{"id":353678,"date":"2024-09-18T09:26:20","date_gmt":"2024-09-18T09:26:20","guid":{"rendered":"https:\/\/www.ninjaone.com\/script-hub\/rechercher-les-entrees-du-cache-dns-linux\/"},"modified":"2024-10-13T19:02:08","modified_gmt":"2024-10-13T19:02:08","slug":"rechercher-les-entrees-du-cache-dns-linux","status":"publish","type":"script_hub","link":"https:\/\/www.ninjaone.com\/fr\/script-hub\/rechercher-les-entrees-du-cache-dns-linux\/","title":{"rendered":"Comment rechercher les entr\u00e9es du cache DNS Linux \u00e0 l’aide d’un script Bash pour les professionnels de l’informatique"},"content":{"rendered":"

Dans le monde informatique actuel, une gestion efficace du r\u00e9seau est cruciale. Un \u00e9l\u00e9ment cl\u00e9 de cette gestion est la mise en cache du DNS (Domain Name System)<\/a>, qui peut am\u00e9liorer de mani\u00e8re significative les performances du r\u00e9seau en r\u00e9duisant le temps n\u00e9cessaire \u00e0 la r\u00e9solution des noms de domaine.<\/p>\n

Pour les professionnels de l’informatique, en particulier ceux qui g\u00e8rent plusieurs syst\u00e8mes, il est essentiel de comprendre et d’utiliser les informations du cache DNS. Ce billet de blog explore un script Bash con\u00e7u pour rechercher les entr\u00e9es du cache DNS<\/strong> sur les syst\u00e8mes Linux<\/a>, en fournissant une description d\u00e9taill\u00e9e de son fonctionnement, de ses cas d’utilisation et des meilleures pratiques de mise en \u0153uvre.<\/p>\n

Contexte<\/h2>\n

La mise en cache DNS stocke les r\u00e9sultats des requ\u00eates DNS localement sur un appareil, ce qui permet de r\u00e9pondre plus rapidement aux requ\u00eates ult\u00e9rieures portant sur les m\u00eames noms de domaine. Alors que les serveurs n’ont g\u00e9n\u00e9ralement pas de services de cache DNS activ\u00e9s par d\u00e9faut, certains environnements de bureau comme GNOME ou KDE en ont souvent, utilisant des services comme systemd-resolved ou dnsmasq.<\/p>\n

Ce script est con\u00e7u pour aider les professionnels de l’informatique et les fournisseurs de services g\u00e9r\u00e9s (MSP)<\/a> \u00e0 rechercher et \u00e0 r\u00e9cup\u00e9rer les entr\u00e9es du cache DNS sur les syst\u00e8mes Linux. La possibilit\u00e9 d’effectuer des recherches dans les entr\u00e9es du cache DNS peut s’av\u00e9rer cruciale pour r\u00e9soudre des probl\u00e8mes de r\u00e9seau, enqu\u00eater sur des incidents de s\u00e9curit\u00e9 potentiels ou simplement optimiser les performances du r\u00e9seau.<\/p>\n

En fournissant un moyen syst\u00e9matique d’acc\u00e9der \u00e0 ces entr\u00e9es et de les filtrer, le script permet de rationaliser des t\u00e2ches qui, autrement, n\u00e9cessiteraient des m\u00e9thodes plus complexes ou plus longues.<\/p>\n

Le script\u00a0:<\/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
Description d\u00e9taill\u00e9e<\/h2>\n
Le script est structur\u00e9 pour g\u00e9rer les diff\u00e9rents services de cache DNS (systemd-resolved et dnsmasq) qui peuvent \u00eatre pr\u00e9sents sur un syst\u00e8me Linux. Voici une explication \u00e9tape par \u00e9tape du fonctionnement du script :<\/p>\n
1. Configuration des param\u00e8tres :<\/h3>\n