I assume that you are trying to run su - abc
. Because you do not set your command off from the rest of the text in any way, I can't be sure of what you mean.
From the Wikipedia® article Red Hat Linux
Red Hat Linux, assembled by the company Red Hat, was a popular Linux based operating system until its discontinuation in 2004.
Since 2003, Red Hat has discontinued the Red Hat Linux line in favor of Red Hat Enterprise Linux (RHEL) for enterprise environments. Fedora, developed by the community-supported Fedora Project and sponsored by Red Hat, is the free version best suited for home use. Red Hat Linux 9, the final release, hit its official end-of-life on 2004-04-30, although updates were published for it through 2006 by the Fedora Legacy project until that shut down in early 2007.
Before I, or anyone else here, tries to diagnose this problem, I/we would like to know why you are using such an old obsolete OS? The official EOL is one month short of 7 years ago. Why haven't you upgraded?