Scanning - ClamAV Documentation
Description: An open source malware detection toolkit and antivirus engine.

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# Scanning

Table Of Contents

- Scanning
  - Daemon
    - ClamD
    - ClamDScan
      - ClamDScan mode and option interactions
    - ClamDTop
    - On-Access Scanning
      - ClamOnAcc (v0.102+)
    - ClamD (v0.101)
  - One-Time Scanning
    - ClamScan
      - Some basic scans
  - Process Memory Scanning
  - Disclaimers
  - Windows-specific Issues
    - Globbing
    - File paths
      - Socket and libclamav API Input

> Tip: The commands on Windows are generally the same, but you may need to add the `.exe` extension to run the ClamAV applications.

## Daemon

### ClamD

`clamd` is a multi-threaded daemon that uses libclamav to scan files for viruses. Scanning behavior can be fully configured to fit most needs by modifying `clamd.conf`.

As `clamd` requires a virus signature database to run, we recommend setting up ClamAV’s official signatures before running `clamd` using `freshclam`.

The daemon works by listening for commands on the sockets specified in `clamd.conf`. Listening is supported over both Unix local sockets and TCP sockets.

IMPORTANT: `clamd` does not currently protect or authenticate traffic coming over the TCP socket, meaning it will accept commands from any source that can reach that socket. Thus, we strongly recommend following best networking practices when setting up your `clamd` instance. I.e. don’t expose your TCP socket to the Internet.

For details about socket types, command framing, scan commands, streaming file contents, passing file descriptors, and reading one or more scan results, see the ClamD protocol guide.

As with most ClamAV tools, you can find out more about these by invoking the command:

    man clamd

The daemon also handles the following signals as so:

- `SIGTERM` - perform a clean exit
- `SIGHUP` - reopen the log file
- `SIGUSR2` - reload the database

It should be noted that `clamd` should not be started using the shell operator `&` or other external tools which would start it as a background process. Instead, you should run `clamd` which will load the database and then daemonize itself (unless you have specified otherwise in `clamd.conf`). After that, clamd is ready to accept connections and perform file scanning.

Once you have set up your configuration to your liking, and understand how you will be sending commands to the daemon, running `clamd` itself is simple. Simply execute the command:

    clamd

### ClamDScan

`clamdscan` is a `clamd` client, which greatly simplifies the task of scanning files with `clamd`. It sends commands to the `clamd` daemon across the socket specified in `clamd.conf` and generates a scan report after all requested scanning has been completed by the daemon.

Thus, to run `clamdscan`, you must have an instance of `clamd` already running as well.

Please keep in mind, that as a simple scanning client, `clamdscan` cannot change scanning and engine configurations. These are tied to the `clamd` instance and the configuration you set up in `clamd.conf`. Therefore, while `clamdscan` will accept many of the same commands as its sister tool `clamscan`, it will simply ignore most of them as (by design) no mechanism exists to make ClamAV engine configuration changes over the `clamd` socket.

Again, running `clamdscan`, once you have a working `clamd` instance, is simple:

    clamdscan [*options*] [*file/directory/-*]

#### ClamDScan mode and option interactions

`clamdscan` sends scan work to a running `clamd` daemon. What it sends depends first on the socket type, and then on command-line options:

- Unix/local socket:
  - By default, `clamdscan` asks the local daemon to open the paths you provide. The daemon must be able to see those paths and have permission to read them.
  - With `--fdpass`, `clamdscan` opens each file itself and passes the open file to the daemon. This is useful when the daemon runs as a different user or sees a different filesystem view. This option only works with a Unix/local socket and fd-passing support.
  - With `--stream`, `clamdscan` sends file contents to the daemon instead of asking the daemon to open paths.
  - With `--multiscan`, directory scans can use multiple daemon worker threads. If `--stream` or `--fdpass` is also used, `clamdscan` walks the requested paths itself and submits individual file scans while still allowing the daemon to process multiple files in parallel.
  - `--allmatch` is only effective when `clamdscan` is asking the daemon to open paths directly and is not using `--multiscan`, `--stream`, or `--fdpass`.
- TCP socket:
  - When the daemon is remote, `clamdscan` sends file contents instead of local paths because client paths may not exist on the daemon host.
  - When the daemon is local and `clamdscan` can determine that it is local, `clamdscan` may ask the daemon to open local paths directly.
  - `--stream` forces `clamdscan` to send file contents, even when the daemon is local.
  - `--fdpass` is not available over TCP. Use either `--stream` or `--fdpass` for a scan, based on the socket type and how the daemon can access the files.
  - With `--multiscan`, local directory scans may use multiple daemon worker threads. Remote scans and `--stream` scans are handled as individual file scans, while still allowing the daemon to process multiple files in parallel.
  - `--allmatch` is only effective when `clamdscan` is asking a local daemon to open paths directly and is not using `--multiscan` or `--stream`.

