{"id":353758,"date":"2024-09-18T11:34:29","date_gmt":"2024-09-18T11:34:29","guid":{"rendered":"https:\/\/www.ninjaone.com\/script-hub\/ricerca-nella-cache-dns-su-linux\/"},"modified":"2024-10-13T19:02:10","modified_gmt":"2024-10-13T19:02:10","slug":"ricerca-nella-cache-dns-su-linux","status":"publish","type":"script_hub","link":"https:\/\/www.ninjaone.com\/it\/script-hub\/ricerca-nella-cache-dns-su-linux\/","title":{"rendered":"Come cercare in modo efficiente nella cache DNS su Linux utilizzando uno script Bash per professionisti IT"},"content":{"rendered":"

Nell’attuale panorama IT, una gestione efficiente della rete \u00e8 fondamentale. Un componente chiave di questa gestione \u00e8 il caching del DNS (Domain Name System)<\/a>, che pu\u00f2 migliorare in modo significativo le prestazioni della rete riducendo il tempo necessario per risolvere i nomi di dominio.<\/p>\n

Per i professionisti dell’IT, in particolare per quelli che gestiscono pi\u00f9 sistemi, la comprensione e l’utilizzo delle informazioni sulla cache DNS sono fondamentali. In questo articolo analizzeremo uno script Bash progettato per cercare nella cache DNS<\/strong> sui sistemi Linux<\/a>, e forniremo una descrizione dettagliata del suo funzionamento, dei casi d’uso e delle best practice per l’implementazione.<\/p>\n

Background<\/h2>\n

La cache DNS memorizza i risultati delle query DNS localmente su un dispositivo, consentendo di rispondere pi\u00f9 rapidamente alle richieste successive per gli stessi nomi di dominio. Mentre i server in genere non hanno servizi di cache DNS abilitati per impostazione predefinita, alcuni ambienti desktop come GNOME o KDE spesso li hanno, e utilizzano servizi come systemd-resolved o dnsmasq.<\/p>\n

Questo \u00e8 stato progettato per aiutare i professionisti IT e i Managed Service Provider (MSP) <\/a>a cercare e recuperare le voci della cache DNS sui sistemi Linux. La possibilit\u00e0 di cercare tra le voci della cache DNS pu\u00f2 essere fondamentale per la risoluzione di problemi di rete, per indagare su potenziali incidenti di sicurezza o semplicemente per ottimizzare le prestazioni della rete.<\/p>\n

Fornendo un modo sistematico per accedere a queste voci e filtrarle, lo script per cercare nella cache DNS su Linux aiuta a semplificare le attivit\u00e0 che altrimenti richiederebbero metodi pi\u00f9 complessi o lunghi.<\/p>\n

Lo script per cercare nella cache DNS su Linux:<\/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
Analisi dettagliata<\/h2>\n
Lo script per cercare nella cache DNS su Linux \u00e8 strutturato per gestire diversi servizi di cache DNS (systemd-resolved e dnsmasq) che potrebbero essere presenti su un sistema Linux. Ecco una spiegazione passo per passo del funzionamento dello script:<\/p>\n
1. Impostazione dei parametri:<\/h3>\n