resolv.conf随便乱设置的后果
前两天给一台机器设置了iptables规则，之后用命令iptables -L查看规则的时候，发现命令运行的很慢，当初以为是机器负载高没注意，今天在机器上又执行了一遍，发现还是一如既往的卡，这下很奇怪了，用strace跟踪了以下，发现没什么异常，就是ioctl比其他系统调用稍微有点长，但是估算了一下也不会卡的这么离谱，因为当时系统几乎没有负载，又扫了一遍strace的跟踪结果，发现有几个socket调用耗时都在5s以上：
0.000072 socket(PF_FILE, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 4
0.000056 connect(4, {sa_family=AF_FILE, path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)
0.000052 socket(PF_FILE, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 4
0.000050 connect(4, {sa_family=AF_FILE, path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)
0.000096 socket(PF_INET, SOCK_DGRAM|SOCK_NONBLOCK, IPPROTO_IP) = 4
5.005054 socket(PF_INET, SOCK_DGRAM|SOCK_NONBLOCK, IPPROTO_IP) = 5
0.000079 socket(PF_INET, SOCK_RAW, IPPROTO_RAW) = 4
0.000071 socket(PF_FILE, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 4
0.000054 connect(4, {sa_family=AF_FILE, path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)
0.000050 socket(PF_FILE, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 4
0.000064 connect(4, {sa_family=AF_FILE, path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)
0.000061 socket(PF_INET, SOCK_DGRAM|SOCK_NONBLOCK, IPPROTO_IP) = 4
5.005085 socket(PF_INET, SOCK_DGRAM|SOCK_NONBLOCK, IPPROTO_IP) = 5
0.000061 socket(PF_INET, SOCK_DGRAM|SOCK_NONBLOCK, IPPROTO_IP) = 4
5.005134 socket(PF_INET, SOCK_DGRAM|SOCK_NONBLOCK, IPPROTO_IP) = 5
0.000063 socket(PF_INET, SOCK_DGRAM|SOCK_NONBLOCK, IPPROTO_IP) = 4
5.005065 socket(PF_INET, SOCK_DGRAM|SOCK_NONBLOCK, IPPROTO_IP) = 5
0.000061 socket(PF_INET, SOCK_DGRAM|SOCK_NONBLOCK, IPPROTO_IP) = 4
5.005189 socket(PF_INET, SOCK_DGRAM|SOCK_NONBLOCK, IPPROTO_IP) = 5
0.000062 socket(PF_INET, SOCK_DGRAM|SOCK_NONBLOCK, IPPROTO_IP) = 4
5.005199 socket(PF_INET, SOCK_DGRAM|SOCK_NONBLOCK, IPPROTO_IP) = 5
0.000063 socket(PF_INET, SOCK_DGRAM|SOCK_NONBLOCK, IPPROTO_IP) = 4
5.005187 socket(PF_INET, SOCK_DGRAM|SOCK_NONBLOCK, IPPROTO_IP) = 5
然后发现在socket建立的时侯dns解析到几个不知名的ip上面去了，应该是这一造成iptables命令输出结果比较卡的，于是查看resolv.conf文件，发现果然里面配置有问题，遂替换成正常的dnsip后，再次执行iptables命令时就恢复正常了。
