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Systemd – run a script before system shutdown

Here systemd will execute /srv/app_shutdown_script.sh before the system reboots. Refer to the following steps. Create a systemd Unit file with the following content. # cat /etc/systemd/system/exec-before-shutdown.service [Unit] Description=Shutdown run script…

logrorate: error: lines must begin with a keyword or a filename (possibly in double quotes)

Logrotate command returns the following error: # logrotate -vf /etc/logrotate.d/mylog reading config file mylog reading config info for /var/log/mylog.log error: iptables:1 lines must begin with a keyword or a filename…

How to convert a .cer to .pem format

The following OpenSSL command will convert a .cer file to .pem format. $ openssl x509 -inform der -in certificate.cer -outform pem -out certificate.pem

Squid configuration to allow internet access to specific AD group

Squid is a caching web proxy server helps in speeding up a web server by caching repeated requests, caching web, DNS and other computer network lookups for a group of…

Squid Kerberos authentication configuration on Linux/Debian/Ubuntu/CentOS

Squid is a caching web proxy, provides a wide variety of uses, including speeding up a web server by caching repeated requests, caching web, DNS and other computer network lookups…

How to create a keytab or service principal on windows

A keytab file is used to store the SPN(Service Principal) credentials for communicating with the KDC or AD Domain Controller or a Kerberos server. This file contains sensitive information to…

Configure a Linux system as a wifi router or hotspot

This article provide a simple and precise steps to create a Wi-Fi Hotspot or router on Ubuntu / Debian / Fedora / CentOS / RHEL/ Arch Linux system using nmcli…

Convert SBI term home loan to Maxgain

One can easily convert SBI term home Loan Account to SBI Maxgain home loan account. This conversion is only allowed once with a certain conversion and switch over fee. You…

sudo log configuration on Linux

Enabling sudo log helps system administrators to track the activities of sudo users and this helps in system auditing. sudo logging logs all sudo commands executed on Linux system. This...

sudo-io configuration on Linux

sudo-io is needed to log all sudo commands executed on Linux system with the command input and output stream. This article provides a step by step instruction to configure sudo-io...

DRBD Cheat Sheet

DRBD is a distributed replicated storage system for the Linux platform. It is implemented as a kernel driver, several userspace management applications, and some shell scripts. This article describes about...

Remove a faulty node and add a new node on Pacemaker cluster

Sometimes cluster nodes may fail from cluster due to disk failure, operating system crash or some other reason. Here in this demonstration we will configure, how to remove a failed...

Understanding Squid Access Log

Many times we find difficulty to understand SQUID access logs and hardly there are a few references available. This article provides complete details about understanding SQUID access logs.

How to Remove DRBD Device|Volume

In a cluster some times it might required to decommission exiting cluster and create new cluster according to the new requirement. In this demonstration we will remove or destroy DRBD…

Replace Volume|Disk On DRBD Pacemaker Cluster

It is an obvious behavior that DRBD cluster volume or disk may fail. In order to maintain High Availability we need to replace the failed volume or disk without affecting...

Pacemaker PostgreSQL Cluster Configuration on CentOS|RHEL 7

Without a cluster environment, if a server goes down for any reason that affects entire production. In order to overcome this issue, we need to configure servers in cluster so…

Pacemaker DRBD MariaDB|MySQL Cluster on CentOS|RHEL 7

Without a cluster environment, if a server goes down for any reason that affects entire production. In order to overcome this issue, we need to configure servers in cluster so...

Jenkins installation on Linux – Centos/RHEL|Ubuntu/Debian

Jenkins is the Continuous Integration and Continuous Delivery tool used for devops. Jenkins helps to automate the non-human part of the software development process, here we will see how to…

PaceMaker Cluster Command Cheat Sheet

This article contains all pacemaker cluster administration commands to manage a PaceMaker cluster. You can refer to the command sheet to manage any PaceMaker cluster. Topic How to manage PaceMaker...

