Linux

• SSL Linux
• Configure local https on ubuntu
• install OpenSSL locally on Ubuntu
• MULTIVERSIONS ON UBUNTU BOX
• kernel tuning/troubleshooting
• filesystems tuning

SSL Linux

Configure local https on ubuntu

mkcert for simplicity or openssl for more control, and then configure your web server (e.g., Apache) to use the generated certificates. The recommended method is to install and use mkcert, which generates a trusted, local Certificate Authority (CA) to create self-signed certificates for localhost or custom hostnames without browser warnings. Alternatively, you can generate a self-signed certificate using openssl, which requires more manual steps to create the key, certificate, and to trust it in your browser. 

1. Install mkcert: Install the tool to manage local certificate authorities and certificates.
   • sudo apt install mkcert
2. Install the local CA: Run mkcert to install a local CA that your system will trust.
   • mkcert -install
3. Create a certificate: Generate a certificate and key for your local site (e.g., localhost) or domain. Point to note here in case of domain, ip address should be mapped to it  before this command.
   • mkcert localhost 127.0.0.1
   • sudo mkcert drupalwithdata.offline.com

Configure your server: Configure your specific application or web server to use the generated localhost.pem (certificate) and localhost-key.pem (key) files. 

1. Install openssl: Ensure openssl is installed. It is usually pre-installed on Ubuntu.
2. Generate a private key and a certificate signing request (CSR):
   • openssl req -new -newkey rsa:2048 -nodes -keyout localhost.key -out localhost.csr
3. Generate the self-signed certificate: Use the CSR and private key to create the certificate.
   • openssl x509 -req -days 365 -in localhost.csr -signkey localhost.key -out localhost.crt
4. Configure your web server:
   • For Apache:
     • Enable the SSL module: sudo a2enmod ssl.
     • Configure your site's virtual host to point to your certificate (localhost.crt) and private key (localhost.key) files.
     • Restart Apache: sudo systemctl restart apache2.
   • For other servers: Configure your server's settings to use the .crt and .key files.
5. Trust the certificate:
   • This is an optional but recommended step to avoid browser warnings.
   • Install certificate utilities: sudo apt-get install libnss3-tools.
   • Import and trust the certificate into the browser's database (using pk12util for Firefox or certutil for other applications). 

• After generating the certificates and configuring your server, you may still see a browser warning because the certificate is "self-signed" and not issued by a public Certificate Authority.
• You will need to accept the security risk to proceed to your local serve

install OpenSSL locally on Ubuntu

compile and install it from source by first installing build tools, then downloading and extracting the OpenSSL source code, and finally running the config, make, and make install commands with the appropriate prefix and flags. For the simplest local installation, download the source, change to the directory, and use ./config --prefix=/openssl --openssldir=/openssl, followed by make and make install, then update your ~/.bash_profile with the correct PATH and LD_LIBRARY_PATH. 

# Install build tools
sudo apt update
sudo apt install build-essential zlib1g-dev

# Create a working directory and download OpenSSL source
cd /usr/local/src/
wget https://www.openssl.org/source/openssl-1.1.1k.tar.gz
tar -xf openssl-1.1.1k.tar.gz
cd openssl-1.1.1k

# Configure and build (using --prefix to specify local install)
./config --prefix=~/openssl --openssldir=~/openssl
make

# Install to the local directory
make install

1. Edit the bash profile:
   bash

2. nano ~/.bash_profile
   

3. Add the following lines at the end of the file (adjusting username if necessary):
   bash

4. export PATH=$HOME/openssl/bin:$PATH
   export LD_LIBRARY_PATH=$HOME/openssl/lib:$LD_LIBRARY_PATH
   export LDFLAGS="-L $HOME/openssl/lib -Wl,-rpath,$HOME/openssl/lib"
   

5. Save and close the file, then reload your profile:
   bash

source ~/.bash_profile

1. Check the version to ensure you are using the new installation:
   bash

2. openssl version
   

   This should output the version you installed (e.g., OpenSSL 1.1.1k 25 Mar 2025).

