Linux高性能服务器编程，书中的 shell 命令

记录《Linux高性能服务器编程》书里面讲解到的若干 shell 命令

arp 命令查看ARP高速缓存：

[root@VM_0_10_centos heliang]# arp -a
? (169.254.128.11) at fe:ee:0b:ca:e5: [ether] on eth0
? (169.254.128.5) at fe:ee:0b:ca:e5: [ether] on eth0
? (169.254.0.15) at fe:ee:0b:ca:e5: [ether] on eth0

所有知名应用层协议使用的端口号可以在  /etc/services  文件中找到

cat  /etc/servies

tcpdump抓包

tcpdump -i eth0 -ent

DNS服务器IP地址

cat  /etc/resolv.conf

根据域名查出ip

[heliang@localhost Desktop]$ host -t A  7haogonglu.com
7haogonglu.com has address 118.89.235.163
 
[heliang@localhost Desktop]$ host -t A www.baidu.com
www.baidu.com is an alias for www.a.shifen.com.
www.a.shifen.com has address 112.80.248.75
www.a.shifen.com has address 112.80.248.76

tcpdump观察 ipv4头部结构

 tcpdump -ntx -i lo

然后，打开另一个终端，输入下面的 telnet命令

 telnet 127.0.0.1

如果你电脑提示，没有telnet命令，请参考这里的文档。

用-s 选项指定要发送的字节数

[heliang@VM_0_10_centos ~]$ ping 7haogonglu.com  -s 666
PING 7haogonglu.com (118.89.235.163) 666(694) bytes of data.
674 bytes from 118.89.235.163: icmp_seq=1 ttl=63 time=0.443 ms

只抓取  ICMP  报文

[root@VM_0_10_centos heliang]# tcpdump -ntv -i eth0 icmp
tcpdump: listening on eth0, link-type EN10MB (Ethernet), capture size  bytes
IP (tos 0x0, ttl , id , offset , flags [DF], proto ICMP (), length )
    172.21.0.10 > 118.89.235.163: ICMP echo request, id , seq , length
IP (tos 0x0, ttl , id , offset , flags [DF], proto ICMP (), length )
    118.89.235.163 > 172.21.0.10: ICMP echo request, id , seq , length 

tcpdump抓取某个端口的数据

tcpdump  -n  -i  eth0  port    

nc 网络命令，监听12345端口数据（没有这个命令的，需要安装:    yum  install  -y   nc）

nc  -p    127.0.0.1

iperf网络工具，没有的需要安装

yum   -y   install   iperf
 
iperf  -s 

修改squid配置文件

vi   /etc/squid/squid.conf

telnet 远程登录

telnet  192.168.12.10   

查看某个端口网络状态

netstat  -nt | grep  

可以通过修改内核参数来快速回收被关闭的socket

vi  /proc/sys/net/ipv4/tcp_tw_recycle 

修改内核参数，来强制TCP接收缓冲区和发送缓冲区的大小没有限制

vi  /proc/sys/net/ipv4/tcp_rmem 
 
vi  /proc/sys/net/ipv4/tcp_wmen

监听某个端口的数据情况

 tcpdump -nt -i eth0 port 12345

tcpdump -nt -i eth0 port 
 
IP 192.168.1.101. > 192.168.1.100.italk: Flags [S], seq , win , options [mss ,sackOK,TS val  ecr ,nop,wscale ], length 
 
IP 192.168.1.100.italk > 192.168.1.101.: Flags [S.], seq , ack , win , options [mss ,sackOK,TS val  ecr ,nop,wscale ], length 
 
IP 192.168.1.101. > 192.168.1.100.italk: Flags [.], ack , win , options [nop,nop,TS val  ecr ], length 
 
IP 192.168.1.101. > 192.168.1.100.italk: Flags [P.], seq :, ack , win , options [nop,nop,TS val  ecr ], length 
 
IP 192.168.1.100.italk > 192.168.1.101.: Flags [.], ack , win , options [nop,nop,TS val  ecr ], length 
 
IP 192.168.1.101. > 192.168.1.100.italk: Flags [F.], seq , ack , win , options [nop,nop,TS val  ecr ], length 
 
IP 192.168.1.100.italk > 192.168.1.101.: Flags [F.], seq , ack , win , options [nop,nop,TS val  ecr ], length 
 
IP 192.168.1.101. > 192.168.1.100.italk: Flags [.], ack , win , options [nop,nop,TS val  ecr ], length 

gethostbyname通常先在本地 /etc/hosts 配置文件中查找主机，如果没有找到，再去访问DNS服务器

vi  /etc/hosts

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