ROOTKIT HUNTER FREQUENTLY ASKED QUESTIONS (FAQ)
===============================================

The latest version of this FAQ can be found on the RKH web site.
(https://sourceforge.net/p/rkhunter/rkh_code/ci/develop/tree/files/FAQ)


===========================================================

 1. GENERAL QUESTIONS

   1.1) What is Rootkit Hunter?
   1.2) What are rootkits?
   1.3) Can I help with the development of this project?
   1.4) I like your software! How can I thank you?


 2. INSTALLATION QUESTIONS

   2.1) How do I install Rootkit Hunter?
   2.2) How do I create a Rootkit Hunter RPM file?


 3. USAGE QUESTIONS

   3.1) Rootkit Hunter tells me there is something wrong with
        my system. What do I do?
   3.2) Rootkit Hunter tells me that I have vulnerable applications
        installed. But I have fully patched my server! How is this
        possible?
   3.3) How can I automatically run Rootkit Hunter every day?
   3.4) What is the meaning of the test names?
   3.5) Can rkhunter handle filenames with spaces in them?
   3.6) What does the following warning mean:
          Determining OS... Warning: this operating system is not
          fully supported!
   3.7) I have just installed Rootkit Hunter, and I am already
        getting warning messages. Why is that?
   3.8) When I used the '--propupd' option, Rootkit Hunter told me
        I had some missing hashes. What does this mean?
   3.9) I run rkhunter in cron and in the emailed output I get some
        strange characters. Why is this?
   3.10) When I used the '--propupd' option, Rootkit Hunter told me
         that it had found more files than it was searching for. How
         is this possible?


 4. ERROR AND WARNING MESSAGES

   4.1) What does the following warning mean:
          The file of stored file properties (rkhunter.dat) is empty,
          and should be created. To do this type in
          'rkhunter --propupd'.
   4.2) Rootkit Hunter skips some checks, and the logfile indicates
        that certain commands are missing. What can I do?
   4.3) I get warnings from PHP like:
          PHP Warning: Function registration failed - duplicate name
          - pg_update in Unknown on line 0. What does this mean?
   4.4) After performing some updates, all, or some, binaries in the
        file properties checks are marked with a 'Warning'.
        What can I do?


 5. UPDATING QUESTIONS

   5.1) Rootkit Hunter tells me that I have multiple versions
        installed. How it this possible?
   5.2) Can I be notified when a new release will be available?


 6. WHITELISTING EXAMPLES

   6.1) Common whitelisting examples

===========================================================

1. GENERAL QUESTIONS
====================

1.1) What is Rootkit Hunter?

A.   Rootkit Hunter (RKH) is an easy-to-use tool which checks
     computers running UNIX (clones) for the presence of rootkits
     and other unwanted tools.


1.2) What are rootkits?

A.   Most times they are self-hiding toolkits used by blackhats,
     crackers and scriptkiddies, to avoid the eye of the sysadmin.


1.3) Can I help with the development of this project?

A.   Yes, everyone can help in some way. For example:

     Help your fellow Rootkit Hunter users on the rkhunter-users
     mailing list;

     Send a copy of an undetected rootkit to us so that it can
     be added and help others;

     Translate RKH messages to your native language. Details of
     how to do this are in the README file. For the template
     see the standard language file i18n/en.

     Are you a package maintainer? If so, then please submit
     your changes to us so that everyone can benefit from them;

     Are you an end-user? FOSS, and hence RKH, ultimately depends
     upon you. Contributing is your responsibility, not someone
     elses. Whatever you contribute is very much welcomed. For
     example, contribute or discuss enhancing Rootkit Hunter with
     us; submit a patch or discuss enhancements; file a bug
     report; or test the application by using it on your servers.


1.4) I like your software! How can I thank you?

A.   Simple - by contributing. See question 1.3 above.


===========================================================

2. INSTALLATION QUESTIONS
=========================

2.1) How do I install Rootkit Hunter?

A.   Instructions on installing RKH can be found in the README file.


2.2) How do I create a Rootkit Hunter RPM file?

A.   The RKH source contains an rkhunter.spec file which will
     allow an RPM to be built. To build the RPM run the following
     command:

            rpmbuild -ta rkhunter-<version>.tar.gz

     The last part of the displayed build process should indicate
     where the RPM file has been written. However, it will usually
     be found in '/usr/src/redhat/RPMS/noarch'.

