linux操作系统百思不得其解的问题

有一个技术问题百思不得其解：用reboot命令重启linux操作系统，系统时间却变快了6个多小时，不知道是为什么。
附日志：
Apr 1 15:23:24 dsqh-rac1 shutdown: shutting down for system reboot
Apr 1 15:23:24 dsqh-rac1 init: Switching to runlevel: 6
Apr 1 15:23:24 dsqh-rac1 su(pam_unix)[14389]: session closed for user oracle
Apr 1 15:23:24 dsqh-rac1 gconfd (oracle-21868): Received signal 15, shutting down cleanly
Apr 1 15:23:24 dsqh-rac1 gconfd (oracle-21868): Exiting
Apr 1 15:23:24 dsqh-rac1 su(pam_unix)[5264]: session closed for user root
Apr 1 15:23:24 dsqh-rac1 su(pam_unix)[1728]: session closed for user oracle
Apr 1 21:47:50 dsqh-rac1 su(pam_unix)[30154]: session closed for user root
Apr 1 21:47:50 dsqh-rac1 su(pam_unix)[6343]: session closed for user root
Apr 1 21:47:50 dsqh-rac1 gdm(pam_unix)[13448]: session closed for user oracle
Apr 1 21:47:50 dsqh-rac1 hald[11934]: Timed out waiting for hotplug event 1120. Rebasing to 1121
Apr 1 21:47:51 dsqh-rac1 haldaemon: haldaemon -TERM succeeded
Apr 1 21:47:51 dsqh-rac1 messagebus: messagebus -TERM succeeded
Apr 1 21:47:51 dsqh-rac1 atd: atd shutdown succeeded
Apr 1 21:47:51 dsqh-rac1 xfs[10266]: terminating