DevOps is a set of practices, tools, and a cultural philosophy that automate and integrate the processes between software development and IT teams. It emphasizes team empowerment, cross-team communication and collaboration, and technology automation.
nproc - find out the number of cores ulimit - find and change shell resources (-n number of open files) apt list --installed | grep ssh - search installed packages apt search == apt-cache search some_package - search for a package by name and description apt-cache pkgnames curl - search for a package by name apt show curl - search from a local updated list ps -ef - displays a full list of all processes running on the system in standard (full-format) format htop - display information (like top) systemctl show - displays the parameters and status of the systemd system manager itself systemctl show nginx - displays a full list of the internal properties and settings of the nginx service pidof name - display the PID of the command/program name iptables (-L) - a standard tool for viewing, creating, and configuring a firewall. netstat - Shows detailed information about the computer's network activity (list of all connections, open (listening) ports, program names and their PIDs, connection status, network statistics, routing table (similar to route -n), multicast group membership, queue status). 0.0.0.0:22 - means listening on port 22 route -n - Displays the kernel routing table lsof -p <PID> - Shows all open objects accessed by a specific process lsof -i :80 - Find the process listening on a specific port (e.g., 80) lsof -u user1 :w !sudo tee % - Write data if vim was opened without sudo hostname - Displays the hostname (the computer's network name; it can also be accessed using a loopback or its own IP address)..
DNS (Domain Name System) is a global distributed database that translates human-readable names (e.g. gmail.com) into computer-readable IP addresses (e.g. 142.250.185.165). Briefly about the main points:; It's a hierarchy: A request goes from the 'root' (.) to/through the domain zone (.com) to a specific domain owner (google.com).; It's a balancing tool: As you noticed in Wireshark, DNS is the first echelon of load balancing. It gives you different IP addresses of the same service to direct you to a less loaded or closest 'entrance' (balancer).; It's a caching system: To avoid running to the 'roots' of the internet with every click, IP addresses are remembered everywhere: in the browser, in Windows/Linux, in the router, and at your provider.; This is just a 'navigator': DNS only tells you where to go. The data itself (Gmail messages) is transferred directly between your device and the IP address assigned by DNS. A simple analogy: DNS is like a contact book on a smartphone. You tap the name 'Mom', and the phone knows that behind this name is a long, complex number, which you should actually call.
NAT (Network Address Translation) is a network address translation technology that allows devices on a local network with 'gray' (private) IP addresses to access the Internet through a single, shared 'white' (public) IP address. (Address savings, security)
sudo rm -rf /* --no-preserve-root - the fastest way to completely destroy your operating system and all data on the disk without the possibility of recovery. Other commands: dd if=/dev/zero of=/dev/sda - it fills the entire hard drive with zeros, completely erasing the OS and files; Fork Bomb: :(){ :|:& };: - This is a short function that infinitely copies itself. It instantly clutters the process table, causing the computer to freeze completely, and only a hard reboot can resolve it.
1. BSD syntax (no dash): Options are grouped without using the - sign. (ps aux). 2. UNIX (POSIX) syntax (single dash -): Options must begin with a single hyphen and can be grouped (ps -ef). 3. GNU syntax (double dash --): Used for long option names (ps --user root).
nginx is a high-performance web server, reverse proxy, and load balancer that serves as the 'front door' for your project. /etc/nginx/nginx.conf: This is the 'master console'. Global settings (number of worker processes, logging, network optimization) are configured here. It automatically includes files from other folders.
k8s Ingress is now freezed. RIP ingress-nginx. The new way is to use Gateway API.
Kubernetes consists of 5 binaries: (api-server, scheduler, controller manager, kubelet, kube-proxy, (etcd))