ClamAV (Magyar)

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fordítani
a csodálatos nemzetállamunk ékes magyar nyelvére.
Megjegyzés:
Partial translation, started 2025-06-24. (Megbeszélés a(z)
Talk:ClamAV (Magyar)
oldalon.)
A
Clam AntiVirus
(ClamAV) egy nyílt forráskódú (GPL) vírusírtó szoftver az UNIX-os rendzerekre.
Számos segédprogramot kínál, köztük egy rugalmas és skálázható, többszálú démont, egy parancssori szkennert és egy fejlett eszközt az automatikus adatbázis-frissítésekhez. Mivel a ClamAV fő felhasználási területe a fájl/mail szerverek, elsősorban a rosszindulatú programokat észleli a beépített aláírások segítségével, és nem egy hagyományos végpontbiztonsági csomag.
A rosszindulatú szoftverek elleni termékek jelenlegi helyzete Linuxon több tényező miatt nem megfelelő:
Korlátozott választék: A Windowshoz képest kevesebb felhasználó/ügyfél van, ami miatt a vállalatoknak korlátozott az érdeklődésük a Linuxra való termékfejlesztés iránt.
Kényelmetlenkedés: Ez a tudatosság és a rosszindulatú programok elleni védelem hiányához vezet. Ez hiányt teremt a proaktív védelmi mechanizmusokban.
a jellemzők hiánya: A meglévő eszközökből gyakran hiányoznak a fejlett funkciók, amelyek a Windows vírusírtó termékekben gyakoriak, így kevésbé hatékonyak Linuxon.
Ez elég rossz lehet, mert a vírusok mennyisége növekszik a Linuxon, és mert a szerverek és az IoT eszközök száma is növekszik.
Jelenleg Linuxon a kevés létező és aktívan fejlesztett rosszindulatú programok elleni megoldás egyike a ClamAV.
Telepítés
Install
the
clamav
package.
This will install the following tools:
clamd: ClamAV Daemon
clamonacc: On-Access real-time protection
clamdscan: A simple scanning client
clamdtop: A resource monitoring interface for clamd
freshclam: Daemon for virus signature updates
clamconf: Tool to create and check configuration files
All ClamAV related tools, services and daemons communicate with clamd via a socket.
By default this is done via a local socket, "LocalSocket."
ClamAV also provides the possibility to enable communication via remote locations by using a network socket which is configured and names as "TCPSocket".y exists.
Figyelmeztetés
Please note the following warning about clamd port security when changing the configuration to use TCPSocket instead of LocalSocket.  Generally use an local unix socket but note that this port is not authenticated or protected.
For more details see:
https://blog.clamav.net/2016/06/regarding-use-of-clamav-daemons-tcp.html
https://docs.clamav.net/manual/Usage/Scanning.html#clamd-v0101
(Daemon and then ClamD section)
Another important thing to note is that when using LocalSocket, then clamd will need to be run under a user with the right permissions to scan the files you plan on including in your monitoring.
Beállítás
Default configuration files should already exist. Otherwise, you can manually create them by using
clamconf
:
# clamconf -g freshclam.conf > freshclam.conf
# clamconf -g clamd.conf > clamd.conf
# clamconf -g clamav-milter.conf > clamav-milter.conf
The following files contain the relevant configuration options.
freshclam:
/etc/clamav/freshclam.conf
clamd:
/etc/clamav/clamd.conf
clamd mail filtering:
/etc/clamav/clamav-milter.conf
Last but not least you can check your config files by running
clamconf
The default installation will create "sane" default configurations such as: a
clamav
system user, a
clamav
group, and the required
clamd
configuration files.
Additional recommended configurations can be set:
/etc/clamav/clamd.conf
# Log time with each message.
# Default: no
LogTime yes

# Log additional information about the infected file, such as its
# size and hash, together with the virus name.
ExtendedDetectionInfo yes

# Run as another user (clamd must be started by root for this option to work)
# Default: don't drop privileges
User clamav

# Maximum depth directories are scanned at.
# Default: 15
MaxDirectoryRecursion 20

DetectPUA yes
HeuristicAlerts yes
ScanPE yes
ScanELF yes
ScanOLE2 yes
ScanPDF yes
ScanSWF yes
ScanXMLDOCS yes
ScanHWP3 yes
ScanOneNote yes
ScanMail yes
ScanHTML yes
ScanArchive yes
Bytecode yes
AlertBrokenExecutables yes
AlertBrokenMedia yes
AlertEncrypted yes
AlertEncryptedArchive yes
AlertEncryptedDoc yes
AlertOLE2Macros yes
AlertPartitionIntersection yes
Enabling real-time protection OnAccessScan
On-access scanning is the real-time protection daemon which will scan the file while reading, writing or executing it. It can be configured to either notify on detection or prevent/block on detection.
Configuration OnAccessScan is done via editing the
/etc/clamav/clamd.conf
configuration file.
The following changes are required for OnAccessScan to work:
/etc/clamav/clamd.conf
# Exclude the UID of the scanner itself from checking, to prevent loops
OnAccessExcludeUname clamav
The following additional changes are recommended and will put the On-Access Scanner into notify-only mode:
/etc/clamav/clamd.conf
# Set the mount point where to recursively perform the scan,
# this could be every path or multiple path (one line for path)
OnAccessMountPath /

