Skip to content

cyber-security

Blog

Blog Categories

  • in DevOps
  • 1 min read

How to remove unnecessary Package in Oracle Linux Server

List Installed Packages

Before uninstalling, check which packages are installed:

dnf list installed
or for older versions:

rpm -qa

Identify Unnecessary Applications

  • Use dnf list installed to find applications you don’t need

  • Check running services: 

    systemctl list-units --type=service --state=running

  • Use ps aux or top to find unnecessary processes.

Remove Applications Using dnf

For newer Oracle Linux versions (8+), use: 

sudo dnf remove package_name -y

For example:

sudo dnf remove httpd -y  # Removes Apache HTTP Server
sudo dnf remove libreoffice* -y  # Removes LibreOffice and related packages

To remove multiple packages at once:

sudo dnf remove package1 package2 package3 -y

Remove Applications Using rpm (If dnf Is Not Available)

sudo rpm -e package_name
If dependencies prevent removal, force it with:

sudo rpm -e --nodeps package_name

Remove Unused Dependencies

After uninstalling, clean up unused packages:

sudo dnf autoremove -y

Disable and Remove Unnecessary Services

  • Disable a service before removing it
sudo systemctl disable service_name --now
  • Check if the service is disabled:
systemctl status service_name
  • Remove the service package:

sudo dnf remove package_name -y
For example, to remove firewalld:

sudo systemctl disable firewalld --now
sudo dnf remove firewalld -y

Clear Cache and Free Up Space

After removing applications, clean up system cache:

sudo dnf clean all
sudo rm -rf /var/cache/dnf/*

Check disk usage:

df -h
  • in DevOps
  • 2 min read

How to tune Oracle Linux Server Performance

Update System Packages

Keep your system and kernel updated 

sudo dnf update -y

Optimize Kernel Parameters

Modify sysctl.conf for better memory and network performance

sudo vi /etc/sysctl.conf
Add or modify these lines: 
vm.swappiness=10
vm.dirty_ratio=20
vm.dirty_background_ratio=10
net.core.somaxconn=1024
net.ipv4.tcp_max_syn_backlog=2048

Apply changes without rebooting:

sudo sysctl -p

Enable Performance Profiles

Use tuned to apply performance optimizations

sudo dnf install tuned -y
sudo systemctl enable --now tuned
sudo tuned-adm profile throughput-performance

Optimize Disk I/O

Set the correct I/O scheduler for SSD:

echo "none" | sudo tee /sys/block/sd*/queue/scheduler

Use iotop to monitor disk usage:

sudo dnf install iotop -y
sudo iotop

Optimize Memory Usage

Increase file descriptors limit:

sudo vi /etc/security/limits.conf
Add:

* soft nofile 65535
* hard nofile 65535

Reduce swapping:

sudo sysctl -w vm.swappiness=10

Optimize Network Performance

Enable TCP Fast Open:

sudo sysctl -w net.ipv4.tcp_fastopen=3
Increase connection tracking limit:

sudo sysctl -w net.netfilter.nf_conntrack_max=100000

Use Oracle Linux UEK (Unbreakable Enterprise Kernel)

Check if you're using UEK:

uname -r
If not, install and enable it:

sudo dnf install kernel-uek -y
sudo grubby --set-default /boot/vmlinuz-$(ls /boot | grep uek | tail -1)
sudo reboot

Disable Unnecessary Services

List enabled services:

sudo systemctl list-unit-files --type=service | grep enabled
Disable unused services:

sudo systemctl disable servicename --now

Use Oracle Linux Ksplice (Live Kernel Patching)

Enables zero-downtime kernel patching:

sudo dnf install ksplice-uptrack -y
sudo systemctl enable --now uptrack

Monitor Performance

Use built-in tools: 

top      # Process monitoring
htop     # Enhanced top (install with `sudo dnf install htop -y`)
iostat   # Disk I/O (install with `sudo dnf install sysstat -y`)
vmstat   # Memory and CPU stats

What is -h vs --help in Linux command?

-h vs --help

To sum up, the Linux shell provides access to help information for commands through both -h and —help.

However, —help is a more uniform and universal option that may be used with a variety of commands. Shorter and occasionally used, -h can have varying availability and significance.

It is advised to use --help to reliably obtain help information, particularly for commands that are unknown.

  • in DevOps
  • 1 min read

How to install icedtea-web with OpenJDK-8?

