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