Master Linux Essentials: Time, Users, Networking, and System Monitoring Commands
This guide walks through essential Linux system fundamentals, covering time management, hostname and OS details, user and group configuration, core networking tools, disk usage commands, and real‑time process and memory monitoring, providing practical examples and command syntax for each topic.
Linux System Time
Use date to view current time, date -s "YYYY-MM-DD HH:MM:SS" to set time, and ntpdate -u ntp.api.bz to synchronize with NTP servers.
Hostname and OS Information
Display hostname with hostname. Change it by editing /etc/hostname and /etc/hosts, then reboot. Use uname -a to show kernel and OS details; options -m, -n, -r, -s, -v, -p, -i, -o provide specific fields.
User and Group Management
User account info is stored in /etc/passwd and /etc/shadow; group info in /etc/group and /etc/gshadow. Example line root:x:0:0:root:/root:/bin/bash is parsed into username, password placeholder, UID, GID, description, home directory, and shell.
Commands: useradd [options] username – create a user (options: -c, -d, -e, -f, -g, -G, -m, -M, -n, -r, -s, -u). usermod [options] username – modify a user. userdel [-r] username – delete a user; -r removes home files. usermod -a -G group username – add user to additional group. id username – show UID/GID. groups username – list groups.
Network Utilities
Basic commands: curl URL – fetch a web page. wget URL – download a file. w3m URL / links URL – text browsers. ping host – test connectivity. mtr [options] host – traceroute with statistics. host domain – DNS lookup. ifconfig / ip link show / ip addr show – view and configure interfaces. ifdown/ifup interface – disable/enable interface. netstat [options] – display sockets, routing, and listening ports. iftop – real‑time traffic monitor (options -i, -B, -n, -N, -F, etc.).
Disk Usage
Check overall storage with df -h. Inspect directory sizes with du --max-depth=1 -h. The tree -L 3 command shows a three‑level directory tree; options -d, -a, -f, -L control output.
Process Monitoring
Use top for dynamic view of CPU, memory, and process list (keys: space refresh, M sort by memory, P sort by CPU, q quit). ps -aux or ps -ef list processes; pstree -p shows a tree with PIDs.
Memory Information
Show memory usage with free -h and detailed stats from /proc/meminfo.
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