I am using CENTOS 4.3 - kernel 2.6.9-42.0.2.EL with rkhunter version 1.2.8, but the rkhunter program show me problem on file /bin/kill.
I compare files /bin/kill with other CENTOS 4 and it has same size.
I guess problem is rkhunter.
Yes and no. Your issue is likely caused by prelink, which alters binaries to load more quickly. This runs as part of a daily cron by default, so files can and in all likelihood will change over time. You should consider either adjusting rkhunter, or telling prelink to not mess with certain file directories.