I know it's a reply for an older post, but things in the Linux world have changed.
The Linux install script for UT2003 was made with what is now an older version of Makeself (2.0.1 v. 2.1). Here's a
HOWTO with links to the homepage and a tutorial for Makeself if you are interested.
You need to lie to the installer or it won't run. You do this by passing some information as described below.
First, we need to set a workable POSIX version value.
# export _POSIX2_VERSION=199209
Second, set a usable libc version.
# export SETUP_LIBC=glibc-2.1
Then third, tell the installer that we are running on a 32-bit system (in case you are installing on a 64-bit system. Otherwise, disregard this line.).
# linux32 ./linux_installer.sh