How to update clamav virus database9/23/2023 ![]() ![]() Assuming this test is successful, FreshClam overwrites the CVD/CLD files in the ClamAV virus database directory and optionally notifies any running ClamD instances that new signatures are available. Once the CVDs have been downloaded or updated from CDIFFs, FreshClam defaults to performing a test of the signature - it loads the signature sets into memory the same way that ClamD or ClamScan would. This is sometimes preferred to patching when a significant portion of the CVD changes, like when a large portion of daily is migrated to main in a single update.Ĥ. A zero-byte CDIFF indicates that FreshClam should download the CVD instead. On rare occasions, the ClamAV team may intentionally publish a CDIFF that is empty. If a CDIFF cannot be downloaded successfully, FreshClam will stop attempting to apply CDIFFs and will download the CVD directly. Assuming each of those CDIFFs exists on the server (only the last 90 days worth are currently kept) and is downloaded successfully, FreshClam will apply them in order until the CVD has been successfully updated. To update via CDIFF, FreshClam determines the version of the database on disk and requests every CDIFF between that version and the latest. For example, for an update where 10,000 signatures were removed from daily, the corresponding CDIFF was only around 60 KB in size. Each CDIFF contains the lines to be added or removed to the various text-based ClamAV signature files in the CVD, and these CDIFFs are relatively small, even when many signatures have been added or removed. For example, the CDIFF for daily corresponding to the DNS record shown above would be daily-26104.cdiff. For the official signature sets that exist on disk, though, FreshClam copies them to a temporary directory and attempts to update them in place using signed CDIFF files.Ī ClamAV CDIFF file is generated every time a new release of the daily.cvd or main.cvd is made, and the files exist on the mirror server using the following format: -.cdiff. This is an expensive operation in terms of bandwidth because daily.cvd and main.cvd are, currently, 105 MB and 117 MB, respectively. For any of the official signature sets that can’t be found, FreshClam will download the corresponding CVD from the server indicated by DatabaseMirror in nf (the default is ). These CLD files are uncompressed and unsigned versions of the CVD that have had CDIFFs applied.ģ. For main and daily, if the CVD can’t be found it also looks for main.cld and daily.cld. FreshClam checks the ClamAV virus database directory (indicated by the DatabaseDirectory value in the nf that FreshClam uses) for existing instances of main.cvd, daily.cvd, or bytecode.cvd. The version of the most recently published bytecode.cvd (333)Ģ.The version of the most recently published daily.cvd (26104).The version of the most recently published main.cvd (59).The most recently released ClamAV version (0.103.1).Several of the fields included in the TXT record contents are: An example TXT file record can be seen in the output below: A DNS request is made to for a TXT record containing information about the latest signature sets. Here’s a full technical breakdown of how FreshClam works:ġ. The FreshClam utility facilitates the downloading and updating of official signature sets. main.cvd contains signatures previously in daily.cvd that have shown to have a low false-positive risk. ![]()
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