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A free scan shows the junk files, broken settings and background clutter dragging Windows down - then fixes them in one click.Free scan · Windows 10 & 11If ping 203.0.113.25 succeeds but ping server.example returns unknown host, your network path is probably working and hostname resolution is not. The IP test goes straight to an address; the hostname test must first pass through Linux’s name-service stack, including /etc/hosts, DNS, NSS, and sometimes mDNS or a local resolver.
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Fix the failing layer rather than changing routes or firewall rules at random. Confirm the name, test the same lookup path applications use, inspect resolver ownership and configuration, then make the correction in the service that manages your DNS settings.
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A successful IP ping proves only that the kernel can send traffic to that address and receive replies (subject to the limits of ICMP and the remote host’s firewall). It does not prove that Linux can translate a name into an address. Name translation happens before ping opens its network connection.
SUSE’s administration guidance describes this condition directly: when ping reports unknown host, “the name service is not configured correctly or the host name used was incorrect.” The two broad possibilities are therefore a wrong name and a broken local lookup path. A typo, an incomplete short name, a missing search domain, an unavailable DNS server, an incorrect NSS rule, or an mDNS mismatch can all produce the same symptom.
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The most useful distinction is whether every lookup method fails or only one. Linux applications normally use the Name Service Switch (NSS) through the system resolver libraries. A tool such as host or dig can query DNS more directly, so it may succeed while an application using NSS still fails.
Run a short diagnostic sequence first
Use the exact hostname that fails, replacing NAME below. Run these commands as the affected user; elevated privileges are not needed for reading the usual files.
- Verify spelling and qualification. Try the fully qualified domain name (FQDN), such as
server.example.com, rather than relying on a short name such asserver. A short name works only when an appropriatesearchdomain is configured. - Test the application lookup path. Run
getent hosts NAME. This uses NSS, the path most command-line programs and many libraries use. An address line means NSS resolved the name; no output or a “not found” result means the NSS path did not. - Compare another resolver client. Run
host NAMEor, on systems using systemd-resolved,resolvectl query NAME. SUSE recommendshostfor checking whether a hostname translates to an address. Record whether the result contains an address, an authoritative error such asNXDOMAIN, or a timeout. - Identify the resolver in use. Check
systemctl status systemd-resolvedandresolvectl statuswhen systemd-resolved may be present. Also inspect the target of/etc/resolv.confwithls -l /etc/resolv.conf. The symlink and service status reveal whether a local stub, NetworkManager, DHCP client, or a static file owns the settings. - Inspect the two key configuration files. Read
/etc/resolv.confand/etc/nsswitch.conf. Look for valid nameservers, search domains, and a sensiblehosts:line. - Query a DNS server directly. If
digis installed, rundig NAME @SERVER, replacingSERVERwith a nameserver shown by your configuration. A timeout points to reachability, filtering, or a server problem. A valid DNS answer combined with a failinggetentresult points toward NSS ordering, local policy, or caching.
Keep the results together. The combination of getent, host/resolvectl, and direct dig testing usually identifies the layer without guesswork.
Check /etc/resolv.conf without breaking resolver ownership
/etc/resolv.conf records the nameserver addresses and, commonly, the search domain used by the host. A typical static-looking file contains one or more lines such as nameserver 192.0.2.53 and possibly search example.com. An empty file, an unreachable private address, or a stale nameserver from an old network explains why IP traffic works while names fail.
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Do not assume that the visible file is the authoritative configuration. On many distributions it is a symbolic link generated by systemd-resolved or NetworkManager. A hand edit can appear to fix the problem, then disappear after a reboot, DHCP lease renewal, VPN connection, or network restart. First determine which component owns the file; then change the DNS server or search domain in that component’s configuration.
What to verify
- At least one listed
nameserveris reachable from the current network and is intended for this connection. - The
searchdomain matches the local network or VPN when you expect short names to work. - There are no stale entries from a disconnected interface, previous VPN, or old office network.
- The file’s format is valid: one directive per line, with no copied prompt characters or unrelated text.
If DHCP or NetworkManager normally supplies DNS, renew the connection or restart that manager after correcting its settings instead of repeatedly editing the generated file.
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Inspect NSS: the hosts: line controls lookup order
NSS determines where Linux looks for host information and in what order. Open /etc/nsswitch.conf and locate the line beginning with hosts:. A common baseline is:
hosts: files dns
Here, files checks /etc/hosts first and dns then consults the configured DNS resolver. Real systems may add modules for mDNS, LDAP, or local caches. The order and return conditions matter: a module can stop the search before DNS is attempted.
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Correct an early-return rule
One failure pattern documented for Red Hat systems involves an erroneous [NOTFOUND=return] action or stale caching module. If an earlier source reports “not found” and the action says to return immediately, the DNS module later on the line is never reached. Remove the bad action or place the intended DNS source where it can be consulted, preserving any organization-required modules.
