ClamAV
Clam AntiVirus is an open source (GPL) anti-virus toolkit for UNIX. It provides a number of utilities including a flexible and scalable multi-threaded daemon, a command line scanner and advanced tool for automatic database updates. Because ClamAV's main use is on file/mail servers for Windows desktops, it primarily detects Windows viruses and malware with its built-in signatures.
Contents
Installation
Updating database
Update the virus definitions with:
# freshclam
If you are behind a proxy, edit /etc/clamav/freshclam.conf and update HTTPProxyServer, HTTPProxyPort, HTTPProxyUsername and HTTPProxyPassword.
The database files are saved in:
/var/lib/clamav/daily.cvd /var/lib/clamav/main.cvd /var/lib/clamav/bytecode.cvd
Start/enable clamav-freshclam.service so that the virus definitions are kept recent.
Starting the daemon
freshclam before starting the service for the first time or you will run into troubles/errors which will prevent ClamAV to start correctly.The service is called clamav-daemon.service. Start it and enable it to start at boot.
Testing the software
In order to make sure ClamAV and the definitions are installed correctly, scan the EICAR test file (a harmless signature with no virus code) with clamscan.
$ curl https://www.eicar.org/download/eicar.com.txt | clamscan -
The output must include:
stdin: Eicar-Test-Signature FOUND
Otherwise; read the Troubleshooting part or ask for help in the Arch Forums.
Adding more databases/signatures repositories
ClamAV can use databases/signature from other repositories or security vendors.
To add the most important ones in a single step, install clamav-unofficial-sigsAUR.
This will add signatures/databases from e.g. MalwarePatrol, SecuriteInfo, Yara, Linux Malware Detect, etc. For the full list of databases, see the description of the GitHub repository.
Set up clamav-unofficial-sigs
Enable the clamav-unofficial-sigs.timer.
This will regularly update the unofficial signatures based on the configuration files in the directory /etc/clamav-unofficial-sigs.
To update signatures manually, run the following:
# clamav-unofficial-sigs.sh
To change any default settings, refer and modify /etc/clamav-unofficial-sigs/user.conf.
clamav-freshclam.service started in order to have official signature updates from ClamAV mirrors.MalwarePatrol database
If you would like to use the MalwarePatrol database, sign up for an account at https://www.malwarepatrol.net/.
In /etc/clamav-unofficial-sigs/user.conf, change the following to enable this functionality:
malwarepatrol_receipt_code="YOUR-RECEIPT-NUMBER" # enter your receipt number here malwarepatrol_product_code="8" # Use 8 if you have a Free account or 15 if you are a Premium customer. malwarepatrol_list="clamav_basic" # clamav_basic or clamav_ext malwarepatrol_free="yes" # Set to yes if you have a Free account or no if you are a Premium customer.
Source: https://www.malwarepatrol.net/clamav-configuration-guide/
Scan for viruses
clamscan can be used to scan certain files, home directories, or an entire system:
$ clamscan myfile $ clamscan --recursive --infected /home $ clamscan --recursive --infected --exclude-dir='^/sys|^/dev' /
If you would like clamscan to remove the infected file add to the command the --remove option, or you can use --move=/dir to quarantine them.
You may also want clamscan to scan larger files. In this case, append the options --max-filesize=4000M and --max-scansize=4000M to the command. '4000M' is the largest possible value, and may be lowered as necessary.
Using the -l /path/to/file option will print the clamscan logs to a text file for locating reported infections.
Using the milter
Milter will scan your sendmail server for email containing virus.
Copy /etc/clamav/clamav-milter.conf.sample to /etc/clamav/clamav-milter.conf and adjust it to your needs. For example:
/etc/clamav/clamav-milter.conf
MilterSocket /run/clamav/clamav-milter.sock MilterSocketMode 660 FixStaleSocket yes User clamav PidFile /run/clamav/clamav-milter.pid TemporaryDirectory /tmp ClamdSocket unix:/var/lib/clamav/clamd.sock LogSyslog yes LogInfected Basic
Create /etc/systemd/system/clamav-milter.service:
/etc/systemd/system/clamav-milter.service
[Unit] Description='ClamAV Milter' After=clamav-daemon.service [Service] Type=forking ExecStart=/usr/bin/clamav-milter --config-file /etc/clamav/clamav-milter.conf [Install] WantedBy=multi-user.target
Enable and start clamav-milter.service.
OnAccessScan
On-access scanning requires the kernel to be compiled with the fanotify kernel module (kernel >= 3.8). Check if fanotify has been enabled before enabling on-access scanning.
$ zgrep FANOTIFY /proc/config.gz
On-access scanning will scan the file while reading, writing or executing it.
