High Performance Linux Clusters with OSCAR, Rocks, OpenMosix, and MPI [Electronic resources] نسخه متنی

6.5 Using switcher

switcher
is a script that simplifies changes to a user's
environment. It allows the user to make, with a single command, all
the changes to paths and environmental variables needed to run an
application. switcher is a script that uses the
modules package.

The modules package is an interesting package in
its own right. It is a general utility that allows users to
dynamically modify their environment using
modulefiles. Each
modulefile contains the information required to
configure a shell for a specific application. A user can easily
switch to another application, making required environmental changes
with a single command. While it is not necessary to know anything
about modules to use
switcher, OSCAR installs the modules system and,
it is available should you need or wish to use it.
modules can be downloaded from http://modules.sourceforge.net/.

switcher is designed so that changes take effect
on future shells, not the current one. This was a conscious design
decision. The disadvantage is that you will need to start a new shell
to see the benefits of your change. On the positive side, you will
not need to run switcher each time you log in.
Nor will you need to edit your
"dot" files such as

.bashrc . You can make your changes once and
forget about them. While switcher is currently
used to change between the two MPI environments provided with OSCAR,
it provides a general mechanism that can be used for other tasks.
When experimenting with switcher, it is a good
idea to create a new shell and test changes before closing the old
shell. If you have problems, you can go back to the old shell and
correct them.

With

switcher , tags are used to group similar
software packages. For example, OSCAR uses the tag
mpi for the included MPI systems. (You can list
all available tags by invoking switcher with
just the --list option.) You can easily list the
attributes associated with a tag.

[sloanjd@amy sloanjd]$ switcher mpi --list
lam-7.0
lam-with-gm-7.0
mpich-ch_p4-gcc-1.2.5.10

In this example, we see the attributes are the two available MPI
implementations.

You use the --show option to use

switcher to determine the default MPI
environment.

[sloanjd@amy sloanjd]$ switcher mpi --show
system:default=lam-7.0
system:exists=true

Alternately, you can use the which command:

[sloanjd@amy sloanjd]$ which mpicc
/opt/lam-7.0/bin/mpicc

From the path, we can see that we are set up to use LAM/MPI rather
than MPICH.

To change the default to MPICH, simply assign the desired attribute
value to the tag.

[sloanjd@amy sloanjd]$ switcher mpi = mpich-ch_p4-gcc-1.2.5.10
Attribute successfully set; new attribute setting will be effective for
future shells

The change will not take effect immediately, but you will be using
MPICH the next time you log in (and every time you log in until you
run switcher again.) After the first time you
make a change, switcher will ask you to confirm
tag changes. (Also, the very first time you use
switcher to change a tag,
you'll receive a tag "does not
exist" error message that can be safely ignored.)

As root, you can change the default tag for everyone using the
--system flag.

[root@amy root]# switcher mpi = lam-7.0 --system

One last word of warning! If you make a typo when entering the value
for the attribute, switcher will not catch your
mistake.