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cd # change directory to name or ..
mv # move a file
cp # copy a file
rm # remove (delete) a file
mkdir # make a directory
rmdir # remove a directory
chmod # change the permissions of a file, ugo+rwx
su # switch user or superuser. su passwd to change password.
more # show the contents of a text file
tail -20 # show the last 20 lines of a file
head -20 # show the first 20 lines of a file
cat # list the file, or concatenate files
ls -la # show the files in the directory, with details
man # show the manual page for a command
grep # cat file | grep hello shows all lines in file with the word hello
ps -aux # shows what the cpu is running
kill -9 pid # kills a process
man # show the manual page for a command