Monthly Archives: November 2018


A simple way to find which DHCP server gave you an IP

Recently, we were trying to find which DHCP server was responding to the messages on the network. Using a DHCP-enabled client on a Fedora 26 GNU/Linux we grepped the contents of journalctl to find the DHCP acknowledgment messages (DHCPACK) and figure out the IP of the DHCP server.

The command we used was the following:

sudo journalctl | grep DHCPACK;

And it gave us results such as the ones below:

[[email protected] ~]$ sudo journalctl | grep DHCPACK
Nov 12 13:08:28 sys-net dhclient[578]: DHCPACK from 10.1.101.252 (xid=0x80ec760c)
Nov 12 13:08:34 sys-net dhclient[720]: DHCPACK from 10.1.101.252 (xid=0x2ed6486f)
Nov 12 11:51:19 sys-net dhclient[1248]: DHCPACK from 10.1.101.252 (xid=0xe3dd491c)
Nov 12 12:02:09 sys-net dhclient[1407]: DHCPACK from 10.1.101.252 (xid=0x1fa42c2d)
Nov 12 12:11:03 sys-net dhclient[1508]: DHCPACK from 10.1.101.252 (xid=0x91c3990a)
Nov 12 12:14:06 sys-net dhclient[1607]: DHCPACK from 10.1.101.252 (xid=0x57ebb515)
Nov 12 12:19:27 sys-net dhclient[1710]: DHCPACK from 10.1.101.252 (xid=0x5450c250)
Nov 12 12:19:39 sys-net dhclient[1776]: DHCPACK from 10.1.101.252 (xid=0x2c38d517)
Nov 12 12:39:53 sys-net dhclient[1837]: DHCPACK from 192.168.1.1 (xid=0xe7a1182d)
Nov 12 12:40:51 sys-net dhclient[1837]: DHCPACK from 192.168.1.1 (xid=0xe7a1182d)
Nov 12 12:41:51 sys-net dhclient[1837]: DHCPACK from 192.168.1.1 (xid=0xe7a1182d)
Nov 12 12:42:44 sys-net dhclient[1837]: DHCPACK from 192.168.1.1 (xid=0xe7a1182d)
Nov 12 12:43:33 sys-net dhclient[1837]: DHCPACK from 192.168.1.1 (xid=0xe7a1182d)
Nov 12 12:44:31 sys-net dhclient[1837]: DHCPACK from 192.168.1.1 (xid=0xe7a1182d)
Nov 12 12:46:20 sys-net dhclient[2053]: DHCPACK from 192.168.1.1 (xid=0xbb006001)

It is important to use sudo or else you will not be seeing messages from other users and the system. As, only users in groups ‘adm’, ‘systemd-journal’, ‘wheel’ can see all messages.


youtube-dl does not work properly on Qubes 4.0 – Fedora 26

While working on a GNU/Linux Fedora 26 virtual machine running under the Qubes 4.0 OS, we installed youtube-dl through dnf to download some media off the net.

sudo dnf install youtube-dl;

When we tried to use it, we got the error youtube_dl.utils.RegexNotFoundError: Unable to extract Initial JS player signature function name. This issue was resolved years ago, so it led us to the conclusion that our version of youtube-dl was out of date. To test this hypothesis, we updated youtube-dl with pip.

sudo pip install --upgrade youtube_dl;

After the update was complete, we tried to use youtube-dl, this time with success!!

Full Logs:

[[email protected] Music]$ youtube-dl
bash: youtube-dl: command not found...
[[email protected] Music]$ sudo dnf install youtube-dl
Last metadata expiration check: 0:52:47 ago on Sat Nov 10 10:43:46 2018.
Dependencies resolved.
================================================================================
Package Arch Version Repository Size
================================================================================
Installing:
youtube-dl noarch 2018.04.16-1.fc26 updates 2.6 M

Transaction Summary
================================================================================
Install 1 Package

Total download size: 2.6 M
Installed size: 11 M
Is this ok [y/N]: y
Downloading Packages:
youtube-dl-2018.04.16-1.fc26.noarch.rpm 270 kB/s | 2.6 MB 00:09 
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Total 258 kB/s | 2.6 MB 00:10 
Running transaction check
Transaction check succeeded.
Running transaction test
Transaction test succeeded.
Running transaction
Preparing : 1/1 
Installing : youtube-dl-2018.04.16-1.fc26.noarch 1/1 
Running scriptlet: youtube-dl-2018.04.16-1.fc26.noarch 1/1 
Running as unit: run-rfddd15fff2d14d109826a90f59325e97.service
Verifying : youtube-dl-2018.04.16-1.fc26.noarch 1/1 
Notifying dom0 about installed applications

