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Install CSF (ConfigServer Security & Firewall) on Ubuntu 20.04 LTS

Last Updated: Fri, May 15, 2020
Linux Guides Security System Admin Ubuntu


ConfigServer Security & Firewall (CSF) is a popular security tool for Linux. It provides a simple interface for iptables to protect Linux servers. CSF comes with multiple features: a stateful packet inspection firewall (SPI), intrusion detection, a login failure daemon, DDOS protection, and control panel integration. This tutorial covers installation, basic configuration, and essential commands for CSF on Ubuntu 20.04.

1. Deploy Ubuntu Server

2. Prepare for CSF Installation

Ubuntu 20.04 comes with UFW firewall by default, which must be removed before installing CSF.

# apt remove ufw

Install the CSF dependencies.

# apt install perl zip unzip libwww-perl liblwp-protocol-https-perl

CSF requires Sendmail to send alerts to the administrator.

# apt install sendmail-bin

3. Install CSF

  1. Change to /usr/src

    # cd /usr/src
  2. Download the CSF distribution.

    # wget
  3. Extract CSF.

    # tar -xzf csf.tgz
  4. Change to /usr/src/csf

    # cd csf
  5. Run the install script.

    # sh
  6. Verify the required iptables modules for CSF are available.

    # perl /usr/local/csf/bin/

    Confirm that all tests report OK, and you see the following result.

    RESULT: csf should function on this server
  7. Verify CSF status after installation.

    # csf -v 

    You should see a result similar to:

    csf: v14.02 (generic)
    *WARNING* TESTING mode is enabled - do not forget to disable it in the configuration

4. Configure CSF

  1. CSF runs in TESTING mode by default. Edit /etc/csf/csf.conf to disable TESTING mode.

    # nano /etc/csf/csf.conf
  2. Locate the line TESTING = "1", and change the value to "0".

    TESTING = "0"
  3. Locate the line RESTRICT_SYSLOG = "0", and change the value to "3". This means only members of the RESTRICT_SYSLOG_GROUP may access syslog/rsyslog files.

  4. Save the configuration file.

  5. Stop and reload CSF with the -ra option.

    # csf -ra

Common CSF Commands & Configuration

Start CSF

# csf -s 

Stop CSF

# csf -f 

Restart CSF

You must restart CSF each time the configuration file changes.

# csf -ra 

Allow IP traffic by port

  1. Edit /etc/csf/csf.conf

    # nano /etc/csf/csf.conf
  2. Locate the following lines and add the required ports.

    # Allow incoming TCP ports
    TCP_IN = 20,21,22,25,26,53,80,110,143,443,465,587,993,995,2077”
    # Allow outgoing TCP ports
    TCP_OUT = 20,21,22,25,26,37,43,53,80,110,113,443,465,873,2087”
  3. Restart CSF for the changes to take effect.

    # csf -ra

Allow or deny by IP address

Use the -d option to deny by IP, for example,

# csf -d

Use the -a option to allow by IP, for example,

# csf -a

Remove IP from the allow list.

# csf -ar

Remove IP from the deny list.

# csf -dr

Deny file

Block IPs by adding a entry to /etc/csf/csf.deny.     # deny this IP    # deny this network 

Allow file

Add trusted IPs to /etc/csf/csf.allow.     # trust this IP

Check all listening ports with the -p option.

# csf -p

More Information

For more information, see the CSF website.

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