How to Flush DNS Cache in Linux

How to Flush DNS Cache in Linux

Every time you browse the internet, your Linux system quietly stores DNS information in the background, creating a cache that speeds up your web experience. While this mechanism works seamlessly most of the time, there are moments when outdated or corrupted DNS records cause frustrating connectivity issues, slow website loading, or complete inability to access certain domains. Understanding how to clear this cache becomes essential for maintaining a healthy, responsive system that connects reliably to the internet.

DNS cache flushing refers to the process of clearing stored domain name system records from your computer's temporary memory. This action forces your system to retrieve fresh DNS information from authoritative servers, resolving conflicts between cached data and current network configurations. Whether you're troubleshooting connection problems, implementing network changes, or enhancing your privacy, knowing multiple approaches to flush DNS cache gives you control over your system's networking behavior.

Throughout this comprehensive guide, you'll discover practical methods for clearing DNS cache across different Linux distributions and DNS resolver services. You'll learn specific commands for systemd-resolved, dnsmasq, NSCD, and BIND, understand when flushing cache becomes necessary, and gain insights into verifying your actions worked correctly. By the end, you'll possess the knowledge to confidently manage DNS cache on any Linux environment, from desktop workstations to production servers.

Understanding DNS Cache in Linux Systems

DNS caching in Linux operates differently than in Windows or macOS because Linux doesn't implement a system-wide DNS cache by default. Instead, caching behavior depends entirely on which DNS resolver service your distribution uses. Modern Linux systems typically employ systemd-resolved, while others might use dnsmasq, NSCD (Name Service Cache Daemon), or BIND as a local caching nameserver. Each service maintains its own cache with distinct characteristics and clearing procedures.

The absence of a universal caching mechanism means that understanding your specific configuration becomes paramount. Some minimal Linux installations perform DNS lookups directly without any caching layer, sending queries to configured nameservers for every request. This approach eliminates caching concerns but sacrifices the performance benefits of storing frequently accessed DNS records locally. Most desktop and server distributions, however, include at least one caching service to optimize network performance.

"The DNS cache serves as a temporary memory that prevents your system from repeatedly asking the same questions, but when that memory holds wrong answers, clearing it becomes the only solution."

Applications themselves may also implement internal DNS caching independent of system-level services. Web browsers like Firefox and Chrome maintain their own DNS caches, as do some programming language runtimes and network libraries. This layered caching architecture means that truly clearing all DNS information sometimes requires addressing multiple components. However, for most troubleshooting scenarios, clearing the system-level cache resolves the majority of DNS-related issues.

Identifying Your DNS Resolver Service

Before attempting to flush DNS cache, you must determine which resolver service handles DNS on your system. The most reliable method involves checking which processes are listening on port 53 (the standard DNS port) or examining your system's DNS configuration files. Running sudo systemctl status systemd-resolved will immediately reveal if systemd-resolved is active on your distribution. For systems using dnsmasq, the command sudo systemctl status dnsmasq provides similar information.

Examining the /etc/resolv.conf file offers additional clues about your DNS configuration. If this file contains a nameserver entry pointing to 127.0.0.53, your system uses systemd-resolved. An entry pointing to 127.0.0.1 typically indicates dnsmasq or BIND running locally. Some systems use /etc/resolv.conf as a symlink to files managed by systemd or NetworkManager, which you can verify with ls -l /etc/resolv.conf.

Flushing DNS Cache with systemd-resolved

The systemd-resolved service has become the standard DNS resolver for many modern Linux distributions, handling both DNS caching and DNSSEC validation. This service integrates deeply with systemd's networking stack, providing a unified approach to name resolution across the system. Flushing its cache requires specific systemd commands that communicate directly with the resolved daemon rather than traditional service restart procedures.

The primary command for clearing systemd-resolved cache is straightforward and executes instantly without disrupting network connectivity. Open your terminal and execute sudo systemd-resolve --flush-caches or the newer syntax sudo resolvectl flush-caches. Both commands accomplish the same goal, with resolvectl being the preferred method in recent systemd versions. The operation completes silently without output, which is normal behavior indicating successful cache clearing.

