4.1.1 CLS Private Address – Off Campus via VPN

Rarely the College network connecting to the Public Address from home is broken, but the internal College network is working. In these rare cases, you can often start up the Algonquin VPN software at home to connect to the College network, and then use the Private Address to connect through the VPN to the CLS. This is usually slower than connecting directly to the Public Address, but it may be the only method available.

Use the private address clserver when you are using the Algonquin VPN.

5.1.1 SSH Via clserver

Use the model SSH command line below, with these notes:

1. Type your usual eight-character Algonquin userid (the same userid you use for Blackboard). Do not use abcd0001! Replace the userid abcd0001, below, with your usual Algonquin userid. Your 8-character login userid must be all lower-case letters; do not use any capital letters.

2. Choose the correct host name in your SSH command below:
   • On Campus address (school): clserver

3. On your first connection, you will be asked to accept the server encryption key. Answer yes (use the full word) to accept the host key, if asked “Are you sure”.

4. Make sure the login banner says COURSE LINUX SERVER when you connect! If this is not true, you are trying to log in to the wrong machine.

   If you use the correct host name and don’t see any banner but get an immediate disconnection, your IP address is probably locked out. See the section above on Getting locked out of the server.

5. When it asks for your password, use your special Course Linux Server password. The Course Linux Server does not use your Algonquin network or Blackboard password. The password will not echo as asterisks on your screen as you type it; you will be typing your password “blind”.

   Your instructor can tell you your special Course Linux Server password. If you need your password reset, see your Linux instructor; do not go to ITS.

Your SSH command line will look similar to this (you must make the above changes first):

$ ssh abcd0001@clserver
Are you sure you want to continue connecting (yes/no)? yes
*** COURSE LINUX SERVER ***
abcd0001@clserver's password: 
Welcome to Ubuntu 16.04.2 LTS (GNU/Linux 4.8.0-52-generic x86_64)
-bash-4.2$

When you have logged in successfully, you will see a your CLS BASH shell prompt (default bash-4.2$). You can type Linux commands at this prompt.

When you are done with your session on the CLS, type exit to log out of the shell and close SSH. Do not simply close the Terminal program; always exit the shell first to avoid leaving behind a “ghost” login on the CLS. (“Ghost” logins do eventually time out and go away.)

5.1.2 SSH session time-out or broken pipe

If your SSH session times out or gets broken pipe errors, here is a suggestion from Oliver Bett:

Add the following line to your /etc/ssh/ssh_config file and it should keep the connection active.

ServerAliveInterval 120

I’ve set my interval to 120 seconds and seems to do the trick.

5.1.3 SSH using alternate Port numbers

The default SSH Port number is port 22. If you need to use a non-default Port number when connecting (your instructor will tell you this), specify the port number on the SSH command line using the -p option:

    $ ssh -p 2222 abcd0001@some.example.com

Make sure the login banner says COURSE LINUX SERVER when you connect! If this is not true, you are trying to log in to the wrong machine.

5.2.1 PuTTY Configuration options for Windows users

Before you connect using PuTTY the first time, you must set the following PuTTY Configuration options in the PuTTY Configuration dialog box. Read this whole section before you log in!

Failure to make the configuration changes below may result in your laptop keypad not working or your PuTTY session being disconnected in the middle (“Network error: Software caused connection abort”) and your session becoming inactive.

Category: Terminal:
    Features (Enabling and disabling advanced terminal features)
        Disable application keypad mode: ON
Category: Connection:
    Seconds between keepalives: 55
    Disable Nagle's algorithm: ON
    Enable TCP keepalives: ON
    Internet protocol version: IPv4

Category: Session:
    Host Name (or IP address):

* cst8207.idallen.ca (when off-campus, e.g. home) * OR clserver (when on campus at Algonquin) Connection type: SSH Port: 22 Saved Sessions: (choose your own name; see below)

After making the above configuration settings, save your settings using any name you choose:

1. Go to the PuTTY Configuration dialog box Session Category.
2. In the Session Category, enter a session name in the Saved Sessions box. You might choose the name on campus CLS for the on-campus host name, and off campus CLS for the off-campus host name.
3. Use the Save button to save the session using the given name.

