cd - change dir
ls - list files & dirs
cp - copy file
mv - move/rename file
rm - remove file/dir
mkdir - create dir
rmdir - remove dir
ln - link file (symbolic or hard)
chown - change owner or owner and group
chgrp - change group
chmod - change permissions
echo - prints information on the stdout
cat - show the contents of a file
cut - cuts a line in parts(shows only one column of a file)
tail - shows N lines from the end of a file
head - shows N lines from the beginning of a file
less - view contents of a file with support for paging and search
wc - word/line count
touch - creates empty file if not existing or changes its last modified date if existing
ps - show process list
pstree - show process list tree
pgrep - search trough the process list
pwd - show current directory
date - show current date, set date
grep - search for string with regular expression
bzip2 - GNU BZip2 archiver
gzip - GNU Zip archiver
tar - GNU Tar archiver
df - filesystem usage
du - file space usage
kill - send signal to a process
killall - to all processes like name
mount - mount a device
umount - umount a device