"Clearing DNS cache through systemd-resolved happens instantaneously and transparently, making it the most seamless method available on modern Linux distributions."

To verify that the cache flush succeeded, you can examine the current cache statistics using sudo systemd-resolve --statistics or sudo resolvectl statistics. This command displays detailed information about cache entries, including the current cache size, number of hits and misses, and other relevant metrics. Immediately after flushing, you should observe the cache size reset to zero or near-zero values, confirming that stored DNS records have been cleared.

Advanced systemd-resolved Management

Beyond simple cache flushing, systemd-resolved offers granular control over DNS behavior through various configuration options. The main configuration file resides at /etc/systemd/resolved.conf, where you can adjust cache settings, configure DNS servers, enable or disable DNSSEC, and control DNS-over-TLS behavior. Modifications to this file require restarting the systemd-resolved service with sudo systemctl restart systemd-resolved to take effect.

For troubleshooting complex DNS issues, systemd-resolved provides detailed query information through the resolvectl query command. This tool allows you to perform manual DNS lookups while observing which nameservers are contacted, whether results come from cache, and if DNSSEC validation succeeds. Running resolvectl query example.com returns not just the IP address but also metadata about the resolution process, making it invaluable for diagnosing DNS problems.

• 🔄 Automatic cache management: systemd-resolved automatically expires old entries based on TTL values, reducing the need for manual intervention
• 🔒 DNSSEC validation: Built-in support for DNS Security Extensions provides cryptographic verification of DNS responses
• 🌐 Per-interface DNS: Different network interfaces can use different DNS servers, with systemd-resolved intelligently routing queries
• 📊 Comprehensive statistics: Detailed metrics about cache performance help identify patterns and potential issues
• ⚡ Zero-downtime flushing: Cache clearing happens without interrupting active connections or requiring service restarts

Clearing DNS Cache in dnsmasq

The dnsmasq service functions as a lightweight DNS forwarder and DHCP server, popular in home networks, embedded systems, and older Linux distributions. Unlike systemd-resolved, dnsmasq doesn't provide a dedicated command for cache flushing. Instead, you must send a specific signal to the running dnsmasq process or restart the service entirely to clear cached DNS records.

The most elegant method involves sending the HUP signal to dnsmasq, which instructs it to reload its configuration and clear the cache without terminating the service. Execute sudo killall -HUP dnsmasq or identify the process ID with pidof dnsmasq and then run sudo kill -HUP [PID]. This approach maintains service continuity while effectively clearing all cached DNS entries, making it suitable for production environments where service interruption must be minimized.

Alternatively, restarting the dnsmasq service through systemd provides a more forceful cache clearing method. The command sudo systemctl restart dnsmasq stops the service completely, clears all cache and state information, then starts it fresh. This method takes slightly longer than sending a HUP signal but guarantees a completely clean slate, which can be beneficial when troubleshooting persistent DNS issues that might involve corrupted cache data.

Configuring dnsmasq Cache Behavior

The dnsmasq configuration file, typically located at /etc/dnsmasq.conf, contains numerous options for controlling cache size and behavior. The cache-size directive determines how many DNS records dnsmasq stores, with the default usually set to 150 entries. Increasing this value to 1000 or higher improves performance on busy systems but consumes more memory. Setting cache-size=0 completely disables caching, forcing dnsmasq to forward every DNS query to upstream nameservers.

For environments requiring frequent cache clearing, you might consider reducing the cache TTL or implementing automated cache flushing through cron jobs. The max-cache-ttl option limits how long records remain cached regardless of their original TTL values, while min-cache-ttl sets a minimum caching duration. These settings help balance performance with the need for fresh DNS data in dynamic network environments.

"When working with dnsmasq, the HUP signal provides the perfect balance between cache clearing and service continuity, making it ideal for production systems."

