代理服务器，可以通过其来实现防火墙功能与网络浏览数据分析等功能。与iptables不同，防火墙功能也是作用在应用层。
[root@paly ~]#yum install squid
Loaded plugins: fastestmirror
Setting up Install Process
Repository base is listed more than once in the configuration
Loading mirror speeds from cached hostfile
base | 3.7 kB 00:00
epel | 4.7 kB 00:00
extras | 3.3 kB 00:00
updates | 3.4 kB 00:00
Package 7:squid-3.1.23-24.el6.i686 already installed and latest version
Nothing to do
[root@paly ~]#vim /etc/squid/mime.conf
[root@paly ~]#vim /etc/squid/squid.conf
[root@paly ~]#id squid
uid=23(squid) gid=23(squid) groups=23(squid),88(wbpriv)
[root@paly ~]#vim /etc/squid/squid.conf
[root@paly ~]#/etc/init.d/squid start
Starting squid: .. [ OK ]
[root@paly ~]#/etc/squid/squid.conf^C
[root@paly ~]#/etc/init.d/squid restart
Stopping squid: 2022/04/06 01:23:17| WARNING: Could not determine this machines public hostname. Please configure one or set 'visible_hostname'.
2022/04/06 01:23:17| WARNING: Could not determine this machines public hostname. Please configure one or set 'visible_hostname'.
................ [ OK ]
Starting squid: ... [ OK ]
[root@paly ~]#hostname
paly
[root@paly ~]#vim /etc/hosts
[root@paly ~]#/etc/init.d/squid restart
Stopping squid: ................ [ OK ]
Starting squid: . [ OK ]
[root@paly ~]#
[root@paly ~]#service iptables stop
iptables: Setting chains to policy ACCEPT: filter [ OK ]
iptables: Flushing firewall rules: [ OK ]
iptables: Unloading modules: [ OK ]
[root@paly ~]#vim /etc/squid/squid.conf
[root@paly ~]#/etc/init.d/squid restart
Stopping squid: ................ [ OK ]
Starting squid: . [ OK ]
[root@paly ~]#vim /etc/squid/squid.conf
[root@paly ~]#/etc/init.d/squid restart
Stopping squid: ................ [ OK ]
Starting squid: . [ OK ]
[root@paly ~]#
[root@paly ~]#netstat -tulnp | grep squid
tcp 0 0 :::3128 :::* LISTEN 21879/(squid)
udp 0 0 0.0.0.0:46476 0.0.0.0:* 21879/(squid)
udp 0 0 :::54449 :::* 21879/(squid)
[root@paly ~]#
