How to Scan for Rootkits, backdoors and Exploits Using ‘Rootkit Hunter’ in Linux

Guys, if you are a regular reader of you will notice that this is our third article on security tools. In our previous two articles, we have given you all the guidance in how to secure Apache and Linux Systems from Malware, DOS, and DDOS attacks using mod_security and mod_evasive and LMD (Linux Malware Detect).

Again we are here to introduce a new security tool called Rkhunter (Rootkit Hunter). This article will guide you on a way to install and configure RKH (RootKit Hunter) in Linux systems using source code.

Rootkit Hunter - Scans Linux Systems for Rootkits, backdoors and Local Exploits
Rootkit Hunter – Scans Linux Systems for Rootkits, backdoors, and Local Exploits

What Is Rkhunter?

Rkhunter (Rootkit Hunter) is an open-source Unix/Linux based scanner tool for Linux systems released under GPL that scans backdoors, rootkits, and local exploits on your systems.

It scans hidden files, wrong permissions set on binaries, suspicious strings in the kernel, etc. To know more about Rkhunter and its features visit

Install Rootkit Hunter Scanner in Linux Systems

Step 1: Downloading Rkhunter

First, download the latest stable version of the Rkhunter tool by going to or use the below Wget command to download it on your systems.

# cd /tmp
# wget

Step 2: Installing Rkhunter

Once you have downloaded the latest version, run the following commands as a root user to install it.

# tar -xvf rkhunter-1.4.6.tar.gz 
# cd rkhunter-1.4.6
# ./ --layout default --install
Sample Output
Checking system for:
 Rootkit Hunter installer files: found
 A web file download command: wget found
Starting installation:
 Checking installation directory "/usr/local": it exists and is writable.
 Checking installation directories:
  Directory /usr/local/share/doc/rkhunter-1.4.2: creating: OK
  Directory /usr/local/share/man/man8: exists and is writable.
  Directory /etc: exists and is writable.
  Directory /usr/local/bin: exists and is writable.
  Directory /usr/local/lib64: exists and is writable.
  Directory /var/lib: exists and is writable.
  Directory /usr/local/lib64/rkhunter/scripts: creating: OK
  Directory /var/lib/rkhunter/db: creating: OK
  Directory /var/lib/rkhunter/tmp: creating: OK
  Directory /var/lib/rkhunter/db/i18n: creating: OK
  Directory /var/lib/rkhunter/db/signatures: creating: OK
 Installing OK
 Installing OK
 Installing OK
 Installing OK
 Installing backdoorports.dat: OK
 Installing mirrors.dat: OK
 Installing programs_bad.dat: OK
 Installing suspscan.dat: OK
 Installing rkhunter.8: OK
 Installing CHANGELOG: OK
 Installing FAQ: OK
 Installing LICENSE: OK
 Installing README: OK
 Installing language support files: OK
 Installing ClamAV signatures: OK
 Installing rkhunter: OK
 Installing rkhunter.conf: OK
Installation complete

Step 3: Updating Rkhunter

Run the RKH updater to fill the database properties by running the following command.

# /usr/local/bin/rkhunter --update
# /usr/local/bin/rkhunter --propupd
Sample Output
[ Rootkit Hunter version 1.4.6 ]

Checking rkhunter data files...
  Checking file mirrors.dat                                  [ Updated ]
  Checking file programs_bad.dat                             [ No update ]
  Checking file backdoorports.dat                            [ No update ]
  Checking file suspscan.dat                                 [ No update ]
  Checking file i18n/cn                                      [ No update ]
  Checking file i18n/de                                      [ No update ]
  Checking file i18n/en                                      [ No update ]
  Checking file i18n/tr                                      [ No update ]
  Checking file i18n/tr.utf8                                 [ No update ]
  Checking file i18n/zh                                      [ No update ]
  Checking file i18n/zh.utf8                                 [ No update ]
  Checking file i18n/ja                                      [ No update ]
File created: searched for 177 files, found 131, missing hashes 1

Step 4: Setting Cronjob and Email Alerts

Create a file called under /etc/cron.daily/, which then scans your file system every day and sends email notifications to your email id. Create the following file with the help of your favorite editor.

