Servers & O.S.

Michael L. Collard, Ph.D.

Department of Computer Science, The University of Akron

Views of DevOps

  • DevOps during Dev (Development)
  • DevOps during Ops (Operations), including deployment
  • Example: Testing
    • Require testing during deployment
    • But it also requires testing during development
  • Combined view: Extend development approach into deployment

Code Integration

  • Once common practice to infrequently commit to the central repository
  • The central repository became quite different than developers repository (or branch), so developer's dealt with complicated code integration
  • merge hell or integration hell
  • Integrating changes often took more time than developing a solution
  • If code integration is painful, then developers wait, making it more painful

Continuous Integration (CI)

  • Local Workflow (multiple times per day):
  • Develop, test locally
  • Commit
  • Separate build server, building on each commit:
  • Compile/build
  • Run tests
  • Deploy an artifact

Common CI Practices

  • Version-control repository
  • Automate the build to a single command, preferably without options
  • Build runs tests
  • Everyone commits to the baseline frequently, i.e., at least once per day
  • Every commit to the baseline is built
  • Every bug-fix commit comes with a test case
  • Keep the build fast
  • Test in a clone of the production environment
  • Make it easy to get the latest deliverables
  • Anyone can see the results of the build and the changes that made it
  • Automate deployment

Continuous Deployment (CD)

  • Automated deployments
  • Once CI is done, then CD can take over
  • E.g., changes to the website automatically appear
  • Continuous Delivery
    • Delivery of new version in a continuous fashion
    • Allow for manual deployments
    • E.g., post a new version of the installer, and the user chooses when to install
  • Often Continuous Deployment is used when it really means Continuous Delivery
  • Since CD is the end part of CI, the term CI/CD is used


  • Development
    • Develop on a local machine
    • Commit to version control, e.g., Git
    • Automated testing triggered by commit
  • Operations (among other things)
    • Generate installers
    • Test installers
    • Post installers
  • Note: What part is development and what part is deployment is not fixed

DevOps Systems

  • Remote systems for deployment and operations
  • Remote systems for development
  • Use similar approaches and technologies to extend development into operations
  • Create one long toolchain


  • Much of development is automated (or should be automated)
  • Parts of operation may be manual. Why?
  • Requires manual "sign off"
  • How operations were performed in the past
  • More interactions with other parts of the organization
    • Training
    • Legal
    • Administrative

Example: Bad Old Days

  • A long-running Linux system requires a configuration change, e.g., fix a "Too many open files" error
  • Change is made manually to the system
  • Unexpected outage
  • When the server is back up, the configuration change has disappeared


  • Manual
  • Keep careful documentation, which operators religiously apply at every reboot
  • Automated
  • Configure that system so that it has the change

Hardware Platforms

Evolution of Servers

  • Mainframes
    • Expensive to purchase and operate
    • Run all services on one large server
  • Minicomputer, PC
    • Not as expensive, could afford more than one
    • Segment services by requirements: hardware, security issues, reliability
  • Virtual Machine (VM)
    • Easy to configure a new server
    • One set of services per VM
  • Containers
    • Almost unlimited
    • One service per container

O.S. & Servers

  • Mainframes
    • O.S. has to work for all potential services
  • Minicomputer, PC
    • Can tune one overall O.S. for each server
    • Or use a different O.S.
  • Virtual Machine (VM)
    • One O.S. per VM
  • Containers
    • Pick O.S. for application

Operating Systems for DevOps

  • Windows 10, Windows Server
    • Develop on Windows 10, operate on Windows Server
  • Linux distributions
    • Develop and operate
  • macOS
    • Develop


  • A Unix-like operating system that uses the Linux kernel
  • A premier example of “open source”
  • Center of the largest collaborative software effort
  • Typically used in O.S. work

Parts of “Linux”

