Linux Basics

Linux Distros Linux

Users

Root

root is the name of the system administrator account.
Root has user id 0 and nominally unlimited privileges.

Exceptions:
In modern UNIX systems, SELinux or Apple's SIP (aka rootless system), even root is limited in what it can do.

NOTE: For the rest, read this answer: https://unix.stackexchange.com/a/291467

Groups

File System Heirarchy

/

/boot

/boot/efi

/home

/bin

/sbin

/lib

/proc

Process information virtual file system

/dev

System devices virtual files
/dev/ram - Ramdisk device
/dev/tty
/dev/null
/dev/zero
/dev/initrd - Bootloader initialized ramdisk
/dev/loop
/dev/mouse
/dev/random
/dev/rtc
etc.

/sys

/swap

/root

/usr

/usr/share   
/usr/bin   
/usr/lib   
/usr/include   
/usr/local   
/usr/src

/opt

Manually installed binaries

/var

/run

/media

/mnt

/srv

/tmp