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

The Physics and Astronomy Department currently has three PC workstations running Linux (Mandrake 7.2), which 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. I urge all of you to take full advantage of this resource, particularly if you do not have routine access to the ``console'' of a Unix system. These machines have dual reasonably fast processors and good graphics cards, so are ideal platforms for developing and running computational- and graphics-intensive applications. Let me know immediately if you have any problems using them.

Machine Processor Memory Disk Graphics
lnx1.physics.ubc.ca 2 x 700 Mhz PIII 512 Mb 20 Gb nVidia GEForce 2 MX (32Mb)
lnx2.physics.ubc.ca 2 x 700 Mhz PIII 512 Mb 20 Gb nVidia GEForce 2 MX (32Mb)
lnx3.physics.ubc.ca 2 x 800 Mhz PIII 512 Mb 20 Gb nVidia GEForce 2 MX (32Mb)

As the term progresses, additional PCs running Linux should become available in Room 205. These machines will be slower, will have less powerful graphics than lnx[123], and may not have all of the software which is installed on lnx[123]. For these reasons, when the additional machines come on-line, you will typically want to use them principally for remote access (via ssh) to lnx[123].

Please make careful note of the following:

  1. You must get an account on the Physics & Astronomy server, physics.ubc.ca before you can get an account on the lnx machines. Undergraduates can get an account by "self-registering" in the Computer Lab. Graduate students, and graduate students only can see Mary Ann Potts, for an account.

  2. Your password on the lnx machines will be the same as your password on physics.ubc.ca.

  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 physics.ubc.ca. We have set things up so that you can access your lnx files directly from physics (see below), but for security reasons, it will not be possible to directly access your physics files from the lnx machines.

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 no fewer than 11 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.

IMPORTANT!!: 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; alternatively right or left-click on the icon labelled with your username. Type Enter.
  2. Right or left-click on Session in the upper left corner of the login window and select either KDE or Gnome.
  3. Return to the login-prompt type-in, type your password, then Enter.
It is imperative that you select some specific window manager from the Session menu when you first log-in; otherwise after you enter your password, the screen may simply blank for an instant, and return you to the log-in 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
/home/jdoe
jdoe now logs into lnx2 and executes the same command sequence: 

[jdoe@lnx1 ~]$ ssh lnx2
Warning: Permanently added 'lnx2,142.103.238.212' (RSA) to the list of known hosts.
jdoe@lnx2's password: 
No mail.
[jdoe@lnx2 ~]$ cd
[jdoe@lnx2 ~]$ pwd
/d/lnx1/home/jdoe
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
/home/jdoe

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 

/d/lnx1/home
/d/lnx2/home
/d/lnx3/home
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.