     NOTE: The RKH development team do not support any third-party
     RPM files. However, the rkhunter.spec file will be maintained. 


===========================================================

3. USAGE QUESTIONS
==================

3.1) Rootkit Hunter tells me there is something wrong with my
     system. What do I do?

A.   Prior to any incident it is recommended that you have read
     "Intruder Detection Checklist". This is available from
     http://web.archive.org/web/20080109214340/http://www.cert.org/tech_tips/intruder_detection_checklist.html
     This document will tell you what to check, and makes it easier
     for you to find out and answer any questions.

     If you are unsure as to whether your system is compromised,
     you can get a second opinion from sources such as the
     rkhunter-users mailing list, the Linux-oriented forum
     LinuxQuestions.org, or even IRC. Please note you need to 
     subscribe before posting to the rkhunter-users mailing list.

     If a file property check fails, then it is possible you have
     what is called a 'false positive'. Sometimes this will happen
     due to package updates, customised configurations or changed
     binaries. If so, then please check further:

       1. If you run a file integrity checker, for example Aide,
          Samhain, or Tripwire, consult the results from running those
          tools. Note they must be installed directly after the O/S
          installation in order to be useful, and you must keep a copy
          of the binary, configuration files and databases off-site.
          Also note that running those tools, and Rootkit Hunter, is no
          substitute for updating software when updates are released,
          and proper host and network hardening.

       2. If you don't run a file integrity checker you can possibly
          use your distributions package management system if it is
          configured to deal with verification.

       3. Run 'strings <file>' and check the results for untrusted file
          paths (for example, /dev/.hiddendir).

       4. Check recently updated binaries and their original source.

       5. Run 'file <file>' and compare the results with other files,
          especially trusted binaries. If some binaries are statically
          linked and others are all dynamic, then they could have been
          trojaned.

     If you have a warning from another part of the checks, then
     please subscribe first and then email the rkhunter-users mailing list
     and tell us about your system configuration:
        The purpose of the server
           (for example: web server, intranet fileserver, shell server);
        The (approximate) date of the incident and when you found out;
        The running distribution name, release and kernel version;
        Whether any passwd or shadow file data has changed;
        Any anomalies you find from reading the system, daemon, IDS
           and firewall logs;
        If all the installed software was recently updated;
        What services are or were running at the time;
        If you found setuid root files in directories for temporary
           files;
        Any anomalies you find from reading user shell histories.

     If your system is infected with a rootkit, cleaning it up is
     not an option. Restoring is also not an option unless you are
     skilled, and have autonomous and an independent means of
     verifying that the backup is clean, and does not contain
     misconfigured or stale software. Never trust a compromised
     machine. Period.

     Read "Steps for Recovering from a UNIX or NT System Compromise".
     This is available from
     http://www.cert.org/tech_tips/win-UNIX-system_compromise.html

     A clean install of the system is recommended after backing up
     the full system. To do this follow these steps:

       1. Stay calm. Be methodical.

       2. From another machine inform users, and the network,
          facility or host owner, that the machine is compromised.

       3. Get the host offline or make sure the firewall is raised
          to only allow network traffic to and from your management
          IP address or range.

       4. Backup your data. If you do not intend to investigate the
          problem, then do not backup any binaries or binary data
          which you cannot verify.

       5. Verify the integrity of your backup by visual inspection
          (authentication data, configurations, log files), or by
          using a file integrity checker or your distributions
          package management tools.

       6. Install your host with a fresh install. Whilst you are
          updating and configuring the software and services,
          restrict network access to the system using authentication
          features like accounts, PAM, firewall, TCP wrappers, and
          daemon configurations. Make sure you properly harden the
          machine.

       7. Investigate the old log files, and the tools used if
          possible. Also investigate the services which were
          vulnerable at the time of attack.


3.2) Rootkit Hunter tells me that I have an out-of-date or unsecure
     application installed. But I have fully patched my server!
     How is this possible?

A.   Some distributions, for example Red Hat and OpenBSD, do patch
     old versions of software. However, Rootkit Hunter thinks it is
     an old version, and so sees it as being unsecure.

     It is possible to whitelist specific applications, or specific
     versions of an application. The configuration file contains more
     details about this.

     If you wish you can skip the application version check completely
     by adding the 'apps' test name to the DISABLE_TESTS option in your
     rkhunter configuration file.


