{"id":353609,"date":"2024-09-23T11:35:23","date_gmt":"2024-09-23T11:35:23","guid":{"rendered":"https:\/\/www.ninjaone.com\/script-hub\/linux-dns-cache-durchsuchen\/"},"modified":"2024-10-13T19:02:06","modified_gmt":"2024-10-13T19:02:06","slug":"linux-dns-cache-durchsuchen","status":"publish","type":"script_hub","link":"https:\/\/www.ninjaone.com\/de\/script-hub\/linux-dns-cache-durchsuchen\/","title":{"rendered":"Wie man im Linux-DNS-Cache effizient mit einem Bash-Skript f\u00fcr IT-Experten sucht"},"content":{"rendered":"

In der heutigen IT-Welt ist eine effiziente Netzwerkverwaltung ausschlaggebend. Eine Schl\u00fcsselkomponente davon ist das DNS (Domain Name System)<\/a>-Caching, das die Netzwerkleistung erheblich verbessern kann, indem sie die Zeit f\u00fcr die Aufl\u00f6sung von Domainnamen verk\u00fcrzt.<\/p>\n

F\u00fcr IT-Experten, insbesondere f\u00fcr diejenigen, die mehrere Systeme verwalten, ist das Verst\u00e4ndnis und die Nutzung von DNS-Cache-Informationen von entscheidender Bedeutung. Dieser Blog-Beitrag befasst sich mit einem Bash-Skript, das DNS-Cache-Eintr\u00e4ge<\/strong> auf Linux-Systemen<\/a> durchsuchen kann<\/strong>, und bietet eine detaillierte Aufschl\u00fcsselung der Funktionsweise, der Anwendungsf\u00e4lle und der Best Practices f\u00fcr die Implementierung.<\/p>\n

Kontext<\/h2>\n

Beim DNS-Caching werden die Ergebnisse von DNS-Abfragen lokal auf einem Ger\u00e4t gespeichert, was eine schnellere Beantwortung nachfolgender Anfragen f\u00fcr dieselben Domainnamen erm\u00f6glicht. W\u00e4hrend Server im Allgemeinen keine standardm\u00e4\u00dfig aktivierten DNS-Cache-Dienste haben, ist dies bei bestimmten Desktop-Umgebungen wie GNOME oder KDE oft der Fall, die Dienste wie systemd-resolved oder dnsmasq verwenden.<\/p>\n

Dieses Skript soll IT-Experten und Managed Service Providern (MSPs)<\/a> helfen, DNS-Cache-Eintr\u00e4ge auf Linux-Systemen zu suchen und abzurufen. Die M\u00f6glichkeit, DNS-Cache-Eintr\u00e4ge zu durchsuchen, kann f\u00fcr die Behebung von Netzwerkproblemen, die Untersuchung potenzieller Sicherheitsvorf\u00e4lle oder einfach die Optimierung der Netzwerkleistung entscheidend sein.<\/p>\n

Das Skript bietet eine systematische M\u00f6glichkeit, auf diese Eintr\u00e4ge zuzugreifen und sie zu filtern, und tr\u00e4gt so zur Rationalisierung von Aufgaben bei, die andernfalls komplexere oder zeitaufw\u00e4ndigere Methoden erfordern w\u00fcrden.<\/p>\n