`--allmatch` is not useful with `--multiscan`; use it only for scans where `clamdscan` is asking a local daemon to open paths directly. For quarantine, choose one action for a scan: `--move`, `--copy`, or `--remove`.

Quarantine actions such as `--move`, `--copy`, and `--remove` are performed by `clamdscan`, not by `clamd`. For directory scans with quarantine actions enabled, `clamdscan` resolves the action path for each file before requesting the scan. When `--multiscan` is also enabled, `clamdscan` submits individual file scans so it can preserve the scan result to action-path association while still allowing `clamd` to process multiple files in parallel.

### ClamDTop

`clamdtop` is a tool to monitor one or multiple instances of `clamd`. It has a colorized ncurses interface, which shows each job queued, memory usage, and information about the loaded signature database for the connected `clamd` instance(s). By default it will attempt to connect to the local `clamd` as defined in `clamd.conf`. However, you can specify other `clamd` instances at the command line.

To learn more, use the commands

    man clamdtop

or

    clamdtop --help

### On-Access Scanning

The ClamOnAcc application provides On-Access Scanning for Linux systems. On-Access Scanning is a form of real-time protection that uses ClamD to scan files when they’re accessed.

#### ClamOnAcc (v0.102+)

ClamAV’s On-Access Scanning (`clamonacc`) is a client that runs in its own application alongside, but separately from the `clamd` instance. The On-Access Scanner is capable of preventing access to/from any malicious files it discovers–based on the verdict it receives from `clamd`–but by default it is configured to run in notify-only mode, which means it will simply alert the user if a malicious file is detected, then take any additional actions that the user may have specified at the command line, but it will not actively prevent processes from reading or writing to that file.

> Disclaimer: Enabling Prevention mode will seriously impact performance if used on commonly accessed directories.

> Tip: You can run ClamOnAcc multiple times simultaneously, each with a different config. If you want to enable Prevention-mode for one directory, while sticking to notify-only mode for any other monitored directories, that’s an option!

On-Access Scanning is primarily set up through `clamd.conf`. However, you can learn more about all the configuration and command line options available to you by reading the On-Access Scanning User Guide.

Once you have set up the On-Access Scanner (and `clamd`) to your liking, you will first need to run `clamd` before you can start it. If your `clamd` instance is local, it is required you run clamd as a user that is excluded (via `OnAccessExcludeUname` or `OnAccessExcludeUID`) from On-Access scanning events (e.g.) to prevent `clamonacc` from triggering events endlessly as it sends scan requests to `clamd`:

    su - clamav -c "/usr/local/bin/clamd

After the daemon is running, you can start the On-Access Scanner. `clamonacc` must be run as root in order to utilize its kernel event detection and intervention features:

    sudo clamonacc

It will run a number of startup checks to test for a sane configuration, and ensure it can connect to `clamd`, and if everything checks out `clamonacc` will automatically fork to the background and begin monitoring your system for events.

### ClamD (v0.101)

In older versions, ClamAV’s On-Access Scanner is a thread that runs within a `clamd` instance. The On-Access Scanner is capable of blocking access to/from any malicious files it discovers–based on the verdict it finds using the engine it shares with `clamd`–but by default it is configured to run in `notify-only` mode, which means it will simply alert the user if a malicious file is detected, but it will not actively prevent processes from reading or writing to that file.

On-Access Scanning is primarily set up through `clamd.conf`. However, you can learn more about all the configuration and command line options available to you by reading the On-Access Scanning User Guide.

Once you have set up the On-Access Scanner to your liking, you will need to run `clamd` with elevated permissions to start it.

    sudo clamd

## One-Time Scanning

### ClamScan

`clamscan` is a command line tool which uses libclamav to scan files and/or directories for viruses. Unlike `clamdscan`, `clamscan` does not require a running `clamd` instance to function. Instead, `clamscan` will create a new engine and load in the virus database each time it is run. It will then scan the files and/or directories specified at the command line, create a scan report, and exit.

