml

<?xml version="1.0" encoding="utf-8"?>
This XML file declares which signature|privileged permissions should be granted to privileged
applications that come with the platform
    <privapp-permissions package="net.junsun.idattestation">
        <permission name="android.permission.READ_PRIVILEGED_PHONE_STATE"/>

Setup Bitcoin/ElectrumX/Lightning Network on Raspberry Pi 4

In the previous post I described the process of setting up a headless Raspberry Pi 4 (8GB) with remote VNC desktop access. It includes 1GB SDD drive, which is needed to run bitcoin full node with full archive of blockchain transactions.

In this post I will describe the process I used to set up a powerful multi-purpose Bitcoin node for the cryptocurrency community, that includes the following elements.

  • Bitcoin core – the default and standard bitcoin full node software that started the whole thing
  • ElectrumX server – de-centralized cryptocurrency wallet server. Wallet software needs it to make payments/transfers etc.
  • Lighnting Network Daemon (LND) – Level 2 network built on top of bitcoin to facilitate fast and cheap small amount payments.

Install and Run Bitcoin Core

tar xzf bitcoin-0.21.0-aarch64-linux-gnu.tar.gz
sudo cp -a bitcoin-0.21.0/* /usr/local/
  • Run bitcoin-qt -txindex and start populating the blockchain data. It will take 2+ days and will consume >350GB in disk space!
    • DON’T SELECT “prune” MODE! Otherwise Electrum server won’t work.
  • Configure bitcoin for hardening and interactions with ElectrumX/LND
    • Create ~/.bitcoin/bitcoin.conf file. See sample setup below.
    • In this setup, we don’t listen to incoming peers over IPv4/IPv6 for enhanced privacy. New transactions will be broadcasted to Tor network only.
    • I also disabled wallet feature for better privacy again.
    • zmq (ZeroMQ) is needed for LND connection.
# index all transactions; LND/ElectrumX needs it

# bitcoin-qt accept RPC or not; needed for EPS/ElectrumX

# EPS needs wallet feature; electrumx does not

# don't broadcast transactions from our own wallet; will submit through Tor
# only useful when disablewallet==0

# # Maximum number of inbound+outbound connections. default 125

# enable electrumx server and LND

# Listening for peers, enabled by default except when 'connect' is being used
# we don't export bitcoin ports or accept any incoming connections,
# because we would expose our own transactions to peers associated with our IP
# We only connect outgoing through tor

# outgoing traffic use onion/tor only (default any)

# debug logging - values: 0, 1, net, ....

# needed by LND; I don't understand

Install ElectrumX Server

  • Install dependencies
sudo apt install -y python3-pip libleveldb-dev
sudo pip3 install aiohttp aiorpc
sudo pip3 install pylru
sudo pip3 install plyvel
  • Clone the the repo and install into /usr/local.
    • Note there are 2 primary electrumx repos on Make sure choose “spesmilo” one. The other one, albeit older, stopped supporting bitcoin due to recent segwit address introduction.
git clone
cd ~/electrumx
sudo python3 install
  • Add user to ssl-cert group to access the private SSL key
sudo usermod -a -G ssl-cert $USER
  • If bitcoin core has finished initial data sync, you can start ElectrumX server with the following script. Make sure you forward port 50001 and 50002 to the Raspberry Pi 4.

# REQUIRED env variables
export DB_DIRECTORY=$HOME/.electrumx/db
export COIN=Bitcoin

# Optional env variables
export PUBLIC_IP=$(curl -s
export SERVICES=rpc://localhost:8000,tcp://:50001,ssl://:50002
export REPORT_SERVICES=ssl://$PUBLIC_IP:50002
export SSL_CERTFILE=/etc/ssl/certs/ssl-cert-snakeoil.pem
export SSL_KEYFILE=/etc/ssl/private/ssl-cert-snakeoil.key

# replace with your wallet address!
export DONATION_ADDRESS="bc1q52we5s8qyddhvrfscjn4qyn5nvq8hf92k9rt2w"

# log all sent transactions

Install LND

Lightning Network in some sense is more complex than bitcoin. You are strongly suggested to review some basic concepts before setting up the software. There are multiple LN server implementations. LND is a popular one.

  • Install the pre-built binary image for ARM64
tar xzf lnd-linux-arm64-v0.12.0-beta.rc6.tar.gz
sudo cp lnd-linux-arm64-v0.12.0-beta.rc6/* /usr/local/bin
  • Set up config file
mkdir ~/.lnd
wget -O ~/.lnd/lnd.conf
  • Below is a sample setup based on my own node
  • Run LND with “lnd” command
    • First time run, you will need to create a wallet, lncli create
    • For later running, you will need to unlock wallet, lncli unlock
      • If you like to automate LND startup, you will likely need lncli unlock --stdin option to pass in the wallet password via a script.
  • (Optional) if you like to set up a public LND node so that others can reach you, enable port forward on port 9735. You need to be a public node to participate in LN routing.

