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  • All the cloud and DevOps tools are made to run on Linux
  • Ubuntu is based on the Debian architecture
  • CentOS is based on the Red Hat Enterprise Linux (RHEL) architecture

User Accounts

  • Root user has unlimited access to the system
  • Root user needs to grant a normal user root previlege by making an entry in the /etc/sudoers file. The normal user can then escalate their previlege by prefixing their command with sudo

Important Commands

  • echo $SHELL - get shell type
  • mkdir -p user/abdur/add - make directory hierarchy
  • cat > file.txt - add contents to a file
  • whoami - get user info
  • id - get user's id and group
  • su <username> - switch user
  • sudo su - - switch to root user
  • ssh <username>@ - ssh as a user into a system
  • wget <file-url> -O file.txt - download a file

Package Managers

  • Package managers download the necessary dependencies when installing packages in Linux
  • CentOS uses Yum, an RPM (RedHat Package Manager) based package manager
    • attachments/Pasted image 20220915104247.jpg
  • Commands
    • yum install ansible - install a package
    • yum repolist - list the repositories
    • yum list - list installed packages
    • yum list <package-name> - search for a package in the list of installed packages
    • yum remove <package-name> - remove a package
    • yum --show-duplicates list <package-name> - list all the installed versions of a package
    • yum install ansible- - install a specific version of a package


  • Services in Linux help us configure software to run in the background and ensure that they run automatically even if the servers are rebooted. Eg. Docker
  • If there are multiple interdependent services, they should follow the order of startup.
  • systemctl command is used to manage systemd services
  • Commands - might need to use sudo
    • systemctl start httpd - start an service (HTTPD)
    • systemctl stop httpd - stop a running service
    • systemctl status httpd - check the status of a service
    • systemctl enable httpd - configure the service to start at startup
    • systemctl disable httpd - configure the service to not start at startup
    • systemctl daemon-reload - reload the systemd

Configure an application as a Service

  • Let's assume a Python server app that runs at port 5000 and prints "Hello World"
  • We want to configure this app as a service
  • Create a new file my_app.service in the /etc/systemd/system directory and paste the following in it
    ExecStart=<command to start your app>
  • systemctl daemon-reload - reload the systemd to let it know that a new service has been configured
  • systemctl start my_app - start your app as a service
  • To configure the service to run when the system boots up, add the following to the service file
  • To add description
    Description=My best Python app
  • To restart the application if it crashes
  • To run scripts before and after running the app

Docker as a Service

  • Once Docker is installed, the Docker daemon runs as a background process that listens for docker commands
  • Docker installation creates a service file with the following contents
    • attachments/Pasted image 20220921225448.jpg

Last updated: 2022-09-22