Amir

A focused guide to installing `tcpdump` on CentOS 7 and CentOS 8, including the repository fixes both distros now need (CentOS 8 is EOL and points at vault.centos.org; CentOS 7 reached EOL in June 2024), SELinux and firewalld notes, and a smoke-test capture to confirm it actually works.

`fdisk` is the oldest, most widely-installed partition editor on Linux. This guide covers listing disks, creating and deleting partitions, working with GPT versus MBR, writing changes safely, and the modern alternatives (`parted`, `gdisk`, `sfdisk`) you should reach for when `fdisk` is the wrong tool.

Step-by-step guide to installing Wireshark and Npcap on Windows Server, including silent install for headless and Server Core hosts, capture permissions, the command-line tools (tshark, dumpcap), first captures, and practical recipes for diagnosing real production issues.

ipconfig is the built-in Windows tool for inspecting IP configuration, releasing and renewing DHCP leases, and clearing the DNS cache. This guide covers the flags you will actually use, how to read the output, and the recipes that solve the most common networking problems on Windows.

The 504 Gateway Timeout meaning is precise: a server acting as a gateway reached the upstream it was supposed to talk to, but the upstream did not finish responding in time. It almost never means "the internet is broken" — it means something further down the chain is slow. This guide explains what 504 actually means, who returns it, and how to find the real root cause instead of just raising timeouts.

tcpdump is the de-facto command-line packet analyzer for system administrators. This guide covers installation on Linux, macOS, and Windows, the most useful flags, BPF filter syntax, and practical recipes for diagnosing real network problems on a server.

Monitor REST and JSON APIs with Xitoring — validate status codes, JSON body fields, headers, and authenticated requests from global probing nodes.

Configure DNS uptime checks in Xitoring to verify resolution, validate record values, and catch propagation issues across resolvers worldwide.

Monitor FTP servers with Xitoring uptime checks — verify the server is listening, accepting connections, and responding with the expected banner from probing nodes worldwide.

Use Xitoring heartbeat checks to monitor cron jobs, scheduled scripts, and background workers — get alerted the moment something stops running on time.

Configure HTTP uptime checks in Xitoring to verify that your websites and web apps respond correctly — with status codes, keyword matching, custom headers, and global probing.

Monitor your TLS-protected websites end-to-end with Xitoring HTTPS checks — combining status code, keyword, and certificate validation from probing nodes around the world.

Configure IMAP uptime checks in Xitoring to confirm your mail server is reachable, listening on the right port, and returning the expected greeting to email clients.

Learn how to configure ICMP ping uptime checks in Xitoring to monitor reachability of servers, routers, switches, and any device with an IP address.

Set up POP3 uptime checks in Xitoring to monitor mail-retrieval servers, verify the greeting banner, and confirm clients can connect on every relevant port.

Configure SMTP uptime checks in Xitoring to verify your mail servers are accepting connections, returning the expected banner, and ready to send mail on every relevant port.

Configure TCP uptime checks in Xitoring to monitor any service listening on a port — databases, queues, custom protocols, and SaaS endpoints — from probing nodes around the world.

Configure UDP uptime checks in Xitoring to monitor connectionless services — DNS, NTP, syslog, game servers, VoIP — by sending a probe payload and validating the response.

Set up Discord webhook notifications in Xitoring to receive server and website alerts directly in your Discord channels.

Learn how to configure Email notifications in Xitoring to receive instant alerts when your servers or websites experience issues.

Configure Google Chat webhook notifications in Xitoring to receive monitoring alerts directly in Google Workspace.

Configure Gotify with Xitoring to receive self-hosted push notifications via web socket for your monitoring alerts.

Integrate MatterMost with Xitoring to receive monitoring alerts in your self-hosted team communication platform.

Set up Microsoft Teams notifications in Xitoring to receive incident alerts directly in your Teams channels via incoming webhooks.

Configure ntfy (notify) with Xitoring to receive push notifications via a simple HTTP-based pub-sub service.

Connect Atlassian Opsgenie with Xitoring for intelligent alert routing, on-call management, and incident response automation.

Integrate PagerDuty with Xitoring to automatically create and resolve incidents with on-call scheduling and escalation policies.

Configure phone call alerts in Xitoring so you never miss a critical incident — receive voice call notifications when your infrastructure needs immediate attention.

Install the Xitoring mobile app and receive instant push notifications on your phone when incidents occur on your monitored infrastructure.

Set up Pushbullet notifications in Xitoring to bridge alerts between your phone, tablet, and computer seamlessly.

Set up Pushover notifications in Xitoring to get real-time push alerts on your Android, iPhone, iPad, and desktop.

Integrate Slack with Xitoring to receive real-time incident alerts in your team channels — keep your whole team informed instantly.

Set up SMS notifications in Xitoring to receive text message alerts on your phone when critical incidents occur on your servers or websites.

Connect Spike.sh with Xitoring for simple and effective on-call alerting and incident management.

Integrate Splunk On-Call (formerly VictorOps) with Xitoring for timeline-based incident management and team coordination.

