Archive for the ‘Debian’ Category

Analyze disk space usage in Linux / BSD with du / find and filelight /qdirstat / baobab GUI disk usage analyzers to check what takes up your disk space on Unix like OSes

Friday, April 21st, 2023


If you're a Desktop Linux or BSD UNIX user and your hard disk / external SSD / flash drive etc. space starts to be misteriously disapper due to whatever reaseon such as a crashing applications producing rapidly log error / warning messages leading quickly to filling up the disk or out of a sudden you have some Disk space lost without knowing what kind of data filled up the disk or you're downloading some big sized bittorrent files forgotten in your bittorrent client or complete mirroring a large website and you suddenly get the result of root directory ( / ) getting fully or nearly filled up, then you definitely would want to check out what has disk activity has eaten up your disk space and leaing to OS and Aplication slow responsiveness.

For the Linux regular *nix user finding out what is filling the disk is a trivial task with with find / du -hsc * but as people have different habits to use find and du I'll show you the most common ways I use this two command line tools to identify disk space low issues for the sake of comparison.
Others who have better easier ways to do it are very welcome to share it with me in the comments.

1. Finding large files on hard disk with find Linux command tool

host:~# find /home -type f -printf "%s\t%p\n" | sort -n | tail -10
2100000000    /home/hipo/Downloads/MameUIfx incl. ROMs/MameUIfx incl. ROMs-6.bin
2100000000    /home/hipo/Downloads/MameUIfx incl. ROMs/MameUIfx incl. ROMs-7.bin
2100000000    /home/hipo/Downloads/MameUIfx incl. ROMs/MameUIfx incl. ROMs-8.bin
2100000000    /home/hipo/Downloads/MameUIfx incl. ROMs/MameUIfx incl. ROMs-9.bin
2815424080    /home/hipo/.thunderbird/h3dasfii.default\
2925584895    /home/hipo/Documents/.git/\
4336918067    /home/hipo/Games/Mames_4GB-compilation-best-arcade-games-of-your-14_04_2021.tar.gz
6109003776    /home/hipo/VirtualBox VMs/CentOS/CentOS.vdi
23599251456    /home/hipo/VirtualBox VMs/Windows 7/Windows 7.vdi
33913044992    /home/hipo/VirtualBox VMs/Windows 10/Windows 10.vdi

I use less rarely find on Desktops and more when I have to do some kind of data usage analysis on servers, of course for my Linux home computer and any other Linux desktop machines, or just a small incomprehensive analysis du cmd is much more appropriate to use.

2. Finding large files Megabyte occupying space files sorted in Megabytes and Gigas with du

  • Check main 10 files sorted in megabytes that are hanging in a directory

pcfkreak:~# du -hsc /home/hipo/*|grep 'M\s'|sort -rn|head -n 10
956M    /home/hipo/last_dump1.sql
711M    /home/hipo/hipod
571M    /home/hipo/from-thinkpad_r61
453M    /home/hipo/ultimate-edition-themes
432M    /home/hipo/metasploit-framework
355M    /home/hipo/output-upgrade.txt
333M    /home/hipo/Плот
209M    /home/hipo/Work-New.tar.gz
98M    /home/hipo/DOOM64
90M    /home/hipo/mp3

  • Get 10 top larges files in Gigabytes that are space hungry and eating up your space

pcfkreak:~# du -hsc /home/hipo/*|grep 'G\s'|sort -rn|head -n 10
156G    total
60G    /home/hipo/VirtualBox VMs
37G    /home/hipo/Downloads
18G    /home/hipo/Desktop
11G    /home/hipo/Games
7.4G    /home/hipo/ownCloud
7.1G    /home/hipo/Документи
4.6G    /home/hipo/music
2.9G    /home/hipo/root
2.8G    /home/hipo/Documents

If you want to still work on the console terminal but you don't want to type too much you can use ncdu (ncurses) text tool, install it with

# apt install –yes ncdu

 For the most lazy ones or complete Linux newbies that doesn't want to spend time typing / learing or using text commands or softwares you can also check what has eaten up your full disk space with GUI tools as well.

There are at least 3 tools to use to check in Graphical Interface what has occupied your disk space on Linux / BSD, I'm aware of:

3. Filelight GUI disk usage analysis Linux tool

For those using KDE or preferring a shiny GUI interface that will capture the eye, perhaps filelight would be the option of choice tool to get analysis sum of your directory sturctures and file use on the laptop or desktop *unix OS.

unix-desktop:~# apt-cache show filelight|grep -i description-en -A 7
Description-en: show where your diskspace is being used
 Filelight allows you to understand your disk usage by graphically
 representing your filesystem as a set of concentric, segmented rings.
 It is like a pie-chart, but the segments nest, allowing you to see both
 which directories take up all your space, and which directories
 and files inside those directories are the real culprits.
Description-md5: 397ff9a469e07a772f22460c66b66875

To use it simply go ahead and install it with apt or yum / dnf or whatever Linux package manager your distro uses:

unix-desktop:~# apt-get install –yes filelight


4. GNOME DIsk Usage Analyzer Baobab GUI tool

For those being a GNOME / Mate / Budgie / Cinnamon Graphical interface users baobab shold be the program to use as it uses the famous LibGD library.

unix-desktop:~# apt-cache show baobab|grep -i description-en -A10
Description-en: GNOME disk usage analyzer
 Disk Usage Analyzer is a graphical, menu-driven application to analyse
 disk usage in a GNOME environment. It can easily scan either the whole
 filesystem tree, or a specific user-requested directory branch (local or
 It also auto-detects in real-time any changes made to your home
 directory as far as any mounted/unmounted device. Disk Usage Analyzer
 also provides a full graphical treemap window for each selected folder.
Description-md5: 5f6072b89ebb1dc83433fa7658814dc6



5. Qdirstat graphical application to show where your disk space has gone on Linux

Qdirstat is perhaps well known tool to track disk space issues on Linux desktop hosts, known by the hardcore KDE / LXDE / LXQT / DDE GUI interface / environment lovers and as a KDE tool uses the infamous Qt library. I personally don't like it and don't put it on machines I use because I never use kde and don't want to waste my disk space with additional libraries such as the QT Library which historically was not totally free in terms of licensing and even now is in both free and non free licensing GPL / LGPL and QT Commercial Licensing license.

unix-desktop:~# apt-cache show qdirstat|grep -i description-en -A10
Description-en: Qt-based directory statistics
 QDirStat is a graphical application to show where your disk space has gone and
 to help you to clean it up.
 QDirStat has a number of new features compared to KDirStat. To name a few:
  * Multi-selection in both the tree and the treemap.
  * Unlimited number of user-defined cleanup actions.
  * Properly show errors of cleanup actions (and their output, if desired).
  * File categories (MIME types) and their treemap color are now configurable.
  * Exclude rules for directories are easily configurable.
  * Desktop-agnostic; no longer relies on KDE or any other specific desktop.


That shiny fuzed graphics is actually a repsesantation of all directories the bigger and if one scrolls on the colorful gamma a text with directory and size or file will appear. Though the graphical represantation is really c00l to me it is a bit unreadable, thus I prefer and recommend the other two GUI tools filelight or baobab instead.

6. Finding duplicate files on Linux system with duff command tool

Talking about big unknown left-over files on your hard drives, it is appropriate to mention one tool here that is a console one but very useful to anyone willing to get rid of old duplicate files that are hanging around on the disk. Sometimes such copies are produced while copying large amount of files from place to place or simply by mistake while copying Photo / Video files from your Smart Phone to Linux desktop etc. 

