This lesson is under construction. Learn from it at your own risk. If you have any feedback, please fill out our General Feedback Survey.
- Lesson 7: Packages, Software, Libraries
Everything that isn’t hardware.
Sofware is what makes modern computers useful. When you install a piece of software you can then invoke that program using your computer to do a useful task.
Software is everything running on a compuer, from web-browsers to the operating system itself.
- Code that is run on a Computer.
Libraries are pieces of code that are used by multiple programs, but which are not usually run on their own.
For Example: Your OS might come with a “MathFunction” library for a given programming langauge since math is something almost every program ends up doing at least a little bit.
- Often used to make development easier.
- Rarely run on it’s own.
- Shared code.
- Binaries are linked dynamically to libraries (kind of like DLL’s in Windows)
$ ldd /usr/bin/nano linux-vdso.so.1 => (0x00007ffc1fdcd000) libncursesw.so.5 => /lib64/libncursesw.so.5 (0x00007ff2cfaee000) libtinfo.so.5 => /lib64/libtinfo.so.5 (0x00007ff2cf8c4000) libc.so.6 => /lib64/libc.so.6 (0x00007ff2cf500000) libdl.so.2 => /lib64/libdl.so.2 (0x00007ff2cf2fc000) /lib64/ld-linux-x86-64.so.2 (0x000055e46c4b4000)
Package Managers are the tool used to manage Software and Libraries (together called Packages) in your OS. Some are very easy to use, some work very well, and none of them are perfect.
- Automagically manage software and libraries on your system.
- Android Play Store
- Apple App store
- apt (Debian/Ubuntu)
- yum (CentOS/Fedora/RHEL)
Take care of installation and removal of software
While all package managers don’t have every feaure listed below, most of them end up accomplishing most of these tasks out of necessity.
- Install, upgrade, and uninstall packages easily.
Below is a hypothetical package manager carrying out these operations:
$ pkg-mgr install firefox Finding [firefox] on pkg-mgr servers............................... Downloading [firefox].............................................. Are you sure you want to install [firefox]? (Y/n) y Installing [firefox]............................................... Cleaning up........................................................ $ pkg-mgr upgrade firefox Checking for updates to [firefox].................................. Packages [firefox] are up to date. Nothing to do! $ pkg-mgr uninstall firefox Are you sure you want to un-install [firefox]? (Y/n) y Removing [firefox]................................................. [firefox] successfully uninstalled!
The package manager took the name of a program you wanted, found it on some trusted servers, downloaded the package, and placed the downloaded files in the correct place. It seems obvious but they weren’t always around, especially not in their current form.
- Resolve package dependencies.
Resolving dependencies is when you download all of the packages another package needs to run.
- Program foo and program bar both need library baz.
- You install foo first.
- Your package manager installs baz.
- You then install bar.
- Your package manager checks that it already has the baz dependency.
- It installs bar without installing baz again.
- Install packages from a central repository.
Most package managers download packages from a pre-defined set of trusted servers. This is for security reasons related to trust.
Plus – how else would it find the packages? Google?
- Search for information on installed packages and files.
You can usually search all packages and descriptions for a given string. For instance:
$ pkg-mgr search python Search Results: - python2 : The python programming language (version 2) - pyhton3 : The python programming langauge (version 3) - virualenv : A program for managing python virtual environments.
- Download and install pre-built binaries (usually).
- Package managers used to download the source code for a program and would compile the code locally. Now packages are built once on a server and the binaries (which are much smaller) are downloaded to your computer.
- Find package that provide a required library or file.
- This is like reverse-searching an image and it can be useful when developing software. Very useful when you’re trying to find a dependency during development or while building a program from source.
These are package managers used to install system packages like Web-browsers, terminals, network managers, etc. Although they are default OS package managers, a package manager itself is really just a package itself, so one can install any package manager they want.
- yum - RPM Package manager with repo support
- rpm - low level package manager tool used by yum
- Used by RedHat, CentOS, Fedora and others
- apt - Debian package manager with repo support
- dpkg - low level package manager tool used by apt
- Used by Debian, Ubuntu, Linux Mint and others
- XML repository format
- Automatic metadata syncing
- Supports a plugin module system to make it extensible
- Checks all dependencies before downloading
- Upgrade and Dist-Upgrade
- Dist-Upgrade applies intelligent upgrading decisions during a major system upgrade
- Can completely remove all files including config files
These two managers accomplish the same tasks as any modern Linux package manager but differ in their exact file-format, command-line interfaces, and tons of other minutia necessary in writing a package manager.