Das Skript:<\/h2>\n
#!\/usr\/bin\/env bash\r\n\r\n# Description: Find DNS Cache entries on a Linux system. Supports systemd-resolved and dnsmasq(requires log-facility to be configured).\r\n#\r\n# Servers usually do not have a DNS cache service installed by default.\r\n# systemd-resolved is commonly installed along with most Desktop Environments, such as GNOME and KDE.\r\n#\r\n# Release Notes: Initial Release\r\n#   By using this script, you indicate your acceptance of the following legal terms as well as our Terms of Use at https:\/\/www.ninjaone.com\/terms-of-use.\r\n#   Ownership Rights: NinjaOne owns and will continue to own all right, title, and interest in and to the script (including the copyright). NinjaOne is giving you a limited license to use the script in accordance with these legal terms. \r\n#   Use Limitation: You may only use the script for your legitimate personal or internal business purposes, and you may not share the script with another party. \r\n#   Republication Prohibition: Under no circumstances are you permitted to re-publish the script in any script library or website belonging to or under the control of any other software provider. \r\n#   Warranty Disclaimer: The script is provided \u201cas is\u201d and \u201cas available\u201d, without warranty of any kind. NinjaOne makes no promise or guarantee that the script will be free from defects or that it will meet your specific needs or expectations. \r\n#   Assumption of Risk: Your use of the script is at your own risk. You acknowledge that there are certain inherent risks in using the script, and you understand and assume each of those risks. \r\n#   Waiver and Release: You will not hold NinjaOne responsible for any adverse or unintended consequences resulting from your use of the script, and you waive any legal or equitable rights or remedies you may have against NinjaOne relating to your use of the script. \r\n#   EULA: If you are a NinjaOne customer, your use of the script is subject to the End User License Agreement applicable to you (EULA).\r\n\r\n# A comma separated list of keywords to search for in the DNS cache. Example: \"google,comcast,cloudflare\"\r\nkeywords_to_search=$1\r\n# A multiline custom field to save the DNS cache entries.\r\nmultiline_custom_field=$2\r\n\r\n# Check if the multilineCustomField is set\r\nif [[ -n \"${multilineCustomField}\" && \"${multilineCustomField}\" != \"null\" ]]; then\r\n    multiline_custom_field=$multilineCustomField\r\nfi\r\n\r\n# Check if the keywordsToSearch is set\r\nif [[ -n \"${keywordsToSearch}\" && \"${keywordsToSearch}\" != \"null\" ]]; then\r\n    keywords_to_search=$keywordsToSearch\r\nfi\r\n\r\n# Check if the keywords_to_search is set\r\nif [[ -z \"${keywords_to_search}\" ]]; then\r\n    echo \"[Info] keywords_to_search is not set.\"\r\n    exit 1\r\nelse\r\n    # Split the keywords_to_search into an array\r\n    OLDIFS=$IFS\r\n    IFS=',' read -r -a keywords <<<\"${keywords_to_search}\"\r\n    IFS=$OLDIFS\r\n    # Trim trailing and leading whitespace from each keyword\r\n    keywords=(\"${keywords[@]\/ \/}\")\r\n\r\nfi\r\n\r\n# Check if the multiline_custom_field is set\r\nif [[ -z \"${multiline_custom_field}\" ]]; then\r\n    echo \"[Info] multilineCustomField is not set.\"\r\nfi\r\n\r\n# Check if ninjarmm-cli command exists in the default path\r\nninjarmm_cli=\"\/opt\/NinjaRMMAgent\/programdata\/ninjarmm-cli\"\r\nif [[ -z $ninjarmm_cli ]]; then\r\n    echo \"[Error] The ninjarmm-cli command does not exist in the default path. Please ensure the NinjaRMM agent is installed before running this script.\"\r\n    exit 1\r\nelse\r\n    # ninjarmm-cli command exists in the default path\r\n    echo -n\r\nfi\r\n\r\n# Check that we are running as root\r\nif [[ $EUID -ne 0 ]]; then\r\n    echo \"[Error] This script must be run as root.\"\r\n    exit 1\r\nfi\r\n\r\n# Check for which dns cache service is installed\r\nif [ \"$(command -v resolvectl)\" ]; then\r\n    # resolvectl is installed\r\n    dns_cache_service=\"resolvectl\"\r\nelif [ \"$(command -v dnsmasq)\" ]; then\r\n    # dnsmasq is installed\r\n    dns_cache_service=\"dnsmasq\"\r\nelse\r\n    # no dns cache service is installed\r\n    echo \"[Error] No DNS cache service is installed on this system that this script supports.