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DNS is a shared, hierarchical service for finding records across a network; a hosts file is a local text file that maps names to addresses on one machine. Use a hosts-file entry for a small, intentional, machine-specific override or bootstrap mapping. Use DNS when names need to be shared, centrally maintained, or changed across a network.
How DNS and a hosts file differ
Both can help translate a hostname into an IP address, but they operate at different scales and are managed differently. A hosts file contains explicit mappings read locally. DNS stores resource records on networked servers and distributes responsibility through a hierarchy.
| Question | Hosts file | DNS |
|---|---|---|
| Where does it apply? | To the machine that reads the file. | Across clients that use the relevant DNS service. |
| Where are mappings maintained? | In a text file maintained on each relevant machine. | On DNS servers, with responsibility partitioned through the hierarchy. |
| What can it represent? | Explicit address-to-hostname mappings and aliases. | Multiple resource-record types, not only hostname-to-address mappings. |
| Best fit | Small, stable local mappings, bootstrapping, isolated systems, or deliberate overrides. | Shared, growing, or changing name spaces. |
How does the hosts file work?
The file is a plain-text list of address and hostname mappings. A line can associate an IPv4 or IPv6 address with a canonical hostname and aliases. If the machine’s name-resolution path reads a matching entry, it can use that local mapping rather than needing to obtain the address from a DNS server.
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Because the mapping is local, it affects only machines with the corresponding entry. A stale or incorrect entry can therefore send that machine to an unintended address until the entry is corrected or removed. On Linux, the file is commonly /etc/hosts. Microsoft documents the Windows path as %SystemRoot%System32DriversEtchosts.
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How DNS handles names differently
DNS is a naming service built around resource records and a hierarchical namespace. Rather than copying one ever-growing flat file to every computer, responsibility for information can be divided among DNS servers. That distribution makes DNS a better fit as networks and their name spaces grow or change.
DNS also supports record types beyond basic hostname-to-address mappings. Responses may be cached; DNS records can specify a time to live (TTL), which bounds how long a cached answer is intended to remain valid.
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What happens during a lookup?
There is no safe universal rule that the hosts file always wins or that DNS is always checked first. The lookup path depends on the operating system, its resolver configuration, and sometimes the application.
Windows
In the Windows flow Microsoft documents, the DNS Client checks its resolver cache, which can include mappings loaded from the hosts file as well as DNS answers retained according to their TTL. If the name is not resolved locally, the client can query a DNS server. A DNS server may answer from its own cache or continue querying other servers. Treat this as a Windows-specific description, not a rule for every platform or configuration.
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Linux name resolution commonly uses the Name Service Switch (NSS) framework. The order and sources are configured through /etc/nsswitch.conf, so the exact sequence can vary. The Linux hosts(5) manual says edits to /etc/hosts normally take effect immediately, except when an application caches file content.
Other systems
Resolver behavior is platform-specific. For macOS or another system, check current operating-system documentation and the machine’s resolver configuration rather than assuming it follows the Windows or Linux examples above.
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Choose a hosts-file entry for a local, limited need
- You need a mapping on one machine rather than throughout a network.
- You are bootstrapping a system or working with an isolated machine.
- You need a deliberate local override and can track and remove it when it is no longer needed.
Each machine that needs the mapping must have the appropriate local entry, so manual maintenance becomes awkward when the list is large or changes often.
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Choose DNS for shared or changing names
- Multiple machines need consistent name resolution.
- Records need to be centrally maintained as machines or addresses change.
- The name space is large enough to benefit from hierarchy and distributed responsibility.
- You need DNS record types beyond simple local hostname-to-address mappings.
Where to find the hosts file
| Platform | Location or guidance | Resolver detail |
|---|---|---|
| Linux | /etc/hosts is the common location. |
Lookup sources and order depend on NSS configuration, including /etc/nsswitch.conf. |
| Windows | %SystemRoot%System32DriversEtchosts |
The Windows DNS Client loads configured mappings into its resolver cache; the broader process depends on configuration. |
| macOS | Consult current Apple documentation or the system’s resolver configuration. | No platform-specific lookup order is established here. |
What to check if a change does not take effect
- Confirm that the entry is in the hosts file on the machine making the request, and that the hostname and address are correct.
- Check the operating system’s resolver configuration; lookup order is not identical across platforms.
- Allow for application or operating-system caching. On Windows, hosts-file mappings are loaded into the DNS Client resolver cache; on Linux, an application may cache file contents.
- Remove temporary overrides when they are no longer intended, so they do not continue directing that machine to an outdated address.
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