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Details
Redhat / CentOS
In this part of RHCSA exam preparation you will learn how to manually change into a different boot targets. This article will also teach you how to set a default boot targets to automatically boot into graphical or multi-user target on Red Hat Enterprise Linux system.

In this tutorial you will learn:
  • How to check default boot target
  • How to manually switch between different targets
  • How to set default boot to multi-user target
  • How to set default boot to graphical target

Details
Redhat / CentOS
In this part of RHCSA exam preparation we will turn our attention to links. There are two types of link, hard links and soft links. In this article we will talk about how to create and remove links and will also discuss some basic background behind both, the hard links and the soft links.

In this tutorial you will learn:
  • What are symbolic (soft) links
  • What are hard links
  • How to create a symbolic link
  • How to create a hard link
  • How to remove link

Details
Redhat / CentOS
ALTTEXT
UNDER CONSTRUCTION
RHCSA is a must have certification for anyone serious about getting a Linux system administration job. This RHCSA Exam Preparation Guide is currently under construction but is regularly updated with new topics. Please check back later.

If you are a beginner or somewhat new to GNU/Linux do not waste time by waiting but get started with a GNU/Linux command line basics before you do anything else. Understanding the GNU/Linux command line is an absolute must and will take you a long way on your RHCSA exam.

Understand and use essential tools

Operate running systems

  • Boot, reboot, and shut down a system normally
  • Boot systems into different targets manually
  • Interrupt the boot process in order to gain access to a system
  • Identify CPU/memory intensive processes and kill processes
  • Adjust process scheduling
  • Locate and interpret system log files and journals
  • Preserve system journals
  • Start, stop, and check the status of network services
  • Securely transfer files between systems

Configure local storage

Create and configure file systems

  • Create, mount, unmount, and use vfat, ext4, and xfs file systems
  • Mount and unmount network file systems using NFS
  • Extend existing logical volumes
  • Create and configure set-GID directories for collaboration
  • Configure disk compression
  • Manage layered storage
  • Diagnose and correct file permission problems

Deploy, configure, and maintain systems

  • Schedule tasks using at and cron
  • Start and stop services and configure services to start automatically at boot
  • Configure systems to boot into a specific target automatically
  • Configure time service clients
  • Install and update software packages from Red Hat Network, a remote repository, or from the local file system
  • Work with package module streams
  • Modify the system bootloader

Manage basic networking

  • Configure IPv4 and IPv6 addresses
  • Configure hostname resolution
  • Configure network services to start automatically at boot
  • Restrict network access using firewall-cmd/firewall

Manage users and groups

  • Create, delete, and modify local user accounts
  • Change passwords and adjust password aging for local user accounts
  • Create, delete, and modify local groups and group memberships
  • Configure superuser access

Manage security

  • Configure firewall settings using firewall-cmd/firewalld
  • Configure key-based authentication for SSH
  • Set enforcing and permissive modes for SELinux
  • List and identify SELinux file and process context
  • Restore default file contexts
  • Use boolean settings to modify system SELinux settings
  • Diagnose and address routine SELinux policy violations

Details
Redhat / CentOS
The hostname of your CentOS 7 Linux is defined by the file /etc/hostname thus setting a new hostname for your system is just a matter of editing this file and replace a current hostname definition line with new one. However, doing so will not update your system;s hostname immediately thus a preferred way of changing a hostname on CentOS 7 Linux is to use nmtui and more specifically its child nmtui-hostname. Using nmtui-hostname tool will make the process of changing your hostname rather simple as executing a single command. The following linux command will change the hostname to linuxconfig.org: 
# nmtui-hostname linuxconfig.org
hostname change centos 7 linux command
Hit the "OK" button on the pop-up dialog and you are done.

Details
Redhat / CentOS
The sudo command allows regular users to execute commands with administrative/root privileges. By adding any user to predefined sudo group wheel will grant root privileges to execute any command as root user. Any attempt to use the sudo command for the non-sudo user will result in: 
user is not in the sudoers file.  This incident will be reported.
In this tutorial you will learn:
  • How to create sudo user on RHEL 8 / CentOS 8 system.
  • How to add existing user to sudoers.

