542 cards
The Secure Shell (SSH) is the workhorse for remote Linux administration, and almost every aspect of it can be customized. The per-user ~/.ssh/config file lets administrators define reusable shortcuts with options such as Hostname, User, Port, and IdentityFile, which makes recurring logins far more convenient than typin...
DNS is the addressing layer of the internet, and Linux administrators must understand its record types. An A record maps a domain to an IPv4 address, AAAA to IPv6, and CNAME creates an alias pointing to another canonical name. Mail delivery relies on MX records pointing to the responsible mail servers, while NS records...
Modern Linux distributions manage services through systemd, and a small set of systemctl verbs covers most needs. systemctl start, stop, and restart control running state, while reload asks a service to re-read configuration without a full restart when supported. systemctl enable adds a unit to the boot sequence, disab...
User account information is split across three traditional files: /etc/passwd (usernames, UIDs, GIDs, home, shell), /etc/shadow (password hashes and aging, readable only by root), and /etc/group (groups and members). useradd -m -s /bin/bash username creates a user with a home directory and Bash shell; new homes are tem...
Linux exposes block devices through a virtual filesystem populated by udev, the kernel's device manager that creates entries under /dev dynamically as hardware appears and disappears. lsblk and lsblk -f present a tree of block devices with their sizes, types, UUIDs, filesystem types, and mountpoints. blkid returns UUID...
Modern Linux networking is configured with the ip family of commands. ip addr shows interfaces with their addresses and state; ip addr add IP/PREFIX dev IFACE assigns one, ip addr del removes a specific address, and ip addr flush dev IFACE removes all. ip link shows link state, while ip link set dev eth0 up or down ena...
The two leading open-source web servers on Linux are nginx and Apache. nginx configuration lives in /etc/nginx/nginx.conf with site definitions under sites-available/ and sites-enabled/; syntax is validated with nginx -t and reloaded without dropping connections via nginx -s reload or systemctl reload nginx. Apache, co...
Process inspection starts with ps (for example, ps aux --sort=-%mem for top memory users and ps -ejH for hierarchy) and pstree -p for a tree view. pgrep returns PIDs matching a name, pkill kills by name or attribute (regex, UID), and killall kills by exact name match. nohup runs commands immune to SIGHUP so they contin...