3.3) How can I automatically run Rootkit Hunter every day?

A.   There are several ways that rkhunter can be run via cron. However,
     it must be remembered that cron will automatically email any output
     produced by the program to the root user. Secondly, when the rkhunter
     '--cronjob' option is used, the program will generally not produce
     any output. It is, therefore, necessary to tell rkhunter what output
     should be shown. Typically this will just be any warning messages,
     and this can be achieved by using the '--rwo' (report warnings only)
     option.

     For the first example, the rkhunter command could be added directly
     to the root crontab:

          30 5 * * * /usr/local/bin/rkhunter --cronjob --update --rwo

     This would run rkhunter at 5:30 (AM) every day. If no output is
     produced by rkhunter, then nothing is emailed to root. Any output
     this is produced, which would only be warning messages, is
     automatically emailed to root by the cron process.

     Note that the '--update' option has been included. Rkhunter will
     first perform any updates required to its data files, and then
     perform the system checks. This option can be omitted, but it is
     suggested that the option is used regularly to ensure that the
     rkhunter data files are kept up todate.

     If it is wished that all the normal output of rkhunter, as seen when
     running rkhunter from the command-line, is emailed to root, then this
     is possible. The '--rwo' option should be removed, and the '--cronjob'
     option replaced by '--sk --nocolors --check'.

     The next example is of a cronjob script. For Linux systems this
     script could be put in to the /etc/cron.daily directory, so that
     it will be automatically run every day.

     The script might look like this:

          #!/bin/sh

          ( /usr/local/bin/rkhunter --cronjob --update --rwo && echo "" ) \
            | /bin/mail -s "Rkhunter daily run on `uname -n`" root

          exit 0

     Because we are piping any output through to the mail command, it is
     required to use 'echo ""' when there are no warnings. Without this,
     the mail command would issue its own warning about there being no
     message body.

     If it is wished to include the date in the output, then something
     like this could be used instead:

          #!/bin/sh

          ( date; /usr/local/bin/rkhunter --cronjob --update --rwo ) \
            | /bin/mail -s "Rkhunter daily run on `uname -n`" root

          exit 0

     Finally, it is possible to run rkhunter in quiet-mode, whereby no
     output will be produced at all. However, if the return code indicates
     that warnings were found, then we get cron to mail the root user.
     For example:

          30 5 * * * /usr/local/bin/rkhunter --cronjob --update --quiet \
                     || echo "Rkhunter daily run on `uname -n` has produced warning messages"

     An alternative to the above example would be to use:

          30 5 * * * /usr/local/bin/rkhunter --cronjob --update --quiet

     and then simply set the MAIL-ON-WARNING option in the configuration
     file with the root email address. This way, rkhunter produces no
     output, and so nothing is emailed to root by cron. However, if any
     warnings are found during the system check, then a notice message is
     emailed to root by rkhunter itself.

     Note: The '--quiet' option in the above two examples is not actually
     necessary, but was included for clarity. The '--cronjob' option assumes
     the '--quiet' option, and so, as mentioned above, when rkhunter is run
     with the '--cronjob' option no output is generally produced.


3.4) What is the meaning of the test names?

A.   See the README file for information about the test names.


3.5) Can rkhunter handle filenames with spaces in them?

A.   Generally yes for the tests themselves, but not for configuration options.
     Additionally, Some tests may not like filenames with the colon (:) character
     in them.


3.6) What does the following warning mean:

       Determining OS... Warning: this operating system is not
       fully supported!

A.   This is a message from older versions of rkhunter. Upgrade to
     a newer version.


3.7) I have just installed Rootkit Hunter, and I am already
     getting warning messages. Why is that?

A.   The first run of rkhunter after an installation will usually give
     some warning messages. One of the checks is whether the file of
     file properties (called 'rkhunter.dat') exists. This file won't
     exist until rkhunter is run with the '--propupd' option. There is
     also a check to see if any commands have been replaced by a script.
     To avoid these warning messages you can whitelist the commands in
     your configuration file. Similarly if there are warnings about
     hidden files or directories, then these can be whitelisted. Look in
     the configuration file and you will find examples of these.

     Once these changes have been made, then re-run rkhunter and no
     warnings should appear. Obviously warning messages from other
     checks indicate that something else is wrong, and so should be
     investigated.

