Archivematica provides antivirus capabilities through the ClamAV antivirus engine. The default antivirus settings are configured to capture the largest possible number of viruses across the largest breadth of file types and sizes possible.
If configuration of ClamAV is required then you can do this through various environment variables inside the operating system.
Clamdscan or Clamscan¶
Clamscan is a standalone application. Clamdscan is a server-based implementation of the same tool.
Depending on your method of deployment, the Archivematica MCP Client will need
to have the environment variable
CLAMAV_CLIENT_BACKEND set to one of two
Archivematica will look for one of these values. If a value is not recognised then it will default to Clamdscan.
It is recommended that you employ Clamdscan for virus checking.
Clamscan is slower than Clamdscan because the process has to be started and the virus database reloaded for each file that is passed to it.
Clamdscan’s utility is due in part to the antivirus definition database only being loaded once when the service is started. Files are passed to the service by stream or by filesystem reference.
To illustrate the difference in performance, a 1 MB image file can be scanned by Clamdscan in an average of 2 seconds. Using Clamscan the average for the same file will be 1 minute 20 seconds.
Antivirus settings and their impacts¶
Antivirus in Archivematica is configured using environment variables. These are documented in detail on the Archivematica GitHub pages for the MCPClient environment variables.
There are three values for antivirus that can impact whether a file is scanned or not - MaxFileSize, MaxScanSize, and StreamMaxLength. If any of these are exceeded, Archivematica cannot guarantee that a file has been scanned in its entirety for viruses.
Given that Archivematica cannot guarantee in such cases that all instances of any virus have been detected, a PREMIS event will not be recorded.
From the ClamAV manual pages:
MaxFileSize SIZE Files larger than this limit won't be scanned. Affects the input file itself as well as files contained inside it (when the input file is an archive, a document or some other kind of container). MaxScanSize SIZE Sets the maximum amount of data to be scanned for each input file. Archives and other containers are recursively extracted and scanned up to this value. The size of an archive plus the sum of the sizes of all files within archive count toward the scan size. For example, a 1M uncompressed archive containing a single 1M inner file counts as 2M toward the max scan size. StreamMaxLength** SIZE Close the STREAM session when the data size limit is exceeded. **Clamdscan Only Notes: All options expressing a size are limited to max 2GB. Values in excess will be reset to the maximum.
Configuration of ClamAV values¶
Defaults in Archivematica are set to:
MaxFileSize=2000M MaxScanSize=2000M StreamMaxLength=2000M Where M is the unit Megabytes
Clamscan defaults cannot be set above 2GB (2000M) as per this link to ClamAV Bug 11958 (note that you must create an account with Bugzilla to view bugs for the ClamAV project).
Configuration is done via environment variable or deployment script, e.g. Ansible playbook.
The defaults for the ClamAV Ansible role can be configured in the default configuration file before proceeding with the Ansible installation process.
Impact of various configuration settings¶
Where defaults are increased, processing times of transfers will be slower for transfers with larger digital files. More digital files will be completely scanned.
Where defaults are decreased, processing times of transfers will be faster for all digital files. Fewer digital files will be completely scanned.
Virus definition updates¶
An update service called
freshclam is run regularly to update virus
definitions in Archivematica. To see when the virus database was last updated
you can review the log at the following location:
If the Scan for Viruses microservice is reporting that a file is too big but the defaults you have set look accurate, then there is a chance the MCP Client configuration needs updating. The microservice will look at the environment variables:
To determine whether to pass the file to the virus scanner. These values are configured in Ansible environment variables or inside the operating system environment itself.