Save one configuration session that uses the off-campus Public host name and another configuration session that uses the on-campus host name that uses the Private IP address.

If you are on-campus at Algonquin College, you must connect to the CLS using the Private address clserver to avoid connection problems. The Private address only works on-campus at Algonquin College (or via the VPN).

Read the rest of this section to the end before you first Open a session. Your session will time out and become inactive if you don’t log in within a minute of clicking on Open.

Once you have saved both the on-campus and off-campus settings, choose the correct setting and use the Load button to load it, then use the Open button to start the session and connect to the CLS.

On your first connection, a PuTTY Security Alert dialog box will appear and you will be asked to accept the server’s host encryption key. Click on “yes”:

Next, you will be prompted with the line login as: to enter your login userid. Type your usual eight-character Algonquin userid (the same userid you use for Blackboard). Do not use abcd0001! Replace the userid abcd0001, below, with your usual Algonquin userid. Your 8-character login userid must be all lower-case letters; do not use any capital letters.

Make sure the login banner says COURSE LINUX SERVER when you connect! If this is not true, you are trying to log in to the wrong machine.

If you use the correct host name and don’t see any banner but get an immediate disconnection, your IP address is probably locked out. See the section above on Getting locked out of the server.

When it asks for your password, use your special Course Linux Server password. The Course Linux Server does not use your Algonquin network or Blackboard password. The password will not echo as asterisks on your screen as you type it; you will be typing your password “blind”.

Your instructor can tell you your special Course Linux Server password. If you need your password reset, see your Linux instructor; do not go to ITS.

Your PuTTY session will look similar to this (you must make the above changes):

login as: abcd0001
*** COURSE LINUX SERVER ***
abcd0001@clserver's password:
Welcome to Ubuntu 16.04.2 LTS (GNU/Linux 4.8.0-52-generic x86_64)
-bash-4.2$

When you have logged in successfully, you will see a bash-4.2$ shell prompt. You can type Linux commands at this prompt.

When you are done with your session on the CLS, type exit to log out of the shell and close PuTTY. Do not simply close PuTTY; always exit the shell first to avoid leaving behind a “ghost” login on the CLS. (“Ghost” logins do eventually time out and go away.)

Optional: If you have IPv6 connectivity at home, you can experiment using the IPv6 host name ipv6.cst8207.idallen.ca and Internet protocol version: IPv6 to connect to the Course Linux Server.

5.2.2 Changing and saving PuTTY Configuration options

Using the mouse on the little screen icon in the top-left corner of your PuTTY session, you can bring down a menu that lets you change your PuTTY options for the current session. You can then re-save the changed settings to be available for your future sessions.

If you do not re-save the changes options, they will be lost and you will get the old settings when you re-start PuTTY.

$ mail -s "This is the subject" user@example.com
$ who | mail -s "Here is the list of users" user@example.com

8.2.1 Failure to Send and mailq

Mail messages sent to users on other machines from the CLS can fail to be sent either because the SMTP port on the other mail server is down temporarily (perhaps because the mail server is down), or because the machine name used in the EMail address is not an SMTP mail server at all (user error), so the SMTP port will never be open.

To see the queued EMail messages on the CLS, run the command: mailq

The mailq command shows you the queue of all undelivered mail messages for all users on the machine. (RTFM for more details.)

An outgoing EMail to a server that does not run any EMail service will sit in the outgoing queue on the CLS for some period of time, usually five days, until it times out and gets bounced back to your CLS Linux mailbox under /var/mail/.

If you see EMail messages of yours queued to incorrect servers that you want deleted right away, you need to get super-user help. Only super-users (your instructors) can delete queued mail messages.

Provide the super-user with a list of your queue EMail IDs that you want deleted. The super-user will use the postsuper -d command and one or more queue IDs to delete specific queued outgoing EMail messages.