First, edit the /etc/clamav/clamd.conf configuration file by adding the following to the end of the file (you can also change the individual options):
/etc/clamav/clamd.conf
# Enables on-access scan, requires clamav-daemon.service running ScanOnAccess true # Set the mount point where to recursively perform the scan, # this could be every path or multiple path (one line for path) OnAccessMountPath /usr OnAccessMountPath /home/ OnAccessExcludePath /var/log/ # Flag fanotify to block any events on monitored files to perform the scan OnAccessPrevention false # Perform scans on newly created, moved, or renamed files OnAccessExtraScanning true # Check the UID from the event of fanotify OnAccessExcludeUID 0 # Specify an action to perform when clamav detects a malicious file # it is possible to specify an inline command too VirusEvent /etc/clamav/detected.sh # WARNING: clamd should run as root User root
Next, create the file /etc/clamav/detected.sh and add the following. This allows you to change/specify the debug message when a virus has been detected by clamd's on-access scanning service:
/etc/clamav/detected.sh
#!/bin/bash
PATH=/usr/bin
alert="Signature detected: $CLAM_VIRUSEVENT_VIRUSNAME in $CLAM_VIRUSEVENT_FILENAME"
# Send the alert to systemd logger if exist, othewise to /var/log
if [[ -z $(command -v systemd-cat) ]]; then
echo "$(date) - $alert" >> /var/log/clamav/infected.log
else
# as "emerg", this could cause your DE to show a visual alert. Happen in Plasma. but the next visual alert is much nicer
echo "$alert" | /usr/bin/systemd-cat -t clamav -p emerg
fi
#send an alrt to all graphical user
XUSERS=($(who|awk '{print $1$NF}'|sort -u))
for XUSER in $XUSERS; do
NAME=(${XUSER/(/ })
DISPLAY=${NAME[1]/)/}
DBUS_ADDRESS=unix:path=/run/user/$(id -u ${NAME[0]})/bus
echo "run $NAME - $DISPLAY - $DBUS_ADDRESS -" >> /tmp/testlog
/usr/bin/sudo -u ${NAME[0]} DISPLAY=${DISPLAY} \
DBUS_SESSION_BUS_ADDRESS=${DBUS_ADDRESS} \
PATH=${PATH} \
/usr/bin/notify-send -i dialog-warning "clamAV" "$alert"
done
If you are using AppArmor, it is also necessary to allow clamd to run as root:
# aa-complain clamd
Restart the clamav-daemon.service.
Source: http://blog.clamav.net/2016/03/configuring-on-access-scanning-in-clamav.html
Troubleshooting
Error: Clamd was NOT notified
If you get the following messages after running freshclam:
WARNING: Clamd was NOT notified: Cannot connect to clamd through /var/lib/clamav/clamd.sock connect(): No such file or directory
Add a sock file for ClamAV:
# touch /var/lib/clamav/clamd.sock # chown clamav:clamav /var/lib/clamav/clamd.sock
Then, edit /etc/clamav/clamd.conf - uncomment this line:
LocalSocket /var/lib/clamav/clamd.sock
Save the file and restart clamav-daemon.service.
Error: No supported database files found
If you get the next error when starting the daemon:
LibClamAV Error: cli_loaddb(): No supported database files found in /var/lib/clamav ERROR: Not supported data format
This happens because of mismatch between /etc/clamav/freshclam.conf setting DatabaseDirectory and /etc/clamav/clamd.conf setting DatabaseDirectory.
/etc/clamav/freshclam.conf pointing to /var/lib/clamav, but /etc/clamav/clamd.conf (default directory) pointing to /usr/share/clamav, or other directory. Edit in /etc/clamav/clamd.conf and replace with the same DatabaseDirectory like in /etc/clamav/freshclam.conf. After that clamav will start up successfully.
Error: Can't create temporary directory
If you get the following error, along with a 'HINT' containing a UID and a GID number:
# can't create temporary directory
Correct permissions:
# chown UID:GID /var/lib/clamav & chmod 755 /var/lib/clamav
Tips and tricks
Run in multiple threads
Using clamscan
When scanning a file or directory from command line using clamscan only single CPU thread is used. This may be ok in cases when timing is not critical or you don't want computer to become sluggish. If there is a need to scan large folder or USB drive quickly you may want to use all available CPUs to speed up the process.
clamscan is designed to be single-threaded, so xargs can be used to run the scan in parallel:
$ find /home/archie -type f -print | xargs -P $(nproc) clamscan
In this example the -P parameter for xargs runs clamscan in as many processes as there are CPUs (reported by nproc at the same time. --max-lines and --max-args options will allow even finer control of batching the workload across the threads.
Use the following version if filenames may contain spaces or other special characters (as USB and ex-Windows drives frequently do):
$ find /home/archie -type f -print0 | xargs -0 -P $(nproc) clamscan
Using clamdscan
If you already have clamd daemon running clamdscan can be used instead (see #Starting the daemon):
$ clamdscan --multiscan --fdpass /home/archie
Here the --multiscan parameter enables clamd to scan the contents of the directory in parallel using available threads. --fdpass parameter is required to pass the file descriptor permissions to clamd as the daemon is running under clamav user and group.
The number of available threads for clamdscan is determined in /etc/clamav/clamd.conf via MaxThreads parameter clamd.conf(5). Even though you may see that the number of MaxThreads specified is more than one (current default is 10), when you start the scan using clamdscan from command line and do not specify --multiscan option, only one effective CPU thread will be used for scanning.