In the tcsh, you can use unlimit to raise the per-process FD limit up to
the hard limit (64 is the default soft limit).

But as Bakul mentioned, select() won't like anything greater than 256.

But even if you increase FD_SETSIZE for your own program's internals,
you have to worry about libraries which use a fixed FD_SETSIZE and
manipulate fd_sets using descriptors beyond the FD_SETSIZE range.  This
often makes for hard to find stack-twiddling corruption!

==John