By default, when loading databases, `clamscan` will check the location to which `freshclam` installed the virus database signatures. This behavior, along with a myriad of other scanning and engine controls, can be modified by providing flags and other options at the command line.

There are too many options to list all of them here. So we’ll only cover a few common and more interesting ones:

- `--log=FILE` - save scan report to FILE
- `--database=FILE/DIR` - load virus database from FILE or load all supported db files from DIR
- `--official-db-only[=yes/no(*)]` - only load official signatures
- `--max-filesize=#n` - files larger than this will be skipped and assumed clean
- `--max-scansize=#n` - the maximum amount of data to scan for each container file
- `--leave-temps[=yes/no(*)]`- do not remove temporary files
- `--file-list=FILE` - scan files from FILE
- `--quiet` - only output error messages
- `--bell` - sound bell on virus detection
- `--cross-fs[=yes(*)/no]` - scan files and directories on other filesystems
- `--move=DIRECTORY` - move infected files into DIRECTORY
- `--copy=DIRECTORY` - copy infected files into DIRECTORY
- `--bytecode-timeout=N` - set bytecode timeout (in milliseconds)
- `--heuristic-alerts[=yes(*)/no]` - toggles heuristic alerts
- `--alert-encrypted[=yes/no(*)]` - alert on encrypted archives and documents
- `--nocerts` - disable authenticode certificate chain verification in PE files
- `--disable-cache` - disable caching and cache checks for hash sums of scanned files

To learn more about the options available when using `clamscan` please reference:

    man clamscan

and

    clamscan --help

Otherwise, the general usage of clamscan is:

    clamscan [options] [file/directory/-]

#### Some basic scans

Run this to scan the files in the current directory:

    clamscan .

This will scan the current directory. At the end of the scan, it will display a summary. If you notice in the clamscan output, it only scanned something like 60 files, even though there are more files in subdirectories. By default, clamscan will only scan files in the current directory.

Run this to scan all the files in the current directory:

    clamscan --recursive .

Run this to scan ALL the files on your system, it will take quite a while. Keep in mind that you can cancel it at any time by pressing `Ctrl-C`:

Linux/Unix:

    clamscan --recursive /

Windows:

    clamscan.exe --recursive C:\

## Process Memory Scanning

> Note: This feature requires running ClamAV as Administrator.

`clamscan` and `clamdscan` are able to scan the virtual memory of currently executing processes. To do so, use the `--memory` option:

    clamscan --memory

The `--kill` and `--unload` options allow for killing/unloading infected loaded modules.

## Disclaimers

> Disclaimer: ClamAV doesn’t have a “quick scan” mode. ClamAV is malware detection toolkit, not an endpoint security suite. It’s up to you to decide what to scan. A full system scan is going to take a long time with ClamAV or with any anti-virus software.

> Disclaimer 2: ClamScan, ClamOnAcc, and ClamDScan each include `--remove` options for deleting any file which alerts during a scan. This is generally a terrible idea, unless you’re monitoring an upload/downloads directory. False positives happen! You do not want to have the wrong file accidentally deleted. Instead, consider using `--move` or perhaps just `--copy` and set up script with the ClamD `VirusEvent` feature to notify you when something has been detected.

## Windows-specific Issues

### Globbing

Since the Windows command prompt doesn’t take care of wildcard expansion, minimal emulation of unix glob() is performed internally. It supports `*` and `?` only.

### File paths

Please always use the backslash as the path separator. SMB Network shares and UNC paths are supported.

#### Socket and libclamav API Input

The Windows version of ClamAV requires all the input to be UTF-8 encoded.

This affects:

- The API, notably the `cl_scanfile()` function
- ClamD socket input, e.g. the commands `SCAN`, `CONTSCAN`, `MULTISCAN`, etc.
- ClamD socket output, i.e replies to the above queries

For legacy reasons ANSI (i.e. `CP_ACP`) input will still be accepted and processed as before, but with two important remarks:

1. Socket replies to ANSI queries will still be UTF-8 encoded.
2. ANSI sequences which are also valid UTF-8 sequences will be handled as UTF-8.

As a side note, console output (stdin and stderr) will always be OEM encoded, even when redirected to a file.