Introduction Automating tasks at startup is essential for server administration, ensuring services and scripts execute without manual intervention. CentOS , a popular Linux distribution, provides multiple ways to run bash scripts on boot time. This guide covers various approaches, their use cases, and step-by-step implementations. Methods to Run a Bash Script on Boot Time on CentOS 1. Using crontab with @reboot Cron jobs are a powerful way to schedule tasks. The @reboot directive in crontab allows executing scripts upon system startup. Steps: Open the crontab editor: crontab -e Add the following line: @reboot /path/to/your/script.sh Save and exit. Ensure the script has executable permissions: chmod +x /path/to/your/script.sh Pros: Simple and effective. Cons: Requires crontab configuration and user-specific settings. 2. Using systemd service (Recommended for CentOS 7+) Systemd is a modern service manager that provides better control over startup scripts. Steps: Create a new system...

Introduction Learn how to create and configure a user in Linux using the `useradd` command. This comprehensive guide covers creating a user, assigning groups, and configuring sudo privileges without a password. Managing user accounts is a fundamental task for any Linux system administrator. Whether you are setting up a new server or adding users to an existing system, understanding how to create and configure users efficiently is crucial. In this tutorial, we will explore how to use the `useradd` command to create a new user in Linux, assign them to specific groups, and enable them to execute sudo commands without requiring a password. Why Use `useradd` for User Creation? The `useradd` command is a powerful tool that allows system administrators to create user accounts with specific options such as User ID (UID), Group ID (GID), home directory, shell, and more. Unlike graphical user interfaces, `useradd` provides a streamlined way to automate user creation through scripts, making it i...

How to use shell script parse xml file . In this tutorial, I will use grep command, awk command and sed command Reading xml file extracting value in linux . For example xml person file as below <person>   <sex>Male</sex>   < firstname >Huu</ firstname >   <lastname>Phan</lastname>   <sex>female</sex>   < firstname >Miranda</ firstname >   <lastname>Kerr</lastname> </person> How to extracting value Huu and Miranda  of < firstname > < /firstname > Use grep command [huupv@huupv huuphan.com]$ grep -oP '(?<=<firstname>).*(?=</firstname)' person.xml Use awk command [huupv@huupv huuphan.com]$ awk -F "[><]" '/firstname/{print $3}' person.xml Use sed command [huupv@huupv huuphan.com]$ sed -n '/firstname/{s/.*<firstname>//;s/<\/firstname.*//;p;}' person.xml  The result, Shell script parse xml in linux

rename command similar with mv command. This command is slightly more advanced than mv  command. How to rename multiple files in linux. The syntax rename command rename [options] expression replacement-file For example, basic use rename command [huupv@huupv huuphan.com]$  rename file huu file1.txt The same output How to rename all file extension .txt to .atxt file [huupv@huupv huuphan.com]$ rename .txt .atxt *.txt The same output Use option --verbose in rename command [huupv@huupv huuphan.com]$ rename -v foo huu foo?.atxt The same ouput `foo2.atxt' -> `huu2.atxt' `foo3.atxt' -> `huu3.atxt' Details more information rename command man rename

Introduction Learn how to set up an OpenVPN server on CentOS 7 with this comprehensive step-by-step guide. Ensure your network's security and privacy with one of the most reliable VPN solutions available. Perfect for both beginners and advanced users. Setting up a secure and reliable VPN is essential for ensuring privacy and data protection, especially in today's increasingly interconnected world. OpenVPN is one of the most trusted and robust VPN solutions available, providing a high level of security and flexibility for both businesses and individual users. This guide will walk you through the process of setting up an OpenVPN server on CentOS 7, offering step-by-step instructions to help you establish a secure connection that meets your specific needs. Step 1: Prepare install OpenVPN server sudo yum update -y sudo yum install epel-release -y sudo yum update -y sudo yum install -y openvpn easy-rsa Configure Ip forwarding for OpenVPN Server vim /etc/sysctl.conf The c...