\"\r\n    echo \"\"\r\n    echo \"[Info] Supported DNS cache services: systemd-resolved, dnsmasq\"\r\n    echo \"[Info] systemd-resolved commonly installed along with a Desktop Environment.\"\r\n    echo \"[Info] Servers usually do not have a DNS cache service installed by default.\"\r\n    echo \"\"\r\n    echo \"[Info] Installing a DNS cache is not recommended on servers.\"\r\n    exit 1\r\nfi\r\n\r\n# Check if the dns_cache_service is resolvectl\r\nif [[ \"${dns_cache_service}\" == \"resolvectl\" ]]; then\r\n    systemdVersion=$(systemctl --version | head -1 | awk '{ print $2}')\r\n    if [ \"$systemdVersion\" -lt 254 ]; then\r\n        echo \"[Error] The version of systemd is less than 254. The resolvectl show-cache command is not available. Currently system version is ${systemdVersion}.\"\r\n        exit 1\r\n    fi\r\n    # Get the DNS cache entries from resolvectl\r\n    # https:\/\/github.com\/systemd\/systemd\/pull\/28012\r\n    if ! dns_cache=$(resolvectl show-cache 2>\/dev\/null); then\r\n        # Check if the systemd-resolved service is active\r\n        if [[ $(systemctl is-active systemd-resolved) != \"active\" ]]; then\r\n            echo \"[Warn] The systemd-resolved service is not active.\"\r\n        # Check \/etc\/resolv.conf that the nameserver is set to the default IP address 127.0.0.53 for systemd-resolved to work\r\n        elif ! grep -q \"^nameserver 127.0.0.53\" \/etc\/resolv.conf; then\r\n            echo \"[Warn] The nameserver in \/etc\/resolv.conf is not set to an IP address 127.0.0.53 .\"\r\n            echo \"[Info] The nameserver in \/etc\/resolv.conf should be set to an IP address 127.0.0.53 for systemd-resolved to work.\"\r\n        else\r\n            echo \"[Warn] Failed to get the DNS cache entries. Is systemd-resolved installed, configured, and running?\"\r\n        fi\r\n        echo \"\"\r\n        echo \"[Info] Supported DNS cache services: systemd-resolved, dnsmasq\"\r\n        echo \"[Info] systemd-resolved commonly installed along with a Desktop Environment.\"\r\n        echo \"[Info] Servers usually do not have a DNS cache service installed by default.\"\r\n        echo \"\"\r\n        echo \"[Info] Installing a DNS cache is not recommended on servers.\"\r\n        exit 0\r\n    fi\r\n\r\n    dns_cache_entries=\"\"\r\n    # Get the DNS cache entries from resolvectl based on the keywords provided\r\n    for keyword in \"${keywords[@]}\"; do\r\n        # Example DNS cache entry:\r\n        # consto.com IN A 123.123.123.123\r\n        # consto.com IN AAAA 2001:0db8:85a3:0000:0000:8a2e:0370:7334\r\n        dns_cache_entries+=\"DNS Cache Records Matching: ${keyword}\"\r\n        dns_cache_entries+=$'\\n' # newline\r\n        dns_cache_entries+=$(echo \"$dns_cache\" | grep -i -E \"${keyword}\")\r\n        dns_cache_entries+=$'\\n' # newline\r\n    done\r\n    # Print the DNS cache entries\r\n    echo \"\" # newline\r\n    echo \"$dns_cache_entries\"\r\n# Check if the dns_cache_service is dnsmasq\r\nelif [[ \"${dns_cache_service}\" == \"dnsmasq\" ]]; then\r\n    if [ -f \"\/etc\/dnsmasq.conf\" ]; then\r\n        echo \"[Info] dnsmasq configuration file exists.\"\r\n    else\r\n        echo \"[Warn] The dnsmasq configuration file does not exist and is likely not installed or configured.\"\r\n        echo \"\"\r\n        echo \"[Info] Supported DNS cache services: systemd-resolved, dnsmasq\"\r\n        echo \"[Info] systemd-resolved commonly installed along with a Desktop Environment.\"\r\n        echo \"[Info] Servers usually do not have a DNS cache service installed by default.\"\r\n        echo \"\"\r\n        echo \"[Info] Installing a DNS cache is not recommended on servers.\"\r\n        exit 0\r\n    fi\r\n    # Check that log-queries is enabled in the dnsmasq configuration file\r\n    if ! grep -q \"log-queries\" \/etc\/dnsmasq.conf; then\r\n        echo \"[Warn] The 'log-queries' option is not enabled in the dnsmasq configuration file.