Table of parts: https://docs.google.com/document/d/1IIOkivkS0lV9QIL16b_OjT480BxZHQfKswvvS-CVZlw/view

Building existing programs and libraries

Glossary about directories

Source directory - where you unpacked the source code

Example: /home/vi/progs/dropbear

Build directory - where program is being built (object files, static libs, resulting executables)

Example: /home/vi/progs/dropbear

Destination directory - where files needed for the program to work (executables, resources, dynamic libraries) are copied by make install

Example: /home/vi/progs/dropbear/prefix

Target directory (prefix) - where the program expects its files to be

Example: /usr/local

topics:

dependencies
.tar.gz, .tar.bz2, .tar.xz
autogen.sh , autoreconf -i
./configure
make install
DESTDIR
prefix
pkg-config
tar -xvf htop-1.0.1.tar.gz

Exercise 1

Download the source code of "htop" program and build it. Alternative: http://neil.brown.name/wiggle/

$ apt-file search libncursesw

lib32ncursesw5: /lib32/libncursesw.so.5

lib32ncursesw5: /lib32/libncursesw.so.5.9

lib32ncursesw5-dev: /usr/lib32/libncursesw.a

lib32ncursesw5-dev: /usr/lib32/libncursesw.so

libncursesw5: /lib/x86_64-linux-gnu/libncursesw.so.5

libncursesw5: /lib/x86_64-linux-gnu/libncursesw.so.5.9

libncursesw5: /usr/share/doc/libncursesw5

libncursesw5-dbg: /usr/lib/debug/libncursesw.so.5

libncursesw5-dbg: /usr/lib/debug/libncursesw.so.5.9

libncursesw5-dbg: /usr/share/doc/libncursesw5-dbg

libncursesw5-dev: /usr/lib/x86_64-linux-gnu/libncursesw.a

libncursesw5-dev: /usr/lib/x86_64-linux-gnu/libncursesw.so

libncursesw5-dev: /usr/share/doc/libncursesw5-dev

libx32ncursesw5: /usr/libx32/libncursesw.so.5

libx32ncursesw5: /usr/libx32/libncursesw.so.5.9

libx32ncursesw5-dev: /usr/libx32/libncursesw.a

libx32ncursesw5-dev: /usr/libx32/libncursesw.so

Exercise 2

Install the built htop program into /usr/local

Exercise 3 *

Create a Debian package for your htop

checkinstall --install=no --fstrans

Cross-compilation

GCC terms:

Build - where the compilation of a compiler will be run now;

Host - where the resulting compiler will be run;
Target (for compilers)

Simplified "pseudocode session":

x86$ # Let's compile a compiler.

x86$ ./configure --build=x86 --host=arm --target=mips

x86$ make

Compilation of a compiler successful.

x86$ # OK, now we have a compiler. Let's run it…

x86$ ./the_compiler hello.c -o hello

Error: Can't run ./the_compiler. It's for ARM, not for X86.

x86$ # So copy it to ARM.

x86$ scp the_compiler arm:

x86$ ssh arm

arm$ ./the_compiler hello.c -o hello

Compilation successful

arm$ ./hello

Error: Can't run ./hello. It's for MIPS, not for ARM.

arm$ scp hello mips:./ && ssh misp

misp$ ./hello

Hello, world.

Exercise 4

Build dropbear from source code.

Соберите из исходного кода dropbear.

Configuration and using of SSH

Exercise 1

Start dropbear instance you have configured and connect to it from localhost;

Generate rsa and dss keys;
Start dropbear;
Try connecting to somebody else's dropbear server;
Stop server and change (generate again) the keys;
Try to connect again. Resolve the issue;
Setup a guest user account and start dropbear as root;
Try to connect to other's server to log in successfully;
Copy a file to and from peer;
Try starting a GUI application over SSH connection;
Try setting up pubkey authentication (authorized_keys) to avoid entering the password.

TODO: insert dropbrear launch and key generation commands here

Linux file system, part 2

$ dd if=/dev/zero bs=1M count=64 of=qqq

# losetup /dev/loop3 qqq

# mkfs.ext4 /dev/loop3

# mount -t ext4 /dev/loop3 /home/user/somedir

# echo qqq > /home/user/somedir/somefile

…

# umount /home/user/somedir

# losetup -d /dev/loop3

block devices, character devices
"mount" command
losetup
loop mounts
nodev,noexec,nosuid
FUSE
"stat" command revisited
find -xdev; du -x

Exercise 1

Execute commands from this chapter.

Выполните команды из главы.

