LUKI NOTES

If you are looking for simple password management in Unix, pass maybe the answer. It utilizes GPG to encrypt the stored passwords. It stores the encrypted passwords as text files in a tree of directories. Each directory can maintain a separate GPG key for encrypting the passwords stored inside it. How easy is it? The following command shows how we can store a password and set AWS/access-key-id as the variable name to access it in the future. pass insert AWS/access-key-id The previous command will automatically create a directory named AWS inside the  ~/.password-store  directory which is the default location of pass storage. It also creates a file named access-key-id.gpg inside the ~/.password-store/AWS directory. To access the value we can call the following command. pass AWS/access-key-id There are some steps we need to run for utilizing the tool. Install pass using package manager Create a GPG key pair record Initialize the pass storage wit...

I've ever gotten stuck on updating the VSCode server on my remote server because of an unstable connection between my remote server and visualstudio.com that host the updated server source codes. The download and update process failed over and over so I couldn't remotely access my remote files through VSCode. The solution is by downloading the server source codes through a host with a stable connection which in my case I downloaded from a cloud VPS server. Then I transfer the downloaded source codes as a compressed file to my remote server through SCP. Once the file had been on my remote sever, I extracted them and align the configuration. The more detailed steps are as follows. First, we should get the commit ID of our current VSCode application by clicking on the About option on the Help menu. The commit ID is a hexadecimal number like  92da9481c0904c6adfe372c12da3b7748d74bdcb . Then we can download the compressed server source codes as a single file from the host. ...

A self-signed certificate is very useful for us when we are in a development or closed environment and require a secure communication channel between nodes in our system like implementing HTTPS for client-server communication. To make our self-signed certificate to be recognized by all nodes in the system, we should generate the CA certificate and distribute it to all nodes. This CA certificate is used to verify and determine the issuer of the self-signed certificate. It is like a stamp on a certificate that ensures the certificate is issued by the authority informed in the certificate itself. OpenSSL CLI tool will be used for this purpose. The following steps can be run to generate valid self-signed and CA certificates. Generate a private CA key Generate a public CA certificate Generate a private key for the target server Generate a CSR for the server Generate a public server certificate and sign it with the CA certificate Before we start the certificate generatio...

There are several tools and services in the market that we can use to deploy and manage Kubernetes clusters. Some tools allow us to self-manage the cluster without charge, some require us to subscribe for the license, and some services are provided as a Kubernetes as a Service such as Amazon EKS and Red Hat OpenShift Dedicated. For development purposes or small-scale service, there is a free tool to manage Kubernetes clusters named minikube which is available for Windows, Linux, and MacOS. To build the cluster, Minikube supports several virtualization technologies such as Hypervisor, KVM, Docker, and so on. In this writing, we will try to utilize Docker as the virtualization solution and run it in Ubuntu 22.04. In general, we will run through the following steps. Install Minikube Install Docker Allow a non-root user to access Docker Start Minikube Enable Ingress extension Install Kubectl Install Minikube First, we need to install Minikube's depen...

Gitlab actively updates its products including the Community Edition (CE). The easiest way to install Gitlab CE on a Linux machine is by using the package manager. To add the repository to our system, we can run the following command. sudo apt update curl -s https://packages.gitlab.com/install/repositories/gitlab/gitlab-ce/script.deb.sh | sudo bash Before we run the upgrade process, we should follow the recommendation of the version order. If not, we may end up breaking our Gitlab service. Upgrading one version to another version far greater may require upgrading from previous versions first, step by step. To check our current Gitlab version, we can visit <OUR_GITLAB_ADDRESS>/help . The upgrade recommendation can be found  HERE . Note, we are also suggested to upgrade our Gitlab regularly for security reasons. We can get the list of available versions HERE . To apply the upgrade on our machine, we can run the following command. sudo apt-get install gitlab-ce=<VERSI...

If we maintain a Linux machine with a low memory capacity while we are required to run an application with high memory consumption, enabling swap memory is an option. Ansible can be utilized as a helper tool to automate the creation of swap memory. A swap file can be allocated in the available storage of the machine. The swap file then can be assigned as a swap memory. Firstly, we should prepare the inventory file. The following snippet is an example, you must provide your own configuration. [server] 192.168.1.2 [server:vars] ansible_user=root ansible_ssh_private_key_file=~/.ssh/id_rsa Secondly, we need to prepare the task file that contains not only the tasks but also some variables and connection information. For instance, we set /swapfile  as the name of our swap file. We also set the swap memory size to 2GB and the swappiness level to 60. - hosts: server become: true vars: swap_vars: size: 2G swappiness: 60 For simplicity, we only check the...

