Hi, all We have been using SL4.6/4.7 (i386 and X86_64) on several nodes and have experienced kernel panic frequently during the system rebooting or system shutdown or even by /etc/init.d/ip_tables restart since last summer in 2008. This is a known bug and still unresolved as reported at the upstream vender's bugzilla. https://bugzilla.redhat.com/show_bug.cgi?id=456664 With several investigation, this Kernel panic related to [ip_conntrack] occurs in the the following condition in our environment. 1) Kernel is kernel-smp-2.6.9-78.1EL (SMP or hugemem) (Aug. 2008) to kernel-smp-2.6.9-78.13EL (SMP or hugemem) (latest kernel) 2) ip-tables is enabled and in /etc/sysconfig/iptables-config IPTABLES_MODULES="ip_conntrack_ftp" is included. In this situation, during the rebooting or /etc/init.d/iptables stop or /etc/init.d/iptables restart operations, kernel panic relating with [ip_conntrack] accrues. This kernel bug is still unresolved. However, there is a workaround to avoid this problem. It is described in the comment 31 in https://bugzilla.redhat.com/show_bug.cgi?id=456664 > We have discovered that when the following is in the iptables-config: > > IPTABLES_MODULES="ip_conntrack_ftp ip_nat_ftp iptable_nat ipt_REJECT iptable_mangle" > > and on the 2.6.9-78.0.1 ( or .5) RHEL4 version kernel, the kernel > panic does not occur when iptables is stopped. We have tested this workaround in several nodes of SL4.6/7 (both i386 and X86_64) with the kernel 2.6.9-78.0.13.ELsmp. After updating the /etc/sysconfig/iptables-config to include IPTABLES_MODULES="ip_conntrack_ftp ip_nat_ftp iptable_nat ipt_REJECT iptable_mangle", the first rebooting failed with kernel panic because this update was not reflected. But in the second rebooting and also /etc/init.d/ip_tables stop or /etc/init.d/ip_tables restart command, the kernel panic does not occur. So I think this is the current best workaround against this kernel panic of kernel-smp-2.6.9-78.* (1-13) relating to [ip_conntrack] or [ip_tables]. PS: This problem does not occure at SL 5.2 (kernel 2.6.18-*) Best Regards, Takashi Ichihara (RIKEN)