This is where the duff command line utility might be super beneficial for you.

unix-desktop:~# apt-cache show duff|grep -i description-en -A3
Description-en: Duplicate file finder
 Duff is a command-line utility for identifying duplicates in a given set of
 files.  It attempts to be usably fast and uses the SHA family of message
 digests as a part of the comparisons.

Using duff tool is very straight forward to see all the duplicate files hanging in a directory lets say your home folder.

unix-desktop:~#  duff -rP /home/hipo

/home/hipo/music/var/Quake II Soundtrack – Kill Ratio.mp3
/home/hipo/mp3/Quake II Soundtrack – Kill Ratio.mp3
2 files in cluster 44 (7913472 bytes, digest 98f38be49e2ffcbf90927f9357b3e24a81d5a649)
2 files in cluster 45 (2807808 bytes, digest ce9067ce1f132fc096a5044845c7fac73e99c0ed)
/home/hipo/music/var/Quake II Suondtrack – March Of The Stoggs.mp3
/home/hipo/mp3/Quake II Suondtrack – March Of The Stoggs.mp3
2 files in cluster 46 (3506176 bytes, digest efcc401b4ebda9b0b2367aceb8e334c8ba1a357d)
/home/hipo/music/var/Quake II Suondtrack – Quad Machine.mp3
/home/hipo/mp3/Quake II Suondtrack – Quad Machine.mp3
2 files in cluster 47 (7917568 bytes, digest 0905c1d790654016c2ecf2949f78d47a870c3822)
/home/hipo/music/var/Cyberpunk Group – Futureshock!.mp3
/home/hipo/mp3/Cyberpunk Group – Futureshock!.mp3

-r (Recursively search into all specified directories.)

P (Don't follow any symbolic links.  This overrides any previous -H or -L option.  This is the default.  Note that this only applies to directories, as sym‐
             bolic links to files are never followed.)

7. Deleting duplicate files with duff

If you're absolutely sure you know what you're doing and you have a backup in case if something messes up during duplicate teletions, to get rid of lets say any duplicate Picture files found by duff run sommething like:

# duff -e0 -r /home/hipo/Pictures/ | xargs -0 rm

!!! Please note that using duff is for those who absolutely know what they're doing and have their data recent data. Deleting the wrong data by mistake with the tool might put you in the first grade and you'll be the only one to blame  🙂 !!!

Wrap it Up

Filling up the disk with unknown large files is a task to resolve that happens often. For the unlazy on Linux / BSD / Mac OS and other UNIX like OS-es the easiest way is to use find or du with some one liner command. For the lazy Windows addicted Graphical users filelightqdirstat or baobab GUI disk usage analysis tools are there.
If you have a lot of files and many of thems are duplicates you can use duff to check them out and remove all unneded duplicates and save space. 
Hope this article, was helpful for someone.
That's all folks, enjoy your data profilactics, if you know any other good easy command or GUI tools or hints for drive disk space profilactics please share.

How to install and configure AIDE ( Advanced Intrusion Detection Environment ) on Debian GNU / Linux 11 to monitor files for changes

Thursday, March 9th, 2023


How to install and configure AIDE ( Advanced Intrusion Detection Environment ) on Debian GNU / Linux 11 to monitor files for changes

Having a intrusion detection system is essential to keeping a server security to good level and being compliant with PCI (Payment Card Industry) DSS Standards. It is a great thing for the sake to protect oneself from hackers assaults. 

There is plenty of Intrusion Detection systems available all around since many years, in the past one of main ones for Linux as older system administrators should remember was Tripwire – integrity tool for monitoring and alerting on specific file change(s) on a range of systems

Tripwire is still used today but many today prefer to use AIDE that is a free software replacement for Tripwire under GPL (General Public License), that is starting to become like a "standard"  for many Unix-like systems as an inexpensive baseline control and rootkit detection system.

In this article I'll explain shortly how to Install / Configure and Use AIDE to monitor, changes with files on the system.

But before proceeding it is worthy to mention on some of the alternatives companies and businesses choose to as an IDS (Intrusion Detection Systems), that is useful to give a brief idea of the sysadmins that has to deal with Security, on what is some of the main Intrusion Detection Systems adopted on UNIX OSes today:

  • Samhain

    An integrity checker and host intrusion detection system that can be used on single hosts as well as large, UNIX-based networks. It supports central monitoring as well as powerful (and new) stealth features to run undetected in memory, using steganography. Samhain is an open-source multiplatform application for POSIX systems (Unix, Linux, Cygwin/Windows).

  • OSSEC 
    OSSEC uses a centralized, cross-platform architecture allowing multiple systems to be monitored and managed.
  • Snort
    IDS which has the capabilities to prevent attacks. By taking a particular action based on traffic patterns, it can become an intrusion prevention system (IPS). – written in Pure C.
  • Zeek (Bro)
    Zeek helps to perform security monitoring by looking into the network's activity. It can find suspicious data streams. Based on the data, it alert, react, and integrate with other tools – written in C++.
  • Maltrail (Maltrail monitors for traffic on the network that might indicate system compromise or other bad behavior. It is great for intrusion detection and monitoring. – written in Python).

1. Install aide deb package

# apt -y install aide

root@haproxy2:~# aide -v
Aide 0.17.3

Compiled with the following options:


Default config values:
config file: <none>
database_in: <none>
database_out: <none>

Available hashsum groups:
md5: yes
sha1: yes
sha256: yes
sha512: yes
rmd160: yes
tiger: yes
crc32: yes
crc32b: yes
haval: yes
whirlpool: yes
gost: yes
stribog256: no
stribog512: no

Default compound groups:
R: l+p+u+g+s+c+m+i+n+md5+acl+selinux+xattrs+ftype+e2fsattrs+caps
L: l+p+u+g+i+n+acl+selinux+xattrs+ftype+e2fsattrs+caps
>: l+p+u+g+i+n+acl+S+selinux+xattrs+ftype+e2fsattrs+caps
H: md5+sha1+rmd160+tiger+crc32+haval+gost+crc32b+sha256+sha512+whirlpool
X: acl+selinux+xattrs+e2fsattrs+caps

2. Prepare AIDE configuration and geenrate (initialize) database

Either you can use the default AIDE configuration which already has a preset rules for various files and directories to be monitored,
or you might add up additional ones.

  • For details on configuration of aide.conf accepted options "man aide.conf"

The rules and other configurations resides lays under  /etc/aide/ directory

The AIDE database is located under /var/lib/aide

root@server:~# ls -al /var/lib/aide/
общо 33008
drwxr-xr-x  2 root root     4096  9 мар 12:38 ./
drwxr-xr-x 27 root root     4096  9 мар 12:01 ../
-rw——-  1 root root 16895467  9 мар 16:03 aide.db
-rw——-  1 root root 16895467  9 мар 18:49

Also, details about major setting rules config regarding how AIDE will run via cronjob as with most debian services are into /etc/default/aide

Default aide.conf config is in /etc/aide/aide.conf if you need custom stuff to do with it simply edit it.