These are also package managers for programming languages! They can be used to download packages developed in a specific language, but mostly they are used to provide libraries and tools for a specific language.
- Python: pip
- Ruby: gem, rubygems
- Haskell: cabal
- NodeJS: npm
- ... and so on forever ...
Below are a few more notable/interesting package managers.
- The Source-based package manager for Gentoo.
- An Arch User Repository wrapper for Pacman, the Arch Linux Package manager.
- A ‘Fully Functional/Transactional’ package manager.
- An Open Source package manager for OSX.
- A package manager for Windows.
Despite the fact that we have package managers sometimes they aren’t an option for package installation. The package may not registered with the package manager, we want to use a newer/older version of the package, or we want to develop with a custom version of the package. When this happens we have to install from source. This is scary until you do it once or twice and then you realize it’s not that bad.
How to install a package from source:
- Download source code .zip (Zip) or .tar.xz/bz2/xz (Tarball)
First you need to obtain the source code. This is done by downloaded an archive of the code, which is basically a way to put the code in a box so it can be transferred as a single file.
- Unpack the downloaded code.
Once you have the soruce code you need to unpack it. This is either using the tar program or unzip program depending on the type of archive.
- Run the setup and configuration scripts.
These scripts can run a series of checks and configuration from detecting the OS you’re running to make optimizations all the way to yelling at you to manually install a dependency.
If you’re not sure what setup and config scripts to run, check the source code’s README file. It should have one. If not, try running make config, make, and make install. If all else fails look up “How to install <package name>” or “How to install a <package langauge> from source”.
- Build the program.
Just like in programing class, when you run gcc myfile.c -o a.out you will be building a binary from all of the soruce files you downloaded. Unlike class you will be running a wrapper like make or build which will run many commands for you automagically.
- Resolve any unmet dependencies and repeat last two steps until it works.
This is by far the most painful part of the manuall installation process. If the install fails it will hopefully tell you why and hint at any libraries or external packages you need to install. Thankfully you can still use your package manager to install dependencies.
- Place the binaries in a consistent location.
You’ll need to place binaries (have the +x bit flipped) in a place that your shell can find them. You should place it in a directory in your PATH environment variable.
These are the steps that a from-source package manager follows, you just have to do the by hand.
Using grep as an example:
$ wget http://mirrors.kernel.org/gnu/grep/grep-3.1.tar.xz $ tar -Jxvf grep-3.1.tar.xz $ cd grep-3.1 $ ./configure --prefix=$HOME/bin/ $ make $ make install
- Install the git, gcc, make and ncurses-devel packages via package manager.
- Clone https://github.com/mtoyoda/sl.git using git
- Build the software using make
- Copy the compiled sl binary into the directory ~/local/bin/.
- Update your $PATH to include $HOME/local/bin
- Run ‘whereis sl‘ to ensure it’s in your path
- Run sl and see what happens!
$ sudo yum install git gcc make ncurses-devel $ git clone https://github.com/mtoyoda/sl.git $ cd sl $ make gcc -O -o sl sl.c -lncurses $ mkdir -p ~/local/bin $ cp sl ~/local/bin/ $ echo "export PATH=$HOME/local/bin:$PATH" >> ~/.bashrc $ source ~/.bashrc $ whereis sl sl: /home/dobc/local/bin/sl $ sl
- Check the current version of grep
- Double check it’s location using which
- Download the latest tarball: http://mirrors.kernel.org/gnu/grep/grep-3.1.tar.xz
- Unpack using tar
- cd into the unpacked folder
- Run ‘./configure --prefix=$HOME/local/‘, ‘make‘ and then ‘make install‘
- Run ‘hash -r‘ to ensure your environment knows about the new binary
- Check the current version of grep (it should be 3.1 now!)
- Double check it’s location using which
$ grep --version grep (GNU grep) 2.20 $ which grep alias grep='grep --color=auto' /usr/bin/grep $ wget http://mirrors.kernel.org/gnu/grep/grep-3.1.tar.xz $ tar -Jxvf grep-3.1.tar.xz $ cd grep-3.1 $ ./configure --prefix=$HOME/local/ $ make $ make install $ hash -r $ grep --version grep (GNU grep) 3.1 $ which grep alias grep='grep --color=auto' ~/local/bin/grep