 Last lesson, the Windows Operating System was discussed along with the Windows command shell  Unix is a computer operating system, that similarly manages file operations, network connections, user accounts/ permissions/ logins, and processes.  Unix has a shell like the Windows shell, but with slight differences in command names, options  CS department uses a UNIX server  All SI110 students and instructors have an account Operating Systems Part II2

 Access rona using the ssh program  ssh = s ecure sh ell: allows secure data communication, remote shell services or command execution and other secure network services between two networked computers that connects, via a secure channel over an insecure network, a server and a client  ssh gives a secure shell that  Accepts keyboard inputs from the local machine  Displays output on the local machine -- BUT--  Executes commands on the rona server – NOT YOUR COMPUTER Operating Systems Part II3

 Command ssh  “ ssh ” is the command  is the argument  – the user to login as  “rona.cs.usna.edu” – the computer to login to  A new window will pop up prompting you for your password  Use your ACADEMY domain password  Note: You will not see your password as you type it in! Operating Systems Part II4

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 When you login, you will start in your home directory  Path: /home/username  Note: there is no “drive” letter in Unix  Unix has a single file hierarchy that simply starts at forward slash /  Analogous to the C:\Users\username directory in Windows  Only place can create files and folders Operating Systems Part II6

WindowsUnixSummaryEx (Windows)Ex (Unix) dirls list contents of current directory C:> dir $ ls cdpwddisplay current directory C:> cd $ pwd cd path change current directory C:> cd \Users\m $ cd /home/m copy path1 path2 cp path1 path2 copy file path1 to name/location path2 C:> copy foo.txt bar.txt $ cp foo.txt bar.txt move path path mv path path move file path1 to name/location path2 C:> move foo.txt..\backup\ $ mv foo.txt../backup/ del path rm path delete file path C:> del foo.txt $ rm foo.txt rmdir path delete folder/directory path C:> rmdir images $ rmdir images mkdir path create folder/directory path C:> mkdir images $ mkdir images type path cat path print file path to screen C:> type index.html $ cat index.html Notepad path nano path Open file path in a text editor (nano doesn't require the GUI) C:> Notepad foo.txt $ nano foo.txt whoami Tells the username for the account that is executing the command. C:> whoami $ whoami

 “ssh” to your rona account  How? In a Windows command shell type  ssh  Enter your password (you won’t see it)  Now you should be logged in  Type “hostname” – what shows up?  Type “whoami” – who shows up?  What does ls do? 8

 Under the normal course of events, a process's owner must match a file's owner in order for OS to allow the process access to the file. except... if the process runs as administrator (called "root" in Unix), in which case it gets to access everything! So... if a bad guy manages to get an administrator (or "root" in Unix) shell on your machine, it's game over. Note: A user can change the permissions on a file or directory they own to allow access to other users, or even to disallow themselves access! Operating Systems Part II9

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