Java

sudo dnf update -y

sudo dnf install java-1.8.0-openjdk-devel -y

java -version

Find the Java Installation Path 

sudo alternatives --config java

Set JAVA_HOME Environment Variable 

/usr/lib/jvm/java-11-openjdk-11.0.16.1.1-1.el8_6.x86_64


vi ~/.bashrc

vi ~/.bash_profile

vi /etc/profile


export JAVA_HOME=/usr/lib/jvm/java-11-openjdk-11.0.16.1.1-1.el8_6.x86_64
export PATH=$JAVA_HOME/bin:$PATH
Verify the Setup

echo $JAVA_HOME

java -version

IcedTea-Web

sudo dnf install epel-release -y

sudo dnf install icedtea-web -y

javaws -viewer

javaws /path/to/application.jnlp
javaws URL

JVM Settiing

javaws -viewer
  • in DevOps
  • 2 min read

How to setup Java Environment Variables

Windows

Download and Install Java

  • Download latest version or your required version Java (Java Oracle , OpenJDK)
  • Install on your system

Set JAVA_HOME and PATH

  • Right-click on This PC (or My Computer) and select Properties.
  • Click on Advanced system settings.
  • In the System Properties window, click Environment Variables.

Add JAVA_HOME:

  • Under System variables, click New.
  • Set Variable name as JAVA_HOME.
  • Set Variable value as the path where Java is installed. For example: C:\Program Files\Java\jdk-XX(replace XX with the version number).

Update PATH:

  • Under System variables, find the Path variable, select it, and click Edit.
  • Click New and add %JAVA_HOME%\bin

Verify Setup:

  • Open a new command prompt and type

java -version
javac -version
echo %JAVA_HOME%
- You should see the Java version and the JAVA_HOME path.

Windows

  • Right click on the 'My Computer' icon on your desktop and select 'Properties'.
  • Click the 'Advanced' tab.
  • Click the 'Environment Variables' button.
  • Click 'New'.
  • In the 'Variable name' field, enter 'JAVA_HOME'.
  • In the 'Variable value' field, enter the directory (including its full path) where you installed the JDK.
  • Restart the computer.

Linux

For your current user:

  • Open up a shell / terminal window
  • vi ~/.profile (replace vi with your favorite text editor)
  • Add export JAVA_HOME=/path/to/java/home/dir on its own line at the end of the file
  • Add export PATH=$JAVA_HOME/bin:$PATH on its own line immediately after
  • Save, and restart your shell
  • Running java -version should give you the desired results

For all users in the system:*

  • Open up a shell / terminal window
  • vi /etc/profile (replace vi with your favorite text editor)
  • Add export JAVA_HOME=/path/to/java/home/dir on its own line at the end of the file
  • Add export PATH=$JAVA_HOME/bin:$PATH on its own line immediately after
  • Save, and restart your shell
  • Running java -version should give you the desired results
  • If you are using a GUI, you may not need to open up the shell. Instead, you might be able to open the file directly in a graphical text editor.

Linux (Ubuntu or other distros):

Install Java

  • Install Java using the package manager for your Linux distribution: 

    sudo apt update
sudo apt install default-jdk

  • For specific versions (like OpenJDK 11), use: 

sudo apt install openjdk-11-jdk

FAQ Setting JAVA_HOME

  • in France
  • 2 min read

How to recover my lost NEPH Number ?

Have you already obtained a NEPH, but lost it or it is no longer active?

It's not a problem , we have solutions to allow you to resume your training!

👉 If you have the possibility, contact your old driving school so that they can give you your NEPH and your code result ( if you obtained it ).

👉If your driving school no longer has it or has left the face of the earth, don't panic! You can request your NEPH from the driving license department of your department of residence .

👉 If you are in possession of your NEPH but it appears to be inactive ( unable to register for the code test, for example ), you can request to have your NEPH reactivated by the driving license department in your department of residence.

  • in OpenSSL
  • 1 min read

OpenSSL Certificate Authority

OpenSSL is a free and open-source cryptographic library that provides several command-line tools for handling digital certificates. Some of these tools can be used to act as a certificate authority.

A certificate authority (CA) is an entity that signs digital certificates. Many websites need to let their customers know that the connection is secure, so they pay an internationally trusted CA (eg, VeriSign, DigiCert) to sign a certificate for their domain.

In some cases it may make more sense to act as your own CA, rather than paying a CA like DigiCert. Common cases include securing an intranet website, or for issuing certificates to clients to allow them to authenticate to a server (eg, Apache, OpenVPN).

OpenSSL Certificate Authority

  • in DevOps
  • 1 min read

Rocky Linux yum update failed

 Curl error (28): Timeout was reached for https://mirrors.rockylinux.org/

[root@rocky ~]# yum update
Rocky Linux 9 - BaseOS                                                                                                                               0.0  B/s |   0  B     03:02
Errors during downloading metadata for repository 'baseos':
  - Curl error (28): Timeout was reached for https://mirrors.rockylinux.org/mirrorlist?arch=x86_64&repo=BaseOS-9 [Failed to connect to mirrors.rockylinux.org port 443: Connection timed out]
Error: Failed to download metadata for repo 'baseos': Cannot prepare internal mirrorlist: Curl error (28): Timeout was reached for https://mirrors.rockylinux.org/mirrorlist?arch=x86_64&repo=BaseOS-9 [Failed to connect to mirrors.rockylinux.org port 443: Connection timed out]

Solution

  1. Stop the system firewall 
`systemctl status firwalld