Here is an Example:
Lets say you want to omit some directory to not be monitored by aide, which would otherwise do, i.e.
omit /var/log/* from monitoring

# At the end of file /etc/aide/aide.conf



  • Initialize the aide database first time

Run aideinit command, aideinit will create a new baseline database –  /var/lib/aide/ (a baseline)
Note that, /var/lib/aide/aide.db is the old database that aide uses to check against for any changes of files / directories on the configured monitored filesystem objects.

root@server:~# aideinit
Running aide –init…

debug1: client_input_channel_req: channel 0 rtype reply 1
debug1: client_input_channel_req: channel 0 rtype reply 1
debug1: client_input_channel_req: channel 0 rtype reply 1
debug1: client_input_channel_req: channel 0 rtype reply 1
debug1: client_input_channel_req: channel 0 rtype reply 1
Start timestamp: 2023-03-09 12:06:16 +0200 (AIDE 0.17.3)
AIDE initialized database at /var/lib/aide/

Number of entries:      66971

The attributes of the (uncompressed) database(s):

 SHA256    : nVrYljiBFM/KaKCTjbaJtR2w6N8vc8qN
 SHA512    : S1ZNB0DCqb4UTmuqaalTgiQ3UAltTOzO
 RMD160    : xaUnfW1+/DJV/6FEm/nn1k1UKOU=
 TIGER     : nGYEbX281tsQ6T21VPx1Hr/FwBdwF4cK
 CRC32     : fzf7cg==
 HAVAL     : yYQw/87KUmRiRLSu5JcEIvBUVfsW/G9H
 WHIRLPOOL : 6b5y42axPjpUxWFipUs1PtbgP2q0KJWK
 GOST      : sHAzx7hkr5H3q8TCSGCKjndEiZgcvCEL

End timestamp: 2023-03-09 12:38:30 +0200 (run time: 32m 14s)

Be patient now, go grab a coffee / tea or snack as the command might take up to few minutes for the aide to walk through the whole monitored filesystems and built its database.

root@server:~# echo cp /var/lib/aide/aide.db{.new,}
cp /var/lib/aide/ /var/lib/aide/aide.db


root@server:~# cp /var/lib/aide/aide.db{.new,}

root@server:~# aide –check –config /etc/aide/aide.conf

Start timestamp: 2023-03-09 13:01:32 +0200 (AIDE 0.17.3)
AIDE found differences between database and filesystem!!

  Total number of entries:      66972
  Added entries:                1
  Removed entries:              0
  Changed entries:              7

Added entries:

f+++++++++++++++++: /var/lib/aide/aide.db

Changed entries:

d =…. mc.. .. . : /etc/aide
d =…. mc.. .. . : /root
f <…. mci.H.. . : /root/.viminfo
f =…. mc..H.. . : /var/lib/fail2ban/fail2ban.sqlite3
d =…. mc.. .. . : /var/lib/vnstat
f =…. mc..H.. . : /var/lib/vnstat/vnstat.db
f >b… mc..H.. . : /var/log/sysstat/sa09

Detailed information about changes:

Directory: /etc/aide
 Mtime     : 2023-03-09 12:04:03 +0200        | 2023-03-09 12:51:11 +0200
 Ctime     : 2023-03-09 12:04:03 +0200        | 2023-03-09 12:51:11 +0200

Directory: /root
 Mtime     : 2023-03-09 12:06:13 +0200        | 2023-03-09 12:51:11 +0200
 Ctime     : 2023-03-09 12:06:13 +0200        | 2023-03-09 12:51:11 +0200

File: /root/.viminfo
 Size      : 18688                            | 17764
 Mtime     : 2023-03-09 12:06:13 +0200        | 2023-03-09 12:51:11 +0200
 Ctime     : 2023-03-09 12:06:13 +0200        | 2023-03-09 12:51:11 +0200
 Inode     : 133828                           | 133827
 SHA256    : aV54gi33aA/z/FuBj2ZioU2cTa9H16TT | dnFdLVQ/kx3UlTah09IgEMrJ/aYgczHe
             TzkLSxBDSB4=                     | DdxDAmPOSAM=

3. Test aide detects file changes

Create a new file and append some text and rerun the aide check


root@server:~# touch /root/test.txt
root@server:~# echo aaa > /root/test.txt
root@server:~# aide –check –config /etc/aide/aide.conf


Start timestamp: 2023-03-09 13:07:21 +0200 (AIDE 0.17.3)
AIDE found differences between database and filesystem!!

  Total number of entries:      66973
  Added entries:                2
  Removed entries:              0
  Changed entries:              7

Added entries:

f+++++++++++++++++: /root/test.txt
f+++++++++++++++++: /var/lib/aide/aide.db

Changed entries:

d =…. mc.. .. . : /etc/aide
d =…. mc.. .. . : /root
f <…. mci.H.. . : /root/.viminfo
f =…. mc..H.. . : /var/lib/fail2ban/fail2ban.sqlite3
d =…. mc.. .. . : /var/lib/vnstat
f =…. mc..H.. . : /var/lib/vnstat/vnstat.db
f >b… mc..H.. . : /var/log/sysstat/sa09


The same command can be shortened for the lazy typist:

root@server:~# aide -c /etc/aide/aide.conf -C

The command will basically try to check the deviation between the AIDE database and the filesystem.

4. Limiting AIDES Integrity Checks to Specific Files / Directories

In order to limit the integrity checks to a specific entries for example /etc, pass the –limit REGEX option to AIDE check command where REGEX is the entry to check.

For example, check and update the database entries matching /etc, you would run aide command as shown below;

root@server:~# aide -c /etc/aide/aide.conf –limit /etc –check


AIDE found differences between database and filesystem!!
Limit: /etc

  Total number of entries:      66791
  Added entries:                0
  Removed entries:              0
  Changed entries:              2

Changed entries:

d =…. mc.. .. . : /etc/aide
d =…. mc.. .. . : /etc/default

Detailed information about changes:

Directory: /etc/aide
 Mtime     : 2023-03-09 15:59:53 +0200        | 2023-03-09 16:43:03 +0200
 Ctime     : 2023-03-09 15:59:53 +0200        | 2023-03-09 16:43:03 +0200

Directory: /etc/default
 Mtime     : 2023-03-09 12:06:13 +0200        | 2023-03-09 18:42:12 +0200
 Ctime     : 2023-03-09 12:06:13 +0200        | 2023-03-09 18:42:12 +0200

The attributes of the (uncompressed) database(s):

 SHA256    : sjCxyIkr0nC/gTkNmn7DNqAQWttreDF6
 SHA512    : vNMpb54qxrbOk6S1Z+m9r0UwGvRarkWY
 RMD160    : anhm5E6UlKmPYYJ4WYnWXk/LT3A=
 TIGER     : 5e1wycoF35/ABrRf7FNypZ45169VTuV4
 CRC32     : EAJlFg==
 HAVAL     : R5imONWRYgNGEfhBTc096K+ABnMFkMmh
 GOST      : F5zO2Ovtvf+f7Lw0Ef++ign1znZAQMHM

End timestamp: 2023-03-09 20:02:18 +0200 (run time: 1m 32s)

5. Add the modified /root/test.txt to AIDE list of known modified files database

root@server:~# aide –update –config /etc/aide/aide.
  ERROR: cannot open config file '/etc/aide/aide.': No such file or directory


root@server:~# ​ aide –update –config /etc/aide/aide.conf

Start timestamp: 2023-03-09 18:45:17 +0200 (AIDE 0.17.3)
AIDE found differences between database and filesystem!!
New AIDE database written to /var/lib/aide/

  Total number of entries:      66791
  Added entries:                0
  Removed entries:              0
  Changed entries:              8

