How cloud-init systemd service is activated on Ubuntu 16.04 (xenial)

Recently I've trace how cloud-init is being run. First, I try to find service file in /etc/system/system or /lib/systemd/system. Although I can locate the unit files, I can't see any systemd target that will bring up these cloud-init services. I did't see how is activated by systemd.

Finally, I found that cloud-init project utilize the systemd generator to generate the unit files dynamically. The dynamic unit files is located at /run/system/generator.early/ With this unit file, when the is activated by systemd, the will also be activated. Then the systemd will further activate related cloud-init service in /etc/systemd/system/

Below is the dynamic unit file.

$ ll /run/systemd/generator.early/
lrwxrwxrwx 1 root root 37 Jul 14 07:52 /run/systemd/generator.early/ -> /lib/systemd/system/

If I want to disable cloud-init, there are several ways to do it.

  1. Mask the default cloud-init systemd generator.
    ln -sf /dev/null /etc/systemd/system-generator/cloud-init-generator
  2. Add kernel parameter cloud-init=disabled or touch /etc/cloud/cloud-init.disabled. This kernel parameter will be processed by cloud-init systemd generator. See


use snapper to Travel back in time and compare (The ultimate snapshot tool for Linux)

Snapper is a great tool for making snapshot on linux. You can download it on ArchLinux/Debian/OpenSUSE/Ubuntu

Personally I use btrfs as underlying file system. Here are some basic command to snapshot my data.

# install snapper
sudo apt install -y snapper

# Suppose /dev/sda3 is formatted as btrfs file system.
# mount the file system
sudo mount /dev/sda3 /mnt

# create a btrfs subvolme "data"
sudo btrfs subvolume create /mnt/data
# unmount /dev/sda3
sudo umount /mnt

# mount only the subvolume "data", instead of whole file system
sudo mount -o subvol=data /dev/sda3 /data

# create the snapper config for "/data" folder. The config name could be anything, here I choose "data"
sudo snapper -c data create-config /data

# By default, the snapper will make a snapshot per hour, just like Mac OS's Time machine.
# Check the snapshot list
# sudo snapper -c data list 
Type   | #    | Pre # | Date                            | User | Cleanup  | Description | Userdata
single | 1 |       | Tue 16 Aug 2016 09:17:02 AM CST | root | timeline | timeline    |         
single | 2 |       | Tue 16 Aug 2016 10:17:02 AM CST | root | timeline | timeline    |         
single | 3 |       | Tue 16 Aug 2016 11:17:03 AM CST | root | timeline | timeline    |         
single | 4 |       | Tue 16 Aug 2016 12:17:03 PM CST | root | timeline | timeline    |      

# In fact, you can find the underlying snapshot in "data" subvolume
sudo mount /dev/sda3 /mnt
ls -al /mnt/data/.snapshots/
drwxr-x--- 1 root root 230 Aug 16 12:17 ./
drwxr-xr-x 1 root root 340 Aug 15 10:47 ../
drwxr-xr-x 1 root root  32 Aug 16 09:17 1/
drwxr-xr-x 1 root root  32 Aug 16 10:17 2/
drwxr-xr-x 1 root root  32 Aug 16 11:17 3/
drwxr-xr-x 1 root root  32 Aug 16 12:17 4/

If your root file system is also a btrfs subvolume. That would be even better. You can snapshot your whole system!

sudo snapper -c root create-config /

LXD container Getting Started

Below I give some simple command to run a ubuntu:16.04 lxd container. LXD container is fast, very efficient, very low-footprint virtual machine. I recommend people who didn't need low-level system control (such as disk, loopback device) give it a try. I think this kind of lightweight virtual machine would benefit people who study machine learning or similar scientific computing.

