[root@liumiaocn ~]# uname -a
Linux mail.163.com 3.10.0-514.el7.x86_64 #1 SMP Tue Nov 22 16:42:41 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux
[root@liumiaocn ~]# 
[root@liumiaocn ~]# cat /etc/redhat-release 
CentOS Linux release 7.3.1611 (Core) 
[root@liumiaocn ~]#

[root@liumiaocn ~]# rpm -qa |grep squid
squid-migration-script-3.5.20-12.el7.x86_64
squid-3.5.20-12.el7.x86_64
[root@liumiaocn ~]# 

[root@liumiaocn ~]# sysctl -a |grep -w ip_forward
net.ipv4.ip_forward = 1
[root@liumiaocn ~]# 

[root@liumiaocn ~]# grep -n 'http_access deny all' /etc/squid/squid.conf
56:http_access deny all
[root@liumiaocn ~]#

[root@liumiaocn ~]# grep -n http /etc/squid/squid.conf |grep -w all
56:http_access allow all
[root@liumiaocn ~]#

[root@liumiaocn ~]# systemctl start squid
[root@liumiaocn ~]# systemctl status squid
● squid.service - Squid caching proxy
  Loaded: loaded (/usr/lib/systemd/system/squid.service; disabled; vendor preset: disabled)
  Active: active (running) since Tue 2018-06-05 20:07:56 CST; 8s ago
 Process: 28548 ExecStart=/usr/sbin/squid $SQUID_OPTS -f $SQUID_CONF (code=exited, status=0/SUCCESS)
 Process: 28540 ExecStartPre=/usr/libexec/squid/cache_swap.sh (code=exited, status=0/SUCCESS)
 Main PID: 28551 (squid)
  Memory: 14.3M
  CGroup: /system.slice/squid.service
      ├─28551 /usr/sbin/squid -f /etc/squid/squid.conf
      ├─28553 (squid-1) -f /etc/squid/squid.conf
      └─28557 (logfile-daemon) /var/log/squid/access.log
Jun 05 20:07:56 liumiaocn systemd[1]: Starting Squid caching proxy...
Jun 05 20:07:56 liumiaocn squid[28551]: Squid Parent: will start 1 kids
Jun 05 20:07:56 liumiaocn squid[28551]: Squid Parent: (squid-1) process 28553 started
Jun 05 20:07:56 liumiaocn systemd[1]: Started Squid caching proxy.
[root@liumiaocn ~]#

[root@liumiaocn ~]# grep nameserver /etc/squid/squid.conf
dns_nameservers 8.8.8.8 8.8.4.4
[root@liumiaocn ~]# 
[root@liumiaocn ~]# systemctl restart squid
[root@liumiaocn ~]#