Basic Unix Commands

Knowing basic Unix commands should allow you to navigate your Unix or Linux system, confirm current system status and manage files or directories.

Getting help in Unix
man – view manual pages for Unix commands

Time and Date commands
date – show current date and time
sleep – wait for a given number of seconds
uptime – find out how long the system has been up

Unix users commands
These commands allow you to get basic information about Unix users in your environment.

id – print user identity
passwd – change user password
who – find out who is logged into the system
last – show history of logins into the system

Unix file operations
Navigating filesystem and managing files and access permissions:

ls – list files and directories
cp – copy files (work in progress)
rm – remove files and directories (work in progress)
mv – rename or move files and directories to another location
chmod – change file/directory access permissions
chown – change file/directory ownership

Text file operations in Unix
Most of important configuration in Unix is in clear text files, these commands will let you quickly inspect files or view logs:

cat – concatenate files and show contents to the standard output
more – basic pagination when viewing text files or parsing Unix commands output
less – an improved pagination tool for viewing text files (better than more command)
head – show the first 10 lines of text file (you can specify any number of lines)
tail – show the last 10 lines of text file (any number can be specified)

Unix directory management commands
Navigating filesystems and managing directories:

cd – change directory
pwd – confirm current directory
ln – make links and symlinks to files and directories
mkdir – make new directory
rmdir – remove directories in Unix

Unix system status commands
Most useful commands for reviewing hostname configuration and vital stats:

hostname – show or set server hostname
w – display system load, who's logged in and what they are doing
uname – print Unix system information

Networking commands in Unix
Most useful commands for inspecting network setup and exploring network connections and ports:

ifconfig – show and set IP addresses (found almost everywhere)
ip – show and set IP addresses (in recent Linux versions)
ping – check if remote host is reachable via ICMP ping
netstat – show network stats and routing information

Process management
Listing processes and confirming their status, and stopping processes if needed:

ps – list processes
top – show tasks and system status
kill – kill a process (stop application running)

Remote access commands
ssh is really the only way to go, but it's important to know telnet as well:

telnet – clear-text (insecure) remote access protocol
ssh – Secure SHell – encrypted remote access client

File transfers  commands
Always useful to know how to copy files between servers or just download some package from the web:

ftp – clear-text (insecure!) File Transfer Protocol client
sftp – secure (encrypted) version of FTP
scp – secure (encrypted) version of cp command
wget – download files from remote servers, HTTP/HTTPS and FTP