Changed entries:

d =…. mc.. .. . : /etc/aide
d =…. mc.. .. . : /etc/default
d =…. mc.. .. . : /root
f >…. mci.H.. . : /root/.viminfo
f >…. mci.H.. . : /root/test.txt
f =…. mc..H.. . : /var/lib/fail2ban/fail2ban.sqlite3
d =…. mc.. .. . : /var/lib/vnstat
f =…. mc..H.. . : /var/lib/vnstat/vnstat.db

Detailed information about changes:

Directory: /etc/aide
 Mtime     : 2023-03-09 15:59:53 +0200        | 2023-03-09 16:43:03 +0200
 Ctime     : 2023-03-09 15:59:53 +0200        | 2023-03-09 16:43:03 +0200

Directory: /etc/default
 Mtime     : 2023-03-09 12:06:13 +0200        | 2023-03-09 18:42:12 +0200
 Ctime     : 2023-03-09 12:06:13 +0200        | 2023-03-09 18:42:12 +0200

Directory: /root
 Mtime     : 2023-03-09 15:59:53 +0200        | 2023-03-09 18:44:34 +0200
 Ctime     : 2023-03-09 15:59:53 +0200        | 2023-03-09 18:44:34 +0200

File: /root/.viminfo
 Size      : 16706                            | 16933
 Mtime     : 2023-03-09 15:59:53 +0200        | 2023-03-09 18:44:34 +0200
 Ctime     : 2023-03-09 15:59:53 +0200        | 2023-03-09 18:44:34 +0200
 Inode     : 136749                           | 133828
 SHA256    : KMHGoMVJo10BtafVrWIOLt3Ht9gK8bc+ | rrp8S3VftzZzvjBP1JC+PBpODv9wPKGw
             9uHh/z7iJWA=                     | TA+hyhTiY+U=
 SHA512    : ieDHy7ObSTfYm5d8DtYcHKxHya13CS65 | PDAJjyZ39uU3kKFo2lHBduTqxMDq4i01
             ObMYIRAre6IgvLslEs0ZodQFyrczMyRt | 1Kvm/h6xzFhHtFgjidtcemG8wDcjtfNF
             +d6SrW0gn3skKn2B7G09eQ==         | Z7LO230fgGeO7UepqtxZjQ==
 RMD160    : nUgg/G4zsVGKzVmmrqltuYUDvtg=     | jj61KAFONK92mj+u66RDJmxFhmI=
 TIGER     : 3vPSOrla5k+k2br1E2ES4eNiSZ2novFX | mn4kNCzd8SQr2ID2VSe4f4l0ta7pO/xo
 CRC32     : NDnMgw==                         | AyzVUQ==
 HAVAL     : Q9/KozxRiPbLEkaIfnBUZdEWftaF52Mw | 6jADKV6jg7ZVr/A/oMhR4NXc8TO1AOGW
             7tiR7DXhl0o=                     | NrYe+j6UcO0=
 WHIRLPOOL : vB/ZMCul4hN0aYd39gBu+HmZT/peRUI8 | mg6c1lYYVNZcy4mVzGojwraim8e3X2/R
             KDkaslNb8+YleoFWx0mbhAbkGurc0+jh | urVvEmbsgTuUCJOuf9+OrEACiF0fbe/x
             YPBviZIKcxUbTc2nGthTWw==         | t+BXnSQWk08OL9EI6gMGqA==
 GOST      : owVGTgU9BH3b0If569wQygw3FAbZIZde | ffx29GV2jaCB7XzuNjdiRzziIiZYnbi3
             eAfQfzlRPGY=                     | Ar7jyNMUutk=

File: /root/test.txt
 Size      : 4                                | 8
 Mtime     : 2023-03-09 13:07:12 +0200        | 2023-03-09 18:44:34 +0200
 Ctime     : 2023-03-09 13:07:12 +0200        | 2023-03-09 18:44:34 +0200
 Inode     : 133828                           | 136751
 SHA256    : F+aC8GC1+OR+oExcSFWQiwpa1hICImD+ | jUIZMGfiMdAlWFHu8mmmlml4qAGNQNL5
             UOEeywzAq3Y=                     | 6NhzJ1sYFZE=
 SHA512    : d+UmFKFBzvGadt5hk+nIRbjP//7PSXNl | ixn20lcEMDEtsJo3hO90Ea/wHWLCHcrz
             Pl16XRIUUPq2FCiQ4PeUcVciukJX7ijL | seBWunbBysY0z3BWcfgnN2vH05WfRfvA
             D045ZvGOEcnmL6a6vwp0jw==         | QiNtQS1tStuEdB3Voq54zQ==
 RMD160    : I6waxKN3rMx4WTz4VCUQXoNoxUg=     | urTh1j1t3UHchnJGnBG4lUZnjI4=
 TIGER     : cwUYgfKHcJnWXcA0pr/OKuxuoxh+b9lA | prstKqCfMXL39aVGFPA0kX4Q9x7a+hUn
 CRC32     : UD78Dw==                         | zoYiEA==
 HAVAL     : bdbKR9LvPgsYClViKiHx48fFixfIL/jA | ZdpdeMhw4MvKBgWsM4EeyUgerO86Rt82
             F3tjdc2Gm8Y=                     | W94fJFRWbrM=
 WHIRLPOOL : OLP0Y4oKcqW2yEvme8z419N1KE4TB9GJ | Xk8Ujo3IU2SzSqbJFegq7p1ockmrnxJF
             biHn/9XgrBz4fQiDJ8eHpx+0exA9hXmY | R3Rfstd1jWSwLFNTEwfbRRw+TARtRK50
             EbbakMJJdzLt1ipKWiV9gg==         | iWJeHLsD5dZ+CzV0tf4sUg==
 GOST      : ystISzoeH/ZznYrrXmxe4rwmybWMpGuE | GhMWNxg7Is0svJ+5LP+DVWbgt+CDQO+3
             0PzRnVEqnR8=                     | 08dwBuVAwB8=

File: /var/lib/fail2ban/fail2ban.sqlite3
 Mtime     : 2023-03-09 15:55:01 +0200        | 2023-03-09 18:45:01 +0200
 Ctime     : 2023-03-09 15:55:01 +0200        | 2023-03-09 18:45:01 +0200
 SHA256    : lLilXNleqSgHIP1y4o7c+oG5XyUPGzgi | NCJJ2H6xgCw/NYys1LMA7hOWwoOoxI8Y
             RHYH+zvlAL4=                     | 4SJygfqEioE=
 SHA512    : iQj2pNT4NES4fBcujzdlEEGZhDnkhKgc | ClQZ5HMOSayUNb//++eZc813fiMJcXnj
             QDlGFSAn6vi+RXesFCjCABT7/00eEm5/ | vTGs/2tANojoe6cqpsT/LaJ3QZXpmrfh
             ILcaqlQtBSLJgHjMQehzdg==         | syVak1I4n9yg8cDKEkZUvw==
 RMD160    : Xg4YU8YI935L+DLvkRsDanS4DGo=     | SYrQ27n+/1fvIZ7v+Sar/wQHulI=
 TIGER     : 2WhhPq9kuyeNJkOicDTDeOeJB8HR8zZe | o1LDZtRclri2KfZBe5J3D4YhM05UaP4E
 CRC32     : NQmi4A==                         | tzIsqg==
 HAVAL     : t1ET+84+8WgfwqlLy4R1Qk9qGZQRUbJI | MwVnjtM3dad/RuN2BfgsySX2DpfYq4qi
             z2J0ROGduXc=                     | H1pq6RYsA6o=
 WHIRLPOOL : xKSn71gFIVhk5rWJIBaYQASl0V+pGn+3 | m5LEXfhBbhWFg/d8CFJhklOurmRSkDSG
             N85R0tiCKsTZ2+LRkxDrzcVQdss2k8+z | LC/vICnbEWzLwrCuMwBi1/e5wDNIY8gK
             oqExhoXtPsMaREjpCugd3Q==         | mvGn40x+G4cCYNZ6lGT9Zg==
 GOST      : WptpUlfooIlUjzDHU8XGuOU2waRud5SR | i6K4COXU0nyZ1mL3ZBuGUPz/ZXTj8KKQ
             E/tnoBqk+q0=                     | L6VNyS8/X2Y=

