Physics 410: Physics and Astronomy Computer Lab PC/Linux Machines

The Physics and Astronomy Department currently has three PC workstations running Linux (Mandrake 9.2), that you will be able to use during this course. They are located in Hennings 205, at the end of the room closest to the door, towards the exterior wall. These machines have dual reasonably fast processors and good graphics cards, so are suitable platforms for developing and running computational- and graphics-intensive applications. Let me know immediately if you have any problems using them.

2 x 700 MHz PIII
512 MB
20 GB
32 MB NVidia
2 x 700 MHz PIII
512 MB
20 GB
32 MB NVidia
2 x 800 MHz PIII
512 MB
20 GB
32 MB NVidia

In addition, there are nine older, and significantly less powerful PCs located on the same side of the lab, which are currently configured as "X-terminals", and which are served by the machine You can login to lts1 from any of these machines, and from there you can open one or more terminal applications and, from those, ssh to any of the lnx boxes. This configuration of the older PCs as X-terminals is new, so there may still be some glitches that need to be worked out. Again, contact me immediately should you encounter problems.

NOTE: During the term, Physics 410 students have priority use of the lnx consoles. However, the other PCs in the room may be reserved from time to time for use in other courses. Please refer to the Lab Schedule for times when the lab is booked for such purposes.

Please make careful note of the following:

  1. You must get an account on the Physics & Astronomy server, before you can get an account on the lnx machines. Undergraduates can get an account on physics by "self-registering" in the Computer Lab. Graduate students, and graduate students ONLY can see Mary Ann Potts, for an account. This account will also provide you with access to lts1 via the X-terminal PCs.
  2. Your password on the lnx machines will be the same as your password on
  3. Please do NOT change your password on the lnx machines, unless you think it absolutely essential. If you do change it, it will have to be changed on each of lnx1, lnx2 and lnx3 separately.

Note that your home directory on these machines ("the lnx machines") will be distinct from your home directory on, but that you will have a common home directory on and Those of you who had physics accounts prior to approximately August 2003 may find that adjustments need to be made to your shell-start up files to take into account this commonality. Again, contact me if you have any questions in this regard.

At the current time, it is not possible to access your lnx files directly from physics (lts1) or vice versa.

Notes on Linux Desktop Environments: Over the past few years, great progress has been made in equipping Linux with powerful graphical user interfaces (GUIs, window managers) to the core operating system and major applications. When you login to the console of one of the lnx machines, you can select from five such interfaces. I recommend that you use one of the following window managers

Windows afficionados should feel especially comfortable with KDE. Both interfaces have extensive on-line help facilites.

Initial login procedure: When first logging-in at a console of one of the lnx machines, do the following:

  1. Type your username in the login-prompt type-in.
  2. Click on the Session icon on the lower task bar, and select either KDE or GNOME.
  3. Return the mouse to the login-prompt type-in area, hit Enter, type your password at the prompt, then hit Enter again.

IMPORTANT!!: Note on X-terminal Desktop Environments: At the current time you can only use Gnome, NOT KDE, on the X-terminal PCs. In an ideal world, this would get fixed shortly, but unfortunately the problem has persisted for over a year. (If you do choose KDE from the login window on one of the X-terms, the system will (probably) initiate your login, present you with a KDE start-up wizard, etc., but you will also encounter error-message pop-ups, and eventually will be returned to the login screen.)

Note on lnx home directories: The lnx machines have access to each others' disks via NFS (Network File System). The process of attaching a remote file system to a directory name within the local Unix system (i.e. to a directory name somewhere within the file hierarchy rooted in /) is known as mounting the file system. In a shell, you can generate a listing of all of the file systems currently mounted with the Unix df command. For example, you can see the output of df as executed on lnx1 HERE.

Again, each of you has a single home directory on the lnx machines, and that directory is physically located on one of the machines lnx1, lnx2 or lnx3. (I leave it as an exercise for you to determine on which specific machine yours is located.) Let's consider the case of the ``test'' user jdoe, whose home directory is physically located on lnx1, within the file system /home:

[jdoe@lnx1 ~]$ cd
[jdoe@lnx1 ~]$ pwd
jdoe now logs into lnx2 and executes the same command sequence:
[jdoe@lnx1 ~]$ ssh lnx2
Warning: Permanently added 'lnx2,' (RSA) to the list of known hosts.
jdoe@lnx2's password:
No mail.
[jdoe@lnx2 ~]$ cd
[jdoe@lnx2 ~]$ pwd
This behaviour can be understood by looking at the specific part of the output from df which tells us about the file systems from lnx1 which have been mounted on lnx2:
[jdoe@lnx2 ~]$ df | grep lnx1
lnx1:/home 19449328 7048332 11413004 38% /d/lnx1/home
Since the remote, physical file system lnx1:/home has been mounted on the local file system /d/lnx1/home, when logged into lnx2, jdoe's working directory is indeed /d/lnx1/home/jdoe.

Moreover, things have been set up so that you can use the "long" form of your home directory on all of the machines, so that, for example, jdoe can execute the following:

[jdoe@lnx1 ~]$ cd /d/lnx1/home/jdoe
[jdoe@lnx1 ~]$ pwd

Note that the specific name of the local mount point, e.g. /d/lnx1/home, is a matter of convention ('d' for disk, then the hostname, then the remote file system name); other system administrators will use different conventions for NFS mounts.

Finally, as mentioned above, you can access your lnx home directories directly from physics since the /home filesystems on the lnx machines are NFS-mounted on physics as

Thus, for example, on physics, any of
physics% cd /d/lnx1/home/userid
physics% cd /d/lnx2/home/userid
physics% cd /d/lnx3/home/userid
should take you to your lnx home directory. As always, contact me immediately if you have any questions, or encounter any problems, regarding this issue.

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