Exercise 2

Get inode and device number for the following files:

Узнайте номер устройства и inode для задействованных файлов:

/home
/
/dev
/home/user/qqq
/home/user/somedir
/home/user/somedir/somefile

Exercise 3

Try to make chroot'table system with some commands inside:

ldd /bin/bash
Also bring "ls".
Also bring your "pseudo-bash"
chroot /path/to/my/dir /bin/bash

Boot process of a Linux system

bootloader
linux kernel parameters
initrd/initramfs
init process, runlevels

Excersize 1

Enter GRUB menu. Inspect the kernel parameters.

Зайдите в меню GRUB. Посмотрите на параметры ядра.

Excersize 2

Try booting the system from GRUB console. Try to use minimal necessary number of parameters.

Запустите систему из консоли GRUB. Постарайтесь использовать минимум параметров.

Excersize 3

Try booting the system, overriding init to /bin/bash. Use "exec /sbin/init" to continue booting.

Попробуйте запустить систему, используя /bin/bash вместо init'а. Используйте "exec /sbin/init" чтобы продолжить загрузку.

Open source licenses

"metadata" for source code;
Primarily consider distribution;

Primary glossary:

License
Distribution
Derived product
Source code
Trivial source code
Linking
Aggregating
Usage
Library/Component
System library
Program
Assets
"viral" license
Public domain
Multiple licenses
Patents

Main types of licenses

(note: I'm not a lawyer and this can't be a real legal advice)

	Pub domain CC0	Permissive MIT / BSD	LGPL GPL with linking exception	GPL
Can I just use it in a distributable project without asking anyone and without distributing any source code?	Yes	Yes*	Only if unchanged	No
Can I use it in a distributable project distributing changes to the library in question and making sure the library can be replaced by end user?	Yes	Yes*	Yes	No
Can I use it in Open Source project?	Yes	Yes*	Yes	Yes*
Can I remove information about original author and write myself as an author instead?	No	No	No	No
Can I use it in my program that I don't distribute at all, just for myself?	Yes	Yes	Yes	Yes
Can I learn from a library and make my own employing similar algorithm, without directly copying or linking any code?	Yes	Yes	Yes	Yes
Can I link my nonfree project statically to it?	Yes	Yes*	Probably no	No
Can I check authenticity of the binary or source library in my project and refuse to use user-changed versions?	Yes	Yes*	"No" by the spirit, "It depends" IRL	No

Gray areas

Not allowed per license does not mean not allowed at all. Author may declare exception, including for profit.
GPL: Really system library or not? Court may decide.
GPL/LGPL: Really using and depending or not really? Court may decide.

For example, there is API which both GPL and permissive library implements. User can replace the permissive library with GPL one. What if instructions of such replacement are published to user forum? What if program can discover all libraries that implement this API? What if program downloads the library from internet and installs it automatically?

Who is user or your program? The one who configures it or one who uses its results?

Exercise 1

Can I use libmatroska in my open source project? Proprietary project?

Exercise 2

Can you use libpng in your proprietary project? To which column in the table above does belong its license?

Exercise 3 (trickier)

$ /opt/ffmpeg/ffmpeg2015 -version

ffmpeg version n2.5.3 Copyright (c) 2000-2015 the FFmpeg developers built on Feb 10 2015 03:15:42 with gcc 4.7 (Debian 4.7.2-5) configuration: --enable-static --disable-shared --enable-gpl --enable-version3 --enable-nonfree --disable-libass --enable-frei0r --enable-libaacplus --enable-libfaac --enable-libgsm --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --disable-libopencv --enable-libopenjpeg --enable-libopus --disable-librtmp --disable-libschroedinger --enable-libspeex --enable-libtheora --enable-libtwolame --disable-libv4l2 --enable-libvidstab --disable-libvo-aacenc --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libx264 --enable-libxvid --disable-x11grab --disable-ffplay --disable-devices --disable-vdpau --enable-libx265

What does this mean?
Can I use this program to encode personal videos?
Can I make a commercial service that encodes videos using this program (without distributing the program itself)?
Can I give this binary program to a friend?
Can I distribute this binary program in a package with my open source project?
Can I distribute this binary program in a package with my proprietary project?

Community and Open source

Asking smart questions

Good bug report
Good feature request
Good setup/usage question

Getting help on IRC
Getting help on mailing lists
Getting help on StackOverflow
Searching for existing code
Git and Github

Theory

Kernel
Boot loader
Userland
GNU
Open source

License

Library
Package manager
User
Group
Repository
Patch
Diff
Build system
Community

Glossary about directories

Exercise 1

Exercise 2

Exercise 3 *

Cross-compilation

Exercise 4

Exercise 1

Exercise 1

Exercise 3

Excersize 1

Excersize 2

Excersize 3

Main types of licenses

Gray areas

using strace

using gdb

using valgrind

inspecting /proc

grep

find

sed/perl

Signals

Terminal world