Directory: /var/lib/vnstat
 Mtime     : 2023-03-09 16:00:00 +0200        | 2023-03-09 18:45:01 +0200
 Ctime     : 2023-03-09 16:00:00 +0200        | 2023-03-09 18:45:01 +0200

File: /var/lib/vnstat/vnstat.db
 Mtime     : 2023-03-09 16:00:00 +0200        | 2023-03-09 18:45:00 +0200
 Ctime     : 2023-03-09 16:00:00 +0200        | 2023-03-09 18:45:00 +0200
 SHA256    : X/lnJuuSo4jX4HRzxMBodnKHAjQFvugi | oqtY3HTNds/qDNFCRAEsfN5SuO0U5LRg
             2sh2c0u69x8=                     | otc5z1y+eGY=
 SHA512    : U/g8O6G8cuhsqCUCbrElxgiy+naJKPkI | y+sw4LX8mlDWkRJMX38TsYSo1DQzxPOS
             hG7vdH9rBINjakL87UWajT0s6WSy0pvt | 068otnzw2FSSlM5X5j5EtyJiY6Hd5P+A
             ALaTcDFKHBAmmFrl8df2nQ==         | jFiWStMbx+dQidXYZ4XFAw==
 RMD160    : F6YEjIIQu2J3ru7IaTvSemA9e34=     | bmVSaRKN2qU7qpEWkzfXFoH4ZK4=
 TIGER     : UEwLoeR6Qlf2oOI58pUCEDaWk0pHDkcY | 0Qb4nUqe3cKh/g5CQUnOXGfjZwJHjeWa
 CRC32     : Bv3/6A==                         | jvW6mg==
 HAVAL     : VD7tjHb8o8KTUo5xUH7eJEmTWgB9zjft | rumfiWJvy/sTK/09uj7XlmV3f7vj6KBM
             kOkzKxFWqqU=                     | qeOuKvu0Zjc=
 WHIRLPOOL : wR0qt8u4N8aQn8VQ+bmfrxB7CyCWVwHi | FVWDRE3uY6qHxLlJQLU9i9QggLW+neMj
             ADHpMTUxBEKOpOBlHTWXIk13qYZiD+o/ | Wt+Dj9Rz92BG9EomgLUgUkxfiVFO8cMq
             XtzTB4rMbxS4Z5PAdC/07A==         | WaR/KKq3Z7R8f/50tc9GMQ==
 GOST      : l3ibqMkHMSPpQ+9ok51/xBthET9+JQMd | qn0GyyCg67KRGP13At52tnviZfZDgyAm
             OZtiFGYXmgU=                     | c82NXSzeyV0=

The attributes of the (uncompressed) database(s):

 SHA256    : sjCxyIkr0nC/gTkNmn7DNqAQWttreDF6
 SHA512    : vNMpb54qxrbOk6S1Z+m9r0UwGvRarkWY
 RMD160    : anhm5E6UlKmPYYJ4WYnWXk/LT3A=
 TIGER     : 5e1wycoF35/ABrRf7FNypZ45169VTuV4
 CRC32     : EAJlFg==
 HAVAL     : R5imONWRYgNGEfhBTc096K+ABnMFkMmh
 GOST      : F5zO2Ovtvf+f7Lw0Ef++ign1znZAQMHM

 SHA256    : QRwubXnz8md/08n28Ek6DOsSQKGkLvuc
 SHA512    : 238RmI1PHhd9pXhzcHqM4+VjNzR0es+3
 RMD160    : GJWuX/nIPY05gz62YXxk4tWiH5I=
 TIGER     : l0aOjXlM4/HjyN9bhgBOvvCYeqoQyjpw
 CRC32     : KFz6GA==
 HAVAL     : a//4jwVxF22URf2BRNA612WOOvOrScy7
 WHIRLPOOL : MBf+NeXElUvscJ2khIuAp+NDu1dm4h1f
 GOST      : EQnPh6jQLVUqaAK9B4/U4V89tanTI55N

End timestamp: 2023-03-09 18:49:51 +0200 (run time: 4m 34s)

6. Substitute old aide database with the new that includes the modified files

As you see AIDE detected the changes in /root/test.txt

To apply the changes be known by AIDE for next time (e.g. this file was authorized and supposed to be written there) simply move the new generated database
to current aide database.

# copy generated DB to master DB
root@dlp:~# cp -p /var/lib/aide/ /var/lib/aide/aide.db

7. Check once again to make sure recently modified files are no longer seen as changed by AIDE

Recheck again the database to make sure the files you wanted to omit are no longer mentioned as changed

root@server:~# aide –check –config /etc/aide/aide.conf
Start timestamp: 2023-03-09 16:23:05 +0200 (AIDE 0.17.3)
AIDE found differences between database and filesystem!!

  Total number of entries:      66791
  Added entries:                0
  Removed entries:              0
  Changed entries:              3

Changed entries:

f =…. mc..H.. . : /var/lib/fail2ban/fail2ban.sqlite3
d =…. mc.. .. . : /var/lib/vnstat
f =…. mc..H.. . : /var/lib/vnstat/vnstat.db

Detailed information about changes:

File: /var/lib/fail2ban/fail2ban.sqlite3
 Mtime     : 2023-03-09 15:55:01 +0200        | 2023-03-09 16:25:02 +0200
 Ctime     : 2023-03-09 15:55:01 +0200        | 2023-03-09 16:25:02 +0200
 SHA256    : lLilXNleqSgHIP1y4o7c+oG5XyUPGzgi | MnWXC2rBMf7DNJ91kXtHXpM2c2xxF60X
             RHYH+zvlAL4=                     | DfLUQLHiSiY=
 SHA512    : iQj2pNT4NES4fBcujzdlEEGZhDnkhKgc | gxHVBxhGTKi0TjRE8/sn6/gtWsRw7Mfy
             QDlGFSAn6vi+RXesFCjCABT7/00eEm5/ | /wCfPlDK0dkRZEbr8IE2BNUhBgwwocCq
             ILcaqlQtBSLJgHjMQehzdg==         | zuazTy4N4x6X8bwOzRmY0w==
 RMD160    : Xg4YU8YI935L+DLvkRsDanS4DGo=     | +ksl9kjDoSU9aL4tR7FFFOK3mqw=
 TIGER     : 2WhhPq9kuyeNJkOicDTDeOeJB8HR8zZe | 9cvXZNbU+cp5dA5PLiX6sGncXd1Ff5QO
 CRC32     : NQmi4A==                         | y6Oixg==
 HAVAL     : t1ET+84+8WgfwqlLy4R1Qk9qGZQRUbJI | aPnCrHfmZAUm7QjROGEl6rd3776wO+Ep
             z2J0ROGduXc=                     | s/TQn7tH1tY=
 WHIRLPOOL : xKSn71gFIVhk5rWJIBaYQASl0V+pGn+3 | 9Hu6NBhz+puja7uandb21Nt6cEW6zEpm
             N85R0tiCKsTZ2+LRkxDrzcVQdss2k8+z | bTsq4xYA09ekhDHMQJHj2WpKpzZbA+t0
             oqExhoXtPsMaREjpCugd3Q==         | cttMDX8J8M/UadqfL8KZkQ==
 GOST      : WptpUlfooIlUjzDHU8XGuOU2waRud5SR | WUQfAMtye4wADUepBvblvgO+vBodS0Ej
             E/tnoBqk+q0=                     | cIbXy4vpPYc=

