Linux commands

Linux commands: the basics#

A short tutorial of only the commands used for this server. Each page is a list you can come back to:

Page	For
Files and folders	Moving around, reading, copying, editing, searching
Permissions	`ls -l`, `chmod`, `chown`, `sudo`: who can read or change what
Hardware	CPU, memory, temperature, battery, USB devices
Disks and storage	Drives, free space, mounting, disk health
Network	Addresses, open ports, firewall, testing connections
SSH toolbox	Keys, shortcuts, copying files, tunnels, fixing errors
Services and logs	Starting/stopping programs, reading what went wrong
Software and users	Installing, updating, accounts, groups

How to read a command#

sudo  ls  -l  /srv/files
 │    │   │    └── what to act on (a file or folder)
 │    │   └─────── an option ("long list"); options start with -
 │    └─────────── the command
 └──────────────── "as administrator" (optional)

Six things that make the terminal easier#

Do	How
Finish a name for you	Type the first letters, press `Tab`
Repeat an older command	`Up` (keep pressing to go further back)
Search old commands	`Ctrl`+`R`, type a word, `Enter`
Stop a running command	`Ctrl`+`C`
Clear the screen	`clear` or `Ctrl`+`L`
Help for a command	`COMMAND --help`, or `man COMMAND` (`Q` quits)

Joining commands#

Symbol	Meaning	Example
`\|`	Send the output into the next command	`ss -ltn \| grep 8095`
`>`	Write the output into a file (replaces it)	`ip a > network.txt`
`>>`	Add the output to the end of a file	`date >> log.txt`
`&&`	Run the next one only if this one worked	`sudo apt update && sudo apt upgrade`
`~`	Your home folder	`cd ~`
`.` and `..`	This folder, and the one above	`cd ..`
`*`	"Anything" in a name	`ls *.pdf`

Paths#

/                     the top of everything
/home/alex            your home folder (also written ~)
/etc                  settings of the whole system
/srv                  data the server shares (files, backup, ai)
/var/log              logs
/tmp                  temporary files (emptied at restart)

A path starting with / is absolute (from the top). Without / it's relative to the folder you're in. pwd tells you where you are.

Quotes

A name with spaces needs quotes: cat "my file.txt". Single quotes '...' keep everything exactly as typed; double quotes "..." still expand $VARIABLES.