Managing NSCD Cache

The Name Service Cache Daemon (NSCD) caches not only DNS lookups but also other name service information like user accounts, groups, and hosts file entries. This broader caching scope makes NSCD particularly useful on systems with network-based authentication mechanisms like LDAP or NIS. However, it also means that clearing NSCD cache affects more than just DNS resolution, potentially impacting user authentication and other name service functions.

Flushing NSCD's DNS cache requires targeting the specific cache database rather than clearing all cached information. The command sudo nscd -i hosts invalidates only the hosts cache, which contains DNS records, leaving other caches intact. This surgical approach prevents unnecessary disruption to authentication services while still clearing problematic DNS entries. For comprehensive cache clearing across all NSCD databases, use sudo nscd -I to invalidate everything simultaneously.

Service restart provides another method for clearing NSCD cache, accomplished through sudo systemctl restart nscd or the older init-style command sudo service nscd restart. This approach completely reinitializes the daemon, clearing all cache databases and resetting statistics. While more disruptive than selective cache invalidation, restarting ensures that no stale data persists anywhere in NSCD's memory structures.

NSCD Configuration and Optimization

The NSCD configuration file at /etc/nscd.conf controls caching behavior for each name service database independently. For the hosts database specifically, parameters like positive-time-to-live and negative-time-to-live determine how long successful and failed DNS lookups remain cached. Adjusting these values helps tune cache behavior to match your network environment's characteristics and change frequency.

Monitoring NSCD's performance and cache effectiveness requires examining its statistics, accessible through nscd -g. This command displays detailed metrics for each cache database, including hit rates, miss rates, current cache size, and query counts. Regular review of these statistics helps identify whether NSCD provides meaningful performance benefits or if alternative caching solutions might better serve your needs.

Flushing BIND DNS Cache

BIND (Berkeley Internet Name Domain) serves as both an authoritative DNS server and a caching resolver, making it common in enterprise environments and custom network configurations. When configured as a caching nameserver, BIND maintains a sophisticated cache that requires specific management tools. The rndc (Remote Name Daemon Control) utility provides the primary interface for managing BIND, including cache manipulation operations.

Clearing BIND's cache involves the command sudo rndc flush, which removes all cached DNS records from memory. This operation executes immediately and doesn't require restarting the named service, allowing BIND to continue serving DNS queries without interruption. For more targeted cache clearing, sudo rndc flushname example.com removes only records associated with a specific domain, useful when troubleshooting issues with particular websites or services.

BIND also supports clearing negative cache entries separately through sudo rndc flushtree example.com, which removes all cached information for a domain and its subdomains. Negative caching stores information about non-existent domains or failed lookups, preventing repeated queries for known-bad domains. Sometimes negative cache entries become problematic when a previously non-existent domain becomes active, making selective negative cache clearing valuable.

Advanced BIND Cache Management

The BIND configuration file, typically /etc/named.conf or /etc/bind/named.conf, contains numerous directives controlling cache behavior. The max-cache-size option limits total cache memory consumption, preventing BIND from exhausting system resources on busy servers. Setting appropriate limits based on your server's available memory and query load ensures stable operation while maximizing cache effectiveness.

Monitoring BIND's cache statistics provides insights into cache performance and helps identify when manual intervention becomes necessary. The command sudo rndc stats generates detailed statistics files containing cache hit rates, query patterns, and resource utilization metrics. Regular analysis of these statistics helps optimize BIND configuration and determine if cache clearing patterns indicate underlying network or DNS infrastructure issues.

"BIND's rndc tool provides surgical precision for cache management, allowing administrators to clear everything or target specific problematic domains without service disruption."

Browser DNS Cache Considerations

Web browsers maintain independent DNS caches separate from system-level resolvers, creating an additional layer that sometimes requires attention during troubleshooting. Firefox, Chrome, Edge, and other browsers cache DNS lookups to accelerate page loading, but this optimization can cause confusion when system-level cache clearing doesn't resolve connection issues. Understanding browser-specific cache mechanisms completes your DNS troubleshooting toolkit.

