Comprehensive Linux Command Reference Guide

Online Query and Help Commands (2)

man : display command help pages (manual); help : show help for built‑in shell commands such as cd.

File and Directory Operations (18)

ls : list directory contents with attributes.

cd : change the current working directory.

cp : copy files or directories.

find : search for files and directories.

mkdir : create a new directory.

mv : move or rename files/directories.

pwd : print the absolute path of the current directory.

rename : rename files.

rm : remove one or more files or directories.

rmdir : remove empty directories.

touch : create an empty file or update timestamps.

tree : display directory contents in a tree‑like format.

basename : strip directory components, leaving the file name.

dirname : strip the file name, leaving the directory path.

chattr : change file attributes.

lsattr : list file attributes.

file : determine file type.

md5sum : compute and verify an MD5 checksum.

File Content Viewing and Processing (21)

cat : concatenate and display file contents.

tac : display file contents in reverse order.

more : paginate output.

less : paginate output with backward navigation.

head : show the beginning of a file.

tail : show the end of a file.

cut : extract columns based on delimiters.

split : split a file into smaller pieces.

paste : merge lines of files.

sort : sort lines of text.

uniq : filter out duplicate lines.

wc : count lines, words, and bytes.

iconv : convert file encoding.

dos2unix : convert DOS line endings to UNIX.

diff : compare files line by line.

vimdiff : visual file comparison using Vim.

rev : reverse each line of a file.

grep/egrep : filter lines matching patterns.

join : join lines of two files on a common field.

tr : translate or delete characters.

vi/vim : command‑line text editors.

File Compression and Decompression (4)

tar : archive files, optionally compress.

unzip : extract ZIP archives.

gzip : compress files using the gzip algorithm.

zip : create ZIP archives.

System Information Display (11)

uname : show kernel and OS information.

hostname : display or set the system hostname.

dmesg : print kernel ring buffer messages.

uptime : show how long the system has been running and load average.

stat : display file or filesystem status.

du : estimate file space usage.

df : report filesystem disk space usage.

top : real‑time view of running processes and resource usage.

free : display memory usage.

date : show or set the system date and time.

cal : display a calendar.

File Search Commands (4)

which : locate a command by searching $PATH.

find : recursively search directories for files.

whereis : locate binary, source, and manual pages.

locate : find files using a prebuilt database.

User Management Commands (10)

useradd : create a new user.

usermod : modify an existing user.

userdel : delete a user.

groupadd : create a new group.

passwd : change a user's password.

chage : change password expiry information.

id : display a user's UID, GID, and groups.

su : switch to another user account.

visudo : safely edit the sudoers file.

sudo : execute a command with elevated privileges.

Basic Network Operations (11)

telnet : remote login using the Telnet protocol.

ssh : secure remote login using SSH.

scp : secure copy files between hosts.

wget : download files from the web.

ping : test network connectivity.

route : view or modify the kernel routing table.

ifconfig : configure network interfaces.

ifup : activate a network interface.

ifdown : deactivate a network interface.

netstat : display network connections, routing tables, and interface statistics.

ss : another utility to investigate sockets.

Advanced Network Operations (9)

nmap : network scanning and host discovery.

lsof : list open files and the processes using them.

mail : send and receive email.

mutt : terminal‑based email client.

nslookup : query DNS records interactively.

dig : DNS lookup utility.

host : simple DNS query tool.

traceroute : trace the path packets take to a network host.

tcpdump : capture and analyze network traffic.

Disk and Filesystem Commands (16)

mount : mount a filesystem.

umount : unmount a filesystem.

fsck : check and repair a filesystem.

dd : convert and copy files at a low level.

dumpe2fs : dump ext2/3/4 filesystem information.

fdisk : partition a disk (up to 2 TB).

parted : partition disks of any size.

mkfs : create a filesystem on a device.

partprobe : inform the kernel of partition table changes.

e2fsck : check ext2/3/4 filesystems.

mkswap : set up a swap area.

swapon : enable swap.

swapoff : disable swap.

sync : flush filesystem buffers.

resize2fs : resize an ext2/3/4 filesystem.

Permission and Ownership Commands (4)

chmod : change file mode (permissions).

chown : change file owner and group.

chgrp : change group ownership.

umask : set default permission mask.

Login Information Commands (7)

whoami : display the effective username.

who : list users currently logged in.

w : show who is logged on and what they are doing.

last : display recent login history.

lastlog : show the most recent login of all users.

users : list logged‑in users.

finger : display detailed user information.

Built‑in and Miscellaneous Commands (19)

echo : display a line of text.

printf : format and print data.

rpm : manage RPM packages.

yum : high‑level package manager for RPM.

watch : repeatedly execute a command and show output.

alias / unalias : define or remove command aliases.

clear : clear the terminal screen.

history : show command history.

eject : eject removable media.

time : measure execution time of a command.

nc : netcat, a versatile networking utility.

xargs : build and execute command lines from standard input.

exec : replace the shell with a specified program.

export : set environment variables.

unset : remove variables or functions.

type : indicate how a command would be interpreted.

bc : arbitrary‑precision calculator language.

System Management and Performance Monitoring (9)

chkconfig : manage system services at boot.

vmstat : report virtual memory statistics.

mpstat : report per‑processor statistics.

iostat : report CPU and I/O statistics.

sar : collect, report, or save system activity information.

ipcs : report inter‑process communication facilities.

ipcrm : remove IPC resources.

strace : trace system calls and signals.

ltrace : trace library calls.

Shutdown, Reboot, Logout and System Info Commands (6)

shutdown , halt , poweroff : power off the machine.

logout , exit , Ctrl+D : exit the current shell session.

Process Management Commands (15)

bg / fg : move jobs between background and foreground.

jobs : list active jobs.

kill , killall , pkill : terminate processes by PID or name.

crontab : schedule recurring tasks.

ps , pstree : display process information.

nice / renice : adjust process priority.

nohup : run a command immune to hangups.

pgrep : search for processes by name.

runlevel , init : view or change the system runlevel.

service : start, stop, restart, or query system services.