Directory: /var/lib/vnstat
 Mtime     : 2023-03-09 16:00:00 +0200        | 2023-03-09 16:25:01 +0200
 Ctime     : 2023-03-09 16:00:00 +0200        | 2023-03-09 16:25:01 +0200

File: /var/lib/vnstat/vnstat.db
 Mtime     : 2023-03-09 16:00:00 +0200        | 2023-03-09 16:25:01 +0200
 Ctime     : 2023-03-09 16:00:00 +0200        | 2023-03-09 16:25:01 +0200
 SHA256    : X/lnJuuSo4jX4HRzxMBodnKHAjQFvugi | N1lzhV3+tkDBud3AVlmIpDkU1c3Rqhnt
             2sh2c0u69x8=                     | YqE8naDicoM=
 SHA512    : U/g8O6G8cuhsqCUCbrElxgiy+naJKPkI | +8B9HvHhOp1C/XdlOORjyd3J2RtTbRBF
             hG7vdH9rBINjakL87UWajT0s6WSy0pvt | b0Moo2Gj+cIxaMCu5wOkgreMp6FloqJR
             ALaTcDFKHBAmmFrl8df2nQ==         | UH4cNES/bAWtonmbj4W7Vw==
 RMD160    : F6YEjIIQu2J3ru7IaTvSemA9e34=     | 8M6TIOHt0NWgR5Mo47DxU28cp+4=
 TIGER     : UEwLoeR6Qlf2oOI58pUCEDaWk0pHDkcY | Du9Ue0JA2URO2tiij31B/+663OaWKefR
 CRC32     : Bv3/6A==                         | v0Ai4w==
 HAVAL     : VD7tjHb8o8KTUo5xUH7eJEmTWgB9zjft | XA+vRnMNdVGFrO+IZtEA0icunWqBGaCf
             kOkzKxFWqqU=                     | leR27LN4ejc=
 WHIRLPOOL : wR0qt8u4N8aQn8VQ+bmfrxB7CyCWVwHi | HG31dNEEcak2zZGR24W7FDJx8mh24MaJ
             ADHpMTUxBEKOpOBlHTWXIk13qYZiD+o/ | BQNhqkuS6R/bmlhx+P+eQ/JimwPAPOaM
             XtzTB4rMbxS4Z5PAdC/07A==         | xWG7cMETIXdT9sUOUal8Sw==
 GOST      : l3ibqMkHMSPpQ+9ok51/xBthET9+JQMd | y6Ek/TyAMGV5egkfCu92Y4qqk1Xge8c0
             OZtiFGYXmgU=                     | 3ONXRveOlr0=

The attributes of the (uncompressed) database(s):

 SHA256    : sjCxyIkr0nC/gTkNmn7DNqAQWttreDF6
 SHA512    : vNMpb54qxrbOk6S1Z+m9r0UwGvRarkWY
 RMD160    : anhm5E6UlKmPYYJ4WYnWXk/LT3A=
 TIGER     : 5e1wycoF35/ABrRf7FNypZ45169VTuV4
 CRC32     : EAJlFg==
 HAVAL     : R5imONWRYgNGEfhBTc096K+ABnMFkMmh
 GOST      : F5zO2Ovtvf+f7Lw0Ef++ign1znZAQMHM

End timestamp: 2023-03-09 16:27:33 +0200 (run time: 4m 28s)

As you can see there are no new added entries for /root/test.txt and some other changed records for vnstat service as well as fail2ban ones, so the Intrusion detection system works just as we expected it.

8. Configure Email AIDE changed files alerting Email recipient address

From here on aide package has set its own cron job which is automatically doing the check operation every day and any new file modifications will be captured and alerts sent to local root@localhost mailbox account, so you can check it out later with mail command.

If you want to sent the Email alert for any files modifications occured to another email, assuming that you have a locally running SMTP server with a mail relay to send to external mails, you can do it via /etc/default/aide via:


For example change it to a FQDN email address

9.Force AIDE to run AIDE at specitic more frequent time intervals

You can as well install a cron job to execute AIDE at specific time intervals, as of your choice

Lets say you want to run a custom prepared set of files to monitor in /etc/aide/aide_custom_config.conf configure a new cronjob like below:

root@server:~# crontab -u root -e
*/5 * * * * aide -c /etc/aide/aide_custom_config.conf -u && cp /var/lib/custom-aide/aide.db{.new,}

This will execute AIDE system check every 5 minutse and email the report to ealier configured email via /etc/default/aide

10. Check the output of AIDE for changes – useful for getting a files changes from aide from scripts

Check the command exit status.

root@server:~# echo $?

According to AIDE man pages, the AIDE’s exit status is normally 0 if no errors occurred. Except when the –check, –compare or –update command was requested, in which case the exit status is defined as:

   1 * (new files detected?)     +

   2 * (removed files detected?) +

   4 * (changed files detected?)

   Since  those three cases can occur together, the respective error codes are added. For example, if there are new files and removed files detected, the exit status will be 1 + 2 = 3.

   Additionally, the following exit codes are defined for generic error conditions in aide help manual:

   14 Error writing error

   15 Invalid argument error

   16 Unimplemented function error

   17 Invalid configureline error

   18 IO error

   19 Version mismatch error


  • That AIDE checks might be resource intensive
    and could cause a peak in CPU use and have a negative effect on lets very loaded application server machines,
    thus causing a performance issuea during integrity checks !
  • If you are scanning file system wide and you do it frequent, be sure to provide “enough” resources or schedule the scan at a times that the Linux host will be less used !
  • Whenever you made any AIDE configuration changes, remember to initialize the database to create a baseline !

How to filter dhcp traffic between two networks running separate DHCP servers to prevent IP assignment issues and MAC duplicate addresses

Tuesday, February 8th, 2022

Tracking the Problem of MAC duplicates on Linux routers

If you have two networks that see each other and they're not separated in VLANs but see each other sharing a common netmask lets say or, it might happend that there are 2 dhcp servers for example (isc-dhcp-server running on and dhcpd running on can broadcast their services to both LANs (netmask and Local Net LAN The result out of this is that some devices might pick up their IP address via DHCP from the wrong dhcp server.

Normally if you have a fully controlled little or middle class home or office network (10 – 15 electronic devices nodes) connecting to the LAN in a mixed moth some are connected via one of the Networks via connected Wifi to others are LANned and using static IP adddresses and traffic is routed among two ISPs and each network can see the other network, there is always a possibility of things to go wrong. This is what happened to me so this is how this post was born.

The best practice from my experience so far is to define each and every computer / phone / laptop host joining the network and hence later easily monitor what is going on the network with something like iptraf-ng / nethogs  / iperf – described in prior  how to check internet spepeed from console and in check server internet connectivity speed with speedtest-cliiftop / nload or for more complex stuff wireshark or even a simple tcpdump. No matter the tools network monitoring is only part on solving network issues. A very must have thing in a controlled network infrastructure is defining every machine part of it to easily monitor later with the monitoring tools. Defining each and every host on the Hybrid computer networks makes administering the network much easier task and  tracking irregularities on time is much more likely. 