Firefox stores DNS cache that persists across browsing sessions, accessible through the browser's internal configuration pages. Navigate to about:networking#dns to view current DNS cache entries, then click the "Clear DNS Cache" button to flush them immediately. This operation affects only Firefox's internal cache and doesn't modify system-level DNS information, making it safe to perform without administrative privileges.

Chrome and Chromium-based browsers including Edge use a similar internal caching mechanism. Access the DNS cache interface by navigating to chrome://net-internals/#dns and clicking the "Clear host cache" button. Chrome's implementation integrates more tightly with system DNS than Firefox, but maintaining its own cache layer means clearing system cache doesn't automatically clear browser cache. For complete DNS troubleshooting, clearing both system and browser caches ensures no stale records remain anywhere.

When to Flush DNS Cache

Understanding the appropriate circumstances for clearing DNS cache prevents unnecessary interventions while ensuring you address genuine issues promptly. DNS cache flushing becomes necessary when you encounter specific symptoms that indicate cached records no longer match current DNS configurations. Recognizing these scenarios helps you troubleshoot efficiently without resorting to cache clearing as a first response to every network issue.

Website connectivity problems where some sites load correctly while others fail or load outdated content strongly suggest DNS cache issues. When you can ping a domain's IP address directly but cannot access it by name, or when using different DNS servers resolves the problem, cached records likely contain incorrect information. These situations commonly occur after website migrations, DNS configuration changes, or network infrastructure updates that modify domain-to-IP mappings.

"DNS cache becomes your enemy the moment it stores wrong information, but clearing it indiscriminately wastes time and provides no benefit when the cache functions correctly."

Privacy concerns also motivate DNS cache clearing, as cached records create a history of domains you've accessed. While less comprehensive than browser history, DNS cache reveals which domains your system contacted, potentially exposing sensitive information to anyone with system access. Clearing cache after sensitive browsing sessions or before sharing a computer helps maintain privacy, though dedicated privacy tools provide more comprehensive protection.

Common Scenarios Requiring Cache Clearing

• 🔧 Website migration: After moving a website to new hosting, old IP addresses cached locally prevent accessing the new location
• 🏢 VPN connection changes: Switching between VPN and direct connections sometimes leaves incompatible DNS records cached
• ⚠️ DNS poisoning suspicion: Malicious DNS cache entries can redirect traffic to harmful sites, requiring immediate cache clearing
• 🔄 Development and testing: Frequent DNS changes during development work necessitate regular cache clearing to test new configurations
• 📶 Network troubleshooting: Eliminating DNS cache as a variable helps isolate whether connectivity issues stem from DNS or other network layers

Verifying DNS Cache Flush Success

After executing cache clearing commands, confirming that the operation succeeded prevents wasted troubleshooting time based on incorrect assumptions. Different DNS services provide various methods for verification, ranging from statistics commands to actual DNS query testing. Developing a systematic verification approach ensures you know definitively whether cached records have been cleared.

The most direct verification method involves performing a DNS lookup immediately after flushing cache and observing query behavior. Using tools like dig or nslookup, query a domain you know was previously cached. The query time for the first lookup after cache clearing should be noticeably longer than subsequent queries, as the resolver must contact authoritative nameservers rather than retrieving results from cache. Running dig example.com twice in succession shows this pattern clearly, with the second query returning much faster.

Service-specific statistics commands provide quantitative confirmation of cache clearing. For systemd-resolved, sudo resolvectl statistics displays current cache size, which should show zero or minimal entries immediately after flushing. Similarly, sudo rndc status for BIND includes cache statistics that reset after flushing. These metrics offer objective evidence that cache clearing succeeded, removing guesswork from the verification process.

Testing DNS Resolution After Cache Clearing

Comprehensive testing involves querying multiple domains with different characteristics to ensure cache clearing affected all record types. Test both frequently accessed domains and obscure ones, as well as different record types including A records (IPv4), AAAA records (IPv6), MX records (mail), and CNAME records (aliases). The command dig example.com ANY requests all available record types simultaneously, providing a thorough test of DNS resolution functionality.