# Alternatively, add some directories instead of mount points
# OnAccessIncludePath /home

# Prevention doesn't work with OnAccessMountPath.
# It works with OnAccessIncludePath, as long as /usr and /etc are not included.
# Including /var while activating prevention is also not recommended, because
# this would slow down package installation by a factor of 1000.
OnAccessPrevention no

# Perform scans on newly created, moved, or renamed files
OnAccessExtraScanning yes

# Optionallyexclude root-owned processes
# OnAccessExcludeRootUID true
Creating notification popups for alerts
So far ClamAV will silently log any detection but not alert the user. A pop-up to alert the user on any detection can be added.
First add the following line to your clamd configuration:
/etc/clamav/clamd.conf
VirusEvent /etc/clamav/virus-event.bash
Next, allow the
clamav
user to run
notify-send
as any user with custom environment variables via
sudo
:
/etc/sudoers.d/clamav
clamav ALL = (ALL) NOPASSWD: SETENV: /usr/bin/notify-send
Next, create the file
/etc/clamav/virus-event.bash
, make it
executable
and add the following:
/etc/clamav/virus-event.bash
#!/bin/bash
PATH=/usr/bin
ALERT="Signature detected by clamav: $CLAM_VIRUSEVENT_VIRUSNAME in $CLAM_VIRUSEVENT_FILENAME"

# Send an alert to all graphical users.
for ADDRESS in /run/user/*; do
    USERID=${ADDRESS#/run/user/}
    /usr/bin/sudo -u "#$USERID" DBUS_SESSION_BUS_ADDRESS="unix:path=$ADDRESS/bus" PATH=${PATH} \
        /usr/bin/notify-send -u critical -i dialog-warning "Virus found!" "$ALERT"
done
This allows you to change/specify the message when a virus has been detected by clamd's on-access scanning service.
By default,
clamonacc
passes
clamav
the names of just-accessed files for scanning. This is a problem, because files inaccessible to the
clamav
user cannot be scanned this way. Instead, it is possible to instruct
clamonacc
(which always runs as
root
) to use file descriptor passing.
Edit
clamav-clamonacc.service
with the following:
[Service]
ExecStart=
ExecStart=/usr/sbin/clamonacc -F
--fdpass
--log=/var/log/clamav/clamonacc.log
Lastly, you will need to
start/enable
or
restart
the
clamav-clamonacc.service
as well as the
clamav-daemon.service
See:
#Starting the ClamAV + OnAccessScanning daemon
If you get
AppArmor
denials about
clamd
, set the profile to a complain-only mode:
# aa-complain clamd
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
For automatic updates first create and set the required freshclam.log file:
touch /var/log/clamav/freshclam.log
chmod 600 /var/log/clamav/freshclam.log
chown clamav /var/log/clamav/freshclam.log
Start/enable
clamav-freshclam.service
or
clamav-freshclam-once.timer
so that the virus definitions are kept recent.
The
clamav-freshclam.service
launches
freshclam
in daemon mode, defaulting to 12 checks per day (every 2 hours). The frequency can be changed in
/etc/clamav/freshclam.conf
.
The
clamav-freshclam-once.timer
launches the
freshclam
check once per day. The frequency can be changed in
/usr/lib/systemd/system/clamav-freshclam-once.timer
.
Megjegyzés
Freshclam in daemon mode checks on every (service) start.
Over 1 check per hour results in being blocked by the CDN for 24 hours.
The
.timer
unit follows the set schedule, regardless of reboots or service restarts.
You can add additional virus signature databases by following
#Adding more databases/signatures repositories
.
Starting the ClamAV + OnAccessScanning daemon
This will load all virus signatures in RAM. As of February 2024 these signatures require at least 1.6GB of free RAM. Twice that amount of RAM is used shortly, during the periodic update of the signatures.
Megjegyzés
You will need to run
freshclam
before starting the service for the first time or you will run into trouble/errors which will prevent ClamAV from starting correctly.
The daemon is not needed if you only want to perform stand-alone scans. See
Scan for viruses
below.
The daemon by itself does not do anything yet unless you enable On-Access Scanning. See:
#Enabling real-time protection OnAccessScan
The service is called
clamav-daemon.service
.
Start
it and
enable
it to start at boot.
Additionally
start
and
enable
clamav-clamonacc.service
for real-time on access protection.
Szoftver tesztelése
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://secure.eicar.org/eicar.com.txt
| clamscan -
The output
must
include:
stdin: Win.Test.EICAR_HDB-1 FOUND
Real-time protection
You can download and save a the eicar file in one of the directories you configured clamonacc to monitor. For example:
$ cd /home/user/Downloads/
$ wget
https://secure.eicar.org/eicar.com.txt
$ cat eicar.com.txt
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 either
clamav-unofficial-sigs
AUR
(see
GitHub description
) or
python-fangfrisch
AUR
(see
online documentation
). Both will add signatures/databases from popular providers, e.g. MalwarePatrol, SecuriteInfo, Yara, Linux Malware Detect, etc.
Megjegyzés
You still must have the
clamav-freshclam.service
started
in order to have official signature updates from ClamAV mirrors.
Option #1: Set up Fangfrisch
Fangfrisch
was designed as a more secure, flexible and convenient replacement for clamav-unofficial-sigs, and requires
very little configuration
(
/etc/fangfrisch/fangfrisch.conf
).
Most importantly, Fangfrisch never needs to be run with root permissions, unlike clamav-unofficial-sigs.
Create database structure by running:
# sudo -u clamav /usr/bin/fangfrisch --conf /etc/fangfrisch/fangfrisch.conf initdb
Enable
the
fangfrisch.timer
(system-level).
Option #2: 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
.
MalwarePatrol database
If you would like to use the MalwarePatrol database, sign up for an account at
https://malwareblocklist.org/
(for a fee).
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
There are two options for on-demand scanning:
using the stand-alone scanner
clamscan
can be used to scan certain files, home directories, or an entire system:
$ clamscan myfile
$ clamscan --recursive --infected /home/archie
# 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 daemon
clamdscan
is similar to the above but utilizes the daemon, which must be running for the command to work. Most options are ignored since the daemon reads the settings specified in
/etc/clamav/clamd.conf
.
Using the milter
Milter will scan your sendmail server for email containing virus. Adjust
/etc/clamav/clamav-milter.conf
to your needs. For example:
/etc/clamav/clamav-milter.conf
MilterSocket /tmp/clamav-milter.socket
MilterSocketMode 660
FixStaleSocket yes
User clamav
MilterSocketGroup clamav
PidFile /run/clamav/clamav-milter.pid
TemporaryDirectory /tmp
ClamdSocket unix:/run/clamav/clamd.ctl
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
Restart=Always

