nice formatted ls and du
ls -ahnt
du -sh
in the list of the 50 most useful commands:
lsblk
# list block devices
service
# run a System V init script
batch
# executes commands when system load levels permit
comm
# compare two sorted files line by line
dd
# convert and copy a file
iptables
# administration tool for IPv4/IPv6 packet filtering and NAT
whatis
# display one-line manual page descriptions