Video Editing for Debian 11

On linux, when i needed to edit a video I usually go to Kdenlive, I used to think it is THE linux alternative to Adobe Premier Pro, until yesterday, when a friend recommended I try out OpenShot

I am a Gnome user, Kdenlive was designed for KDE, I have always run it in gnome (Unity) and it worked fine, but today, I am feeling adventurous and up for trying OpenShot, openshot too is pyQt which is a bummer, but hey, this is not why we doing this

Reminder
KDE is based on Qt and Gnome is based on GTK. both applications here are meant for KDE, and I don’t really want to install KDE on my machine

This post here is where I will leave my impressions so hang tight.

redis for Laravel on Debian

If you are like me, running only your own projects on a server, you might want to skip authentication

the changes I generally make to the file /etc/redis/redis.conf are

1- At the very beginning, limit the RAM redis can use with the line

maxmemory 2gb

2- Change the supervisor to systemd by modifying the line

supervised no

to

supervised systemd

Now, to test the new config, from the command line, run the following commands

systemctl restart redis-server
redis-cli
ping
config get maxmemory
quit

You have just configured redis and tested your new settings.

Nested virtualization in KVM

The reason I am enabling this in my virtual machine is to develop with android studio under windows or Linux in a dedicated development machine (Let us call it an android development virtual machine), you will need to enable nested virtualization for the virtual android phone that comes with Android studio, there are many occasions where you need nested virtualization, so let us see what we need to do.

1- Check if our system allows nested virtualization with the following line

cat /sys/module/kvm_intel/parameters/nested 

If this returns a Y or a 1, then we are good to go to the next step, if not, then execute the following to enable the feature on the host system

echo 'options kvm_intel nested=1' >> /etc/modprobe.d/qemu-system-x86.conf 

Now, with that out of the way, we can move to the next step

2- Enable nested virtualization in the config of the virtual machine, either with virsh edit or edit the file manually and reload it, whatever you are used to doing should work

virsh edit androiddev

Now, specify either host-model OR host-passthrough, host model is more compatible when moving the virtual machine to a new CPU, while host-passthrough will deliver absolutly all CPU features to the guest os, but is very unfriendly to moving the machine to a different KVM host

<cpu mode='host-model'> 

Giving SFTP access to a user for a certain directory !

In this mini tutorial, I will be adding the user kareem to the system, and allow kareem to sftp into a web directory where he can post his web design work, as usual, the steps first, then whatever explanations !

There are two ways to do this, one to add one user, the other to add a group of users, you can either pick one, or do both !

The part in common between both solutions

apt-get install openssh-server
adduser kareem
Then enter a new password twice for kareem

The interesting thing about this sftp user business is that the directory we will specify as the root for the user kareem has to be owned by root ! so go ahead and create the directory /var/www/html/usr/kareem, then execute the following commands

chown root:root /var/www/html/usr
chmod 755 /var/www/html/usr

chown kareem:kareem /var/www/html/usr/kareem

Now, the user kareem owns a directory within his root directory that he can write to, and can not write outside that directory since he does not have the OS permissions, Now, let us add kareem to the list of people who have sftp access but not ssh access.

Edit /etc/ssh/sshd_config and append the following to the document

Match User kareem
ForceCommand internal-sftp
PasswordAuthentication yes
ChrootDirectory /var/www/html/usr
PermitTunnel no
AllowAgentForwarding no
AllowTcpForwarding no
X11Forwarding no

Now, restart the service by executing the following command

systemctl restart ssh

You are done, try connecting with something like winSCP

Resume bad blocks where it was stopped

The answer to this should be simple, I initiated the test with

badblocks -nsv /dev/sdb

, first, interrupt bad blocks with ctrl+c, the output should be

Checking for bad blocks in non-destructive read-write mode
From block 0 to 1953514583
Checking for bad blocks (non-destructive read-write test)
Testing with random pattern:   0.92% done, 49:38 elapsed. (0/0/0 errors)
 21.32% done, 18:49:24 elapsed. (0/0/0 errors)

Interrupted at block 416437376

Interrupt caught, cleaning up

Okay, so we know what blocks it was supposed to check (1 through 1953514583), and where it was interrupted (416437376)

So i will ask it to resume testing from where it finished (-1), up to the end

badblocks -nsv /dev/sdb 1953514583 416437375

n = Non destructive
s = Show progress
v = tell us about what you find !