# vi /etc/cron.daily/

Add the following lines of code to it and replace “YourServerNameHere” with your “Server Name” and “[email protected]” with your “Email Id“.

/usr/local/bin/rkhunter --versioncheck
/usr/local/bin/rkhunter --update
/usr/local/bin/rkhunter --cronjob --report-warnings-only
) | /bin/mail -s 'rkhunter Daily Run (PutYourServerNameHere)' [email protected]

Set execute permission on the file.

# chmod 755 /etc/cron.daily/

Step 5: Manual Scan and Usage

To scan the entire file system, run the Rkhunter as a root user.

# rkhunter --check
Sample Output
[ Rootkit Hunter version 1.4.6 ]

Checking system commands...

  Performing 'strings' command checks
    Checking 'strings' command                               [ OK ]

  Performing 'shared libraries' checks
    Checking for preloading variables                        [ None found ]
    Checking for preloaded libraries                         [ None found ]
    Checking LD_LIBRARY_PATH variable                        [ Not found ]

  Performing file properties checks
    Checking for prerequisites                               [ OK ]
    /usr/local/bin/rkhunter                                  [ OK ]
    /usr/sbin/adduser                                        [ OK ]
    /usr/sbin/chkconfig                                      [ OK ]
    /usr/sbin/chroot                                         [ OK ]
    /usr/sbin/depmod                                         [ OK ]
    /usr/sbin/fsck                                           [ OK ]
    /usr/sbin/fuser                                          [ OK ]
    /usr/sbin/groupadd                                       [ OK ]
    /usr/sbin/groupdel                                       [ OK ]
    /usr/sbin/groupmod                                       [ OK ]
    /usr/sbin/grpck                                          [ OK ]
    /usr/sbin/ifconfig                                       [ OK ]
    /usr/sbin/ifdown                                         [ Warning ]
    /usr/sbin/ifup                                           [ Warning ]
    /usr/sbin/init                                           [ OK ]
    /usr/sbin/insmod                                         [ OK ]
    /usr/sbin/ip                                             [ OK ]
    /usr/sbin/lsmod                                          [ OK ]
    /usr/sbin/lsof                                           [ OK ]
    /usr/sbin/modinfo                                        [ OK ]
    /usr/sbin/modprobe                                       [ OK ]
    /usr/sbin/nologin                                        [ OK ]
    /usr/sbin/pwck                                           [ OK ]
    /usr/sbin/rmmod                                          [ OK ]
    /usr/sbin/route                                          [ OK ]
    /usr/sbin/rsyslogd                                       [ OK ]
    /usr/sbin/runlevel                                       [ OK ]
    /usr/sbin/sestatus                                       [ OK ]
    /usr/sbin/sshd                                           [ OK ]
    /usr/sbin/sulogin                                        [ OK ]
    /usr/sbin/sysctl                                         [ OK ]
    /usr/sbin/tcpd                                           [ OK ]
    /usr/sbin/useradd                                        [ OK ]
    /usr/sbin/userdel                                        [ OK ]
    /usr/sbin/usermod                                        [ OK ]
[Press  to continue]

Checking for rootkits...

  Performing check of known rootkit files and directories
    55808 Trojan - Variant A                                 [ Not found ]
    ADM Worm                                                 [ Not found ]
    AjaKit Rootkit                                           [ Not found ]
    Adore Rootkit                                            [ Not found ]
    aPa Kit                                                  [ Not found ]

[Press  to continue]

  Performing additional rootkit checks
    Suckit Rookit additional checks                          [ OK ]
    Checking for possible rootkit files and directories      [ None found ]
    Checking for possible rootkit strings                    [ None found ]

[Press  to continue]

Checking the network...

