Articles by Deepak Prasad
Bash Shell Scripting Tutorial (Free Course)
Free Bash shell scripting course: quoting, loops, arrays, pipelines, strict mode, traps, and real admin scripts, each lesson tested on Bash 5.2 on RHEL 10.
Laravel Tutorial for Beginners (Step by Step)
Free Laravel tutorial with 60+ hands-on lessons: install, routing, Blade, Eloquent, auth with Sanctum and Passport, REST APIs, queues, and Docker deploys.
Pandas Tutorial for Data Analysis (with examples)
Free pandas tutorial for Python data analysis: read CSV files, select, clean, merge, group, pivot, and plot DataFrames with runnable examples you can copy.
SQL Tutorial for Beginners (Hands-On with Real Examples)
Free SQL tutorial with 80+ lessons on SELECT, JOINs, GROUP BY, window functions, CTEs, and transactions, with examples for MySQL, PostgreSQL, SQL Server.
OpenSSH Tutorial: Keys, Certificates, Hardening and Remote Access
Free OpenSSH course: SSH keys, certificate authentication with a CA, sshd hardening, port forwarding, and file transfer, tested on RHEL and Ubuntu.
CompTIA PenTest+ (PT0-003) Certification Course
Free CompTIA PenTest+ (PT0-003) course with a Kali and Proxmox lab, all five exam domains, and hands-on labs for recon, AD, web, and reporting.
RHCSA Tutorial: Red Hat Certified System Administrator Course
Free RHCSA course mapped to the Red Hat EX200 objectives on RHEL 10, with hands-on labs for storage, LVM, users, networking, systemd, and SELinux.
Ethical Hacking & Penetration Testing Tutorial (Hands-On)
Free, hands-on ethical hacking course on Kali Linux covering lab setup, recon, password cracking, phishing, web, wireless, and mobile attacks.
Terraform Associate Certification Course
Free Terraform Associate (004) exam prep course covering the full HashiCorp blueprint, with hands-on labs on one Ubuntu VM and no cloud account needed.
Fix userauth_pubkey: key type ssh-rsa not in PubkeyAcceptedKeyTypes
Fix userauth_pubkey: key type ssh-rsa not in PubkeyAcceptedKeyTypes by using rsa-sha2 with the same RSA key, or Ed25519, before any legacy ssh-rsa exception.
Revoke SSH Keys and Certificates with OpenSSH KRL
Create and update an OpenSSH Key Revocation List (KRL), revoke SSH certificates by serial, Key ID, or fingerprint, revoke plain public keys, and make sshd enforce RevokedKeys.
How to Configure OpenSSH Certificate Authentication with an SSH CA
Set up OpenSSH user certificate authentication with an SSH CA: create TrustedUserCAKeys, sign keys with principals and expiry, verify login, revoke with a KRL, then map principals with AuthorizedPrincipalsFile.
Configure SSH Key Authentication in Linux
Set up SSH public key authentication with ssh-keygen, ssh-copy-id, and authorized_keys—connect with a specific identity, use ssh-agent, fix permissions and SELinux, and troubleshoot publickey failures.
ssh-keygen Command in Linux: Generate, Inspect, and Manage SSH Keys
ssh-keygen from OpenSSH creates, inspects, and converts SSH key pairs for public-key login. It writes a private key and a .pub file you copy to a server authorized_keys file.
SSH Authentication Methods in sshd_config (Password, Public Key, PAM)
Configure OpenSSH authentication in sshd_config: password, public key, keyboard-interactive, host-based, GSSAPI, AuthenticationMethods, and Match blocks on Linux.
How to Install Redis on Ubuntu
Install Redis on Ubuntu with sudo apt install redis-server from universe, or add the official packages.redis.io repo for Redis 8.x. Start redis-server with systemd, test with redis-cli ping, set a password, and harden …
dhclient Removed in RHEL 10: Use NetworkManager for DHCP
Why dhclient and dhcp-client are gone on RHEL 10, what replaces them, how to configure and reacquire DHCP with NetworkManager, and how to fix old dhcp=dhclient settings.
OpenSSH PerSourcePenalties: Block Repeated Failed SSH Connections
OpenSSH PerSourcePenalties on Linux: how sshd temporarily refuses noisy source addresses, how to read defaults with sshd -T, how to fix Not allowed at this time, and how exemptions and MaxAuthTries differ from Fail2ban.
RHEL 10 RPM Signing: Sequoia PGP, RPMv6 and PQC
Understand RPM signing changes on RHEL 10 and 10.1: Sequoia PGP verification, RPMv6 signatures, multiple signatures, OpenPGP v6, and hybrid ML-DSA-87+Ed448 post-quantum signing with tested commands.
Access Token vs ID Token vs Refresh Token
Compare OAuth and OIDC access tokens, ID tokens, and refresh tokens by purpose, recipient, validation, and lifecycle, with sanitized Keycloak JWT examples.
Keycloak vs Red Hat Build of Keycloak
Compare Keycloak vs Red Hat Build of Keycloak (RHBK), including support, versions, lifecycle, supported platforms, container images, features, and when to use each.
Keycloak SCIM vs LDAP: Federation vs Provisioning
Compare Keycloak SCIM provisioning with LDAP user federation on Keycloak 26.7: data flow, passwords, lifecycle, Preview limits, and when to use LDAP, SCIM, or both.
Keycloak User Federation vs Identity Brokering: LDAP/AD vs External IdP
Decide whether Keycloak should validate users against LDAP or Active Directory with user federation, or redirect login to an upstream OIDC or SAML identity provider with identity brokering.
LDAP vs SAML vs OIDC vs SCIM: What’s the Difference?
Compare LDAP, SAML, OIDC, and SCIM by purpose, login role, provisioning role, and how they work together for directory access, SSO, and account lifecycle.
What Is Single Sign-On (SSO) and How Does It Work?
Learn what single sign-on is and how SSO works in the browser: IdP vs application sessions, SAML and OIDC, trust between apps and the IdP, and why logout is not always universal.
Identity Provider (IdP) vs Service Provider (SP)
Learn the difference between an identity provider (IdP) and a service provider (SP), how they work together in SSO, SP-initiated versus IdP-initiated login, and how SAML terms map to OIDC OpenID Provider and Relying …
OAuth 2.0 vs OpenID Connect vs SAML: What’s the Difference?
Compare OAuth 2.0, OpenID Connect, and SAML 2.0 by purpose, tokens, flows, and when to choose each protocol, including how Keycloak supports OIDC and SAML clients.
Create and Manage Users in Keycloak: Admin Console and API
Create and manage local Keycloak users—set and reset passwords, required actions, enable and disable accounts, search users, and automate with Admin REST API and kcadm on Keycloak 26.7.3.
Keycloak Custom User Attributes with User Profile
Learn how to add custom user attributes in Keycloak with User Profile—create a department field, set values on users, show fields on registration forms, add validation and permissions, and map attributes into tokens.
Keycloak start vs start-dev: Development and Production Modes
Learn the difference between Keycloak start and start-dev, including HTTP, hostname, HTTPS, cache and database behavior, and when to use each mode.