Linux System Enumeration Basics

hostname
cat /etc/issue
cat /etc/*release
uname -a
uname -r
lscpu

id
whoami
groups bob
groups root
cat /etc/passwd
cat /etc/passwd | grep -v /nologin

free -h
df -h
df -ht ext4
lsblk | grep sd

last
lastlog
w
who
cat /etc/group