/etc/hosts (Manual Host Resolution)
/etc/hosts is a text file that maps hostnames to IP addresses directly, before querying a DNS server. It is widely used as a convenient shortcut when you want to use domain names in a local development or test environment without registering them in DNS. The lookup priority — "check file first, then query DNS" — is controlled by the /etc/nsswitch.conf configuration.
Syntax
# -----------------------------------------------
# /etc/hosts format
# -----------------------------------------------
# {IP address} {hostname} [{alias} ...]
# → Fields are separated by spaces or tabs
# → One IP address per line
# → Multiple hostnames (aliases) can be added to the same IP
# → Everything after # is a comment
# Example: 192.168.1.10 goku.local goku
# -----------------------------------------------
# Loopback addresses (included by default)
# -----------------------------------------------
# 127.0.0.1 localhost
# → IPv4 loopback address
# → Refers to the local machine itself
# ::1 localhost
# → IPv6 loopback address
# -----------------------------------------------
# hosts entry in /etc/nsswitch.conf
# -----------------------------------------------
# hosts: files dns
# → "files" comes first, so /etc/hosts takes priority over DNS
# → "dns" uses the DNS server specified in /etc/resolv.conf
# Example: hosts: files mdns4_minimal [NOTFOUND=return] dns
# → Configuration example when also consulting mDNS (Avahi)
# -----------------------------------------------
# Note: Wildcards are not supported
# -----------------------------------------------
# Wildcard entries such as *.local are not valid in /etc/hosts
# Each hostname must be listed on its own line
Syntax Reference
| Item | Description |
|---|---|
| IP address | An IPv4 or IPv6 address written at the start of each line. This is the destination that the hostname resolves to. |
| Hostname (FQDN) | Written after the IP address. It is common to specify a fully qualified domain name such as goku.local. |
| Alias (short name) | Additional names added after the hostname, separated by spaces. Used to assign multiple names to the same IP address. |
| Comment | Everything after # is treated as a comment and ignored. Comments can also appear at the end of a line. |
| 127.0.0.1 loopback | The IPv4 loopback address. Assigned to localhost and included in the file by default. |
| ::1 loopback | The IPv6 loopback address. Assigned to localhost and included in the file by default. |
| No wildcards | Wildcard entries such as *.local are not supported. Each hostname you want to match must be listed on its own line. |
| Priority in /etc/nsswitch.conf | With the setting hosts: files dns, /etc/hosts (files) is consulted before DNS. Changing this order may cause /etc/hosts to be bypassed. |
| Required permissions | Root privileges are required. Edit the file with sudo vi /etc/hosts or sudo nano /etc/hosts. |
| Immediate effect | Changes take effect as soon as the file is saved. No OS restart or service restart is required. However, applications that cache DNS lookups may need to be restarted. |
Example
/etc/hosts
# ----------------------------------------------- # /etc/hosts example for a local development environment # ----------------------------------------------- # Loopback (default settings) 127.0.0.1 localhost ::1 localhost # ----------------------------------------------- # Service hosts for the Dragon Ball development team # ----------------------------------------------- # Goku's frontend development server 127.0.0.1 goku.local # Vegeta's API server (with alias) 127.0.0.1 vegeta.local vegeta-api.local # Piccolo's database admin panel 127.0.0.1 piccolo.local # Krillin's staging environment (tested with a production-like setup) 192.168.1.20 krillin-staging.local staging.local # Trunks's future environment test server 192.168.1.30 trunks-future.local # ----------------------------------------------- # Blocking (redirect ads and trackers to loopback) # ----------------------------------------------- # To block access to a specific domain, point it to 0.0.0.0 or 127.0.0.1 0.0.0.0 ads.example.com
Run the following command:
$ ping -c 2 goku.local PING goku.local (127.0.0.1) 56(84) bytes of data. 64 bytes from localhost (127.0.0.1): icmp_seq=1 ttl=64 time=0.041 ms 64 bytes from localhost (127.0.0.1): icmp_seq=2 ttl=64 time=0.045 ms --- goku.local ping statistics --- 2 packets transmitted, 2 received, 0% packet loss, time 1000ms rtt min/avg/max/mdev = 0.041/0.043/0.045/0.002 ms $ curl -I http://vegeta-api.local/ HTTP/1.1 200 OK Server: nginx/1.24.0 Content-Type: application/json $ getent hosts krillin-staging.local 192.168.1.20 krillin-staging.local
Overview
/etc/hosts is the most fundamental name resolution mechanism that Linux reads at startup. It is used in a variety of situations — such as environments without a DNS server, environments without network access, or verifying a configuration before registering a domain in production DNS — to map domain names directly to IP addresses. When /etc/nsswitch.conf contains hosts: files dns, the entries in /etc/hosts take priority over DNS, so you can point an existing domain to a different IP locally. Note that wildcards are not supported, so if you need multiple subdomains, each one must be listed on its own line. For configuring network interface IP addresses, see network_interface. For file-based management of user authentication information, see passwd / shadow.
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