Verify the path to confirm it's the local one:bash

which openssl

This should point to ~/openssl/bin/openssl

MULTIVERSIONS ON UBUNTU BOX

sudo apt install apache2 libapache2-mod-fastcgi

sudo apt-get install mysql-server
sudo mysql_secure_installation


sudo apt install software-properties-common
sudo add-apt-repository ppa:ondrej/php
sudo apt update

Use this command to install different versions of php just changing the string 7.1 to the required version
sudo apt install php7.1 php7.1-fpm libapache2-mod-php7.1


NOW ALL SET LAMP is installed and working


Now while u will require to change the php version

This command will change the php version on system
sudo update-alternatives --config php


Disable all version apached modules of php installed, just replace the 7.4 in below command
sudo a2dismod php7.4

Enable the version u need to use with apache, just replace the 8.0 in below command
sudo a2enmod php8.0

Restart the apache
sudo service apache2 restart

kernel tuning/troubleshooting

• Goal: Optimize performance (speed, resource use) for specific workloads (e.g., databases, web servers).
• Key Areas:
  • fs (Filesystem): Too many open files (ulimit -n), I/O schedulers.
  • vm (Virtual Memory): Swappiness (vm.swappiness), dirty ratios, memory management.
  • Networking: TCP/IP settings, buffer sizes.
• Tools: sysctl, /etc/sysctl.conf, make menuconfig (for compiling custom kernels), tuned (profiles). 

• Common Issues: Kernel Panic (system crash), slow performance, device failures.
• Steps:
  1. Identify Cause: Check logs (dmesg, /var/log/), review crash reports (Mac), use journalctl (Linux).
  2. Isolate: Boot in Safe Mode (Mac), use a known good/rescue kernel (Linux), disconnect hardware, remove recent software/drivers.
  3. Check Hardware: Run diagnostics (Apple Diagnostics), check RAM.
  4. Software Conflicts: Look for recently installed or updated apps/drivers causing issues. 

• Baseline: Measure performance before changes.
• Change Incrementally: Adjust one or a few parameters at a time.
• Document: Keep records of all changes and their effects.
• Test Thoroughly: Verify stability and performance after each change. 

• If "kernel" means the Jupyter backend: Restart, update packages (Jupyter, Anaconda), check code for errors, monitor memory. 

filesystems tuning

• I/O Operations: Tuning reads/writes, utilizing asynchronous I/O (AIO) to prevent application blocking, and optimizing read-ahead for sequential access.
• Block Size: Affects data efficiency; larger blocks can speed up large file transfers, while smaller ones suit many small files.
• Caching & Buffers: Increasing file system buffers (numfsbufs) can help with heavy I/O; faster RAM disks for /tmp also boost performance.
• Journaling: Balancing the performance impact of logging changes for data integrity (e.g., using commit options).
• File System Type: Different file systems (Ext4, XFS, NTFS) have unique strengths; tuning depends on the chosen one. 

• Hardware Optimization: Ensure disk controllers use fast DMA modes.
• Read-Ahead/Write-Behind: Boost sequential read/write performance by pre-fetching/delaying writes.
• Direct I/O (DIO): Bypasses the kernel's file cache to reduce CPU load and data copies for specific applications.
• Tuning Profiles (Linux): Use tuned-adm to apply profiles (e.g., throughput-performance, virtual-guest) for workload-specific settings.
• Application-Level: Design apps to gather large data chunks and write them sequentially. 

1. Monitor: Identify bottlenecks using tools like vmstat -v or iostat.
2. Select: Choose parameters relevant to your workload (e.g., database needs high I/O, web server needs low latency).
3. Apply: Use commands like mkfs (for creation), mount options, or tuned-adm to change settings.
4. Test: Verify improvements with performance benchmarks.