Introduction The sed command in Linux is a powerful stream editor that allows users to filter and transform text in various ways. Whether you're working on system administration tasks or programming scripts, mastering sed can significantly improve your efficiency. In this tutorial, we will explore how to use sed with regex to manipulate lines within a file, focusing on printing lines from one point to another. This guide will help you understand the nuances of sed and its regex capabilities, ensuring you can handle text processing with ease. What is the sed Command? The sed (stream editor) command in Linux is used to perform basic text transformations on an input stream (a file or input from a pipeline). It is commonly used for text substitution, but it also allows you to select and manipulate lines, delete text, and more, using regex (regular expressions). Key Features of sed Text Substitution : Replace occurrences of a pattern with a specific string. Line Selection : Selec...

in this tutorial, How to change ssh port another with selinux. The default ssh port 22, when you change port another with rules selinux (SELINUX=enforcing) get error can't change ssh port. Solve problem!( Running command following with root account) File selinux with content SELINUX=enforcing as below: [huupv@huupv ~]$ sudo cat /etc/sysconfig/selinux [sudo] password for huupv: # This file controls the state of SELinux on the system. # SELINUX= can take one of these three values: #     enforcing - SELinux security policy is enforced. #     permissive - SELinux prints warnings instead of enforcing. #     disabled - No SELinux policy is loaded. SELINUX=enforcing # SELINUXTYPE= can take one of these three values: #     targeted - Targeted processes are protected, #     minimum - Modification of targeted policy. Only selected processes are protected. #     mls...

Centos 7 managing services with Systemd. -List all the current loaded targets as command below: $ sudo systemctl list-units -t target Each services has 3 states; enabled, disabled and static. - To list enabled services as command below: $ sudo systemctl list-unit-files --type=service | grep enabled - To start/stop/restart services as command below: # systemctl status <servicename> # systemctl stop <servicename> # systemctl start <servicename> # systemctl restart <servicename> - To check running ntp services as comman below: $ sudo systemctl list-units --type service --all | grep ntp - Set the service to start a boot: # systemctl enable <servicename> - Disable service start-up boot # systemctl disable service The update later related command line "Centos 7 managing services with Systemd" in this article.

tar command is archiving utility. Something, you can retrieve extension .tar.gz or .tar.bz2 file. How to list the contents this without extracting from command line. The syntax tar command as below: tar OPTION File_Name With OPTION : t, --list : List the contents of an archive v : Verbosely list files processed j : Filter archive through bzip2 f : filename  You may reading link as below: Iptables how to How to reset password on centos 7 Bash script example List the contents of .tar.gz file To use tar command for .tar.gz as following: $ tar -tvf links-2.12.tar.gz  The output of links-2.12.tar.gz file as below: -rwxr--r-- 1000/1000      1215 2001-10-05 14:03 links-2.12/mailcap.pl -rwxr-xr-- 1000/1000      4654 2015-06-28 22:13 links-2.12/rebuild -rw-r--r-- 1000/1000       461 2003-05-06 01:10 links-2.12/links_16x16_1.xpm -rw-r--r-- 1000/1000      2410 2003-05-...

awk useful comand examples. How to Output Field Separator Variable, Number of Fields in a record, To print Non-system users and ignoring "nobody" etc.  You may reading link below : How to reset root password on centos 7 CentOS/RHEL Use yum Command To Downgrade Upgrade or Rollback Updates Generate and Verify Files with MD5 Checksum in Linux use inotify-tools on centos For example, the output passwd file use awk command $ cat /etc/passwd | awk -F':' 'BEGIN{ print "Name\tUID,GID\tHomeDirectory" }{print $1"\t"$3,$4"\t"$6}' The output as below: Name UID,GID HomeDirectory root 0 0 /root bin 1 1 /bin daemon 2 2 /sbin adm 3 4 /var/adm lp 4 7 /var/spool/lpd sync 5 0 /sbin shutdown 6 0 /sbin halt 7 0 /sbin mail 8 12 /var/spool/mail operator 11 0 /root games 12 100 /usr/games ftp 14 50 /var/ftp nobody 99 99 / systemd-bus-proxy 999 998 / systemd-network 192 192 / dbus 81 81 / polkitd 998 997 / tss 59 59 /dev/null s...

