Unix: Mail, Editing Files, File Transfer
In this lesson I will cover the following topics
How to log into the Unix host.
How to use mail on the Unix host.
How to edit files on the Unix host.
How to transfer files to and from the Unix host and how to backup your files on the Unix host.
You have a username and password on the Unix system we will be using in this course. That information was sent to you in a separate message (if you didn't get such a message, please contact me as soon as possible). You will need to use a secure shell (SSH) client to log into the system.
Many older network protocols, such as telnet, are highly insecure because the information they transmit over the network is "visible" in unencrypted form on the network cable. People with special tools who are positioned between you and the remote host you are using can watch your session and steal your passwords quite easily. This is bad not only for you, but also for everyone else who uses the same remote host. If your account is compromised the attacker can use it to more easily launch other attacks against the machine or, for that matter, against other machines on the Internet. This is not a hypothetical situation. It happens on the net every day.
To help prevent this problem, all of our Unix systems are running a "secure shell server". If you use an appropriate client, this server will create a terminal session for you but all information sent across the network will be encrypted. Even the initial password that you use to establish the connection will be encrypted on the network.
If you are located on the VTC campus and are using one of the VTC lab machines, then a suitable ssh client should already be installed and available to you. Just run it and connect to the Unix host. If you are using your own machine, and if you are using Windows, you can download and install the free PuTTY program as an ssh client.
Get the files putty.exe and pscp.exe from http://www.putty.org/.
Put pscp.exe into your C:\Windows folder (or any folder in your path). This is the program you will use for transferring files between your system and the Unix host.
Put putty.exe anywhere you like. Make a shortcut on your desktop to the program.
There is no installation that needs to be done for PuTTY. Just run the executable by double clicking on the shortcut.
The first time you run PuTTY a dialog box will appear where you can create a session or manage sessions you've already created. Type the name of the Unix host in the "Host Name" field. Be sure the SSH protocol option is checked. Under "Saved Sessions" type a name for this session. Click on "Save". Click on "Open" to connect to the host you specified. There are numerous other session options you can adjust (see the list of catagories on the left side of the dialog box) but all of the defaults should be fine.
The next time you run PuTTY you should see your session listed in the saved sessions box. You can just double click on the name to start it up again (or click on the name once, and then click on "Load" if you want to edit the session parameters).
The first time you connect to a host you will get a warning message because you don't have the host key for that host stored on your machine. Technically you should verify the authenticity of the host key before accepting it. However, since it's highly unlikely to be bogus in this situation, you are probably safe accepting it without verifying it. Once you have the host key stored on your machine, you won't be warned about it again (unless it changes... a sign that someone might be trying to trick you into using the wrong host).
Using ssh might sound like an annoyance, but I do advise you to use the ssh protocol to access the Unix host if at all possible. Snooping passwords off the network is easier than it might sound. If even one user's password is snooped, then further attacks against the entire machine become much easier. If you are using an operating system other than Windows and would like to configure an ssh client, let me know.
When you first log into the Unix host you may be required to change your password immediately. The password I gave you when I created your account is for temporary purposes only. You should use a password that only you know.
Many Unix systems will periodically expire your password and force you to change it. This is done to enhance the security of the system. If your password is compromised in some way, an attacker will only have access to your account as long as you don't change your password. By changing your password regularly you limit the amount of damage an attacker can do.
To change your password manually you should use the "passwd" command (yes, it is really spelled that way).
pchapin@lemuria:~$ passwd
You will be asked to enter your old password to verify that you are you. Then you will be asked to enter your new password twice. The second time is to verify that you didn't make a typo the first time. None of the passwords will be displayed as you type them.
Choosing a good password is an art. Do not use anyone's name or any normal, correctly spelled word. Do not use the names of fictional characters or places. Do not use significant numbers like birth dates or street addresses. Do not use any of these things spelled backwards. Such passwords are easily guessed. A good password should
If you forget your password, send me email. I can give you a new one.
If you are a regular VTC student you should keep in mind also that the password you use the Unix host is not necessarily the same as the password you use on the main network at VTC. In fact, for security reasons, it would be best if you used different passwords for those two systems.
From now on I will just use a "$" to represent the Unix prompt in my examples. Keep in mind that the prompt is normally longer than that (as I've shown above).
The Unix host is a all fully operational, networked system. It runs 24 hours per day, 7 days per week. It is connected to the Internet at all times. In addition, the Unix host has its own, independent mail software. Thus you are able to send and receive mail there separately from any other Internet mail service you might have.
Your address on the Unix host is your username followed by an '@' followed by the name of the host. For example, if the host name is "lemuria" than my address would be
pchapin@lemuria.cis.vtc.edu
The mail program on the Unix host is called "alpine". It is a text mode program (not graphical) but it is full featured, modern, and quite powerful. You can start the program by just typing "alpine" at the prompt.
$ alpine
Alpine is fairly easy to use. Most of the commands are letters or control characters. There is usually a menu at the bottom of the screen that gives you an idea of what you can do. Note that menu items shown with a "^" are control characters. Thus "^Y" means push the CTRL key, hold it down, and type a "Y" (not case sensitive). In some cases you can navigate the program with the arrow keys on your keyboard.
Try this out. Send a mail message to your Unix address using your regular mail program. Then start alpine and read your mail (it may take a few moments for the mail to arrive). Once you are finished reading a message you can type the letter 'D' (not case sensitive) to delete it. Alternatively you could type the letter 'S' to save it to a folder. If you do that you will be asked to enter the name of the target folder. If the folder does not exist you will be asked if you want to create it. Try sending a message to your usual email address from the Unix host.
