The dateext option for logrotate.conf is enabled by default in centos6
[william.ho@mail10a log]$ ls /var/log
anaconda.ifcfg.log anaconda.xlog btmp-20130401 cron-20130414 ftp.log maillog messages ntpstats secure-20130331 spooler-20130331 wtmp
anaconda.log anaconda.yum.log clamav cron-20130421 httpd maillog-20130331 messages-20130331 openwebmail.log secure-20130407 spooler-20130407 xferlog
anaconda.program.log audit cron dmesg iptraf maillog-20130407 messages-20130407 sa secure-20130414 spooler-20130414 yum.log
anaconda.storage.log boot.log cron-20130331 dmesg.old lastlog maillog-20130414 messages-20130414 sa-update.log secure-20130421 spooler-20130421
anaconda.syslog btmp cron-20130407 dracut.log mail maillog-20130421 messages-20130421 secure spooler tallylog
To disabled it, edit /etc/logrotate.conf and comment the line “dateext”