Google Chrome on Docker Container

If you have a requirement to run Google Chrome browser inside a container we can easily achieve this by using TekFik provided CentOS 7 container. TekFik Centos 7 Container image…

Pacemaker DRBD PostgreSQL Cluster on CentOS|RHEL 7

PostgreSQL, also known as Postgres, is a free and open-source relational database management system emphasizing extensibility and technical standards compliance. It is designed to handle a range of workloads, from…

Rsync on ssh chroot jail

Using OpenSSH you can bind SSH, SFTP, SCP or RSYNC users to their home directory and restrict them to access other directories on the SSH server. In this article we…

SCP on chroot ssh jail

Using OpenSSH you can bind SSH, SFTP, SCP users to their home directory and restrict them to access other directories on the SSH server. In this article we will configure…

SFTP on chroot SSH jail

Using OpenSSH you can bind SSH, SFTP, SCP users to their home directory and restrict them to access other directories on the SSH server. In this article we will configure…

Pacemaker MariaDB|MySQL Cluster on CentOS|RHEL 7

Without a cluster environment, if a server goes down for any reason that affects entire production. In order to overcome this issue, we need to configure servers in cluster so…

Chroot SSH Configuration on Linux|RHEL|CentOS

Using OpenSSH you can bind SSH or SFTP users to their home directory and restrict them to access other directories on the SSH server. In this article we will demonstrate…

Pacemaker Cluster Configuration on Linux|Rhel7|Centos7

Without a cluster environment, if a server goes down for any reason that affects entire production. In order to overcome this issue, we need to configure servers in cluster. Doing…

Pacemaker Apache Cluster Configuration on Linux|Rhel7|Centos7

Without a cluster environment, if a server goes down for any reason that affects entire production. In order to overcome this issue, we need to configure servers in cluster so…

Pacemaker NFS Cluster on Rhel 7|Centos 7

In a production environment, if a server goes down for any reason that affects entire production. In order to overcome this issue, we need to configure servers in the cluster…

How to configure ISCSI Target|Storage server on Linux|CentOS|RHEL

Internet Small Computer Systems Interface(ISCSI) is IP-based storage, works on top of the internet protocol. It caries the SCSI commands over IP network. The major benefits of ISCSI target that,…

How to setup passwordless chroot SFTP on Linux

This article describes a step by step procedure to set up password-less chroot SFTP login between a source and destination system.

SFTP chroot configuration on Linux

SFTP provides secure file transmission method however a SFTP logged in user can browse other sub-directories other than the user’s designated home directory. This article provides a step by step…

Multiple subnet PXE installation with Linux DHCP

In computing, the Pre-boot Execution Environment describes a standardized client-server environment that boots a software or operating system, retrieved from a network, on PXE-enabled clients. On the client side it…

No subnet declaration for ethx

No subnet declaration for eth1 (no IPv4 addresses). Ignoring requests on eth1. If this is not what you want, please write a subnet declaration in your dhcpd.conf file for the…

Linux SFTP verbose Logging sftp commands

sftp is an interactive file transfer program, similar to ftp(1), which performs all operations over an encrypted ssh(1) transport. sftp-server is a program that speaks the server side of SFTP…

SFTP restrict delete or remove or rename permission

sftp is an interactive file transfer program, similar to ftp(1), which performs all operations over an encrypted ssh(1) transport. sftp-server is a program that speaks the server side of SFTP…

How to enable EPEL repository on CentOS or RHEL

EPEL (Extra Packages for Enterprise Linux) is a volunteer-based community effort from the Fedora project to create a repository of high-quality add-on packages that complement the Fedora-based Red Hat Enterprise…

Nginx redirect HTTP to HTTPS

Hypertext Transfer Protocol Secure(HTTPS) is an extension of the Hypertext Transfer Protocol(HTTP). It is used for secure communication over a computer network, and is widely used on the Internet. Using…

How to check setuid and setgid on Linux with find command

Linux find command is a powerful tool to ease system administration and saves a lots of time while working on file filtering or finding a specific type of file from…

Run Apache httpd server from a non-root user privilege

Generally Apache2 or HTTPD service is started by the superuser root account on any Linux distribution. However on a specific instance or requirement you may need to start the Apache…

How to enable OpenShift Auditing

OpenShift is a family of containerization software has many add on features and advantages over Kubernetes. This article describes about OpenShift Auditing.