Details
Redhat / CentOS
This article explains how to open FTP port 21 on RHEL 8 / CentOS 8 Linux system with the firewalld firewall. The FTP protocol is primarily used by file transfer services such as, but not limited to, vsftpd FTP server. For more information visit our introduction guide to firewalld syntax and usage guide.

In this tutorial you will learn:
  • How to open FTP port 21.
  • How to open FTP port 21 permanently.
  • How to list currently open ports/services.
  • How to close/remove open FTP port 21.

Details
Redhat / CentOS
This article explains how to open HTTP port 80 and HTTPS port 443 on RHEL 8 / CentOS 8 system with the firewalld firewall. HTTP and HTTPS protocols are primarily used by web services such as, but not limited to, Apache or Nginx web serves.

For more information about the firewalld firewall visit our introduction guide to firewalld syntax and usage guide.

In this tutorial you will learn:
  • How to open HTTP port 80 and HTTPS port 443.
  • How to open HTTP port 80 and HTTPS port 443 permanently.
  • How to list currently open ports/services.
  • How to close/remove HTTP port 80 and HTTPS port 443.

Details
Redhat / CentOS

In this tutorial we will learn how to install Apache Tomcat 8 application container to RHEL 8 / CentOS 8. We will be using the zip package available to download from the Apache Tomcat website. As this package will not handle setting up the environment, we will create it from the command line.

In this tutorial you will learn:
  • How to install Apache Tomcat from zip file
  • How to create the environment for the Tomcat server from command line
  • How to add basic service file to systemd
  • How to enable autostart, start and stop the Tomcat server
  • How to verify Tomcat is reachable

Details
Redhat / CentOS
Firewalld is a powerful and yet simple to use tool to manage a firewall on RHEL 8 / CentOS 8 Server or GNOME workstation. Firewalld allows to manage open or close ports using predefined services as well as open and close user custom ports.

In this tutorial you will learn:
  • How to open and close ports on RHEL 8 / CentOS 8 with Firewalld.
  • How to open and close services on RHEL 8 / CentOS 8.
  • How to reload firewall configuration.
  • How to list open ports or services.

Details
Redhat / CentOS
The firewall on RHEL 8 / CentOS 8 Linux system is enabled by default allowing for only few services to receive incoming traffic. FirewallD is the default daemon responsible for firewall security feature onRHEL 8 / CentOS 8 Server.
NOTE
The nftables framework replaces iptables as a default network packet filtering feature on RHEL 8.
The following is a list of default firewall opened ports and configured settings on RHEL 8 / CentOS 8 Linux system using the firewalld dynamic firewall daemon: 
# firewall-cmd --list-all
public (active)
  target: default
  icmp-block-inversion: no
  interfaces: enp0s3
  sources: 
  services: cockpit dhcpv6-client ssh
  ports: 
  protocols: 
  masquerade: no
  forward-ports: 
  source-ports: 
  icmp-blocks: 
  rich rules:
In this tutorial you will learn:
  • How to check the firewall status onRHEL 8 / CentOS 8.
  • How to stop firewall on RHEL 8 / CentOS 8.
  • How to start firewall on RHEL 8 / CentOS 8.
  • How to permanently disable firewall on RHEL 8 / CentOS 8.
  • How to enable firewall to start after reboot.

Details
Redhat / CentOS

There are several ways on how to check what version of CentOS is running on your system. The simplest way to check for the CentOS version number is to execute the cat /etc/centos-release command. Identifying the accurate CentOS version may be required to help you or your support team to troubleshoot your CentOS system.

The CentOS version consists of three release versions as illustrated below:

Details
Redhat / CentOS

This guide will show how to install and configure a DNS Server in RHEL 8 / CentOS 8 in caching mode only or as single DNS Server, no master-slave configuration. A reverse and forward zone example is provided.

In this tutorial you will learn:
  • How to install a DNS server in RHEL 8 / CentOS 8
  • How to configure a server as caching only DNS Server
  • How to configure a server as single DNS Server

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