Comparing DNS resolution before and after cache clearing helps identify whether cache issues caused your original problem. Document query results before flushing cache, clear the cache, then repeat the same queries and compare results. Differences in returned IP addresses, resolution times, or error messages indicate that cached records differed from current authoritative data, confirming that cache clearing was necessary and effective.

"Verification transforms cache flushing from hopeful intervention into confirmed solution, providing certainty that your troubleshooting efforts addressed the actual problem."

Troubleshooting Persistent DNS Issues

When clearing DNS cache fails to resolve connectivity problems, the issue likely originates elsewhere in the network stack or DNS infrastructure. Systematic troubleshooting requires examining multiple components including network configuration, DNS server accessibility, firewall rules, and application-specific settings. Understanding the complete DNS resolution chain helps identify where problems actually occur rather than repeatedly clearing cache without addressing root causes.

Testing DNS server connectivity directly isolates whether problems stem from your system's configuration or upstream DNS infrastructure. Execute dig @8.8.8.8 example.com to query Google's public DNS server directly, bypassing local cache and configuration. If this query succeeds while normal queries fail, your system's DNS configuration or local resolver service requires attention. Conversely, if direct queries also fail, network connectivity issues or DNS server problems exist beyond your local system.

Network configuration files sometimes contain errors that persist despite cache clearing, particularly in /etc/hosts which takes precedence over DNS lookups. Examine this file with cat /etc/hosts to identify any manual entries that might override DNS resolution. Incorrect entries here cause consistent resolution failures that cache clearing cannot fix, as the hosts file bypasses DNS entirely for listed domains.

Advanced Diagnostic Techniques

Packet capture tools like tcpdump reveal exactly what DNS queries your system sends and what responses it receives. Running sudo tcpdump -i any port 53 captures all DNS traffic, showing query destinations, response times, and returned data. This low-level visibility exposes issues like queries sent to wrong nameservers, responses blocked by firewalls, or malformed DNS packets that higher-level tools might not reveal.

Examining resolver configuration files provides insights into how your system determines which DNS servers to query. Beyond /etc/resolv.conf, NetworkManager stores connection-specific DNS settings in /etc/NetworkManager/system-connections/. Understanding the complete configuration chain helps identify misconfigurations that prevent proper DNS resolution regardless of cache state.

Automating DNS Cache Management

Environments with frequent DNS changes or strict security requirements benefit from automated cache clearing rather than manual intervention. Creating scheduled tasks through cron or systemd timers ensures cache remains fresh without requiring administrator attention. However, automation should serve specific needs rather than compensating for underlying configuration problems that proper setup would resolve.

Setting up a cron job for periodic cache clearing involves editing the crontab with sudo crontab -e and adding an appropriate schedule line. For example, 0 */6 * * * systemctl reload systemd-resolved clears cache every six hours. Choose intervals that balance freshness requirements against the performance impact of clearing cache, as excessive clearing eliminates caching benefits entirely.

Systemd timers provide more sophisticated scheduling with better logging and dependency management than traditional cron jobs. Creating a timer unit file at /etc/systemd/system/dns-cache-flush.timer with corresponding service unit enables flexible scheduling with systemd's powerful timer syntax. This approach integrates cleanly with systemd-based distributions and provides better visibility into automated maintenance tasks.

Monitoring and Alerting for DNS Issues

Proactive monitoring detects DNS problems before they impact users, reducing reliance on reactive cache clearing. Tools like Nagios, Zabbix, or Prometheus can monitor DNS resolution times, failure rates, and cache hit ratios. Setting appropriate thresholds triggers alerts when DNS performance degrades, enabling investigation before problems escalate.

Custom monitoring scripts using dig or host commands provide lightweight DNS health checks suitable for smaller environments. A simple bash script that queries critical domains and measures response times runs via cron to generate alerts when resolution fails or becomes unacceptably slow. This approach requires minimal infrastructure while still providing valuable visibility into DNS health.

