CentOS 8 - Error: Failed to download metadata for repo 'appstream': Cannot prepare internal mirrorlist: No URLs in mirrorlist

After I had not updated my CentOS 8 for a while, I used the command "yum update" or "dnf update" for the update, but I encountered the below error:

To fix this error, you can run the below commands:

$sudo sed -i 's/mirrorlist/#mirrorlist/g' /etc/yum.repos.d/CentOS-* 
$sudo sed -i 's|#baseurl=http://mirror.centos.org|baseurl=http://vault.centos.org|g' /etc/yum.repos.d/CentOS-*

Reference: Stackoverflow

Failed To install Oracle VirtualBox Guest Additions on AlmaLinux 8

 After the installation of AlmaLinux 8 is completed, I failed to install Guest Additions from Oracle VirtualBox version 6.1, the error is shown as below in the red box:

These are the steps to resolve this error:

$ sudo dnf install epel-release

$ sudo dnf install gcc make perl kernel-devel kernel-headers bzip2 dkms

Reference: TechMint

For the error in the orange box, you can cleanup before the installation using the following commands and then rerun the installation of Guest Additions:

# semanage fcontext -d /opt/VBoxGuestAdditions-6.1.22/other/mount.vboxsf

# restorecon /opt/VBoxGuestAdditions-6.1.22/other/mount.vboxsf

Reference: VirtualBox

apt-get error: Sub-process /usr/bin/dpkg returned an error code (1)

#rm /var/lib/dpkg/info/$nomdupaquet* -f

Command Credit: stackoverflow

L2TP with IPSec PSK VPN Keeps Connecting

 I tried to access from home WiFi to a workplace L2TP/IPSec Pre-Shared Key VPN gateway, but the Windows 10 built-in VPN kept connecting. I had asked my ISP customer service team, and they told me that their technical support team would contact me to sort out this problem. I had a doubt that there would be something to be configured or enabled in my Internet WiFi router. I accessed to the route, and enable ALG switch as the below snapshot, and then I tested it again; the VPN gets connected; booom, it works!

OpenWrt/LEDE UCI-Based DHCP Server & DHCP Client Address Reservation Configuration

 Firmware Version: LEDE Reboot 17.01.5 r3919-38e704be71 / LuCI lede-17.01 branch (git-18.180.55366-b78664c)

DHCP Server Configuration:

uci set dhcp.lan.interface="lan"

uci set dhcp.lan.ra="server"

uci set dhcp.lan.dhcpv4="server"

uci set dhcp.lan.start="1"

uci set dhcp.lan.limit="250"

uci set dhcp.lan.leasetime="120"

uci add_list dhcp.lan.dhcp_option="3,192.168.1.1"

uci add_list dhcp.lan.dhcp_option="6,8.8.8.8"

uci add_list dhcp.lan.dhcp_option="6,8.8.4.4"

uci add_list dhcp.lan.dhcp_option="42,192.168.1.100"

uci show dhcp.lan.interface

uci show dhcp.lan.ra

uci show dhcp.lan.dhcpv4

uci show dhcp.lan.start

uci show dhcp.lan.limit

uci show dhcp.lan.leasetime

uci show dhcp.lan.dhcp_option

DHCP Client Address Reservation:

uci add dhcp host

uci set dhcp.@host[-1].name="EndianEFW"

uci set dhcp.@host[-1].dns="1"

uci set dhcp.@host[-1].mac="08:00:27:F3:9C:74"

uci set dhcp.@host[-1].ip="192.168.1.29"

Save DHCP Configuration:

uci commit dhcp

Spyder IDE complaints, for dependencies, about jedi = 0.17.2 : None (NOK) & parso = 0.7.0 : 0.8.1 (NOK)

 After upgrading Spyder to version 4.2.1 on Ubuntu 18.04, it complaints, for dependencies, about

jedi = 0.17.2 : None (NOK)

parso = 0.7.0 : 0.8.1 (NOK)

I tried to install jedi, and parso using pip3 as below:

pip3 install jedi parso

But it does not fix the error.

It seems the problem is fixed when I install "Anaconda3-2020.11-Linux-x86_64.sh"

cd ~ballah/Downloads

chmod +x Anaconda3-2020.11-Linux-x86_64.sh

sudo ./Anaconda3-2020.11-Linux-x86_64.sh

You can check the dependencies from Help menu whether all they are resolved.

របៀបប្រើជញ្ជីងថ្លឹងDT570

You can download "របៀបប្រើជញ្ជីងថ្លឹងDT570" from here.

T568A-T568B Modular Wiring Guide

 You can download the T568A-T568B Modular Wiring Guide from here.