(Optional) Install RTL

RTL stands for “Ride The Lightning”, which provides a web interface to visually interact with LND. Otherwise you can just the commandline interface, which can be a little boring (and hard)

  • Install package and dependencies
git clone
cd RTL/
sudo apt install nodejs
sudo apt install npm
npm install --only=prod
cp sample-RTL-Config.json RTL-Config.json
vi RTL-Config.json
node rtl.js 
  • In order to run “node rtl.js” successfully, you need to configure RTL-config.json properly. Below is the sample setup derived from my own node.
  "multiPass": "YOUR_RTL_PASSWORD",
  "port": "3000",
  "defaultNodeIndex": 1,
  "SSO": {
    "rtlSSO": 0,
    "rtlCookiePath": "",
    "logoutRedirectLink": ""
  "nodes": [
      "index": 1,
      "lnNode": "Node 1",
      "lnImplementation": "LND",
      "Authentication": {
        "macaroonPath": "/home/ubuntu/.lnd/data/chain/bitcoin/mainnet/",
        "configPath": "/home/ubuntu/.lnd/lnd.conf",
        "swapMacaroonPath": ""
      "Settings": {
        "userPersona": "MERCHANT",
        "themeMode": "DAY",
        "themeColor": "PURPLE",
        "channelBackupPath": "/home/ubuntu/.lnd/backup",
        "enableLogging": false,
        "lnServerUrl": "https://localhost:8080",
        "swapServerUrl": "https://localhost:8081",
        "fiatConversion": false
  • Once RTL starts running, you can open a browser and point at Raspberry Pi 4 IP address at port 3000. You see stats and perform actions with LND.

How You May Benefit

  • Use your own ElectrumX server for increased trust and privacy.
    • In this guide, we disable bitcoin core listening from public IP addresses. All new transactions are broadcasted from Tor. That increases privacy and anonymity.
  • You set up donation wallet address in ElectrumX. It seems people do donate, although not that common.
  • Once you set up LND properly, you can collect routing fees.

Show Your Support

This post is only complete if I can show you how I set up the donation and LN connection. 🙂 And your reading is only complete when you perform one of the following actions. 😛

For donation, Bitcoin wallet address is “bc1qyc48kmpweyx2kpqhq8n6r0ckr2fqsfvz2qxpx4”

For Lightning Network, my node public key is “0362a4372375bd24c5b8f8bb2ea85ae2ccf783808477e68cfb06121694b34d1927”

Appendix A – Reference Links on Lightning Network

Appendix B – How to create inbound liquidity for lightning network

Android AOSP Repo Checkout Method and Size Comparison

Android open source AOSP size has grown to be very huge now, often pushing over 100GB in disk size.  In this post, we look at 3 different ways to check out AOSP and compare their sizes.

1. Full clone – regular checkout with complete history, branch, tags and all files

repo init -u -b android-11.0.0_r4
repo sync -j$(nproc)

2. Partial clone – only clone needed files with smaller-sized files initially, where the left-out files can be fetched later over the network when needed.

repo init -u -b android-11.0.0_r4 --partial-clone --clone-filter=blob:limit=10M
repo sync -j$(nproc)

3. Shallow clone – don’t clone history or previous revisions or other branches/tags

repo init --depth=1 -u -b android-11.0.0_r4
repo sync  -f --force-sync --no-clone-bundle --no-tags -j$(nproc)

Below is the list of disk spaces consumed by each method. Clearly the winner size-wise is shallow clone. The disadvantage is that you don’t have any revision/branch/tag information. If that is OK with you, it is the way to go. Partial clone might work for you if you have fast network, but it does not seem to save much space.

Full clone105GB
Partial clone98GB
Shallow clone77GB

(Added later on 2/10, 2021) Additionally one may wish to set up a local AOSP mirror to reduce check out time. The total size of a full AOSP mirror is around 540GB.

mkdir aosp-mirror
cd aosp-mirror
repo init -u --mirror
repo sync

Set Up Ubuntu/XFCE4 on Headless Raspberry Pi 4 via VNC


The new Raspberry Pi 4 with 8GB RAM is a little attractive  beast that is suitable for  home server.  You can set it up basically fan-less.  I was intrigued and I wanted to set it up headless, running Bitcoin full node, ElectrumX server plus Lightning Network (see my next post).

However, while there are many tutorials around Internet, I just can’t find the ideal one that suit me:

  • It must be 64bit.  Come on!  We are in 2021 already.
    • That rules out 32bit Raspberry Pi OS.
    • The 64bit Raspberry Pi OS (beta) runs fine on the board, but it lacks some basic Linux/UNIX features (e.g., middle mouse button pasting).  The desktop settings keep getting lost.  It is just frustrating.
  • That leaves 64bit Ubuntu, which should be a decent base OS.
  • I want to boot from USB without slow SD card.
  • I want to run headless with remote graphic UI 

The hardware

Below are the components I purchased.  The total cost is $270.  Not exactly dirty cheap, but that is pretty meaty piece. 