Configure Telegram bot notifications in Xitoring to receive instant monitoring alerts in your Telegram groups or direct messages.

Set up webhook notifications in Xitoring to send JSON payloads to any HTTP endpoint when incidents occur — perfect for custom integrations and automation.

Set up WhatsApp notifications in Xitoring to receive incident alerts directly on the messaging app used by billions worldwide.

Connect Xitoring to 5,000+ apps using Zapier — automate workflows and route alerts to any tool your team uses.

Need to verify your mail server is working properly? This guide shows how to monitor SMTP health on Linux using command-line tests, packet inspection, and log analysis.

Define multi-level escalation policies to ensure critical alerts reach the right person at the right time.

Upgrade, downgrade, or manage your Xitoring subscription, payment methods, and invoices.

Invite team members, assign roles, and control access permissions across your Xitoring organization.

Learn how to create HTTP, TCP, DNS, and ping uptime checks with global probing nodes and custom intervals.

Set up email, Slack, Teams, PagerDuty, webhooks, and 20+ other notification channels for your alerts.

Set up automated SSL certificate monitoring with expiry alerts, chain validation, and TLS version checks.

A local dnsmasq cache turns most DNS lookups from a 20–50 ms round trip into a sub-millisecond answer and keeps a server working through an upstream resolver hiccup. This guide installs and configures dnsmasq as a caching-only resolver on RHEL-family systems, points the OS at it the NetworkManager-safe way, verifies the cache with dig, and covers the port-53 and resolv.conf conflicts that break it.

The BitLocker PowerShell module lets you encrypt, check, suspend, unlock and audit drives from a script instead of clicking through the Control Panel — which is the only sane way to do it on servers and fleets. This guide covers Get-BitLockerVolume, enabling BitLocker with TPM, TPM+PIN and password protectors, adding and backing up recovery keys to Active Directory or Entra ID, auto-unlock for data drives, suspend/resume around firmware updates, remote management with Invoke-Command, and the TPM and policy errors that block Enable-BitLocker.

Any server with port 22 open sees thousands of password guesses a day within hours of going online. This guide covers the five controls that actually stop SSH brute-force attacks — key-only authentication, fail2ban, sshd limits, firewall allow-lists and rate limiting, and reducing exposure with a bastion or 2FA — with the exact configuration for Debian/Ubuntu and RHEL-family systems, how to verify each one, and how to recover if you lock yourself out.

vsftpd is the standard FTP server on Linux and, configured correctly, a safe way to give users or systems a chrooted upload area over TLS. This guide installs vsftpd on Ubuntu/Debian and RHEL-family systems, opens the right firewall ports including a passive range, writes a hardened vsftpd.conf with chroot and FTPS, creates a dedicated upload user with a shell-less account, tests from a client, and works through the 500 OOPS, 530 and passive-mode errors that stop most first attempts.

ifconfig still works on most Linux servers, but it has been deprecated for years and is missing from many fresh installs. This guide shows every common ifconfig task — viewing interfaces, bringing them up or down, setting an IP, netmask, MTU, promiscuous mode, aliases and MAC address — with the modern ip command next to each one, how to make changes survive a reboot with netplan or NetworkManager, and what to do when ifconfig says command not found.

Snort 3 is the current generation of the open-source network intrusion detection system. This guide builds it from source on Ubuntu 22.04 and 24.04 (the distribution package is the legacy 2.9 branch), configures HOME_NET and the community rule set, writes and tests a local rule, runs Snort in alert mode on a live interface, installs it as a systemd service, disables the NIC offloading that silently hides traffic from it, and covers the library-path and no-alerts problems that trip up first installs.

Swap is the difference between a slow server and a server whose database just got killed by the OOM killer. This guide shows how to check current swap, create a swap file the right way on ext4, XFS and Btrfs, make it permanent in /etc/fstab, resize or remove it, tune vm.swappiness, when zram is the better choice, and how to tell from vmstat whether the swap you added is actually being thrashed.

strace shows you exactly what a Linux process asks the kernel to do — which files it opens, which sockets it connects to, where it blocks, and which call returned the error you are chasing. This guide covers installing strace, reading its output, filtering by syscall family, attaching to a running PID, following forks, timing calls, the -c summary, and the recipes that solve real incidents: missing config files, permission errors, hangs and slow DNS.

GNU Screen keeps a shell session alive when your SSH connection drops and lets you run several terminals inside one. This guide covers installing it on Debian, Ubuntu, RHEL-family and Alpine systems, the handful of key bindings you actually need, named sessions, detaching and reattaching, logging, a sane .screenrc, and the errors people hit when a session seems to have vanished.

A step-by-step sshd hardening pass for RHEL-family servers: a dedicated login user with sudo, root login off, key-only authentication, idle timeouts, group allow-lists, a non-default port done properly with SELinux and firewalld, and the sshd -t / sshd -T checks that stop you locking yourself out. Written for CentOS Stream, AlmaLinux and Rocky Linux 8/9, with notes on what still applies to end-of-life CentOS 7 and 8.