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:e5:69 [ether] on eth0 ? (169.254.128.5) at fe:ee:0b:ca:e5:69 [ether] on eth0 ? (169.254.0.15) at fe:ee:0b:ca:e5:69 [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 65535 bytes IP (tos 0x0, ttl 64, id 27024, offset 0, flags [DF], proto ICMP (1), length 694) 172.21.0.10 > 118.89.235.163: ICMP echo request, id 14038, seq 6, length 674 IP (tos 0x0, ttl 63, id 27024, offset 0, flags [DF], proto ICMP (1), length 694) 118.89.235.163 > 172.21.0.10: ICMP echo request, id 14038, seq 6, length 674
tcpdump抓取某个端口的数据
tcpdump -n -i eth0 port 23
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 12345 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 23
查看某个端口网络状态
netstat -nt | grep 23
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 12345 IP 192.168.1.101.41308 > 192.168.1.100.italk: Flags [S], seq 1549300689, win 29200, options [mss 1460,sackOK,TS val 2165838 ecr 0,nop,wscale 7], length 0 IP 192.168.1.100.italk > 192.168.1.101.41308: Flags [S.], seq 4085419987, ack 1549300690, win 1448, options [mss 1460,sackOK,TS val 2095126 ecr 2165838,nop,wscale 7], length 0 IP 192.168.1.101.41308 > 192.168.1.100.italk: Flags [.], ack 1, win 229, options [nop,nop,TS val 2165839 ecr 2095126], length 0 IP 192.168.1.101.41308 > 192.168.1.100.italk: Flags [P.], seq 1:513, ack 1, win 229, options [nop,nop,TS val 2165839 ecr 2095126], length 512 IP 192.168.1.100.italk > 192.168.1.101.41308: Flags [.], ack 513, win 8, options [nop,nop,TS val 2095126 ecr 2165839], length 0 IP 192.168.1.101.41308 > 192.168.1.100.italk: Flags [F.], seq 513, ack 1, win 229, options [nop,nop,TS val 2165839 ecr 2095126], length 0 IP 192.168.1.100.italk > 192.168.1.101.41308: Flags [F.], seq 1, ack 514, win 12, options [nop,nop,TS val 2095127 ecr 2165839], length 0 IP 192.168.1.101.41308 > 192.168.1.100.italk: Flags [.], ack 2, win 229, options [nop,nop,TS val 2165840 ecr 2095127], length 0
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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