hosts文件是什么？在哪里？
hosts文件：系统文件，可以记事本打开并编辑。
一般用于域名到ip地址的解析。当用户在浏览器中输入网络的域名时，系统首先会自动从hosts文件中找到对应的ip地址，一旦找到，将用该ip地址打开对应的网页。如果没有找到，则系统会在将网址提交到DMS域名解析服务器进行ip地址的解析。
Windows系统hosts位于 C:\Windows\System32\drivers\etc\hosts（需要管理员权限）
Android（安卓）系统hosts位于 /system/etc/hosts（需要root）
windows的默认hosts文件
# Copyright (c) - Microsoft Corp.
#
# This is a sample HOSTS file used by Microsoft TCP/IP for Windows.
#
# This file contains the mappings of IP addresses to host names. Each
# entry should be kept on an individual line. The IP address should
# be placed in the first column followed by the corresponding host name.
# The IP address and the host name should be separated by at least one
# space.
#
# Additionally, comments (such as these) may be inserted on individual
# lines or following the machine name denoted by a '#' symbol.
#
# For example:
#
# 102.54.94.97 rhino.acme.com # source server
# 38.25.63.10 x.acme.com # x client host # localhost name resolution is handled within DNS itself.
# 127.0.0.1 localhost
# :: localhost
修改hosts后生效的方法
cmd中执行
ipconfig /flushdns
当然重启系统等措施也行。