\"\r\n        echo \"\"\r\n        echo \"[Info] Supported DNS cache services: systemd-resolved, dnsmasq\"\r\n        echo \"[Info] systemd-resolved commonly installed along with a Desktop Environment.\"\r\n        echo \"[Info] Servers usually do not have a DNS cache service installed by default.\"\r\n        echo \"\"\r\n        echo \"[Info] Installing a DNS cache is not recommended on servers.\"\r\n        exit 0\r\n    fi\r\n    # Get the log-facility from the dnsmasq configuration file\r\n    log_facility=$(grep -E \"^log-facility\" \/etc\/dnsmasq.conf | awk '{print $2}')\r\n    if [[ -z \"${log_facility}\" ]]; then\r\n        echo \"[Warn] The 'log-facility' option is not set in the dnsmasq configuration file.\"\r\n        echo \"\"\r\n        echo \"[Info] Supported DNS cache services: systemd-resolved, dnsmasq\"\r\n        echo \"[Info] systemd-resolved commonly installed along with a Desktop Environment.\"\r\n        echo \"[Info] Servers usually do not have a DNS cache service installed by default.\"\r\n        echo \"\"\r\n        echo \"[Info] Installing a DNS cache is not recommended on servers.\"\r\n        exit 0\r\n    fi\r\n    # Check that log_facility is a valid file\r\n    if [[ ! -f \"${log_facility}\" ]]; then\r\n        echo \"[Error] The log facility file '${log_facility}' does not exist.\"\r\n        echo \"\"\r\n        echo \"[Info] Supported DNS cache services: systemd-resolved, dnsmasq\"\r\n        echo \"[Info] systemd-resolved commonly installed along with a Desktop Environment.\"\r\n        echo \"[Info] Servers usually do not have a DNS cache service installed by default.\"\r\n        echo \"\"\r\n        echo \"[Info] Installing a DNS cache is not recommended on servers.\"\r\n        exit 1\r\n    fi\r\n    # Get the DNS cache entries from log_facility\r\n    # Example log_facility file:\r\n    # Jan  1 00:00:00 dnsmasq[12345]: query[A] example.com from\r\n    for keyword in \"${keywords[@]}\"; do\r\n        # Get the DNS cache entries from the log_facility file\r\n        # The awk command parses the log_facility file and extracts the time, query, and host\r\n        if ! dns_cache_entries=$(grep -i -E \"${keyword}\" \"${log_facility}\" | awk 'BEGIN {OFS = \",\";}$5 == \"query[A]\" {time = mktime(sprintf(\"%04d %02d %02d %s\\n\",strftime(\"%Y\", systime()),(match(\"JanFebMarAprMayJunJulAugSepOctNovDec\",$1)+2)\/3,$2,gensub(\":\", \" \", \"g\", $3)));query = $6;host = $8;print time, host, query;}'); then\r\n            echo \"[Error] Failed to get the DNS cache entries.\"\r\n            echo \"$dns_cache_entries\"\r\n            echo \"\"\r\n            echo \"[Info] Supported DNS cache services: systemd-resolved, dnsmasq\"\r\n            echo \"[Info] systemd-resolved commonly installed along with a Desktop Environment.\"\r\n            echo \"[Info] Servers usually do not have a DNS cache service installed by default.\"\r\n            echo \"\"\r\n            echo \"[Info] Installing a DNS cache is not recommended on servers.\"\r\n            exit 1\r\n        fi\r\n    done\r\n    echo \"$dns_cache_entries\"\r\nfi\r\n\r\n# Set the multiline_custom_field\r\nif [[ -n \"$multiline_custom_field\" ]]; then\r\n    if [[ -x \"$ninjarmm_cli\" ]]; then\r\n        if hideOutput=$(echo \"$dns_cache_entries\" | \"$ninjarmm_cli\" set --stdin \"$multiline_custom_field\" 2>&1); then\r\n            echo \"[Info] Successfully set custom field: $multiline_custom_field\"\r\n        else\r\n            echo \"[Error] Failed to set custom field: $multiline_custom_field. Custom Field does not exist or does not have write permissions.\"\r\n            exit 1\r\n        fi\r\n    else\r\n        echo \"[Error] NinjaRMM CLI not found or not executable\"\r\n        exit 1\r\n    fi\r\nfi<\/pre>\n
 <\/p>\n\n
<\/h2>
<\/p><\/div>
<\/a><\/div><\/div>\n
Detailansicht<\/h2>\n
Das Skript ist so aufgebaut, dass es mit verschiedenen DNS-Caching-Diensten (systemd-resolved und dnsmasq) umgehen kann, die auf einem Linux-System vorhanden sein k\u00f6nnen. Im Folgenden wird Schritt f\u00fcr Schritt erkl\u00e4rt, wie das Skript funktioniert:<\/p>\n
1. Parameter einrichten:<\/h3>\n