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If Linux can ping a server’s IP address but reports unknown host for the same server name, the network path is probably working and hostname resolution is not. An IP ping skips DNS and the rest of the host-name service (NSS) chain; a hostname ping must pass through it. Check the name, then trace the exact lookup path with getent, inspect /etc/resolv.conf and /etc/nsswitch.conf, and repair the resolver service that owns those settings.
What “unknown host” means when the IP responds
When you run ping 203.0.113.25, Linux already has an address, so it sends packets without looking up a name. When you run ping app.example.net, the ping program first asks the system name-service path to translate app.example.net into an address. That path can include /etc/hosts, DNS, systemd-resolved, multicast DNS (mDNS), caches and other NSS modules.
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Therefore, a successful IP ping proves only that routing and basic reachability to that address work. It does not prove that a DNS server is configured, reachable, authoritative for the name, or being consulted by applications. SUSE’s administration guidance summarizes the symptom directly: if ping fails with unknown host, “the name service is not configured correctly or the host name used was incorrect.”
Start by checking spelling and whether you are using a short name that requires a search domain. A name such as database may need to become database.corp.example; a typo will produce the same error as a broken resolver.
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Run the same lookup path that applications use
Use this sequence in order. It separates a bad name from a DNS-server problem and from a local NSS configuration problem.
- Ask NSS with
getent. Rungetent hosts NAME. This uses the host lookup order in/etc/nsswitch.conf, which is normally the path used by programs such as ping, curl and many package managers. If it prints an address, the system resolver can resolve the name even if ping was given a different spelling or search context. - Query DNS-oriented tools for comparison. Run
host NAMEor, on a system using systemd-resolved,resolvectl query NAME. SUSE recommendshostto check whether a hostname translates to an address. These commands help show whether DNS itself answers independently of the NSS order. - Record the exact error and name form. Test the fully qualified name (for example,
server.example.net.with a final dot) and the short name separately. A fully qualified query bypasses search-list mistakes; a short name depends on thesearchsettings in the resolver configuration.
The combinations are useful:
getent |
host/resolvectl |
Likely direction |
|---|---|---|
| Fails | Fails | No usable DNS answer, unreachable or incorrect nameserver, wrong name, or a name that is not published in the queried DNS domain. |
| Fails | Works | NSS order, an early-return rule, a local cache/module, or an application-facing resolver path is preventing DNS from being used. |
| Works | Works | The resolver is functioning; check the ping command, spelling, search-domain behavior, or an application-specific environment. |
| Works for a fully qualified name only | Works for a fully qualified name only | The short name is missing a correct search domain or the intended suffix is not being applied. |
Inspect /etc/resolv.conf and identify its owner
/etc/resolv.conf records the nameserver and domain information currently used by the host. Display it with:
cat /etc/resolv.conf
Look for one or more nameserver lines and, where short names are expected, a search line. A missing nameserver, an unreachable private address, or a stale VPN nameserver explains why IP connectivity can continue while names fail. A search list that belongs to an old network can also make a valid short name expand incorrectly.
Do not assume that this file is the authoritative configuration. On many Linux installations it is generated by DHCP, NetworkManager, systemd-resolved or another resolver manager. Check whether it is a symbolic link and which service is active:
ls -l /etc/resolv.confsystemctl status systemd-resolvedresolvectl status
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If systemd-resolved is active, resolvectl status shows the global and per-link DNS servers, search domains and routing domains. Confirm that /etc/resolv.conf points to the file or stub interface used by that design. A hand-edited file can appear correct briefly and then be replaced at reboot, DHCP lease renewal or network restart.
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Check NSS lookup order in /etc/nsswitch.conf
NSS decides where Linux looks for host information and when it stops. Inspect the hosts entry:
grep '^[[:space:]]*hosts:' /etc/nsswitch.conf
A common baseline is:
hosts: files dns
Here, Linux checks /etc/hosts first and DNS second. Other systems include modules for systemd-resolved, mDNS or a local cache. The order matters: a module can return a negative result before DNS is attempted.
Check local entries
Open /etc/hosts and look for a wrong address, duplicate name or missing private mapping. A stale entry can send a name to an old server; an expected internal hostname that exists only in a local hosts file will never resolve if that file is absent or malformed.
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Look for early-return rules
Rules such as [NOTFOUND=return] deliberately stop processing when a module says that a name is not found. Red Hat documents failures in which NSS or a caching module prevents DNS from being attempted because of an inappropriate return condition. If host NAME succeeds but getent hosts NAME fails, inspect these bracketed actions and the modules listed before dns. Remove or reorder an erroneous rule according to the resolver design used by the distribution; do not copy a different distribution’s line blindly.
Test the configured DNS server directly
If the dig utility is installed, query the server shown in /etc/resolv.conf or resolvectl status:
dig NAME @SERVER
Replace NAME and SERVER with the real hostname and nameserver address. A timeout indicates that the server is unreachable, blocked, unavailable over the current interface or not listening on DNS. A response containing an address proves that this server can answer the question, but it does not prove that applications are using it.
