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

The Physics and Astronomy Department now has three PC workstations running Linux (Mandrake 7.1), which you will be able to use for the remainder of the course. 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 fast processors and high-end 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 the machines.

NOTE that all of these machines are in the .physics.ubc.ca domain.

Machine Processor Memory Disk Graphics
lnx1 2 x 700 Mhz PIII 512 Mb 20 Gb nVidia GEForce 2 MX (32Mb)
lnx2 2 x 700 Mhz PIII 512 Mb 20 Gb nVidia GEForce 2 MX (32Mb)
lnx3 2 x 550 Mhz PIII 512 Mb 20 Gb nVidia GEForce 2 MX (32Mb)

Until sometime shortly after the end of the course, your home directory on these machines ("the lnx machines") will be distinct from your home directory on physics.ubc.ca (and those on sgi1.physics.ubc.ca and vnfe1.physics.ubc.ca). However, when logged in to any of the lnx machines you will have the same home directory, and will be able to access and change any of the files rooted within that directory. One twist is that commands like pwd will return somewhat different results depending on which machine you are logged into, as explained here.

Note on lnx home directories: Many of the machines you are using in this course including sgi1, vnfe1 and 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 my workstation 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. 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
Host key not found from the list of known hosts.
Are you sure you want to continue connecting (yes/no)? yes
Host 'lnx2' added 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   2870652  15590684  16% /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.

As always, contact me immediately if you have any questions on this issue.