Since I have such a hybrid network here hosting a couple of XEN virtual machines with Linux, Windows 7 and Windows 10, together with Mac OS X laptops as well as MacBook Air notebooks, I have followed this route and tried to define each and every host based on its MAC address to pick it up from the correct DHCP1 server (that is distributing IPs for Internet Provider 1 (ISP 1), that is mostly few computers attached UTP LAN cables via LiteWave LS105G Gigabit Switch as well from DHCP2 – used only to assigns IPs to servers and a a single Wi-Fi Access point configured to route incoming clients via Linux NAT gateway server.

To filter out the unwanted IPs from the DHCPD not to propagate I've so far used a little trick to  Deny DHCP MAC Address for unwanted clients and not send IP offer for them.

To give you more understanding,  I have to clear it up I don't want to have automatic IP assignments from DHCP2 / LAN2 to DHCP1 / LAN1 because (i don't want machines on DHCP1 to end up with IP like or DHCP2 (to have, as such a wrong IP delegation could potentially lead to MAC duplicates IP conflicts. MAC Duplicate IP wrong assignments for those older or who have been part of administrating large ISP network infrastructures  makes the network communication unstable for no apparent reason and nodes partially unreachable at times or full time …

However it seems in the 21-st century which is the century of strangeness / computer madness in the 2022, technology advanced so much that it has massively started to break up some good old well known sysadmin standards well documented in the RFCs I know of my youth, such as that every electronic equipment manufactured Vendor should have a Vendor Assigned Hardware MAC Address binded to it that will never change (after all that was the idea of MAC addresses wasn't it !). 
Many mobile devices nowadays however, in the developers attempts to make more sophisticated software and Increase Anonimity on the Net and Security, use a technique called  MAC Address randomization (mostly used by hackers / script kiddies of the early days of computers) for their Wi-Fi Net Adapter OS / driver controlled interfaces for the sake of increased security (the so called Private WiFi Addresses). If a sysadmin 10-15 years ago has seen that he might probably resign his profession and turn to farming or agriculture plant growing, but in the age of digitalization and "cloud computing", this break up of common developed network standards starts to become the 'new normal' standard.

I did not suspected there might be a MAC address oddities, since I spare very little time on administering the the network. This was so till recently when I accidently checked the arp table with:

Hypervisor:~# arp -an     5c:89:b5:f2:e8:d8      (Unknown)    00:15:3e:d3:8f:76       (Unknown)


and consequently did a network MAC Address ARP Scan with arp-scan (if you never used this little nifty hacker tool I warmly recommend it !!!)
If you don't have it installed it is available in debian based linuces from default repos to install

Hypervisor:~# apt-get install –yes arp-scan

It is also available on CentOS / Fedora / Redhat and other RPM distros via:

Hypervisor:~# yum install -y arp-scan



Hypervisor:~# arp-scan –interface=eth1    00:16:3e:0f:48:05       Xensource, Inc.    00:16:3e:04:11:1c       Xensource, Inc.    00:15:3e:bb:45:45       Xensource, Inc.    00:15:3e:59:96:8e       Xensource, Inc.    00:15:3e:d3:8f:77       Xensource, Inc.    8c:89:b5:f2:e8:d8       Micro-Star INT'L CO., LTD     5c:89:b5:f2:e8:d8      (Unknown)    00:15:3e:d3:8f:76       (Unknown)

192.168.x.91     02:a0:xx:xx:d6:64        (Unknown)
192.168.x.91     02:a0:xx:xx:d6:64        (Unknown)  (DUP: 2)

N.B. !. I found it helpful to check all available interfaces on my Linux NAT router host.

As you see the scan revealed, a whole bunch of MAC address mess duplicated MAC hanging around, destroying my network topology every now and then 
So far so good, the MAC duplicates and strangely hanging around MAC addresses issue, was solved relatively easily with enabling below set of systctl kernel variables.

1. Fixing Linux ARP common well known Problems through disabling arp_announce / arp_ignore / send_redirects kernel variables disablement


Linux answers ARP requests on wrong and unassociated interfaces per default. This leads to the following two problems:

ARP requests for the loopback alias address are answered on the HW interfaces (even if NOARP on lo0:1 is set). Since loopback aliases are required for DSR (Direct Server Return) setups this problem is very common (but easy to fix fortunately).

If the machine is connected twice to the same switch (e.g. with eth0 and eth1) eth2 may answer ARP requests for the address on eth1 and vice versa in a race condition manner (confusing almost everything).

This can be prevented by specific arp kernel settings. Take a look here for additional information about the nature of the problem (and other solutions): ARP flux.

To fix that generally (and reboot safe) we  include the following lines into


Hypervisor:~# cp -rpf /etc/sysctl.conf /etc/sysctl.conf_bak_07-feb-2022
Hypervisor:~# cat >> /etc/sysctl.conf

# LVS tuning


Press CTRL + D simultaneusly to Write out up-pasted vars.

To read more on Load Balancer using direct routing and on LVS and the arp problem here

2. Digging further the IP conflict / dulicate MAC Problems

Even after this arp tunings (because I do have my Hypervisor 2 LAN interfaces connected to 1 switch) did not resolved the issues and still my Wireless Connected devices via network (ISP2) were randomly assigned the wrong range IPs 192.168.0.XXX/24 as well as the wrong gateway (ISP1).
After thinking thoroughfully for hours and checking the network status with various tools and thanks to the fact that my wife has a MacBook Air that was always complaining that the IP it tried to assign from the DHCP was already taken, i"ve realized, something is wrong with DHCP assignment.
Since she owns a IPhone 10 with iOS and this two devices are from the same vendor e.g. Apple Inc. And Apple's products have been having strange DHCP assignment issues from my experience for quite some time, I've thought initially problems are caused by software on Apple's devices.
I turned to be partially right after expecting the logs of DHCP server on the Linux host (ISP1) finding that the phone of my wife takes IP in 192.168.0.XXX, insetad of IP from (which has is a combined Nokia Router with 2.4Ghz and 5Ghz Wi-Fi and LAN router provided by ISP2 in that case Vivacom). That was really puzzling since for me it was completely logical thta the iDevices must check for DHCP address directly on the Network of the router to whom, they're connecting. Guess my suprise when I realized that instead of that the iDevices does listen to the network on a wide network range scan for any DHCPs reachable baesd on the advertised (i assume via broadcast) address traffic and try to connect and take the IP to the IP of the DHCP which responds faster !!!! Of course the Vivacom Chineese produced Nokia router responded DHCP requests and advertised much slower, than my Linux NAT gateway on ISP1 and because of that the Iphone and iOS and even freshest versions of Android devices do take the IP from the DHCP that responds faster, even if that router is not on a C class network (that's invasive isn't it??). What was even more puzzling was the automatic MAC Randomization of Wifi devices trying to connect to my ISP1 configured DHCPD and this of course trespassed any static MAC addresses filtering, I already had established there.

Anyways there was also a good think out of tthat intermixed exercise 🙂 While playing around with the Gigabit network router of vivacom I found a cozy feature SCHEDULEDING TURNING OFF and ON the WIFI ACCESS POINT  – a very useful feature to adopt, to stop wasting extra energy and lower a bit of radiation is to set a swtich off WIFI AP from 12:30 – 06:30 which are the common sleeping hours or something like that.

