# Installation on Redhat and CentOS Linux Distributions

Below are the steps for installing ClamAV from source on Redhat and CentOS Linux.

## Install prerequisites

1. Install ClamAV dependencies
   1. Install the developer tools

          sudo yum groupinstall "Development Tools"

   2. Install library dependencies

          sudo yum install openssl openssl-devel libcurl-devel zlib-devel libpng-devel libxml2-devel json-c-devel bzip2-devel pcre2-devel ncurses-devel

   3. (very optional) Those wishing to use clamav-milter may wish to install the following

          sudo yum install sendmail sendmail-devel

   CentOS 8 Tip: Some of the above packages such as `json-c-devel` and `sendmail-devel` may not be available for CentOS 8 unless you install the EPEL repository and enable PowerTools. To enable EPEL and PowerTools, run the following:

       sudo yum install epel-release

       sudo yum config-manager --set-enabled PowerTools

       sudo yum update

       sudo yum repolist

2. Install the unit testing dependencies

       sudo yum install valgrind check check-devel

Note: LLVM is also an optional dependency. LLVM will not provide any additional features, but is an alternative method for executing bytecode signatures versus using the built-in bytecode interpreter. Limited performance testing between LLVM and the bytecode interpreter did not yield conclusive evidence that one is "better" than the other. For the sake of simplicity, it is not recommended to install LLVM.

## Download the latest stable release

1. Open a browser and navigate to the ClamAV downloads page
2. Click `clamav-<version>.tar.gz` link to download the latest stable release.

## Extract the source archive

        cd ~/Downloads
        tar xzf clamav-[ver].tar.gz
        cd clamav-[ver]

## Configure the build

ClamAV's configure script should detect each of the above dependencies automatically.

### Typical `./configure` usage

        ./configure --enable-check

Once `./configure` completes, it will print a summary. Verify that the packages you installed are in fact being detected.

Example configure summary output:

        configure: Summary of detected features follows
                    OS          : linux-gnu
                    pthreads    : yes (-lpthread)
        configure: Summary of miscellaneous features
                    check       : -lcheck_pic -pthread -lrt -lm -lsubunit
                    fanotify    : yes
                    fdpassing   : 1
                    IPv6        : yes
        configure: Summary of optional tools
                    clamdtop    : -lncurses (auto)
                    milter      : yes (disabled)
                    clamsubmit  : yes (libjson-c-dev found at /usr), libcurl-devel found at /usr)
        configure: Summary of engine performance features
                    release mode: yes
                    llvm        : no (disabled)
                    mempool     : yes
        configure: Summary of engine detection features
                    bzip2       : ok
                    zlib        : /usr
                    unrar       : yes
                    preclass    : yes (libjson-c-dev found at /usr)
                    pcre        : /usr
                    libmspack   : yes (Internal)
                    libxml2     : yes, from /usr
                    yara        : yes
                    fts         : yes (libc)

### Additional popular `./configure` options

- `--with-systemdsystemunitdir` - Do not install `systemd` socket files. This option disables systemd support, but will allow you to `make install` to a user-owned directory without requiring `sudo`/root privileges:

      ./configure --with-systemdsystemunitdir=no

- `--sysconfdir` - Install the configuration files to `/etc` instead of `/usr/local/etc`:

      ./configure --sysconfdir=/etc

- `--prefix` - Install ClamAV to a directory other than `/usr/local/`:
  - Example 1: Install to a local `./install` directory.

        ./configure --prefix=pwd/install

  - Example 2: Install ClamAV locally on an unprivileged shell account.

        ./configure --prefix=$HOME/clamav --disable-clamav --with-systemdsystemunitdir=no

- `--disable-clamav` - Don't drop super-user priveleges to run `freshclam` or `clamd` as the `clamav`* user.

      ./configure --disable-clamav

  *Tip: Using this `--disable-clamav` means that `freshclam` and `clamd` will run with root privleges if invoked using `sudo`. Running `clamd` or `clamscan` as root is not recommended. Instead of using this option, you can configure `freshclam` or `clamd` to drop to any other user by:
  - setting the `DatabaseOwner` option in `freshclam.conf` and
  - setting the `User` option in `clamd.conf`.

Please see the `./configure --help` for additional options.

## Compile ClamAV

Compile ClamAV with:

    make -j2

## Run ClamAV Unit Tests (Optional)

For peace of mind, it can be helpful to run a small suite of unit and system tests.

Run:

    make check

All tests should pass.* Output will look something like this:

            ...
        PASS: check_clamav
        PASS: check_freshclam.sh
        PASS: check_sigtool.sh
        PASS: check_unit_vg.sh
        PASS: check1_clamscan.sh
        PASS: check2_clamd.sh
        PASS: check3_clamd.sh
        PASS: check4_clamd.sh
        PASS: check5_clamd_vg.sh
        PASS: check6_clamd_vg.sh
        SKIP: check7_clamd_hg.sh
        PASS: check8_clamd_hg.sh
        PASS: check9_clamscan_vg.sh
            ...
        ============================================================================
        Testsuite summary for ClamAV 0.100.2
        ============================================================================
        # TOTAL: 13
        # PASS:  12
        # SKIP:  1
        # XFAIL: 0
        # FAIL:  0
        # XPASS: 0
        # ERROR: 0

Notes:

- The `*.vg.sh` tests will be skipped unless you run `make check VG=1`.
- The `check7_clamd.hg.sh` (helgrind) is presently disabled and will be skipped.
- For details, see: the Git commit

If you have a failure or an error in the unit tests, it could be that you are missing one or more of the prerequisites.