Security Implications of DNS Caching

DNS cache poisoning represents a serious security threat where attackers inject false DNS records into cache, redirecting traffic to malicious servers. Understanding these risks helps you implement appropriate protections and recognize when cache clearing becomes a security response rather than routine maintenance. Modern DNS resolvers include defenses against poisoning, but configuration and vigilance remain essential.

DNSSEC (DNS Security Extensions) provides cryptographic verification of DNS responses, preventing acceptance of forged records. Enabling DNSSEC in systemd-resolved through the DNSSEC=yes option in /etc/systemd/resolved.conf activates validation. While not all domains support DNSSEC yet, enabling validation protects against poisoning for domains that have implemented it, significantly improving security without requiring cache clearing.

"DNS cache becomes a security liability when it stores poisoned records, making immediate cache clearing essential upon detecting suspicious DNS behavior."

Monitoring DNS query patterns helps identify potential security incidents including cache poisoning attempts. Sudden changes in query destinations, unexpected DNS server responses, or resolution of domains to suspicious IP addresses warrant immediate investigation and cache clearing. Combining automated monitoring with rapid cache clearing capability provides defense-in-depth against DNS-based attacks.

Privacy Considerations

DNS queries reveal significant information about your browsing habits and network activity. Even with encrypted HTTPS connections, DNS queries typically transmit in plaintext, exposing domain names to network observers. Regular cache clearing provides minimal privacy benefits, as queries still occur and remain observable during transmission. DNS-over-HTTPS (DoH) or DNS-over-TLS (DoT) provide meaningful privacy improvements by encrypting DNS traffic.

Configuring encrypted DNS protocols in systemd-resolved involves setting DNSOverTLS=yes in the configuration file and specifying DNS servers that support encrypted protocols. This protection prevents network eavesdropping on DNS queries while maintaining cache benefits. Combined with periodic cache clearing for local privacy, encrypted DNS provides comprehensive protection for DNS-related privacy concerns.

Distribution-Specific Considerations

Different Linux distributions implement DNS resolution with varying defaults and preferred tools, requiring adapted approaches for cache management. Understanding your distribution's specific configuration ensures you use appropriate methods rather than applying generic instructions that might not match your system's actual setup. Major distribution families each have characteristic DNS configurations worth recognizing.

Ubuntu and Debian-based distributions increasingly use systemd-resolved by default, making resolvectl flush-caches the appropriate command. However, older versions or minimal installations might use dnsmasq or no caching at all. Checking your specific version's DNS configuration prevents applying wrong procedures that waste time or create confusion about why cache clearing seems ineffective.

Red Hat, CentOS, and Fedora systems traditionally used NSCD for caching, though recent versions have also adopted systemd-resolved. Enterprise Linux environments often maintain NSCD for compatibility with existing configurations and integration with network authentication systems. Understanding your specific RHEL-family distribution's DNS setup ensures you clear the correct cache service.

Arch Linux and Rolling Release Distributions

Arch Linux and similar rolling-release distributions typically provide minimal default configurations, leaving DNS setup to user preference. Many Arch users configure systemd-resolved, but others prefer dnsmasq, unbound, or direct nameserver queries without caching. Consulting your specific configuration rather than assuming defaults prevents errors and ensures effective cache management tailored to your actual setup.

The Arch Wiki provides comprehensive documentation for various DNS configurations, serving as an excellent resource for understanding options and their implications. This documentation-first approach characteristic of Arch Linux helps users make informed decisions about DNS caching rather than relying on potentially inappropriate distribution defaults.

Performance Impact of Cache Clearing

While necessary for troubleshooting and specific scenarios, clearing DNS cache impacts performance by forcing fresh lookups for all subsequent queries. Understanding this trade-off helps you decide when cache clearing provides net benefits versus when alternative approaches better serve your needs. Quantifying performance implications enables informed decisions about cache management strategies.

Immediately after clearing cache, every DNS query requires contacting authoritative nameservers, introducing latency that cached responses would have avoided. For individual workstations, this impact manifests as slightly slower initial page loads after cache clearing. Busy servers or systems with high DNS query rates experience more noticeable performance degradation, potentially affecting user experience or application responsiveness.

