File Administration

• ls [options] [arguments] : List the files in a particular directory or present directory if used without options or arguments
• cd [options] directory: change the present directory
• ln [options] original file link file : Create links b/w files or b/w directories
• ln [options] original file : Create a link to the original file in the present directory
• mkdir [options] directory : Make a directory
• mv [options] source destination : Move and/or rename files and directories
• pwd [option] : prints the current working directory
• rm [options] file : Delete files or directories
• rmdir [options] directory : Remove empty directories
• tar [options] archivename [file(s)] : archive or extract files
• chgrp [options] group files: Change group ownership of one or more files & directories
• chmod [options]mode files: Change access permissions of one or more files & directories
• chown[options] new owner files : Change the ownership of one or more files & directories
• cp [options] source destination : Copy files and directories
• find [start-point] [search-criteria] [search-term] : find files
• gzip [options] filename : compress or expand files
• cat [options] [filenames] [-] [filenames] : Display, combine or create new files.
• cut [options] file : Cut out sections of each line of a file or files
• diff [options] from-file to-file : Display the differences between two files
• grep [options] pattern [file] : Search text and match patterns
• head [options] filename(s) : List the first part of a specified file
• less [options] filename : Display text files
• more [options] filename : Display a text file
• tail [options] filename(s) : List the last part of a specified file

Processes

• crontab [-u user] [-l | -r | -e] : Schedule a task to run at a particular time or interval
• kill [options] PID(s) : sends a signal to terminate a process or processes by PID
• killall [options] command name : sends a signal to terminate a processes by name
• ps [options] : displays a snapshot of the current processes
• top [options] : display system and process information in real time

Network

• ifconfig [arguments] interface [options] : Configure a network interface
• ifconfig [arguments] [interface] : View network interface details
• ip [options] object sub-command [parameters] : network configuration tool
• netstat [options] : network connection monitoring tool
• ping [options] remote server : checks the network connection to a remote server.
• curl [options] [URL] : download or upload files to remote servers.
• host [options] server : checks a computers IP address from its host-name or the reverse
• scp[options]user1@sourcehost:directory/filenameuser2@destinationhost:directory/filename : securely copy files between computers
• sftp [options] [user@] hostname [:directory] : interactively copy files between computers securely
• ssh [options] [login name] server : securely access a remote computer.
• traceroute [options] host-name : trace the route packets take to network host
• wget [options] [URL] : download or upload files from the web non-interactivly.

Miscellaneous

• apt-get install package-name : Install a package
• apt-get remove package-name : Un-install a package
• apt-get update : Update the database of available packages
• apt-get upgrade : Upgrade the packages on the system
• echo [options] [string(s)] : display text on the screen.
• groupadd [options] group : add a group account
• clear : clears the terminal screen.
• man [options] command : display the reference manual for a command.
• modprobe [options] modulename : Load or remove a Linux kernel module
• passwd [options] username : change the user password
• shutdown [options] [time] [message] : shut down or restart a system.
• su [options] [username] : switch to another user.
• sudo [options] command : Execute a command as the superuser
• usermod [options] username : Modify a users account configuration
• useradd [options] username : Add a user account
• who [options] : report the users logged onto the system.
• whoami [options] : report the current user.

File Systems

• fdisk [options] [device] : manipulate partition tables.
• mkfs [options] device : format a partition with a file system
• mount [options] type device directory : Mount storage onto the file system
• umount [options] device and/or directory : Unmount storage from the file system

System Information

• date [options] +format : display or set the date / time
• du [options] file : display the amount space used in files and directories
• free [options] : displays information about free and used memory on the system
• df [options] file : display the amount of free space on filesystems.