Computing at UMBC
An Introduction to the UMBC
Computing Environment
CMSC 121 Introduction to UNIX
Much of the material in these slides was taken from
Dan Hood’s CMSC 121 Lecture Notes.
Your GL Account


GL is short for “General Labs.” Through this account you have access to
various computing resources across the campus.
Your GL Account gives you access to:


Many labs that are maintained by OIT. An listing of these labs can be found at
http://www.umbc.edu/oit/classroomtechnology/labs/lablocation.html. These
labs contain an assortment of dual-bootable Windows 2000 / Linux PCs,
Macintosh's, and several IRIX machines.
You also get remote server access to several UNIX machines...





linux1.gl.umbc.edu, linux2.gl.umbc.edu, linux3.gl.umbc.edu
irix1.gl.umbc.edu, irix2.gl.umbc.edu
solaris.gl.umbc.edu
The username and password on this account are also your username and
password for http://my.umbc.edu/.
Your username is also your e-mail name. You get an e-mail account
automatically when you sign up for a GL account. It is username@umbc.edu,
where username is your logon name.
Your E-mail Account

Can I change my e-mail address?




Sending and Receiving E-mail. There are lots of ways to do this!




Technically no, but you can create multiple aliases that send mail to username@gl.umbc.edu. In
effect, this changes your e-mail address.
To set up e-mail aliases, follow the instructions at
http://www.umbc.edu/oit/sans/helpdesk/alias.html.
You can also set up your e-mail to be forwarded to another account if you wish. See
http://www.umbc.edu/oit/sans/helpdesk/acctforward.html for more details.
Pine - a UNIX, text-based e-mail client.
Netscape / Mozilla / Outlook - bulky clients, graphical. See
http://www.umbc.edu/oit/sans/helpdesk/configuremail.html.
Webmail - UMBC's web-based e-mail client. It’s fast, easy-to-use, and accessible from
anywhere. http://webmail.umbc.edu. There is also a webmail tutorial:
http://www.umbc.edu/oit/sans/helpdesk/email/webmail/.
It is strongly suggested that all CS students lean the Pine e-mail program. It is very
easy to check your mail remotely via ssh, rip in source code, and is very quick and easy
to use (well, once you get used to it). We strongly feel that it is so important that a
whole class will be dedicated to Pine and Pico.
The Andrew File System (AFS)

AFS is distributed network file system.



A file system is simply a collection of files and directories assembled in
such an order that the make sense to the operating system.
AFS is a way of keeping track of your files over the network.
Features



You can access your files using any computer that has an AFS client
installed on it.
All of the lab computers: Windows, Linux, IRIX, and Mac, are capable of
reading this file system.
The files that you maintain in your account will be accessible to you over
the network from any of these computers. No need to store your
information on a flash drive and carry it between machines.
Your Directory on AFS

Every GL account is assigned a directory on AFS,
which contains the home directory, web space, and email folders. On all of the UNIX systems here at
UMBC it will be located at the following location:
/afs/umbc.edu/users/u/s/username/



u is the first letter of your username,
s is the second letter of your username,
and username is your GL account logon name.
Contents of Your AFS Directory

These are the folders that are in your account at the time of creation





Within the home directory:




home - your UNIX home directory.
Mail - this is where all of your e-mail files are kept.
pub - this is where public data can be placed, including web space.
backup - this is a backup copy of your /afs/umbc.edu/users/u/s/username/,
updated nightly.
All of the typical files found in any UNIX environment (.cshrc, .login, etc...)
Windows NT and 2000 Profiles (.2kprofile and .ntprofile directories)
Your files!
Within the Mail directory:


files for all of your mailboxes (inbox, sent-mail, etc...)
certain configuration files (such as .forward, .procmailrc, etc...) that allow you to
manipulate your mail.

