The problem with the "sim" command is that Linux doesn't always look in 
your local directory when you ask it to execute a program. There are two 
ways around this:

1.  You can type "./sim" (without the quotes), which tells it to look for 
"sim" in the local directory, signified by "./"
2.  You can tell it to always look in your local directory by adding the 
following line to the top of the file ".bashrc", which is located in your 
home directory (the directory you find yourself in when you first log in 
to the system):

   export PATH=$PATH:.

If using the .bashrc method (which I recommend, as it is a permanent 
change and will relieve you of the annoyance of having to type "./" every 
time you want to execute a program in your current directory), to get the 
change to take effect, log out of Eustis and then log back in. Then you 
should be able to type "sim" and it will execute just fine if "sim" is in 
your current directory. (Alternatively, type "source .bashrc" to update 
without having to re-log.)

Note that the ".bashrc" file is hidden from view by default (since it 
begins with a dot), but you can see such files by typing "ls -a" instead 
of just "ls" for a directory listing.