Rohan Timalsina

netstat from net-tools prints active sockets, routing tables, interface counters, and protocol statistics on Linux. It is a legacy but still common tool for checking listening ports and connection states on Debian and …

dmidecode reads SMBIOS/DMI tables from firmware and prints hardware inventory: BIOS version, system vendor and serial, board, chassis, processor, and memory layout on Linux.

dpkg is the low-level package manager for .deb archives on Debian and Ubuntu. It installs, removes, configures, and inspects packages in the local dpkg database without resolving repository dependencies.

rpm is the low-level package manager for .rpm archives on RHEL, Fedora, Rocky Linux, and AlmaLinux. It installs, upgrades, erases, queries, and verifies RPM packages and maintains the local RPM database.

nmap (Network Mapper) discovers hosts, scans TCP and UDP ports, detects services and OS fingerprints, and runs NSE scripts. It is the standard CLI tool for network inventory and authorized security audits on Linux.

grep prints lines that match a pattern in files or piped input. Use it to scan logs, filter command output, and count or list matches with GNU grep options.

iotop shows real-time disk read and write bandwidth per process and thread on Linux. It reads kernel I/O accounting so you can see which application is saturating storage during slowdowns.

GNU screen is a terminal multiplexer that keeps shell sessions alive after disconnect, supports multiple windows in one session, and reattaches over SSH when the network drops.

stress spawns worker processes that load CPU, virtual memory, disk I/O, and disk writes so you can test cooling, schedulers, and monitoring under synthetic pressure. It is not installed by default on Ubuntu — install the …

traceroute prints each router hop between your Linux host and a destination by sending probes with increasing TTL values and reporting round-trip times. On Ubuntu it ships as the modern traceroute.db implementation with …

tcpdump captures live network traffic or reads saved pcap files, applies BPF filters for TCP/UDP/ICMP and hosts, and prints or writes packets for troubleshooting and security review.

tune2fs reads and changes tunable parameters on unmounted or read-only-safe ext2, ext3, and ext4 block devices — mount counts, check intervals, volume labels, UUIDs, reserved blocks, default mount options, and feature …

rpmbuild drives the RPM packaging pipeline from a .spec file — %prep, %build, %install, and binary or source RPM output. On Ubuntu, install the rpm package for rpmbuild; native Debian packages use dpkg-buildpackage …

sudo lets permitted users run commands as root or another account using rules in /etc/sudoers and /etc/sudoers.d/. It logs actions, caches credentials for a timeout, and supports non-interactive and environment-control …

su runs a shell or single command with another user and group ID. On Ubuntu it uses PAM for authentication; login mode (-) resets the environment and home directory like a real login.

tee reads standard input and writes a copy to every named file while also sending the same bytes to standard output. Use it in pipelines when you want to save command output and still see it on the terminal.

sar (System Activity Reporter) prints CPU, memory, disk, network, and load averages from live counters or files collected by sysstat under /var/log/sysstat. Install the sysstat package and enable data collection for …

On Ubuntu and Debian, adduser is a high-level wrapper that creates and manages local users and groups. It applies /etc/adduser.conf policy, then calls useradd and related tools to set home directories, shells, UID/GID, …

ss (socket statistics) from iproute2 lists TCP, UDP, UNIX, and other sockets on Linux — states, queues, processes, and filters — faster and richer than legacy netstat.

top shows a live summary of CPU, memory, and tasks, plus a sortable process list. Batch mode (-b) prints snapshots for scripts and logs without the interactive TUI.

rsync copies and synchronizes files locally or over SSH using a delta algorithm — only changed blocks are sent. Archive mode (-a) preserves permissions and timestamps; --delete mirrors removals; --dry-run previews …

scp copies files and directories between hosts over SSH using the SFTP protocol by default. It supports recursion, bandwidth limits, identity keys, and ssh_config options on Ubuntu and most Linux systems.

GNU tar bundles files and directories into a single archive and restores them later. Create with -c, list with -t, extract with -x, and add gzip, bzip2, xz, or zstd compression with -z, -j, -J, or -a.

ssh is the OpenSSH client for encrypted remote login and command execution. It reads ssh_config, negotiates ciphers with the server, and supports port forwarding, jump hosts, and algorithm queries via ssh -Q.

useradd is the low-level shadow-utils command that creates local Linux accounts in /etc/passwd, /etc/shadow, /etc/group, and /etc/gshadow. Use flags such as -m, -u, -g, -G, -s, and -e to control home directories, IDs, …