For example, forwarding you mail to another account, or filtering your incoming email.
Contents of Your AFS Directory

Within the pub directory:




it is empty by default!
This is where you can put files, so that others can readily copy them from
here into their accounts.
You can also have a www directory within your pub directory that allows
you to post files onto the Internet, accessible via
http://userpages.umbc.edu/~username/
The backup directory…


…is a copy of your entire account, that is read-only and taken from the
night before. This is typically done around midnight.
If you were to accidentally delete a file (or screw up a source code file so
it no longer compiles) that you had around yesterday you can go into this
directory and you will be presented with the home, Mail & pub directories
from the day before. You can then simply copy the file from here to
wherever you want.
Getting to Your Files

You should usually save files to your home directory
(/afs/umbc.edu/users/u/s/username/home/). How you access
your home directory depends on the operating system…


UNIX / Linux - your home directory is available to you under the
/afs/umbc.edu/users/u/s/username/home/ directory. Almost all UNIX
shells will start you out in this directory by default.
Windows



Your directory (/afs/umbc.edu/users/u/s/username/) is mapped as the
network drive "T:" on the Windows PCs.
Your home directory (/afs/umbc.edu/users/u/s/username/home/) is
mapped as the network drive "S:".
If you have a www directory in your pub directory
(/afs/umbc.edu/users/u/s/username/pub/www/), it is mapped as the
network drive "W:".
Changing Your Password

Via the Web



Logon to http://my.umbc.edu, click on the Personal tab, then click on
Change my Password.
Follow the on-screen instructions for changing your password (there are
several steps).
Via the UNIX Command Prompt



The standard way to change your password on most all UNIX systems is
through a text-based shell.
To change your password this way, you will need to have shell or terminal
access to one of the GL UNIX machines. This can be in the form of a
shell on one of the dual-boot lab machines, or by way of remote SSH
access.
Once you have your shell open, type passwd at the command prompt.
Changing Your Password
linux1-(11:23am): passwd
passwd: Changing password for eeaton1@UMBC.EDU.
Old password:
New password:
New password (again):
Kerberos password changed.
linux1-(11:24am):

Note that when you type your password, it will not be echoed to the
screen, not even asterisks (*).

Windows?
 You may be inclined to change your password by pressing Ctrl-AltDelete and choosing the "Change Password" option.
 But this has been disabled here in the GL labs at UMBC.
If Someone Knows Your Password



Change it NOW!!!
Your GL password is just that - yours and only yours.
You should not share it with anyone.
If you think someone knows your password. Here is
what you should do...



Change your password immediately.
Report this incident to helpdesk@umbc.edu. OIT keeps a log
of all activities in all UNIX accounts. Any unauthorized
access can be tracked given ample research time.
You are legally liable for any action caused under your
account.
Choosing a Good Password


OIT has suggested the following guidelines for choosing a good password...
Passwords should contain at least:




Passwords should not contain:







7-14 characters
2 numbers or symbols in the first 8 characters
5 different characters (letters, numbers, symbols)
The at sign ( @ ), the number sign ( # ), or the ampersand ( & )
Doubled numbers or symbols (e.g., 99 or %% )
Any words or names spelled forwards, backwards, or in a foreign language
A Social Security number in the first nine characters of the password
Words constructed with similar-looking number substitutions (e.g., 0 for O ; $ for
S ; 1 for i ), for example: capta1nk1rk, mr5p0ck
Note: Passwords are case sensitive. The lowercase ‘c’ is a different letter from
the uppercase ‘C’ . Make sure that the Caps Lock key is not on, unless you
intend to enter all uppercase letters.
If you forget your password, the OIT helpdesk can reset it for you.
Your Quota





Every student on the GL network has a set disk quota. This is the amount of
space given to most students is 25 MB. That is not a lot of storage space! So,
some effort must be made on your part not to exceed this disk quota.
Everything that you store in your directory
(/afs/umbc.edu/users/u/s/username/) counts towards this 25 MB limit with
the exception of your backup directory, which not figured into how much
space you are using.
Exceeding your disk quota can cause any number of problems:
 Lost email messages
 Inability to compile programs
 Abnormal account behavior
To check your usage and overall quota, type quota -v in a UNIX shell. If you
are exceeding your quota, change your browser settings so they cache little (or
nothing at all) to disk. You may then have to manually delete the cached files.
If you need help with this, see an OIT Help Desk consultant.
For more information on how to check your quota, see
http://www.umbc.edu/oit/sans/helpdesk/afs/afs_disk_quota.htm.
Checking Your Quota


Type in the quota -v UNIX command at the command line.
Your output should look something like:
 Doin’ just fine.
linux1-(12:20pm): quota –v
Volume Name
Quota Used
user.dhood2
75000 59158

Nearing the limit.
linux1-(12:20pm): quota –v
Volume Name
Quota Used
user.dhood2
75000 70754