  Performing checks on the network ports
    Checking for backdoor ports                              [ None found ]
  Performing system configuration file checks
    Checking for an SSH configuration file                   [ Found ]
    Checking if SSH root access is allowed                   [ Warning ]
    Checking if SSH protocol v1 is allowed                   [ Warning ]
    Checking for a running system logging daemon             [ Found ]
    Checking for a system logging configuration file         [ Found ]
    Checking if syslog remote logging is allowed             [ Not allowed ]
System checks summary

File properties checks...
    Files checked: 137
    Suspect files: 6

Rootkit checks...
    Rootkits checked : 383
    Possible rootkits: 0

Applications checks...
    Applications checked: 5
    Suspect applications: 2

The system checks took: 5 minutes and 38 seconds

All results have been written to the log file: /var/log/rkhunter.log

One or more warnings have been found while checking the system.
Please check the log file (/var/log/rkhunter.log)

The above command generates a log file under /var/log/rkhunter.log with the check results made by Rkhunter.

# cat /var/log/rkhunter.log
Sample Output
[11:21:04] Running Rootkit Hunter version 1.4.6 on tecmint
[11:21:04] Info: Start date is Mon Dec 21 11:21:04 AM IST 2020
[11:21:04] Checking configuration file and command-line options...
[11:21:04] Info: Detected operating system is 'Linux'
[11:21:04] Info: Found O/S name: Fedora release 33 (Thirty Three)
[11:21:04] Info: Command line is /usr/local/bin/rkhunter --check
[11:21:04] Info: Environment shell is /bin/bash; rkhunter is using bash
[11:21:04] Info: Using configuration file '/etc/rkhunter.conf'
[11:21:04] Info: Installation directory is '/usr/local'
[11:21:04] Info: Using language 'en'
[11:21:04] Info: Using '/var/lib/rkhunter/db' as the database directory
[11:21:04] Info: Using '/usr/local/lib64/rkhunter/scripts' as the support script directory
[11:21:04] Info: Using '/usr/local/sbin /usr/local/bin /usr/sbin /usr/bin /bin /sbin /usr/libexec /usr/local/libexec' as the command directories
[11:21:04] Info: Using '/var/lib/rkhunter/tmp' as the temporary directory
[11:21:04] Info: No mail-on-warning address configured
[11:21:04] Info: X will be automatically detected
[11:21:04] Info: Found the 'basename' command: /usr/bin/basename
[11:21:04] Info: Found the 'diff' command: /usr/bin/diff
[11:21:04] Info: Found the 'dirname' command: /usr/bin/dirname
[11:21:04] Info: Found the 'file' command: /usr/bin/file
[11:21:04] Info: Found the 'find' command: /usr/bin/find
[11:21:04] Info: Found the 'ifconfig' command: /usr/sbin/ifconfig
[11:21:04] Info: Found the 'ip' command: /usr/sbin/ip
[11:21:04] Info: Found the 'ipcs' command: /usr/bin/ipcs
[11:21:04] Info: Found the 'ldd' command: /usr/bin/ldd
[11:21:04] Info: Found the 'lsattr' command: /usr/bin/lsattr

For more information and options please run the following command.

# rkhunter --help

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Ravi Saive
I am an experienced GNU/Linux expert and a full-stack software developer with over a decade in the field of Linux and Open Source technologies

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57 thoughts on “How to Scan for Rootkits, backdoors and Exploits Using ‘Rootkit Hunter’ in Linux”

  1. This whole rkhunter probably only scans the most important changes in the system, but when it comes to removing viruses – it doesn’t. Does anyone know of console antivirus that automatically deals with threats?

  2. Debcheckroot – That also detects a rootkit which is not known by any database (like f.i. NSA rootkits).

    It verifies the sha256 sums of files in the Debian/Ubuntu packages.

  3. I tried unpacking and installing rkhunter from /tmp as indicated in the instructions above but got the error “-bash: ./ Permission denied“. So I tried chmod u+x

    Still didn’t work. After a bit of searching, I found out that on my system the /tmp directory is mounted without execution permissions. I moved the rkhunter installation directory to ~ and successfully ran the rkhunter installer from that location. Thanks.


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