The attached file contains a more complete list of system admin command.
chmod -r -u(ser)/g(roup)/o(ther)/a(ll) -rwx
df disk space usage du estimate file space usage
env check environment variables on another account to troubleshoot dotfiles
free find statistics about memory usage
alias substitute a small or more familiar name in place of a long string
apt-get searches for and installs software packages on Debian-based systems
aspell open source spell checker
bzip2 de/compressing files
chown change file ownership
date find gzip ifconfig less/more pwd(current dir) sudo who(users logged on)
export sets the value of a variable so it is visible to all sub-processes that belong to the current shell
grep searching one or more files for a given character string or pattern
ln link files
ps process manager
finger - Prints descriptions of the specified users.
top Like vmstat, get a view of how the system is performing, see which processes are hogging all the memory
uname helpful when working on different computers which may not be in synch at the OS level
wc word count
w show who is logged on and what they are doing
kill - terminate a process killall
mv - change the name of a directory
uptime - Tell how long the system has been running
umask - get or set the file mode creation mask
watch - execute a program periodically, showing output fullscreen
whereis - locate the binary, source, and manual page files for a command
which show the full path of commands