# check current status of lxd. If you install lxd the first time, it should containing no virtual machines.
lxc list

# if my-ubuntu virtual machine not exist yet.
lxc launch ubuntu:16.04 my-ubuntu
# if my-ubuntu virtual machine already exist.
lxc start my-ubuntu

# check status of my-ubuntu virtual machine
lxc list

# login to root account
lxc exec first -- /bin/bash
# or login to ubuntu account
lxc exec first -- /bin/su - ubuntu

# stop the virtual machine
lxc stop my-ubuntu

# you can even copy virtual machine
lxc copy my-ubuntu my-ubuntu2
# or rename it
lxc mv my-ubuntu stanley-ubuntu
lxc mv stanley-ubuntu my-ubuntu

# delete my-ubuntu virtual machine
lxc delete my-ubuntu

# check my-ubuntu is deleted
lxc list

Varies images is provided by Canonical in

Note that lxd has some limitaions. Such as you can't

  • setup loopback device
  • mount fuse file system
  • have bridged network.
  • load/remove kernel module ... (But if you choose to run a priviledged lxd virtual machine, some limitations might not exist anymore. But I haven't dig into it currently.)

Build Debian/Ubuntu LiveCD

Note that this article introduces how to build Debian/Ubuntu LiveCD iso image from scratch. With this method, you have great flexibility to customize the LiveCD.

However, if you only want to customize the LiveCD a little bit. Such as adding some packages for installation, or changing the preseed configuration, you can refer to DebianCustomCD, Simple-CDD and LiveCDCustomization

Debian Jessie

# within Debian jessie
git clone git://
cd live-build
git checkout debian/4.0.5-1
dpkg-buildpackage -b -uc -us
cd ..
sudo dpkg -i live-build_4.0.5-1_all.deb

sudo apt-get install -y live-images
cp -r /usr/share/live/images/standard .
cd standard/
lb config --source false # optional, would be faster if not build source
sudo lb build
# here we got live-image-amd64.hybrid.iso, about 417MB
# refer to for more information

Ubuntu Xenial 16.04

Automatically build with ubuntu-defaults-builder

sudo apt install -y ubuntu-defaults-builder
sudo apt install -y syslinux-utils
ubuntu-defaults-template myconfig
cd myconfig/
cd ../
ubuntu-defaults-image --package myconfig_0.1_all.deb --components main,restricted,universe,multiverse

# here we got binary.hybrid.iso and livecd.ubuntu.iso

Manually build with live-build

# First, set up the build tools and workspace.
# The scripts require that you work in /build

sudo apt-get install -y genisoimage syslinux-utils # tools for generate ISO image
sudo apt-get install -y memtest86+ syslinux syslinux-themes-ubuntu-xenial gfxboot-theme-ubuntu

sudo -i
apt-get install -y livecd-rootfs
mkdir -p /build/chroot
cd /build
cp -a /usr/share/livecd-rootfs/live-build/auto .

# All the hard work is done with live-build (lb command)
# and we have to configure it with environment variables

export SUITE=xenial
export ARCH=amd64
export PROJECT=ubuntu
export MIRROR=
export BINARYFORMAT=iso-hybrid
export LB_SYSLINUX_THEME=ubuntu-xenial

# Now we can have live-build set up the workspace

lb config --initramfs-compression=gzip 

# And finally, start the build

lb build

[2] Ubuntu live filesystem builds moved to live-build
[3] LocalizedCDImageTools - Ubuntu Wiki
[4] ISO with l10 preloaded for LoCo + UEFI
[5] UbuntuStudio/Seeds - Ubuntu Wiki
[6] Building large-scale Ubuntu derivatives using seeds - Google Docs

[7] ReleaseTeam/CDImageSetup - Ubuntu Wiki

PuDB Python Debugging Tool. A full-screen, console-based Python debugger

I highly recommened pudb, which is a full-screen, console-based visual debugger for Python. The user-interface is nicely designed for python developers.

Here is an example debugging a simple python script:
Introduction to the PuDB Python Debugging Tool

Also, another great tutorial is from Jordi Gutiérrez Hermoso.
Montreal, QC, September 14, 2015 - Jordi Gutiérrez Hermoso presents PuDB, a full-screen, console-based visual debugger for Python.
An interesting comment from the speaker:

Everyone should use a debugger

But If pdb is the only debugger you've every seen, I won't blame you not using a debugger

because the debugger is ugly, not because the source code is ugly

To install pudb on Debian/Ubuntu, you can use apt-get to install the package

# for python 2

sudo apt-get -y python-pudb
# for python 3

sudo apt-get -y python3-pudb

# pudb is even better when debugging with ipython

# so that's install ipython

sudo apt-get install ipython

How to prevent Linux from waking up due to USB devices

最近換了一台工作機,但我發現在 Ubuntu 14.04.3 上,有時候會休眠失敗。
在失敗的時候,機器有 suspend 成功,但是過2秒後機器就會自動醒來。查看了 /var/log/kern.log, /var/log/syslog, /var/log/pm-suspend.log 沒有太異常的訊息。後來上網查了一下,這可能是有 BIOS 有問題或 device 不正常運作。

在 /proc/acpi/wakeup 中,列出了數種 wakeup event, 以下面的表來說,代表了機器開放了 EHC1, EHC2, PWRB, LID0 這幾種 wakeup event

RP06      S4    *disabled
PXSX      S4    *disabled
RP07      S4    *disabled
PXSX      S4    *disabled
EHC1      S0    *enabled   pci:0000:00:1d.0
EHC2      S4    *enabled  pci:0000:00:1a.0
PWRB      S4    *enabled   platform:PNP0C0C:00
LID0      S4    *enabled   platform:PNP0C0D:00

試著開關 wakeup trigger 來找出問題

# ignore XHC device wakeup event

echo "XHC" > /proc/acpi/wakeup
# try suspend, still failed

# ignore EHC1 device wakeup event

echo "EHC1" > /proc/acpi/wakeup
# try suspend, still failed

# ignore EHC1 device wakeup event

echo "EHC2" > /proc/acpi/wakeup
# try suspend. Bingo!! It suspend successfully!

發現只要關閉 EHC2 wakeup trigger, 機器就能正常 suspend。可以放罝一個 upstart script,讓每次開機時,都自動關閉 EHC2 wakeup trigger

# /etc/init/disable-EHC2.conf
start on started dbus
stop on stopping dbus

   sudo -u root sh -c "echo 'EHC2' > /proc/acpi/wakeup"
end script


在 NAS 上架設 ubuntu chroot 環境

今天發現可以透過 Canonical Ltd. 的 linuxcontainer image 快速的在 NAS 上建立一個 chroot 環境。我的機器 cpu 是 armhf ,下面示範建立 Ubuntu 15.04 Vivid 的 chroot 環境。

步驟1:下載 Image,解開後進入 rootfs,並修改 nameserver

mkdir rootfs
tar xvf rootfs.tar.xz -C rootfs
cd rootfs
echo "nameserver" > etc/resolv.conf

步驟2:mount 需要的 sysfs

mount -t proc proc proc/
mount -t sysfs sys sys/
mount -o bind /dev dev/
mount -t devpts pts dev/pts/


chroot . su -l

backports driver

git clone git://
git clone git://
cd backports/
./ --clean --git-revision next-20150525 ../linux-next/ release

cd release/
make menuconfig

使用 UPMOST DVB193 在 Ubuntu 14.04 上看數位電視

手上有一支 UPMOST DVB193 數位電視棒,最近測試了它是不是能在 Ubuntu 14.04 下運作。原本以為需要自己編譯 driver,不過把數位電視棒插入筆電, lsusb 後發現其實 driver 已被 Kernel 收錄成為 built-in driver。 Driver 的訊息如下

filename:       /lib/modules/3.19.0-28-generic/kernel/drivers/media/tuners/it913x.ko
license:        GPL
author:         Antti Palosaari <>
description:    ITE IT913X silicon tuner driver
srcversion:     3A631200871E9FCB4913859
alias:          i2c:it913x
intree:         Y
vermagic:       3.19.0-28-generic SMP mod_unload modversions 
signer:         Magrathea: Glacier signing key
sig_key:        29:4D:C0:12:70:6F:48:B7:CD:DF:63:74:E2:D7:9F:E1:B0:60:92:69
sig_hashalgo:   sha512

所以接下來只要處理好看數位電視的軟體就可以。以 apt-get 安裝好 vlc ,再用 vlc 開啟 channels.conf





sudo apt-get install -y dvb-apps
sudo apt-get install vlc
scan /usr/share/dvb/dvb-t/tw-All >channels.conf

這個 channels.conf ,就可以用 vlc 打開收看。