Cache repopulation happens organically as applications make DNS queries, gradually restoring performance to normal levels. The time required for full repopulation depends on query diversity and frequency. Systems accessing many different domains take longer to rebuild comprehensive cache coverage than those repeatedly accessing a small set of domains. Understanding this repopulation pattern helps set expectations for post-clearing performance.

Optimizing Cache Configuration

Rather than frequently clearing cache, optimizing cache configuration often better addresses underlying issues. Adjusting TTL respect, cache size limits, and negative caching behavior tunes cache performance to match your environment's characteristics. These configuration changes provide lasting improvements compared to the temporary fix that cache clearing represents.

Monitoring cache hit rates reveals whether your cache configuration provides meaningful benefits. Low hit rates suggest that cache size might be insufficient, TTL values don't match query patterns, or query diversity exceeds cache capacity. Addressing these configuration issues improves performance more effectively than repeatedly clearing cache, which temporarily destroys all accumulated performance benefits.

Why doesn't Linux have a universal DNS cache clearing command?

Linux distributions implement DNS caching through various services rather than a built-in kernel-level cache, making cache clearing service-specific. This design philosophy gives administrators flexibility to choose DNS resolvers that match their needs, but requires understanding which service your system uses. The absence of a universal command reflects Linux's modular architecture where different components handle specific functions independently.

How can I tell if clearing DNS cache actually fixed my problem?

Perform the same DNS query or connection attempt that previously failed immediately after clearing cache. If the issue resolves and the domain now resolves to a different IP address or loads correctly, cache clearing succeeded. Use tools like dig or nslookup to compare DNS responses before and after clearing cache, documenting any differences in resolved addresses or response times that indicate cached data was outdated.

Does restarting my computer clear DNS cache?

Restarting clears DNS cache for most resolver services since cache resides in memory and doesn't persist across reboots. However, some configurations write cache to disk or use persistent storage, meaning reboot might not completely clear all cached DNS information. Additionally, application-level caches in browsers persist across reboots, requiring separate clearing procedures even after restarting the system.

Can I disable DNS caching entirely on Linux?

Yes, you can disable DNS caching by stopping and disabling your caching service, then configuring /etc/resolv.conf to point directly to external nameservers. However, this approach sacrifices the performance benefits of caching, causing every DNS query to traverse the network to remote nameservers. Disabling cache makes sense only for troubleshooting or specific scenarios where cache causes more problems than it solves.

How often should I flush DNS cache on my Linux system?

Most systems never require routine DNS cache flushing, as automatic TTL expiration keeps cached records reasonably current. Clear cache only when experiencing specific DNS-related problems, after major network configuration changes, or when security concerns arise. Frequent cache clearing indicates underlying configuration problems that proper DNS setup would resolve more effectively than repeated manual intervention.

Will clearing DNS cache affect other users on my system?

Yes, DNS cache operates system-wide, meaning clearing it affects all users and applications on the system simultaneously. All users experience the performance impact of cache repopulation after clearing. On multi-user systems, coordinate cache clearing to minimize disruption, or investigate whether the DNS issue affects only specific users, suggesting application-level rather than system-level cache problems.

What's the difference between flushing DNS cache and restarting the DNS service?

Flushing cache clears stored DNS records while keeping the service running, causing no interruption to DNS resolution capability. Restarting the service stops and restarts the entire DNS resolver process, causing brief service interruption but also clearing cache and resetting all service state. Flushing is generally preferable unless you suspect service-level problems beyond just cached data.

Can DNS cache corruption cause security vulnerabilities?

Yes, corrupted or poisoned DNS cache can redirect traffic to malicious servers, enabling man-in-the-middle attacks, phishing, or malware distribution. If you suspect cache poisoning, immediately clear cache and investigate how false records entered the cache. Implementing DNSSEC validation and using reputable DNS servers reduces poisoning risk, while monitoring DNS resolution patterns helps detect suspicious activity.