命令netstat-a停了很长时间没有响应(netstat takes a long time)

这个可能是DNS出了问题。

If netstat -a takes a long time for some connections, it suggests delays in resolving the names from the IP addresses of the connection (or service names from port numbers).

A connection can appear in netstat -a and not appear in lsof output. Lsof will only show those endpoints with a coresponding socket. However, a connection with no socket will only appear in netstat -a and perhaps ndd /dev/tcp tcp_status.

A connection in ESTABLISHED that does not appear in lsof output could possibly be a connection that has been ESTABLISHED, but for which the server application has not called accept(). If it persists for a "long time" it suggests that there is some issue with the server application.

The tcp_discon stuff should be considered a MASSIVE KLUDGE and SHOULD NOT be used except in EXTREME CASES.

I would suggest running the netstat -a command under tusc. Between that, and comparing the performance of netstat -an you will likely see resolution delays. Be sure to add the timestamps to the tusc command, and might as well make it verbose so you can see the bind/connect calls on the SOCK_DGRAM sockets involving port 53 for DNS lookups.

there is no rest for the wicked yet the virtuous have no pillows

看完英文解释，再中文简单解释一下

使用#netstat --help 能够查看帮助信息, 如果只使用-a缺省情况下会进行域名解析，如果域名设置有问题，会造成速度响应慢。

1.如果要解决这个问题，可以使用参数-an,不对域名进行解析。同样的问题，在arp命令、route命令上也存在。

2.如果要解决这个问题，可以查看你的DNS设置，是否DNS不通，或者DNS有故障，在修复后再次尝试。

-a 参数列出所有的socket，

-n 参数不对ip地址进行域名解析，显示数字

[root@xiesshavip002 ~]# netstat --help
usage: netstat [-vWeenNcCF] [] -r         netstat {-V|--version|-h|--help}
       netstat [-vWnNcaeol] [ ...]
       netstat { [-vWeenNac] -I[] | [-veenNac] -i | [-cnNe] -M | -s [-6tuw] } [delay]

        -r, --route              display routing table
        -I, --interfaces= display interface table for 
        -i, --interfaces         display interface table
        -g, --groups             display multicast group memberships
        -s, --statistics         display networking statistics (like SNMP)
        -M, --masquerade         display masqueraded connections

        -v, --verbose            be verbose
        -W, --wide               don't truncate IP addresses
        -n, --numeric            don't resolve names
        --numeric-hosts          don't resolve host names
        --numeric-ports          don't resolve port names
        --numeric-users          don't resolve user names
        -N, --symbolic           resolve hardware names
        -e, --extend             display other/more information
        -p, --programs           display PID/Program name for sockets
        -o, --timers             display timers
        -c, --continuous         continuous listing

        -l, --listening          display listening server sockets
        -a, --all                display all sockets (default: connected)
        -F, --fib                display Forwarding Information Base (default)
        -C, --cache              display routing cache instead of FIB
        -Z, --context            display SELinux security context for sockets

  ={-t|--tcp} {-u|--udp} {-U|--udplite} {-w|--raw} {-x|--unix}
           --ax25 --ipx --netrom
  =Use '-6|-4' or '-A ' or '--'; default: inet
  List of possible address families (which support routing):
    inet (DARPA Internet) inet6 (IPv6) ax25 (AMPR AX.25) 
    netrom (AMPR NET/ROM) ipx (Novell IPX) ddp (Appletalk DDP) 
    x25 (CCITT X.25)