     NOTE: When using the '--propupd' option it is the users
           responsibility to ensure that the files on their system are
           genuine. Rootkit Hunter can only inform the user of a change
           to the files, not whether they are the original files or not.
           Although Rootkit Hunter can use a package manager for some
           systems, it must be remembered that the package manager itself
           uses files stored on the system. Those files may have been
           tampered with.

     The logfile will contain further information about each warning
     message. Once the reason for the warning has been found, and you
     believe that rkhunter has given a false-positive result, then
     looking in the configuration file may show you that the relevant
     item can be whitelisted. Also see WHITELISTING EXAMPLES below.


3.8) When I used the '--propupd' option, Rootkit Hunter told me
     I had some missing hashes. What does this mean?

A.   Your system probably uses prelinking (the log file will say if
     it does or not). Sometimes a file may be updated but not be
     prelinked. When this happens RKH cannot determine the files hash
     value. If you run the command 'prelink --verify --sha <file>'
     on the file, it will probably give an error about the files
     dependencies having changed. This is what RKH sees, and flags
     it as a missing hash. If you are sure that the file is genuine,
     then you can try using 'prelink <file>' to correct it. The
     'prelink' command above should then work. Re-run RKH with the
     '--propupd' option to ensure that all the hash values are recorded.


3.9) I run rkhunter in cron and in the emailed output I get some strange
     characters. Why is this?

A.   The problem only occurs when the '--update' or '--versioncheck'
     options are used, and does not occur when rkhunter is run from
     the command-line. It also does not occur if the '--cronjob' or
     '--quiet' options are used in cron.

     The emailed output probably looks something like this:

           [1;33mChecking rkhunter data files...[0;39m
           Checking file mirrors.dat[34C[ [1;32mNo update[0;39m ]

     The 'strange' characters are ANSI color codes and escape sequences,
     and this is why the problem does not occur if rkhunter is run from
     the command-line. The terminal correctly interprets the codes, but
     cron cannot do this.

     The solution is to use the '--nocolors' option in your cron job.
     The '--cronjob' option assumes '--nocolors', which is why the
     problem does not occur when '--cronjob' is used.


3.10) When I used the '--propupd' option, Rootkit Hunter told me
      that it had found more files than it was searching for. How
      is this possible?

A.    The output from rkhunter probably shows something like this:

           File updated: searched for 149 files, found 171

      When rkhunter collects file property information about files
      (commands), it uses generic file names - for example, 'awk'
      and 'sed'. As such, if these files exist in more than one
      directory that is being searched, then it will have found two
      files but only have been looking for one. Secondly, some files
      are symbolic (soft) links to another file. In this instance
      rkhunter will record both the link itself, and the file that
      it points to. So, again, two files have been found. It is,
      therefore, quite possible on some systems for rkhunter to find
      more files than it says it is looking for. It simply indicates
      that rkhunter has found some files more than once.


===========================================================

4. ERROR AND WARNING MESSAGES
=============================

4.1) What does the following warning mean:

       The file of stored file properties (rkhunter.dat) is empty,
       and should be created. To do this type in
       'rkhunter --propupd'.

A.   For rkhunter to perform file property checks, it must first
     have a database file ('rkhunter.dat') containing the property
     values for each file. It can then compare each files current
     values against those stored in the database. Any difference
     indicates that the file has changed. To create and/or update
     the database file use the '--propupd' option.

     NOTE: An additional warning will be displayed stating that it
           is the users responsibility to ensure that the files are
           valid before using the '--propupd' option. That is, the
           user must be sure that the files have not been compromised.


4.2) Rootkit Hunter skips some checks, and the logfile indicates
     that certain commands are missing. What can I do?

A.   You have a choice:

       1) Install the relevant command. You may be able to do this
          simply by running a package updater for your system (for
          example, 'yum' or 'apt-get').

       2) You may be able to disable the check by adding its test
          name to your configuration file. (See the README file
          for more information about the test names.)

       3) If you are sure that the relevant command is present on
          your system, then rkhunter is having a problem locating
          it. Check the logfile for the 'command directories' it
          is using. If the directory containing the command isn't
          listed, then you can set the command directories to use
          by using the '--bindir' command-line option, or the BINDIR
          option in the configuration file.


4.3) I get warnings from PHP like:

        PHP Warning: Function registration failed - duplicate name
        - pg_update in Unknown on line 0. What does this mean?