%Used Partition
79%
64%
%Used Partition
94%<< 64%
<<WARNING
Over the limit. Danger zone.
linux1-(12:20pm): quota –v
Volume Name
Quota Used
user.dhood2
75000 75798
%Used Partition
101%<< 64%
<<WARNING
How to Get Back Under Quota




OIT has made available a tool that goes through your
account and tries to eliminate unnecessary files and
very large files that may be putting you over the limit.
You can issue the oitcleaner command...
Note: that the latter part of this script tries to remove
larger files that are in your account. You have to answer
"y" or "n" whether or not you want to remove these
files.
You can also make sure that you have set up the web
browser to cache as little as possible to disk.
Restoring a Lost File



Remember the backup directory only contains a copy of all of
your files from the night before.
If you need to restore a file that you deleted days ago, or just
minutes ago (assuming minutes ago was still today), then you are
not going to find the file here.
If it is really important and it was in your account overnight for
at least one of these backups, than you may be able to have OIT
see if they can recover the file for you.


Note that this is only done in the rarest and most dire circumstances.
In-class demo of recovering a file, both graphically and from the
console.
The Outlaws: Telnet and FTP





Telnet and FTP refer to basic network utilities (and related protocols) that allows a
user to interact with a remote host using a text-based virtual terminal.
Telnet and FTP are both widespread (they are integrated into many operating systems)
and useful.
You may have telnetted from your home Windows PC to a UMBC Unix server to
check your email with Pine, or transferred files between 2 computers using FTP.
What is wrong with them?
 Telnet and FTP are inherently insecure.
 When you initiate a telnet or FTP connection, your username, password and other
bits of important information are broadcast in cleartext, meaning that they are
visible to anyone located between your computer and the intended server
destination.
 For example, any curious person with a 802.11b-equipped laptop, a packet sniffer
program (designed to intercept and interpret data broadcast across a network),
and a rudimentary grasp of networking could sit within range of UMBC's wireless
networks and grab any usernames and passwords transmitted in cleartext.
 Regardless of where and how you're online, if you use telnet or FTP, you're
putting your vital data at risk.
Because of the vulnerabilities associated with telnet, UMBC's Office of Information
Technology (OIT) prohibited telnet connections to UMBC servers beginning in
January 2003.
SSH (instead of Telnet)




SSH stands for Secure SHell.
It provides terminal or shell access to some remote
computer.
SSH can be viewed as nothing more than a secure
version of telnet.
There are several SSH clients to choose from. Some are
installed in the OIT labs, some you can install, and
others require administrator privileges that you may not
have under Windows (at least in the labs).


Tera Term Pro (available in the UMBC labs)
Putty: http://www.chiark.greenend.org.uk/~sgtatham/putty/
SCP (instead of FTP)




SCP stands for Secure CoPy.
It provides the functionality of a File Transfer Protocol
(FTP) client.
SCP can be viewed as nothing more than a secure
version of FTP.
Again there are many SCP clients out there:


WinSCP (available in the labs): http://winscp.vse.cz/eng/
The Linux command:
scp localfile username@gl.umbc.edu:~/path/filename
Open AFS



AFS is a distributed file system, pioneered at Carnegie Mellon University and
supported and developed as a product by Transarc Corporation (now IBM Pittsburgh
Labs). It offers a client-server architecture for file sharing, providing location
independence, scalability and transparent migration capabilities for data.
IBM branched the source of the AFS product, and made a copy of the source
available for community development and maintenance. They called the release
OpenAFS.
Mounting your UMBC AFS Directory at Home
 Download and install the windows Open AFS client. During installation you will
be prompted for an AFS cell name, you should enter umbc.edu
 When the installation is complete, you will need to reboot. After you reboot, there
will be an icon that looks like a lock in the system tray. Click on this to launch the
OpenAFS dialog.
 Under the Tokens tab, click Obtain New Tokens...
 Be sure that the cell name is umbc.edu and go ahead and enter your username
and password, then press enter. If everything went ok, you should see an entry
under tokens with your GL username.
 Under the Drive Letters tab, click Add...
 Chose an unused drive letter, and enter the path to your root directory on GL
(/afs/umbc.edu/users/u/s/username/), and click enter. If everything went ok,
then you should see the drive letter added under the OpenAFS dialog.
 You should now be able to browse the drive in Windows Explorer.