Occasionally we hit a bug where the ‘whois’ command hangs on one of our CentOS servers and goes CPU-bound. This has been happening on several CentOS versions, including 6.8. Specifically, this is a problem in jwhois, the whois client included in CentOS.
Apparently, CentOS (and RHEL, on whose source code it’s based) is missing a number of fixes that have been added to other Linux versions including Fedora over the last couple of years. So the problem is actually known and a fix has been available for years, it’s just not included in the product.
Comparing the change logs for jwhois between CentOS and Fedora, everything matches up to and including build 4.0-18 in September 2009, but then the two diverge.
On Jan 26, 2010, Fedora received a fix (“Use select to wait for input (patch by Joshua Roys <joshua.roys AT gtri.gatech.edu>)”) for a new 4.0-19 build that resolved bug #469412 for precisely this issue. There are many more changes in Fedora’s jwhois after that, unlike its RHEL and CentOS equivalent, which in all the years since then received only a single update. This is also called 4.0-19, but it was made on Jun 23, 2011 and it includes only two fixes for unrelated issues that were fixed in Fedora’s jwhois updates 4.0-24 (Dec 20, 2010) and 4.0-26 (Mar 15, 2011), but not the earlier select fix or fixes for any of the other issues. CentOS is missing the “jwhois-4.0-select.patch” and that’s why WHOIS hangs.