Installed:
youtube-dl.noarch 2018.04.16-1.fc26

Complete!
[[email protected] Music]$ youtube-dl https://www.youtube.com/watch?list=r6akoO34yUvK8ddtjnzL
 r6akoO34yUvK8ddtjnzL: Downloading webpage
 Downloading playlist: How to cook a banana
 playlist How to cook a banana: Downloading 18 videos
 Downloading video 1 of 18
 ir86d1hTSv1r: Downloading webpage
 ir86d1hTSv1r: Downloading video info webpage
 ir86d1hTSv1r: Extracting video information
 ir86d1hTSv1r: Downloading js player vfls4aurX
ERROR: Signature extraction failed: Traceback (most recent call last):
File "/usr/lib/python3.6/site-packages/youtube_dl/extractor/youtube.py", line 1191, in _decrypt_signature
video_id, player_url, s
File "/usr/lib/python3.6/site-packages/youtube_dl/extractor/youtube.py", line 1102, in _extract_signature_function
res = self._parse_sig_js(code)
File "/usr/lib/python3.6/site-packages/youtube_dl/extractor/youtube.py", line 1163, in _parse_sig_js
jscode, 'Initial JS player signature function name', group='sig')
File "/usr/lib/python3.6/site-packages/youtube_dl/extractor/common.py", line 808, in _search_regex
raise RegexNotFoundError('Unable to extract %s' % _name)
youtube_dl.utils.RegexNotFoundError: Unable to extract Initial JS player signature function name; please report this issue on https://yt-dl.org/bug . Make sure you are using the latest version; see https://yt-dl.org/update on how to update. Be sure to call youtube-dl with the --verbose flag and include its complete output.
(caused by RegexNotFoundError('Unable to extract \x1b[0;34mInitial JS player signature function name\x1b[0m; please report this issue on https://yt-dl.org/bug . Make sure you are using the latest version; see https://yt-dl.org/update on how to update. Be sure to call youtube-dl with the --verbose flag and include its complete output.',)); please report this issue on https://yt-dl.org/bug . Make sure you are using the latest version; see https://yt-dl.org/update on how to update. Be sure to call youtube-dl with the --verbose flag and include its complete output.
[[email protected] Music]$ sudo pip install --upgrade youtube_dl
WARNING: Running pip install with root privileges is generally not a good idea. Try `pip install --user` instead.
Collecting youtube_dl
Downloading https://files.pythonhosted.org/packages/6c/a4/c2e3fbd8b9c7ccbca3f220c4fb0914926669bf9080fb8f2f4db4811706be/youtube_dl-2018.11.7-py2.py3-none-any.whl (1.8MB)
100% |████████████████████████████████| 1.8MB 355kB/s 
Installing collected packages: youtube-dl
Successfully installed youtube-dl-2018.11.7
[[email protected] Music]$ youtube-dl https://www.youtube.com/watch?list=r6akoO34yUvK8ddtjnzL
 r6akoO34yUvK8ddtjnzL: Downloading webpage
 Downloading playlist: How to cook a banana
 playlist How to cook a banana: Downloading 18 videos
 Downloading video 1 of 18
 ir86d1hTSv1r: Downloading webpage
 ir86d1hTSv1r: Downloading video info webpage
 ir86d1hTSv1r: Downloading js player vfls4aurX
WARNING: Requested formats are incompatible for merge and will be merged into mkv.

How to create a video from thousands of images using ffmpeg

We have this simulation that creates several frames demonstrating the life-cycle of an ant colony.
Having thousands of pictures is not very useful most of the times so we decided to create a video out of those frames.
To do so, we decided to use ffmpeg. The names of the files that we generate are 5 digit zero-leading auto increment numbers (e.g 00001.png and 00002.png) so we ended up with the following command:

ffmpeg -framerate 60 -i %05d.png video.mp4;


How to create a video from an audio file and an image using ffmpeg

Recently, we had this audio file ( mp3) that we wanted to upload to youtube.com. As it is known, youtube does not allow uploading audio files. Taking that into consideration we had to create a video with a static image just to upload the audio file to youtube. To do that, we used ffmpeg and the following command:

ffmpeg -loop 1 -i Saturday.png -i 20181020.mp3 -shortest -acodec copy 20181020.mp4;


How we concatenate multiple mp3 files into one using ffmpeg

Recently, we needed to concatenate multiple mp3 files into one. We had at our disposal a machine that had ffmpeg installed.
To perform the merge, we created a list (separated by the character |) of the mp3 files, in the order we wanted them merged and executed the concat operation of ffmpeg to complete our task. Our resulting command was the following

ffmpeg -i "concat:20181021_080743.MP3|20181021_090745.MP3|20181021_100745.MP3" -acodec copy 20181021.mp3