I'm hoping that you can figure out how to do basic things with alpine by just reading the menus and fooling around a bit with the program. Alpine's on-line help is also fairly good (look at the menus for how to enter help). However, if you can't figure out how to do something please post a note to the class list or send email to me and I'll be happy to provide more details.
You might wonder what the point is of using mail on the Unix host. After all, you already have a perfectly good mail program available to you or you wouldn't be taking this course! Nevertheless there are times when you might find it handy to send or receive mail on the Unix host. For example, you could use mail as a way of transferring files to and from the Unix environment. Or you might want to dash off a quick note while you are working on a program and you might find it easiest to just hop into alpine to do it.
As a point of information, alpine is not universal on Unix systems. It is normally something the administrator must download and install. However, since alpine is free and since alpine is good, it is very commonly available.
In order to write programs you will need to create and edit plain text files. I will describe how you can do that on the Unix host. There are several text editors on the system. The one I suggest you use is called "nano". It is not the most powerful or full featured editor by any means. It is actually quite simple. However, to create short text files it's a very good choice and it's quite simple to learn. It will be sufficient for our needs in this course.
The original version of nano was called pico and was created by the same people who created alpine. It looks and acts very much like the editor alpine uses when you compose a mail message. It has the same menus and uses most of the same control keys. To edit the file "afile.txt" with nano, type the command
$ nano afile.txt
Try it out. You should see a mostly blank screen into which you can type your text. Type a few lines and then type ^X (that's CTRL+X) to save the file and exit nano. You should then see another prompt from the Unix host.
After creating a file in this manner you can use the "ls" command to see it. (That's ell-ess, not one-ess)
$ ls
This command displays a list of all your files. It is very handy! Keep in mind that you can store whatever files you like on the Unix host. If you do all of your programming there, as I'm assuming you will, then all of your program files will be stored there. They will not be on your local machine unless you explicit transfer them to your machine. This means that if you can gain access to the network and an SSH client, you can log into the Unix host and do whatever you like with your files there.
Use the command
$ nano afile.txt
To edit the existing file. You should see the material you typed into the file before. Change it and then use ^X to save it and exit pico.
As with alpine, I'm hoping that you'll be able to figure out how to do basic things with nano by just playing around with the program. However, I do encourage you to ask about anything you can't figure out. Remember: there are no stupid questions.
I highly recommend that you backup your files to your personal machine. If something goes wrong with the Unix host or if you accidentally delete a file, then you can use your backup to recover your data. In addition, you might want to write your programs on your local machine so you can do so off-line or so that you can use your own tools. In that case, you'll want to transfer your programs to the Unix host where you can test them. Either way, you'll want to know how to transfer files to and from the Unix host. Here is how.
First, you could just use mail. You could use your mail program to send a message to your Unix address with a file attached. You could then read the message on the Unix host using alpine and save the attachment to a file. Similarly you could use alpine to send a message to your usual address with a file attached. Then you could use your usual mail program to save the attachment to a file on your local machine. I can explain in more detail how to receive and send file attachments using alpine. I can't necessarily help you with your own mail program, but if you have trouble you could post a message to the class mailing list and maybe someone in the class could help.
A more direct way to transfer files to and from the Unix host is to use the "secure copy" program (SCP) to copy files from one host to another using encrypted transfers. If you downloaded and installed pscp.exe as I described above, you can use that program to do secure transfers. Here's how
Open a command prompt on your Windows machine. Use the "cd" command under Windows to change to the directory (folder) where you want to send or receive files.
Type:
C:\> pscp somefile username@lemuria.cis.vtc.edu:
This will send "somefile" to the host named "lemuria.cis.vtc..edu" using the account "username" on the host. Replace "username" with appropriate things for your situation. Note the colon at the end of the command line; that is required.
Type:
C:\> pscp username@lemuria.cis.vtc.edu:somefile .
This will get somefile on the host "lemuria.cis.vtc.edu" (using the account "username") and store it on your local machine in the current directory. The dot represents the current directory on your machine.
The pscp program will prompt you for your password on the Unix host. However, that password will be sent over the network in encrypted form so nobody will be able to capture it.
To make a backup of all your material on the Unix host, you should probably first create a compressed archive of all your files there. Of course right now you don't have much there. But that will change! Use these commands to create the compressed archive:
$ rm -f mystuff.zip $ zip -r mystuff.zip *
The first command deletes any existing "mystuff.zip" file. The second command creates a new one. Note that the last character in that command is an asterick. Note also that spaces are significant!
The single file "mystuff.zip" will contain a (compressed) copy of all your other files. You can then transfer this single file to your local machine. If you ever need to restore a file from this backup, you would first need to extract it from the archive. I can help you do that should it become necessary.
You can use either telnet or ssh to log into the Unix host. Using ssh has the advantage of being more secure, but telnet is simplier.
The Unix host has its own mail system. Use pine to send and receive mail. Although you can certainly use your regular email program for mail, you might find the Unix system's mail easier at times.
Use pico to edit files on the Unix host. Pico behaves very much like pine. It is a relatively limited text editor, but it is easy to use. If you keep files on the Unix system they will be available to you from any point on the network.
You can transfer files to and from the Unix host using the scp protocol, or as file attachments to mail messages.