This is a bug, a funny one, which I experienced on Linux x86 boxes where SQL*Plus would just hang, and do nothing...
That is, if the Linux x86 box has an uptime of more than 200 days, then SQL*Plus would just hang!
I experienced it on a linux x86 Oracle 10g Client installation where I had the client loging in everyday via SQL*Plus to remote boxes and do things. Suddenly it stopped. I checked top on the box where the Oracle 10g client was installed and saw SQL*Plus eating up the box alive! How strange!??
Check the stack trace:
strace $ORACLE_HOME/bin/sqlplus -V 2>&1 |less
you will see lots of jibberish...
Immediately checked metalink I found the Bug 4612267.
Note: 338461.1: SQL*Plus With Instant Client 10.2.0.1 Hangs, When System Uptime Is More Than 248 Days
Oracle support confirmed this, they asked me to patch the installation with applying a one-off patch they gave me on top of the 10.2.0.1.0 Linux Client.