If you are investigating a failure, please do the following:

`cd unit_tests`

Use `less` to read the log for the failed test.
Example:

        less check4_clamd.sh.log`

To submit a bug report regarding unit text failures, please follow these bug reporting steps.

## Install ClamAV

Install ClamAV with:

    make install

Tip: If installing to the default or other system-owned directory, you may need to use `sudo`.

## First time set-up

Note: The following instructions assume you used the default install paths (i.e. `/usr/local`). If you modified the install locations using `--prefix` or `--sysconfdir` options, replace `/usr/local` with your chosen install path.

### `freshclam` config

Before you can use `freshclam` to download updates, you need to create a `freshclam` config. A sample config is provided for you.

1. Copy the sample config. You may need to use `sudo`:

       cp /usr/local/etc/freshclam.conf.sample /usr/local/etc/freshclam.conf

2. Modify the config file using your favourite text editor. Again, you may need to use `sudo`.
   - At a minimum, remove the `Example` line so `freshclam` can use the config.

   Take the time to look through the options. You can enable the sample options by deleting the `#` comment characters.

   Some popular options to enable include:

   - `LogTime`
   - `LogRotate`
   - `NotifyClamd`
   - `DatabaseOwner`

3. Create the database directory. *Tip: You may need to use `sudo`.

       mkdir /usr/local/share/clamav

### `clamd` config (optional)

You can run `clamscan` without setting the config options for `clamd`. However, the `clamd` scanning daemon allows you to use `clamdscan` to perform faster a-la-carte scans, allows you to run multi-threaded scans, and allows you to use `clamav-milter` if you want to use ClamAV as a mail filter if you host an email server.

Additionally, if you are a running modern versions of Linux where the FANOTIFY kernel feature is enabled, `clamd` has a feature run with On-Access Scanning. When properly configured*, On-Access Scanning can scan files as they are accessed and optionally block access to the file in the event that a signature alerted.

Note: At this time, for On-Access Scanning to work, `clamd` must run with `sudo`/root privileges. For more details, please see our documentation on On-Access Scanning.

1. Copy the sample config. You may need to use `sudo`:

       cp /usr/local/etc/clamd.conf.sample /usr/local/etc/clamd.conf

2. Modify the config file using your favourite text editor. Again, you may need to use `sudo`.
   - At a minimum, remove the `Example` line so `freshclam` can use the config.
   - You also need to select a Socket option for `clamd` so `clamdscan` and other utilities can communicate with `clamd`. You must enable one of the following.
     - `LocalSocket`
     - `TCPSocket`

   Take the time to look through the options. You can enable the sample options by deleting the `#` comment characters.

   Some popular options to enable include:

   - `LogTime`
   - `LogClean`
   - `LogRotate`
   - `User`
   - `ScanOnAccess`
     - `OnAccessIncludePath`
     - `OnAccessExcludePath`
     - `OnAccessPrevention`

### Configure SELinux for ClamAV

Certain distributions (notably RedHat variants) when operating with SELinux enabled use the non-standard `antivirus_can_scan_system` SELinux option instead of `clamd_can_scan_system`.

At this time, libclamav only sets the `clamd_can_scan_system` option, so you may need to manually enable `antivirus_can_scan_system`. If you don't perform this step, freshclam will log something like this when it tests the newly downloaded signature databases:

        During database load : LibClamAV Warning: RWX mapping denied: Can't allocate RWX Memory: Permission denied

To allow ClamAV to operate under SELinux, run the following:

    setsebool -P antivirus_can_scan_system 1

### Download / Update the signature database

Before you can run a scan, you'll need to download the signature databases. Once again, you may need to run with `sudo`/root privileges.

If you installed to a location in your system PATH:

    freshclam

If you installed to another location:

    /{path}/{to}/{clamav}/bin/freshclam

### Users and on user privileges

If you are running `freshclam` and `clamd` as root or with `sudo`, and you did not explicitely configure with `--disable-clamav`, you will want to ensure that the `DatabaseOwner` user specified in `freshclam.conf` owns the database directory so it can download signature udpates.

The user that `clamd`, `clamdscan`, and `clamscan` run as may be the same user, but if it isn't -- it merely needs read access to the database directory.

If you choose to use the default `clamav` user to run `freshclam` and `clamd`, you'll need to create the clamav group and the clamav user account the first time you install ClamAV.

        groupadd clamav
        useradd -g clamav -s /bin/false -c "Clam Antivirus" clamav

Finally, you will want to set user ownership of the database directory.
For example:

    sudo chown -R clamav:clamav /usr/local/share/clamav

## Usage

You should be all set up to run scans.

Take a look at our usage documentation to learn about how to use ClamAV each of the utilities.