When dig NAME @SERVER returns a valid answer while getent hosts NAME fails, focus on NSS, a local cache, systemd-resolved routing, or policy software. When the direct query returns NXDOMAIN, the server is reachable but says that the name does not exist in that DNS view. That can be correct for a misspelled name or the wrong split-DNS domain.
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Apply the fix that matches the resolver design
Restore DNS through DHCP, NetworkManager or the active resolver manager
First restore the configuration source that should own DNS. Renew the network connection or reconnect the VPN so the correct nameservers and search domains are supplied. On a system using systemd-resolved, change the DNS settings through the network manager or resolved configuration and then verify with resolvectl status. This is the durable fix because it survives restarts and network changes.
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Use a temporary nameserver only to confirm the diagnosis
In the documented systemd incident, adding nameserver 8.8.8.8 to /etc/resolv.conf restored hostname queries. A similar edit can be a short diagnostic test when policy permits it:
sudo sh -c 'printf "nameserver 8.8.8.8n" > /etc/resolv.conf'
Use the DNS address approved for your network instead when internal names, filtering or split DNS are required. Treat a manual edit as temporary unless you have confirmed that no service manages the file; otherwise it will be overwritten and may expose private queries to an unintended resolver.
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Adjust the hosts: line so that the required sources are present and DNS is reached for ordinary DNS names. Preserve modules your environment needs, such as local files, systemd-resolved or mDNS, and test after each change with getent hosts NAME. Make a backup before editing /etc/nsswitch.conf; a syntax or ordering error can affect every program that resolves hostnames.
Handle .local names as mDNS when appropriate
.local is commonly used for multicast DNS on a local link, not public DNS. Check for an mDNS entry such as mdns4_minimal [NOTFOUND=return] in the hosts: line. Micro Focus has documented cases where that rule makes ping report unknown host even though host or nslookup can resolve the same label through ordinary DNS. Decide whether the name is meant to be mDNS or unicast DNS, then configure the corresponding NSS module and return behavior. A public DNS answer does not automatically make a .local service reachable through mDNS, and vice versa.
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Align systemd-resolved with /etc/resolv.conf
If systemctl status systemd-resolved shows the service is running, confirm that the interface has DNS servers and that the resolver file points to the active design. A running service with an empty link configuration, or a file that points somewhere else, can produce the exact symptom in which IP pings succeed while name pings fail. Correct the link or global DNS settings through the owning network manager, then repeat resolvectl query NAME and getent hosts NAME.
Account for split DNS, search domains and VPNs
Corporate VPNs often provide DNS servers that know internal zones while ordinary internet DNS knows only public names. systemd-resolved can route different domains to different links. If an internal fully qualified name resolves only while the VPN is connected, that behavior may be intentional. Check per-link DNS servers, search domains and routing domains in resolvectl status rather than replacing them with a public server.
For a short name, test the expanded form shown by the intended search domain. If getent hosts printer fails but getent hosts printer.office.example succeeds, repair the search list supplied by DHCP, NetworkManager or the VPN profile. Do not add a search suffix globally if it could cause a sensitive short name to be sent to the wrong DNS service.
Use the results to choose the next action
| Observation | Next check | Typical correction |
|---|---|---|
IP ping works; both getent and host fail |
Read /etc/resolv.conf; run direct dig against its server. |
Restore a reachable, authoritative nameserver through the service that owns DNS. |
host works; getent fails |
Inspect the hosts: line, bracketed return actions and local cache modules. |
Correct NSS order or an early-return rule. |
resolvectl query fails on one link only |
Review per-link DNS and routing domains in resolvectl status. |
Repair the VPN, DHCP or interface-specific DNS configuration. |
| FQDN works; short name fails | Check search and routing-domain settings. |
Restore the intended search suffix or use the FQDN. |
.local fails in ping but appears in DNS tools |
Inspect mDNS NSS modules and [NOTFOUND=return]. |
Configure mDNS for a local-link name or use the correct unicast DNS name. |
Verify the repair and make it persistent
- Run
getent hosts NAMEand confirm the expected address. - Run
host NAMEorresolvectl query NAMEto confirm the DNS view you intend to use. - Ping the hostname with a limited count, for example
ping -c 3 NAME. A resolved name with packet loss is now a reachability or firewall issue, not an unknown-host error. - Restart the network connection or renew its lease, then repeat the lookup. This catches fixes that were only temporary edits to a generated file.
- Test both an internal name and a public name if the machine uses split DNS, and test a
.localname separately if mDNS is required.
The durable solution is the one that survives the event that originally caused the failure: reboot, DHCP renewal, VPN connect or disconnect, network-manager restart, or resolver-service restart. Keep the nameserver ownership, NSS order and name type aligned; changing only the command that happens to work can leave other applications broken.
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