After changing NSS, test with getent hosts NAME rather than relying only on host. The goal is for the same path used by ordinary applications to return an address.
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When systemd-resolved is involved
systemd-resolved can provide a local stub resolver, per-link DNS servers, split DNS domains, and caching. Start with:
systemctl status systemd-resolvedresolvectl status
resolvectl status shows global and link-specific DNS servers, search domains, and routing domains. A VPN interface may own a private DNS server for internal names while the normal interface handles public names. If the required link is down, has no DNS server, or lacks the routing domain for the name, the query can fail even though an IP address remains reachable.
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Check where /etc/resolv.conf points. A design using the systemd-resolved stub normally points to a resolver-managed file; replacing that link with a manually maintained file can bypass the intended per-link behavior. Conversely, a system that does not run systemd-resolved should not point at a stub address that has no listener.
Once the owning design is clear, reconnect the affected link, renew its DHCP information, or correct the resolver manager’s DNS and domain settings. Then rerun resolvectl query NAME and getent hosts NAME.
Common causes and targeted fixes
A typo or missing domain suffix
Try the exact FQDN. If getent hosts server fails but getent hosts server.example.com works, add the correct search domain through DHCP, NetworkManager, systemd-resolved, or the relevant network profile. Do not add a random public suffix: short-name expansion is local policy, not a universal DNS feature.
Stale or invalid DNS servers
If host NAME and dig NAME @SERVER time out, test each configured server separately. Restore the DNS servers supplied by the current network, DHCP lease, VPN, or resolver manager. In one systemd incident, adding nameserver 8.8.8.8 to /etc/resolv.conf immediately restored hostname queries; that is evidence of a missing server, not a general instruction to hard-code a public resolver. Use the DNS service appropriate to the network, especially when internal names are required.
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An incorrect /etc/hosts entry
Review /etc/hosts for a wrong address, duplicate name, or missing private mapping. Because files commonly precedes dns, an incorrect local line can make Linux use the wrong address or prevent the expected DNS result. Correct or remove the stale line, then verify with getent hosts NAME.
“.local” names and mDNS
Names ending in .local are often multicast DNS (mDNS), not ordinary unicast DNS. Inspect the hosts: line for entries such as mdns4_minimal [NOTFOUND=return]. Micro Focus documents cases where this rule causes ping to report unknown host even though host or nslookup can resolve the same name through DNS. Decide whether the name is intended to be mDNS or ordinary DNS, then configure the matching NSS module and service; do not blindly remove mDNS support if local discovery depends on it.
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A private hostname may resolve only while a VPN interface is connected. Compare resolvectl status before and after connecting the VPN and look for the domain’s routing rule and DNS server. If the name is sent to the public resolver instead of the private one, correct the VPN profile or resolver manager rather than changing the remote host’s IP.
Make the repair persistent
Resolver state has an owner. Common owners include DHCP, NetworkManager, systemd-resolved, a VPN client, or a deliberately static configuration. Make the change there:
- DHCP-managed links: correct the DHCP-provided DNS or renew the lease after fixing the network.
- NetworkManager profiles: update the connection’s DNS and search-domain settings, then reactivate the connection.
- systemd-resolved: configure per-link or global DNS through the service’s supported interface and verify with
resolvectl status. - Static servers: maintain
/etc/resolv.confas a static file only when no other manager is expected to generate it. - VPN clients: ensure the client installs the private DNS server and routing domain on connection and removes them on disconnect.
A manual edit to a generated /etc/resolv.conf is a useful diagnostic experiment, but it is not a durable fix if another service will overwrite it.
Compare the resolver designs before changing anything
| Question | What to inspect | Why it matters |
|---|---|---|
| Who owns resolver configuration? | Symlink target of /etc/resolv.conf, service status, network manager, VPN client |
Editing the wrong layer will be overwritten or bypassed |
| Which DNS servers are active? | resolv.conf and resolvectl status |
An unreachable or inappropriate server causes timeouts or NXDOMAIN |
| What is the NSS order? | hosts: in /etc/nsswitch.conf |
Early-return rules or stale caches can prevent DNS from running |
| What kind of name is this? | Ordinary DNS, split DNS, private zone, or .local mDNS |
Each type requires the corresponding server, routing, or NSS module |
| Which tools disagree? | getent, host, resolvectl, and dig |
Disagreement identifies whether the fault is DNS itself or the local lookup path |
Verify the result and avoid false conclusions
- Run
getent hosts NAMEand confirm the expected address. - Run
ping NAMEand verify that it uses the same address you intended; DNS may return multiple addresses. - Repeat the test after reconnecting the network, renewing DHCP, or reconnecting the VPN, depending on the original failure.
- Test a public name and the affected private name separately. A public success does not prove that split-DNS routing is correct.
- Check applications that originally failed. Some programs cache DNS independently, so restart that application after changing resolver state.
If the IP ping later fails too, you have a separate routing, firewall, ICMP, or remote-host problem. Keep that investigation distinct from the original name-resolution error.
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