strace -T -t -o /tmp/nohost sqlplus / as sysdba

查看/tmp/nohost内容，此处省略部分内容

1. 10:05:39 munmap(0x7fb66c71c000, 404774) = 0 <0.000082>
2. 10:05:39 socket(PF_INET, SOCK_DGRAM|SOCK_NONBLOCK, IPPROTO_IP) = 9 <0.000094>
3. 10:05:39 connect(9, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_addr("221.228.255.1")}, 16) = 0 <0.000076>
4. 10:05:39 poll([{fd=9, events=POLLOUT}], 1, 0) = 1 ([{fd=9, revents=POLLOUT}]) <0.000061>
5. 10:05:39 sendto(9, "\23\232\1\0\0\1\0\0\0\0\0\0\5test8\0\0\1\0\1", 23, MSG_NOSIGNAL, NULL, 0) = 23 <0.000201>
6. 10:05:39 poll([{fd=9, events=POLLIN|POLLOUT}], 1, 5000) = 1 ([{fd=9, revents=POLLOUT}]) <0.000062>
7. 10:05:39 sendto(9, "\3d\1\0\0\1\0\0\0\0\0\0\5test8\0\0\34\0\1", 23, MSG_NOSIGNAL, NULL, 0) = 23 <0.000098>
8. 10:05:39 poll([{fd=9, events=POLLIN}], 1, 4998) = 1 ([{fd=9, revents=POLLIN}]) <0.006345>
9. 10:05:39 ioctl(9, FIONREAD, [39]) = 0 <0.000063>
10. 10:05:39 recvfrom(9, "\23\232\201\200\0\1\0\1\0\0\0\0\5test8\0\0\1\0\1\300\f\0\1\0\1\0\0\0"..., 2048, 0, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_addr("221.228.255.1")}, [16]) = 39 <0.000096>
11. 10:05:39 poll([{fd=9, events=POLLIN}], 1, 4991) = 0 (Timeout) <4.996143>
12. 10:05:44 poll([{fd=9, events=POLLOUT}], 1, 0) = 1 ([{fd=9, revents=POLLOUT}]) <0.000100>
13. 10:05:44 sendto(9, "\23\232\1\0\0\1\0\0\0\0\0\0\5test8\0\0\1\0\1", 23, MSG_NOSIGNAL, NULL, 0) = 23 <0.000198>
14. 10:05:44 poll([{fd=9, events=POLLIN}], 1, 5000) = 1 ([{fd=9, revents=POLLIN}]) <0.006851>
15. 10:05:44 ioctl(9, FIONREAD, [39]) = 0 <0.000151>
16. 10:05:44 recvfrom(9, "\23\232\201\200\0\1\0\1\0\0\0\0\5test8\0\0\1\0\1\300\f\0\1\0\1\0\0\0"..., 2048, 0, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_addr("221.228.255.1")}, [16]) = 39 <0.000107>
17. 10:05:44 poll([{fd=9, events=POLLOUT}], 1, 4990) = 1 ([{fd=9, revents=POLLOUT}]) <0.000088>
18. 10:05:44 sendto(9, "\3d\1\0\0\1\0\0\0\0\0\0\5test8\0\0\34\0\1", 23, MSG_NOSIGNAL, NULL, 0) = 23 <0.000120>
19. 10:05:44 poll([{fd=9, events=POLLIN}], 1, 4990) = 1 ([{fd=9, revents=POLLIN}]) <0.008139>
20. 10:05:44 ioctl(9, FIONREAD, [98]) = 0 <0.000074>
21. 10:05:44 recvfrom(9, "\3d\201\203\0\1\0\0\0\1\0\0\5test8\0\0\34\0\1\0\0\6\0\1\0\0\35\17"..., 2009, 0, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_addr("221.228.255.1")}, [16]) = 98 <0.000084>
22. 10:05:44 close(9) = 0 <0.000143>
23. 10:05:44 open("/etc/hostid", O_RDONLY) = -1 ENOENT (No such file or directory) <0.000095>
24. 10:05:44 uname({sys="Linux", node="test8", ...}) = 0 <0.000061>

    问题已经浮出水面了，耗时最长的一步是
    
    
    而且卡在此处足足有5s，而且最终超时，根据上下文判断，此处是一个socket连接，而且还涉及到dns服务器的地址，由此推断应该和解析有关
    
    查看/etc/resolv.conf
    
    
    
    可见配置了dns，其实我将dns注释掉之后sqlplus就恢复了正常，但dns不应该成为导致此问题的根本原因，此处明显是去dns上解析本机了
    
    再来看/etc/hosts
    
    
    再重新查阅了hosts的正确配置之后发现我的hosts配置方法是错误的
    
    
    我的主机名是test8，在我测试邮件的时候，为了骗过邮件服务器，我把hosts里解析随意加了个域名，却从未正式了解过hosts的配置方法，现在正确配置一下
    
    
    
    再测试sqlplus，已经恢复正常
    

25. 10:05:39 poll([{fd=9, events=POLLIN}], 1, 4991) = 0 (Timeout) <4.996143>
26. 1. [root@test8 etc]# cat /etc/resolv.conf
    2. # Generated by NetworkManager
    3. #nameserver 221.228.255.1
    4. nameserver 221.228.255.1
    5. nameserver 218.2.135.1
27. 1. [root@test8 etc]# cat /etc/hosts
    2. 127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4
    3. ::1 localhost localhost.localdomain localhost6 localhost6.localdomain6
    4. 192.168.1.8 test8.com
    5. 192.168.1.29 oem.oracle.com
28. 1. 格式：
    2. 　　一般情况下hosts的内容关于主机名(hostname)的定义，每行为一个主机，每行由三部份组成，每个部份由空格隔开。其中#号开头的行做说明，不被系统解释。
    3. 　　第一部份：网络IP地址；
    4. 　　第二部份：主机名.域名，注意主机名和域名之间有个半角的点，比如 localhost.localdomain
    5. 　　第二部份：主机名(主机名别名） ，其实就是主机名；
29. 1. [root@test8 etc]# cat /etc/hosts
    2. 127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4
    3. ::1 localhost localhost.localdomain localhost6 localhost6.localdomain6
    4. 192.168.1.8 test8.com test8
    5. 192.168.1.29 oem.oracle.com