[Install]
WantedBy=multi-user.target
Your system may require a different
Restart=
directive. It is needed, for example, when an automatism like
logrotate
stops the service.
Enable
and
start
clamav-milter.service
.
For
Postfix
add the following lines to
/etc/postfix/main.cf
:
/etc/postfix/main.cf
smtpd_milters = unix:/tmp/clamav-milter.socket
milter_default_action = tempfail
Check
journalctl
if the permission to access
clamav-milter.socket
for postfix is set accordingly, if not, add user postfix to group
clamav
.
Tippek és trükkök
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 do not want computer to become sluggish. If there is a need to scan large directory 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 -print0 | xargs -0 -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.
This will consume loads of RAM as all processes are individual and will load the signature files. A single thread will consume around 1G (or more) of RAM, and may hang your computer unless OOM is clever enough. You may want to consider using clamdscan instead.
Using clamdscan
If you already have
clamd
daemon running
clamdscan
can be used instead (see
#Starting the ClamAV + OnAccessScanning 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.
Enable TCPSocket
If you enable TCPSocket in
/etc/clamav/clamd.conf
, you must
edit
clamav-daemon.socket
too (see
FS#57669
). The
systemd
socket file needs to be configured with a matching port and IP address:
/etc/systemd/system/clamav-daemon.socket.d/override.conf
[Socket]
ListenStream=
ListenStream=/run/clamav/clamd.ctl
ListenStream=127.0.0.1:3310
And finally
restart
clamav-daemon.socket
to see a Clamd binding at TCP port 3310:
# ss -tulpn | grep clamd
tcp   LISTEN 0      4096       127.0.0.1:3310      0.0.0.0:*    users:(("clamd",pid=599,fd=4),("systemd",pid=1,fd=44))
Hibaelhárítás
Megjegyzés
Make sure the user from which you are running
clamscan
has read permissions for the database files (
/var/lib/clamav/*.c?d
)
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:
Figyelmeztetés
See the warning in
#Installation
[
Hibás hivatkozás
: Érvénytelen szekció]
about clamd port security.
# touch /run/clamav/clamd.ctl
# chown clamav:clamav /run/clamav/clamd.ctl
Then, edit
/etc/clamav/clamd.conf
- uncomment this line:
LocalSocket /run/clamav/clamd.ctl
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
as 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
További olvasnivaló a témában
Wikipedia:ClamAV