How to disable WordPress AutoSave feature

By default, WP automatically saves draft of your post, page or a custom post type every 60 seconds. However, there are situations where we may want to disable this feature….

wordpress autosave page|article|post

Many times we forget to save a post when writing article or posts on a WordPress site. WordPress autosave feature is one of the best feature that gives us a…

Linux capabilities with getcap|setcap and file capabilities

For the purpose of performing permission checks, traditional UNIX implementations distinguish two categories of processes: privileged processes (whose effective user ID is 0, referred to as superuser or root), and…

How to bind tcp|udp ports below 1024 with non-root account|privilege

Port numbers below 1024 are reserved for superuser i.e. root so a normal user cannot bind to ports in this range. Privileged port ranges are defined in kernel source code…

VSFTPD debug or enable verbose logging on VSFTPD server

VSFTPD is a file transfer server provides file transmission over FTP. Having some issue with the VSFTPD server will require to troubleshoot the VSFTPD daemon. This article provides a precise…

SSH login delay|slow

Many times we observe there is some delay in SSH login and the delay might be from 2 seconds to 2 minutes. There are a few troubleshooting steps we need…

How To Setup SSH|SFTP Passwordless Login on Linux|CentOS|RHEL|Ubutu

Secure Shell(SSH) is a cryptographic network protocol for providing secure remote login over an unsecured network. SSH supports remote command-line, login, and remote command execution. This article describes a step…

How to disable IPv6 networking on CentOS|RHEL|Ubuntu|Debian

Internet Protocol Version 6 (IPv6) is a network layer protocol which allows communication and data transfers to take place over the network. IPv6 came into existence in 1998 with the…

To perform the requested action, WordPress needs to access your web server

WordPress throws error on the website upon posting an article or page or uploading an image. "To perform the requested action, WordPress needs to access your web server. Please enter…

Exclude certain|specific logs from Nginx

Nginx logs are needed to track all events generated on the Webserver. However there are some specific events which are not needed to track. turning off of those logs or…

vsftpd – GnuTLS error -15: An unexpected TLS packet was received

File transfer using FileZilla and other FTP client software fails from the VSFTPD server with the error "vsftpd – GnuTLS error -15: An unexpected TLS packet was received". Refer to…

Force Linux system to set dynamic hostname provided by DHCP server

DHCP is the Dynamic host configuration protocol server provides automatic or dynamic IP configuration on the client system. DHCP can also be configured to provide dynamic hostname service to client…

Pointers in C & C++

In C++,Variable is stored in memory blocks.Each memory block has a unique address.So in order to call the value,we stimulate the address of the block.So that address is represented as…

Create a Self-Signed SAN(Subject Alternate Name) Certificate Using OpenSSL

Creating a self-signed certificate using OpenSSL fulfills basic in-house need for an organization. There might be a need to use one certificate with multiple subject alternative names(SAN). This article explains…

Verify that an OpenSSL Private Key Matches a Certificate

OpenSSL is a software library for applications that secure communications over computer networks. This article mentions about precise steps to verify an OpenSSL key against a certificate.

Bind Converting Zone Files Between Text and Raw Formats

With the development of the BIND 9.9 branch, zone file storage for slaved zones has been changed to expect the raw zone format by default in order to provide some…

Bind slave zone convert binary to text format

BIND 9.9.x uses default binary file format for slave zone files in order to improve bind performance. Refer to the solution section to change this behavior.

wget|ftp|lftp download without username and password

GNU wget is a computer program that retrieves content from web servers. It supports downloading via HTTP, HTTPS, and FTP. This article mentions about downing authorized content from remote HTTP/FTP…

How to reload nginx webserver on runtime

Nginx is an open source HTTP Web server and reverse proxy server. In addition to offering HTTP server capabilities, Nginx can also operate as an IMAP/POP3 mail proxy server as…

Difference between Zombie and Orphan Processes

This article provides complete information about Zombie and Orphan process on Linux or Unix Operating system with suitable code example.

FreeRadius(AAA) installation and Configuration on Linux

RADIUS which stands for Remote Authentication Dial In User Service, is a network protocol – a system that defines rules and conventions for communication between network devices for remote user…

Enable the Old ethX Style Network Interfaces Names on CentOS|RHEL7

CentOS 7 has introduced a new naming convention for network interfaces that can result in long interface names. Traditionally, network interfaces in Linux are enumerated as eth[0123…], but these names…

Why to use DHCP

DHCP is useful for automatic configuration of client network interfaces. When configuring the client system, you can choose DHCP instead of specifying an IP address, netmask, gateway, or DNS servers….