The new run should tell you the percentage correctly, but the time counter will be reset to zero, as it is only counting how long this run has been running for

One thing to note is that bad blocks can be used to instruct the filesystem to avoid the bad blocks, but it also allows the disk’s firmware to substitute bad blocks with spare blocks, so that the disk works again with no intervention from your end !

So for my 2TB hard drive…

416437375 = 21% (13 hours)
619014719 = 31.6% (+23:22)
627995199 = 32.15% (+1:04)
667782398 = 34.18% (+4:46)
715469885 = 36.62% (+5:44)
827834875 = 42.38%

While running the tests, you might want to keep an eye on the hard drive temperature with a command like

hddtemp /dev/sdb

To create a log file of the bad blocks, every run should have it’s own file !

badblocks -nsv -o /root/badblocks3.txt /dev/sdb 1953514583 627995198

The concatenation of those files you are creating is very useful in creating a file system if you ever decide to format the drive later !, but the recommended way is using badblocks with the other disk tools directly

while the test is running, you will see 3 numbers that correspond to readerror/writeerror/corruptionerror

webP is the new PNG

Superior in both Lossless compression, and Lossy compression, webp is the new image format by google

Already supported by all web browsers *(that i have tested it with), webP is indeed a promising format, so let us get to compressing our images

I have a big bunch of bitmaps that my scanner spits out (To avoid lossy jpeg compression the scanner’s driver produces), and i need them converted to lossless webp to save space (the first image I compressed went from 552MB bitmap to 183), that is 33% of the original size

So, under linux, this is how i would convert all BMPs into webp images, I think it is exectly the same on windows

on the command line, the command for compressing one image looks like

cwebp -lossless 00.bmp -o 00.webp

Now, the next step is to run them in a batch, copy the following text into a file and name it with the extension

Linux find and replace string in multiple files

On windows, you might have been using text editors that search or search&replace within files in a folder, one such tool i have used in windows is “source edit” by Joacim Andersson (Brixoft Software). that text editor does not seem to be maintained any longer as the developer seems to have moved into making games, but there are certainly many other editors that allow you to do the same thing.

On the other hand, on Linux, I don’t need to do that, the basic tools that come with the operating system allow for that, multi gigabyte files can be searched and have certain text replaced at the speed it takes to read them (Without having to open them for editing)

So, let us assume we have a folder with many text files (Including css or js or html or php files for example), to search that folder, we can combine

grep -Ril "text-to-find-here" /path/to/file/

-R (-r) look for files recursively
-l show file names, not the contents that were found
-i ….

Another tool which is better suited for looking in code is ack (ack-grep) which i will come back to cover in this article, and a newer tool that i have never used is

Now, replacing a string inside a file is simple, there is a cool tool called sed

sed -i '/TEXTTOFIND/ s//TEXTTOREPLACEWITH/g' verylargefile.txt

Gnome terminal tab title

To tell tabs apart fast, you can give every terminal tab a name, just execute the following line inside that terminal window

echo -ne "\033]0;SOME TITLE HERE\007"

I am doing this on the default gnome terminal in Debian 11 (Bullseye), older methods no longer work

You will have to execute this every time in every SSH window to a remote machine, I am looking into a way to making the name permanent !

Installing MacOS in a virtual machine (KVM) under linux

This is a simple task, and it is only simple because of foxlet (@FoxletFox on twitter)

Anyway, let us get to setting it up, to begin with, you don’t need to download MacOS, when using foxlet’s macOS-Simple-KVM, your virtual machine downloads MacOS on it’s own

Step 1: Make sure you have KVM ! and the relevant tools

apt-get install qemu-kvm libvirt-daemon qemu-system qemu-utils python3 python3-pip bridge-utils virtinst libvirt-daemon-system virt-manager

You know, the usual kvm setup ;), I am hoping you already have KVM, if not, see this post and install KVM first

Now that you have kvm, you need to insure that vhost_net is installed, loaded and enabled

modprobe vhost_net
lsmod | grep vhost

You will also need git to download macOS-Simple-KVM

git
git clone https://github.com/foxlet/macOS-Simple-KVM.git

Now, download MacOS base image that will download the rest of the operating system (catalina is the latest ?) options in that script are –high-sierra, –mojave, or –catalina.

./jumpstart.sh --catalina