Hi, all, I am a tyro to the Linux. Recently a problem hits me. I am writing a simple IDS, and I am going to use netfilter in my program. Unfortunately, when I add "#include <linux/skbuff.h>" to the head file, I get lots of redefinition errors, like this: "/usr/include/linux/xxxx.h:22: redefinition of `struct xx', /usr/include/bits/xxxx.h:310: previous definition of `struct xx'". The following are head files that have been included: //////////////////////////// #include <netinet/in.h> #include <netinet/ip.h> #include <netinet/tcp.h> #include <netinet/udp.h> #include <netinet/ip_icmp.h> #include <netinet/if_ether.h> #include <string.h> #include <stdlib.h> #include <stdio.h> #include <signal.h> #include <unistd.h> #include <sys/types.h> #include <sys/socket.h> #include <sys/ioctl.h> #include <linux/sockios.h> #include <linux/if.h> //////////////////////////// Would you please give me a hand? Thank you very much. Yours truely, Jiangbo pirate@xxxxxxxxxxxx 2002-11-07