3. What is MAC Randomization and where and how it is configured across different main operating systems as of year 2022?

Depending on the operating system of your device, MAC randomization will be available either by default on most modern mobile OSes or with possibility to have it switched on:

  • Android Q: Enabled by default 
  • Android P: Available as a developer option, disabled by default
  • iOS 14: Available as a user option, disabled by default
  • Windows 10: Available as an option in two ways – random for all networks or random for a specific network

Lately I don't have much time to play around with mobile devices, and I do not my own a luxury mobile phone so, the fact this ne Androids have this MAC randomization was unknown to me just until I ended a small mess, based on my poor configured networks due to my tight time constrains nowadays.

Finding out about the new security feature of MAC Randomization, on all Android based phones (my mother's Nokia smartphone and my dad's phone, disabled the feature ASAP:

4. Disable MAC Wi-Fi Ethernet device Randomization on Android

MAC Randomization creates a random MAC address when joining a Wi-Fi network for the first time or after “forgetting” and rejoining a Wi-Fi network. It Generates a new random MAC address after 24 hours of last connection.

Disabling MAC Randomization on your devices. It is done on a per SSID basis so you can turn off the randomization, but allow it to function for hotspots outside of your home.

  1. Open the Settings app
  2. Select Network and Internet
  3. Select WiFi
  4. Connect to your home wireless network
  5. Tap the gear icon next to the current WiFi connection
  6. Select Advanced
  7. Select Privacy
  8. Select "Use device MAC"

5. Disabling MAC Randomization on MAC iOS, iPhone, iPad, iPod

To Disable MAC Randomization on iOS Devices:

Open the Settings on your iPhone, iPad, or iPod, then tap Wi-Fi or WLAN


  1. Tap the information button next to your network
  2. Turn off Private Address
  3. Re-join the network

Of course next I've collected their phone Wi-Fi adapters and made sure the included dhcp MAC deny rules in /etc/dhcp/dhcpd.conf are at place.

The effect of the MAC Randomization for my Network was terrible constant and strange issues with my routings and networks, which I always thought are caused by the openxen hypervisor Virtualization VM bugs etc.

That continued for some months now, and the weird thing was the issues always started when I tried to update my Operating system to the latest packetset, do a reboot to load up the new piece of software / libraries etc. and plus it happened very occasionally and their was no obvious reason for it.


6. How to completely filter dhcp traffic between two network router hosts
IP / to stop 2 or more configured DHCP servers
on separate networks see each other

To prevent IP mess at DHCP2 server side (which btw is ISC DHCP server, taking care for IP assignment only for the Servers on the network running on Debian 11 Linux), further on I had to filter out any DHCP UDP traffic with iptables completely.
To prevent incorrect route assignments assuming that you have 2 networks and 2 routers that are configurred to do Network Address Translation (NAT)-ing Router 1:, Router 2:

You have to filter out UDP Protocol data on Port 67 and 68 from the respective source and destination addresses.

In firewall rules configuration files on your Linux you need to have some rules as:

# filter outgoing dhcp traffic from to
-A INPUT -p udp -m udp –dport 67:68 -s -d -j DROP
-A OUTPUT -p udp -m udp –dport 67:68 -s -d -j DROP
-A FORWARD -p udp -m udp –dport 67:68 -s -d -j DROP

-A INPUT -p udp -m udp –dport 67:68 -s -d -j DROP
-A OUTPUT -p udp -m udp –dport 67:68 -s -d -j DROP
-A FORWARD -p udp -m udp –dport 67:68 -s -d -j DROP

-A INPUT -p udp -m udp –sport 67:68 -s -d -j DROP
-A OUTPUT -p udp -m udp –sport 67:68 -s -d -j DROP
-A FORWARD -p udp -m udp –sport 67:68 -s -d -j DROP

You can download also with above rules from here

Applying this rules, any traffic of DHCP between 2 routers is prohibited and devices from Net: will no longer wrongly get assinged IP addresses from Network range: as it happened to me.

7. Filter out DHCP traffic based on MAC completely on Linux with arptables

If even after disabling MAC randomization on all devices on the network, and you know physically all the connecting devices on the Network, if you still see some weird MAC addresses, originating from a wrongly configured ISP traffic router host or whatever, then it is time to just filter them out with arptables.

## drop traffic prevent mac duplicates due to vivacom and bergon placed in same network –
dchp1-server:~# arptables -A INPUT –source-mac 70:e2:83:12:44:11 -j DROP

To list arptables configured on Linux host

dchp1-server:~# arptables –list -n

If you want to be paranoid sysadmin you can implement a MAC address protection with arptables by only allowing a single set of MAC Addr / IPs and dropping the rest.

dchp1-server:~# arptables -A INPUT –source-mac 70:e2:84:13:45:11 -j ACCEPT
dchp1-server:~# arptables -A INPUT  –source-mac 70:e2:84:13:45:12 -j ACCEPT

dchp1-server:~# arptables -L –line-numbers
Chain INPUT (policy ACCEPT)
1 -j DROP –src-mac 70:e2:84:13:45:11
2 -j DROP –src-mac 70:e2:84:13:45:12

Once MACs you like are accepted you can set the INPUT chain policy to DROP as so:

dchp1-server:~# arptables -P INPUT DROP

If you later need to temporary, clean up the rules inside arptables on any filtered hosts flush all rules inside INPUT chain, like that

dchp1-server:~#  arptables -t INPUT -F

Set proxy only for apt, apt-get, aptitude package manager on Debian / Ubuntu Linux

Wednesday, December 22nd, 2021




Main console package install apt-get / apt and / aptitude did not use the HTTP Proxy environment variables by default as there is no default proxy set on Debian / Ubuntu / Mint and other deb based distros after OS Install. Under some circunstances for DMZ placed or firewall secured servers, direct access to internet address or even Package repository is only allowed via a proxy and hence the package manager needs to have a proxy host set.
 Setting a global wide proxy on Linux is easily possible by setting http_proxy="" and https_proxy or if FTP connection via ftp_proxy somewhere in /etc/profile , /etc/bashrc or via /etc/environment but as using this Shell variables set it global wide for all applications lynx / links / wget / curl, sometimes it is useful to set the Proxy host only for deb package management tools.

Note that if you want to set a proxy host for deb operations this can be done during initial OS install installation, the Apt configuration file would have been automatically updated then. 

Creating  an Apt Proxy Conf File

Apt loads all configuration files under /etc/apt/apt.conf.d. We can create a configuration specifically for our proxy there, keeping it separate from all other configurations.

  1. Create a new configuration file named proxy.conf.



    # touch /etc/apt/apt.conf.d/proxy.conf
  2. Open the proxy.conf file in a text editor.



    # vi /etc/apt/apt.conf.d/proxy.conf
  3. Add the following line to set your HTTP proxy for apt.



    Acquire::http::Proxy "http://username:password@proxy.server:port/";
  4. Add the following line to set your HTTPS proxy.



    Acquire::https::Proxy "http://username:passw0rd@proxy.server:port/";
  5. Save your changes and exit the text editor.

Your proxy settings will be applied the next time you run Apt.

Simplifying the Configuration

As mentioned by a user in the comments below, there is an alternative way for defining the proxy settings. While similar, it removes some redundancy.

Just like in the first example, create a new file under the /etc/apt/apt.conf.d directory for example /etc/apt/apt.conf.d/proxies, and then add the lines as.

Acquire {
HTTP::proxy "";
HTTPS::proxy "";