Cockpit – allow non-administrative users for errata/software/os update

Linux Cockpit is a web-based interface that provides graphical administrative access to a system. In this article, we’ll configure cockpit to allow non-administrative users to perform system update. Refer to…

Postfix rewrite sender email address [Linux|Unix]

If sender ‘test@example.com’ sends an email, his email address should change to ‘admin@example.com’ and at the receiver’s mailbox, the from address must be shown as ‘admin@example.com’. This article provides a…

dnf extremely slow [Fedora/RHEL/CentOS]

Package installation on Fedora and Centos 8 is extremely slow. Refer to the solution section for resolution.

Chrony symmetric authentication

Chrony is a powerful and fastest time server, mostly used as a time synchronization agent/server on the client system. In this article, we’ll configure a chrony server and a chrony…

IS SKYPE VIDEO LINUX ALWAYS A PROBLEM

This article helps to fix video issue on Skype installed on Linux. Refer to the solution section for resolution.

FTP YUM repository configuration on Linux

In production environment it might not possible to provide internet to all systems due to company policy or to control internet bandwidth. Installing a package from internet it might be…

Apache YUM repository configuration on Linux

In production environment it might not possible to provide internet to all systems due to company policy or to control internet bandwidth. Installing a package from internet it might be…

NFS YUM repository configuration on Linux|Centos|RHEL

In production environment it might not possible to provide internet to all systems due to company policy or to control internet bandwidth. Installing a package from internet it might be…

PXE server configuration on Linux

PXE Server (preboot execution environment) helps to install a system in the network without having a physical media. Instead of using manual installation method by using CD/DVD or pen drive,…

What is Payload in Networking

Payload is the actual data sent to the destination system excluding headers and other extra info of the packet. Consider a letter posted to a friend. Payload is the paper...

YUM repository configuration on CentOS/RHEL with Nginx

In production environment it might not possible to provide internet to all systems due to company policy or to control internet bandwidth. Installing a package from internet it might be…

Convert SSH PEM file to putty PPK file format and vice versa on Linux/Unix

PuTTY doesn’t natively support the private key format (.pem) generated by ssh-keygen or openssh program. You must convert your private key into a .ppk file before you can connect to…

Failed to execute operation: Too many levels of symbolic links

Systemd doesn’t accept a symbolic Unit file for the startup so provide the full path of the Unit file to enable it for startup. Refer to the solution section for…

What is inode

An inode is an entry in inode table that contains information about a file and directory. It is a is a data structure on a traditional Unix-style file system such…

Postfix Active directory/LDAP authentication with Cyrus sasl on Linux

A simple and proven method to configure postfix to provide Active directory authentication to all email users. Refer to the solution section for more information.

How to configure PAM to Audit Login Shell User Activity on Linux

The audit system uses the pam_tty_audit PAM module to enable or disable auditing of TTY input for specific user or all users. When the audited user logs in, pam_tty_audit module…

Audit System Time Changes on Linux|Centos|RHEL|Ubuntu|Debian

On a Linux system, auditing a few system calls we can easily track who makes system time changes. Refer to the solution section to know about related system calls to…

Audit or track system hostname change on Linux|Centos|RHEL|Ubuntu|Debian

On a Linux system, auditing a few system calls and some specific files, we can easily track who makes system hostname change. Refer to the solution section to know about…

Audit or Track All Commands on Linux|Centos|RHEL|Ubuntu|Debian

On a Linux system, we get information about all commands executed on Linux shell by monitoring execve() system call. This article provides information on audit or track all commands on…

How To Check Who Changes or Modifies File or Directory on Linux|centos|ubuntu|RHEL

On a Linux system, we can easily track changes occur to files or directories by using auditd watch rule. This article will help to provide complete information on how to…

What is audit daemon or service in Linux

auditd is a userspace component to the Linux Auditing System. It’s responsible for writing audit records to the disk. Viewing the logs is done with the ausearch or aureport utilities….

Windows Network Installation through Linux PXE Server

PXE Server (preboot execution environment) helps to install a system in the network without having a physical media. Instead of using manual installation method by using CD/DVD or pen drive,…