A.   This may occur during the 'apps' test. It is usually because
     you have updated the Apache version of PHP, but forgot to
     update or recompile the CLI (console version) of PHP. So
     update or recompile it, and then try again.


4.4) After performing some updates, all, or some, binaries in the
     file properties checks are marked with a 'Warning'.
     What can I do?

A.   The first thing would be to verify that the update is the cause
     of the warnings. Checking the system log files should indicate
     what has been updated.

     It is most likely that the stored rkhunter file property values
     need to be recalculated. To do this use the RKH '--propupd'
     option. However, the output of the RKH file properties check
     should only be seen as an indication that the file has changed.
     Updating the stored property values should be done only after
     proper verification of the files using a file integrity checker
     or your distributions package management tools.

     Alternatively, you can use the '--pkgmgr' command-line option, or
     the PKGMGR option in the configuration file, to tell RKH to obtain
     its file properties information from the package manager database.
     See the README file for more information about the package manager
     options.

     NOTES
     =====
     1) If the logfile indicates that a files' hash value has changed
        from some value to 'No hash value found', and your system
        uses prelinking, then the file probably needs to be
        specifically prelinked. This can usually be done by running
        the 'prelink' command on the relevant file. Running RKH with
        the '--propupd' option afterwards will indicate if there
        are still any hash values missing. Check the logfile and
        repeat the above process of prelinking the files.

        RKH will try and determine if your system is using prelinking
        or not. The logfile will contain the result of the check.

     2) If your system uses Libsafe and prelinking, then errors can
        occur. Disable preloading Libsafe in /etc/ld.so.preload.
        Prelink again, and then run 'rkhunter --propupd'.


===========================================================

5. UPDATING QUESTIONS
=====================

5.1) Rootkit Hunter tells me that I have multiple versions
     installed. How it this possible?

A.   Usually you install a tool and upgrade it later. Sometimes
     if you use a 'non-official' updater or package manager
     (for example, from an external party, or build from source
     using an installer like RPM/DEB/TGZ/TXZ), the binaries may be
     installed into a different location from the original. So there
     are then two binaries with the same name, but in different
     locations. You will have to check which are the old binaries,
     and remove them.


5.2) Can I be notified when a new release will be available?

A.   Yes, you can join the rkhunter-announce mailing list. This is
     a low volume list. Details can be found on the RKH web site.

     Additionally, the '--versioncheck' option of rkhunter itself
     will indicate if a new version is available.


===========================================================

6. WHITELISTING EXAMPLES
========================

6.1) After Rootkit Hunter has run you may encounter items in the log
     file you would like to whitelist. First verify that the entries
     are safe to add. The results of running these commands can be
     added to your 'rkhunter.conf.local' configuration file. Please
     adjust the commands, and the location of your 'rkhunter.log' log
     file, and verify the results before adding them. Do not automate
     adding whitelist entries to your configuration file.

     Allow script replacements ("properties" test):
     awk -F"'" '/replaced by a script/ {print "SCRIPTWHITELIST="$2}' rkhunter.log

     Allow processes using deleted files ("deleted_files" test):
     awk '/Process: / {print "ALLOWPROCDELFILE="$3}' rkhunter.log | sort -u

     Allow Xinetd services:
     awk '/Found enabled xinetd service/ {print $NF}' rkhunter.log |\
      xargs -iX grep -e "server[[:blank:]]" 'X' | awk '{print "XINETD_ALLOWED_SVC="$NF}'

     Allow packet capturing applications ("packet_cap_apps" test):
     awk -F"'" '/is listening on the network/ {print "ALLOWPROCLISTEN="$2}' rkhunter.log

     Allow "suspicious" files ("filesystem" test):
     grep '^\[..:..:..\][[:blank:]]\{6\}.*/dev/shm/.*:' rkhunter.log |\
      awk '{print "ALLOWDEVFILE="$2}' | sed -e "s|:$||g"

     Allow hidden directories ("filesystem" test):
     awk '/Warning: Hidden directory/ {print "ALLOWHIDDENDIR="$6}' rkhunter.log

     Allow hidden files ("filesystem" test):
     awk '/Warning: Hidden file/ {print "ALLOWHIDDENFILE="$6}' rkhunter.log |\
      sed -e "s|:$||g"


===========================================================