Use yum Command To Downgrade Upgrade or Rollback Update. How to downgrade the package? How to upgrade the package? How to rollback update the package?. I'm running commands with root account. You may reading link below : How to reset root password on centos 7 Generate and Verify Files with MD5 Checksum in Linux use inotify-tools on centos awk useful commands examples How to  Downgrade Upgrade package use yum command The basic syntax Downgrade package yum downgrade package1 yum downgrade package1 package2 showing multiple versions of a package yum --showduplicates list package For example How to Downgrade php-fpm 7.0.21 roll-back php-fpm 5.3.3 yum downgrade php-fpm The output as bellow Resolving Dependencies --> Running transaction check ---> Package php-fpm.x86_64 0:7.0.20-1.el6.remi will be a downgrade --> Processing Dependency: php-common(x86-64) = 7.0.20-1.el6.remi for package: php-fpm-7.0.20-1.el6.remi.x86_64 ---> Package php-fpm.x86_64 0:7.0...

Introduction Learn how to generate and verify MD5 checksums in Linux with step-by-step instructions. This comprehensive guide will help you ensure file integrity using MD5 checksums, complete with practical examples. File integrity is a crucial aspect of managing data on any Linux system. Whether you're handling sensitive information, distributing software, or simply ensuring that your files haven't been tampered with, MD5 checksums offer a straightforward solution. An MD5 checksum is a 128-bit character string that acts as a unique fingerprint for a file. In this guide, we will cover how to generate and verify MD5 checksums for your files, including creating a sample directory with files for practical demonstration.   What is an MD5 Checksum? An MD5 checksum is a 32-character hexadecimal number generated by the MD5 (Message-Digest Algorithm 5) cryptographic hash function. This checksum is used to verify the integrity of files, ensuring that they have not been altered or corr...

Many methods to reset root password centos 7. if GRUB 2 bootloader then no longer using in single-user mode as well as emergency mode. To below step by step to reset root password centos 7. You may reading link below : awk useful commands examples CentOS/RHEL Use yum Command To Downgrade Upgrade or Rollback Updates Generate and Verify Files with MD5 Checksum in Linux use inotify-tools on centos Step 1: Start the system, on Grub 2 boot screen, you press the e key as shown below. Step 2: In linux16 line or linuxefi on UEFI system, add parameters end line as shown below. rw init=/bin/bash Using Ctrl+A press or Ctrl+E press to start or end a line. Disable paramenters the rhgb and quiet in order to enable system message as shown top. Step 3: you press Ctrl+x to start single user mode passwd Step 4: update selinux information touch /.autorelabel Step 5: To resume the initialization and finish the system boot. exec /sbin/init Video how to reset root password on cen...

inotifywait - wait for changes to files using inotify. When it comes to real-time monitoring of file system events, inotify-tools is an indispensable tool. Especially for CentOS users, mastering inotify-tools can significantly enhance the efficiency of system administration tasks. This guide will walk you through everything you need to know about using inotify-tools on CentOS, from installation to advanced configurations, ensuring that you can leverage its full potential. Introduction to inotify-tools Inotify-tools is a command-line utility that leverages the inotify (inode notify) feature of the Linux kernel, allowing you to monitor file system events. This is incredibly useful for tasks that require real-time responses to file changes, such as automatic backups, log monitoring, and dynamic content updates. Why Use inotify-tools on CentOS? CentOS is widely used in enterprise environments due to its stability and robust performance. By integrating inotify-tools, you can automate and...

Introduction Learn how to install and effectively use the screen command on CentOS/RHEL and Ubuntu-based systems. This guide covers installation, session management, common issues, and FAQs to enhance your Linux terminal experience. In the world of Linux, the terminal is the heart of operations. Whether you're managing servers, running long processes, or multitasking across various projects, keeping your terminal sessions active and organized is essential.  This is where the screen command comes in—a powerful utility that allows you to run multiple terminal sessions from a single console. This article will guide you through the installation, usage, and troubleshooting of the screen command on Linux systems, ensuring you can manage your terminal sessions like a pro. How to Install the screen Command Before diving into the functionalities of the screen command, it’s important to ensure it’s installed on your system. The installation process varies depending on your Linux distribu...

Introduction Learn the essential Linux basic commands that every user and administrator should know. From checking your Ubuntu version to managing users, this comprehensive guide provides step-by-step instructions for each command. Linux is a versatile and powerful operating system, popular among both tech enthusiasts and professionals. Whether you are a beginner or an experienced user, mastering the basic commands is crucial for managing and operating a Linux system efficiently. This guide will walk you through the essential Linux commands, helping you understand how to check system information, manage users, and more. By the end of this guide, you'll be equipped with the foundational skills needed to navigate and control your Linux environment with confidence. How to Check Your Ubuntu Version One of the first tasks when working with a Linux system is to know which version of Ubuntu you are running. This information is vital when installing software, troubleshooting issues, or co...