/etc/hosts文件用于將主機(jī)名映射到IP地址，作為DNS的本地手動替代或補(bǔ)充。它在系統(tǒng)連接到主機(jī)名時首先被檢查，可用于本地開發(fā)、網(wǎng)站屏蔽和DNS更改測試。1. 它通過在系統(tǒng)查找順序中優(yōu)先于DNS，實現(xiàn)對域名解析的本地控制；2. 典型用途包括將localhost指向127.0.0.1或?qū)⒆远x域名指向本地IP；3. 常見應(yīng)用場景有本地開發(fā)測試、屏蔽特定網(wǎng)站和預(yù)演DNS變更；4. 編輯需管理員權(quán)限，并應(yīng)遵循格式規(guī)范以避免錯誤。

The /etc/hosts file is a simple text file used by operating systems to map hostnames to IP addresses. It acts as a local, manual alternative or supplement to DNS (Domain Name System). When you type a domain name like example.com into your browser, your system checks the /etc/hosts file first before querying external DNS servers. This means you can use it to override where a domain resolves — useful for testing, development, or blocking certain websites.

How Does the /etc/hosts File Work?

When your computer needs to connect to a hostname, it follows a lookup order defined by the system. On Unix-like systems (including Linux and macOS), this is often controlled by the nsswitch.conf file, which typically lists "files" (i.e., /etc/hosts) before "dns". So the system will check /etc/hosts first, then go to DNS if no match is found.

A typical line in /etc/hosts looks like this:

127.0.0.1   localhost

This tells the system that when you try to access localhost, it should point to the loopback address 127.0.0.1.

You can add custom entries like:

192.168.1.100   mylocalserver

Now typing mylocalserver in a terminal or browser will point to that local machine on your network.

Common Uses of /etc/hosts

There are several practical reasons people edit the /etc/hosts file:

• Local Development: Web developers often map domains like local.dev or mysite.test to 127.0.0.1 so they can test websites locally without needing a live server.
• Blocking Sites: You can redirect unwanted domains (like ad servers or distracting sites) to 127.0.0.1 or 0.0.0.0. For example:

  0.0.0.0   badsite.com

• Testing DNS Changes: Before switching DNS records live, you can simulate how things will behave by temporarily editing hosts.

It's important to note that changes to this file affect only the local machine — not other devices on your network.

How to Edit the /etc/hosts File

Editing /etc/hosts usually requires administrative privileges because it’s a system-level configuration.

On Linux/macOS, you can open it with a text editor like nano or vim using sudo:

sudo nano /etc/hosts

On Windows, it’s located at C:\Windows\System32\drivers\etc\hosts, and you’ll need to open your text editor as an administrator to make changes.

Some basic tips when editing:

• Always back up the original file before making changes
• Use plain text editors — avoid rich-text formats
• Each entry must be on its own line
• Formatting matters: put the IP address first, then one or more spaces or tabs, then the hostname(s)

If something breaks after editing the file, just restore the backup or remove the line causing issues.

That’s the basics of what the /etc/hosts file does and why it matters. It's a small file but surprisingly powerful when used correctly. Just remember — it's easy to mess up if you're not careful, especially on production systems.

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