Someday, your Virtualbox not start and the display error "Failed to create the VirtualBox COM object". it got somewhat corrupted. The error of Virtualbox "Failed to create the VirtualBox COM object" as below: Location: '/home/huupv/.config/VirtualBox/VirtualBox.xml' , line 1 (0), column 1. /home/vbox/vbox-5.2.14/src/VBox/Main/src-server/VirtualBoxImpl.cpp[554] (nsresult VirtualBox::init()). How to solve problem! Step 1: make sure process VBoxSVC not running Step 2: make a copy file VirtualBox.xml then delete original file. Step 3: Rename VirtualBox.xml-prev file to VirtualBox.xml file. Step 4: try again start VirtualBox. To check not running process VBoxSVC not running use ps command as below: $ ps -ef | grep VBoxSVC huupv 10122 2421 0 22:19 pts/1 00:00:00 grep --color=auto VBoxSVC To check VirtualBox.xml file and Delete VirtualBox.xml file $ ll /home/huupv/.config/VirtualBox/ | grep VirtualBox.xml -rw-----...

Connect access server (VPS) from a linux computer. In this tutorial, I will access server VPS installed OpenVPN server from a linux computer. Ref to How to setup OpenVPN Server on Centos 7 Install openvpn client on linux Run Openvpn client with .ovpn file for example: client.ovpn Install OpenVPN client on linux  Fedora/CentOS/RedHat client sudo yum install openvpn Ubuntu/Debian client sudo apt-get install openvpn Checking Openvpn client version [huupv@huupv ~]$ openvpn --version The output as below: OpenVPN 2.4.6 x86_64-redhat-linux-gnu [SSL (OpenSSL)] [LZO] [LZ4] [EPOLL] [PKCS11] [MH/PKTINFO] [AEAD] built on Apr 26 2018 library versions: OpenSSL 1.1.0h-fips  27 Mar 2018, LZO 2.08 Running the OpenVPN client linux computer with the downloaded client config ovpn file: [huupv@huupv vpn-client-01-config]$ sudo openvpn --config client.ovpn The output OpenVPN client linux connect to server OpenVPN server as below: Sun Jul  1 21:43:35 2018 TUN/TAP de...

Introduction String manipulation is a crucial skill in shell scripting. One common task is to split a string and retrieve specific fields, such as the last one. This can be useful for various purposes, such as parsing file paths, URLs, or command outputs. In this guide, we'll explore different methods to split a string and get the last field in shell scripting, starting from basic techniques and moving towards more advanced examples. How to split a string in shell and get the last field. in this tutorial, i written a small program use bash script split string /www/huu/phan/com/xyz to new path /www/huu/phan/com and last field of new path /www/huu/phan/com is com . How to Split a string in shell and get the last field Input: one_path is /www/huu/phan/com/xyz Output: new_path is  /www/huu/phan/com last_field of new_path is com My bash shell as below: #!/bin/bash ############### # # Author: HuuPV # My blog: www.huuphan.com # ############### # How to split a string in shel...

Introduction Zimbra Collaboration Suite (ZCS) is a powerful, open-source email and collaboration platform. Managing user accounts efficiently is crucial for administrators to maintain security and ensure smooth operations. One essential skill is knowing how to lock and unlock Zimbra accounts via the command line. This capability is particularly useful for handling compromised accounts, maintaining system security, and troubleshooting user access issues. This article provides a comprehensive guide on how to lock and unlock Zimbra accounts from the command line. We’ll cover basic and advanced usage scenarios, helpful tips, and answers to frequently asked questions. By the end, you’ll be equipped to handle account management tasks confidently using Zimbra CLI commands. Why Lock or Unlock Zimbra Accounts? Use Cases for Locking Accounts Security Breaches : Prevent unauthorized access to compromised accounts. Policy Violations : Temporarily restrict access for accounts violating usage polici...

In this tutorial, I use diff command output on screen. How to compare different line by line in  files. How to compare side by side, color , output do not output common lines with diff command. What diff command work? compare files line by line For example my topic, I compare line by line in 2 file: file1.txt and file2.txt The content file1.txt file [huupv@huupv huuphan.com]$ cat file1.txt <####################################> author: huupv My Blog: www.huuphan.com Hello everbody! <####################################> The content file2.txt file [huupv@huupv huuphan.com]$ cat file2.txt <####################################> author: huupv My Blog: www.devopsrole.com Hello everbody! <####################################> The default compare line by line with diff comand [huupv@huupv huuphan.com]$ diff file1.txt file2.txt The output as below: 3c3 < My Blog: www.huuphan.com --- > My Blog: www.devopsrole.com The output nu...