为何我的linux老是死机？请高手帮忙看看

RH9.0  双P3 1G  1G RAM  36G SCSI

Sep 20 10:58:35 antcn login(pam_unix)[26697]: session opened for user antcn by (uid=0)
Sep 20 10:58:35 antcn  -- antcn[26697]: LOGIN ON pts/2 BY antcn FROM 218.79.240.242
Sep 20 10:58:41 antcn  9月 20 10:58:41 su(pam_unix)[26739]: authentication failure; logname=antcn uid=500 euid=0 tty= ruser=antcn rhost=  user=root
Sep 20 10:58:50 antcn  9月 20 10:58:50 su(pam_unix)[26764]: session opened for user root by antcn(uid=500)
Sep 20 11:01:37 antcn login(pam_unix)[26697]: session closed for user antcn
Sep 20 11:01:37 antcn  9月 20 11:01:37 su(pam_unix)[26764]: session closed for user root
Sep 20 11:03:14 antcn vsftpd: warning: can't get client address: Bad file descriptor
Sep 20 11:14:35 antcn vsftpd: warning: can't get client address: Bad file descriptor
Sep 20 11:15:44 antcn login(pam_unix)[8703]: session closed for user root
Sep 20 11:21:45 antcn vsftpd: warning: can't get client address: Bad file descriptor
Sep 20 11:21:45 antcn vsftpd(pam_unix)[28955]: authentication failure; logname= uid=0 euid=0 tty= ruser= rhost=218.242.134.203  user=antcn
Sep 20 11:22:08 antcn vsftpd: warning: can't get client address: Bad file descriptor
Sep 20 11:32:22 antcn vsftpd: warning: can't get client address: Bad file descriptor
Sep 20 11:56:08 antcn vsftpd: warning: can't get client address: Bad file descriptor
Sep 20 12:04:37 antcn login(pam_unix)[3826]: session closed for user antcn
Sep 20 12:04:37 antcn  9月 20 12:04:37 su(pam_unix)[3875]: session closed for user root
Sep 20 13:42:06 antcn syslogd 1.4.1: restart.
Sep 20 13:42:06 antcn syslog: syslogd startup succeeded

被别人攻击21号端口，不死也难怪了~~~

为何不先看看日志后再到这里来提问呢？