  • Linux kernel - manage hardware, run a program, provide security
  • GNU Project – utilities: bash, gcc, emacs, etc.
  • – X Window system
  • GNOME & KDE – desktop environments
  • Many other sources

Forerunners to Linux

  • 1970: Unix Operating System – Thompson & Ritchie
  • 1978: BSD (Berkeley Standard Distribution) - kernel + distribution
  • 1983: GNU Project – Richard Stallman, the goal of a free Unix-like operating system, GPL (General Public License), written in 1989
  • 1987: MINIX – Unix-like operating system for education by Andrew Tannenbaum

Problems with Unix-like O.S.’s for x86

  • GNU Project had many utilities but no kernel (GNU Hurd)
  • BSD based on 6th edition of AT&T Unix, and lawsuits limited development
  • MINIX development was lacking, and limited distribution
  • No good solution for running a Unix-like system on a PC

Linus Torvalds

  • Computer Science student at the University of Helsinki, Finland, in 1991
  • Started to write a terminal emulator (independent of the operating system) for his PC
  • Developed using MINIX and the GNU C Compiler
  • Grew into the Linux kernel
  • Announced what he had started in the newsgroup comp.os.minix in August 1991

What are some reasons that companies supported Linux?

  • Make sure it runs on their hardware, e.g., Intel
  • Distributors of Linux, e.g., RedHat, Novell
  • Embedded devices, e.g., Sony
  • Platform for technical development, e.g., Volkswagen

GNU Project

  • “GNU’s Not Unix”
  • Started by Richard Stallman (rms) in 1983
  • Start of the Free Software Movement and the corresponding FSF (Free Software Foundation)

GNU Four Freedoms

  • 0: The freedom to run the program for any purpose
  • 1: The freedom to study how the program works, and adapt it to your needs
  • 2: The freedom to redistribute copies so you can help your neighbor
  • 3: The freedom to improve the program, and release your improvements to the public, so that the whole community benefits


  • General Public License
  • “Copyleft”
  • Copyright retained by the author
  • GPL Software must be available for free
  • Source code must be made available
  • If other developers make changes, they must distribute it with the pre-change source code

GPL Issues

  • Cannot directly use in proprietary code
  • What about programs developed using GPL editors, compilers, o.s.? – Not a problem
  • What about programs that call a function library, e.g., GNU C library? – LGPL (Lesser General Public License)
  • Companies make money off of services, not off the IP (Intellectual Property) of their code. E.g., srcML

Open Source Licenses

  • Variety including BSD license, Apache License, Mozilla Public License
  • GPL Version 2 in 1991
  • GPL Version 3 in 2008
  • Linux (GPL v2) - individuals hold copyright – Linux stuck with GPL v3 v2
  • GNU Project – individuals assign copyright to FSF

GNU/Linux Distributions (distros)

  • Installation program
  • General configuration
  • Packages of compatible software
  • Dependency handling
  • Support (technical and legal)
  • Updates
  • Security fixes

Differences between Distributions

  • Community-based versus commercial
    • Community: Debian, Slackware, Gentoo, and Arch Linux
    • Commercial: Fedora (Red Hat), openSUSE (SUSE), Ubuntu (Canonical Ltd.)
  • Hardware and device support
  • Number of packages (different software) available
  • Use of proprietary packages
  • Package management
  • Size, software typically installed
  • Security
  • Frequency of updates/releases
  • Support

Why is Linux Often Used for DevOps?

  • Not the only platform used
  • Easy to optimize for size
  • Easy to only include needed packages
  • Not necessarily used to develop but to operate
  • Linux Desktop issues are not a concern

WSL for Windows 10

  • Windows Subsystem for Linux
  • WSL introduced Aug 2016 (Windows 10, Version 1607)
  • Native Linux compatibility (aim)
  • WSL2 introduced in May, 2019, real Linux kernel

State of Unix

  • Linux on servers
  • Android based on Linux
  • macOS based on BSD
  • iOS based on BSD
  • WSL on Windows