Putting it together is simper than setting up a toaster machine. See a couple of pictures below as well.

Step 1 – Prepare SSD drive and USB boot

  • Download and install rpi-imager on your host PC (Linux, Windows, etc)
  • Flush raspberry pi OS into SD card (I used 64bit RPIOS beta, but I think 32bit one should work). This will be a throw-away stepping stone.
  • Insert the SD card to RPI4 and boot from SD card.
    • Insert USB keyboard/mouse into black USB slot (USB2)
    • Connect a HDMI cable to a monitor
    • Use USB type-C power supply, ideally > 2.4A
  • Install (if not already installed) and run rpi-imager on RPI4 booted from SD card.
  • (IMPORTANT) Choose “Ubuntu 20.10 64bit Server” OS image and flush onto the 1TB Samsung SSD drive.
    • I found Ubuntu 20.04LTS don’t work!
  • Follow this link to update EEPROM firmware
  • Follow this link to boot from USB (i.e., SSD driver) first instead of SD card.
  • Remove SD card, and now you should be able to boot from SSD drive.

Step 2 – Fix up the board

  • Connect an Ethernet cable to enable Internet
  • Fix sluggish USB mouse
    • Add “usbhid.mousepoll=0” to /boot/firmware/cmdline.txt; Reboot
  • Install argon 1 fan control
    • curl | bash

Step 3 – Install XFCE desktop

Note choose “lightdm” when install xfce4

sudo apt update
sudo apt dist-upgrade
apt install xfce4 xfce4-goodies
apt install tigervnc-standalone-server novnc firefox

Create /etc/lightdm/lightdm.conf file:


After this you should be able to log into graphic XFCE desktop.

Step 4 – Set up VNC and headless

  • Configure wifi assuming that is what you want to run RPI4
  • Set up VNC password
    • sudo vncpasswd /etc/vncpasswd
  • Modify /etc/X11/xinit/xserverrc file

ARG=`echo $@ | sed -e "s#vt. -novtswitch##"`
# single client mode; VNC password auth; TLS encryption optional;
exec Xvnc -desktop ubuntu -SecurityTypes "VncAuth,TLSVnc" -NeverShared -DisconnectClients -geometry $GEOMETRY -depth $DEPTH -rfbauth /etc/vncpasswd $ARG
  • Make sure WiFi is connected before user logs in so that you can connect via VNC
    • To do this, launch NetworkManager, select “Applications”/”Settings”/”Advanced Network Configuration”
    • Then select the wifi network you are connecting to, and then click on button at the bottom to edit the connection
    • Under “General” tab, check “All users may connect to this network”

After this setup, if you reboot RPI4, you will get text console on display.

Meanwhile you should be able to access RPI4 over VNC remotely

  • On your PC, install VNC viewer (e.g., tigerVNC viewer)
  • Launch the viewer, enter the IP address and port 5900
  • Enter the VNC password
  • You should see XFCE desktop

Step 5 – Optional noVNC to enable web browser access

  • Install noVNC package
    • sudo apt install novnc net-tools
  • Run /usr/share/novnc/utils/
  • On PC, open a browser and point at “http://<RPI4 IP address>:6080/vnc_auto.html”
  • Enter VNC password and you will be connected to the desktop

You can automate this process by adding this to /etc/rc.local or create a small systemd service file.

AWS ARM64 vs. X86_64 – Bitcoin Performance Comparison

I’m running some experiments with bitcoin core software on AWS. I’m intrigued by 2 questions:

  • Which performs better, ARM64 vs X86_64?
  • What is performance loss of 32bit ARM vs 64bit ARM?

The Experiment

  • I fired up a t3.medium instance with ubuntu desktop 20.04(x86_64) image
  • I fired a second instance of t4g.medium type with ubuntu desktop 20.04 (arm64) image
  • To run 32bit ARM program, I followed the chroot approach documented in my previous post and set up an armhf Ubuntu 20.04 (focal) chroot environment
  • Then I download all 3 versions of bitcoin core software from its download site : 32bit ARM, 64bit ARM and 64bit Intel.
  • Run bitcoin-qt from scratch (delete ~/.bitcoin directory if any) and count the time duration for the verifying first 200,000 blocks.
    • Each configuration runs 2 times. We then take the average.
    • Other system variables are monitored to ensure similar running environment. Specifically networking or disk don’t seem to be a factor.

The Results

See results listed below. It seems for bitcoin related workload 64bit ARM version performs 20% faster than 32bit ARM version and 64bit Intel instance.

category64bit ARM 32bit ARM64bit Intel
Instance typet4g.mediumt4g.mediumt3.medium
CPU Graviton2Graviton2Intel Xeon Platinum 8000 series
# CPU cores222
RAM (GB)444
run duration #18’44” (524″)10’24” (624″)11’16″(676″)
run duration #27’30” (450″)9’58″(598″)9’04″(544″)
run duration average487″611″610″
relative performance to 64bit ARM100%80%80%
Pricing (us-west-2/Orgon) ($/hr)0.03360.03360.0416