For this instance, we use a Red Hat Enterprise Linux (RHEL) Server 7.9. Unlike the latest Ubuntu version that commonly utilizes YAML-based configuration and the netplan tool for setting up IP addresses of network interfaces, the RHEL network interface can be configured using the configuration script located in /etc/sysconfig/network-scripts . Several interface configurations and scripts have been automatically generated by RHEL during the installation process. The configuration file is named by its device name such as ifcfg-eth0 for the eth0 device. If we run our RHEL in a VMware-based virtual machine, the device name might be shown up like ens35 or such things. The following configuration is an example of a network configuration with DHCP enabled. #/etc/sysconfig/network-scripts/ifcfg-eth0 TYPE="Ethernet" PROXY_METHOD="none" BROWSER_ONLY="no" BOOTPROTO="dhcp" DEFROUTE="yes" IPV4_FAILURE_FATAL="no" IPV6INIT="yes...

We may limit incoming or outcoming data rates to/from our infrastructure to maintain the stability of our service for customers. Bitrate limitation is an action to limit the number of bits that can be passed through a transmission channel in a period of time. Network throttling is an intentional action to slow down transmission speed in a network channel. It is not only about limiting bitrate but also limiting the allowed number of requests in a period of time. There are several tools and techniques that can be used to apply bitrate limitation and network throttling. Wondershaper It is an easy-to-use tool for Linux and is already in the package repository. It can limit the bit rate that can be achieved by network interfaces in the system. We can install it by running the following command. apt install wondershaper We can choose an interface to have a limitation either or both on download and upload. wondershaper <interface-name> <download-rate-in-bps> <upload-...

VirtualBox is a free solution to host virtual machines on your computer. It provides configuration options for many components on our machine, such as memory, storage, networking, etc. It also allows us to resize our machine storage after its operating system is installed. LVM is a volume manager in a Linux platform that helps us to allocate partitions in the system and configure the storage size that will be utilised for a specific volume group. There are some points to be noticed when we work with LVM on VirtualBox to resize our storage. These are some steps that need to be performed. 1. Stop your machine before resizing the storage. 2. Set the new storage size using the GUI by selecting " File > Tools > Virtual Media Manager > Properties ", then find the desired virtual hard disk name that will be resized. OR , by running a CLI program located in " Program Files\Oracle\VirtualBox\VBoxManage.exe ".  cd "/c/Program Files/Oracle/VirtualBox" ...

The following tools may have been installed in your Linux because some are basic tools. But, if we installed any Linux distribution from the Docker registry which is shipped with only minimal programs, these following tools may be not available by default. net-tools This tool provides tools for network-related tasks such as ifconfig . software-properties-common If you want to enable add-apt-repository command, this tool is required. nano This text editor is usually already available. ca-certificates A deb package that contains certificates provided by the Certificate Authorities. It also contains an updater tool that can be used as a cronjob if needed. gnupg2 GNU Privacy Guard is GNU's tool that can be used to encrypt data and to create digital signatures. GnuPG is a complete replacement for PGP. It includes an advanced key management facility and is compliant with the proposed OpenPGP Internet standard. openssh-client Tools for generating authentication keys and...

By support of WSL (Windows Subsystem for Linux), you can install any Linux distros in a Windows machine. Recommended method from WSL documentation is by downloading the distribution from Microsoft Store or find .appx installation file available in Microsoft website. For running multiple instances of same Linux distribution, you can duplicate the data using export-import procedure, as I have mentioned in another post . Another method that might be more beneficial is by utilizing Docker. Currently, Docker has already had variety of images of Linux distributions in its registry. You can also store your own costumized distribution in Docker registry that can be distributed to any machines instantly. After you had WSL 2 and an installed Linux distribution from Microsoft Store, you are ready to have more Linux instances in your Windows. 1. List all installed distributions in your Windows. wsl --list -v 2. Run the distribution you desired from terminal, for example, you have insta...

WSL (Windows Subsystem for Linux) is a great tool provided by Windows 10 (OS build 20262 or higher) that enables developers to run Linux machines in Windows platform without third-party application like Virtual Box. With support of installed WSL, you can install any Linux distribution available in Microsoft Store . After installation of a Linux distribution, for example Ubuntu 18.04, WSL stored its machine data in %APPDATA%\Local\Packages\CanonicalGroupLimited.Ubuntu18.04onWindows_79rhkp1fndgsc\LocalState . If you need to move the data to another directory/drive in your computer to free some spaces in your main drive, you can perform these following commands. 1. List all distributions in your computer. wsl --list --verbose 2. Export the distribution data. wsl --export <distribution-name> <any-file-name>.tar For example, distribution name is Ubuntu-18.04: wsl --export Ubuntu-18.04 exported-ubuntu-18-04.tar 3. Unregister the distribution. wsl --unregister Ubun...

If you like to use Ubuntu Desktop for your daily works, I recommend some good applications to improve your productivity and convenience. Currently, I use Ubuntu Desktop 18.04. Adjust Brightness Icon . It is a simple application that add functionality to your Ubuntu to adjust brightness of your screen with four level of brightness by clicking its icon on the Taskbar. You can install this application through Ubuntu Software Center. Gnome Tweaks . This application provides several options to configure your desktop and system appearance such as applying dark theme, changing fonts, adding startup application, etc. To use this tools, you can follow this instruction: - In terminal run: > sudo apt install gnome-tweaks gnome-tweak-tool  - Then open the application by running: > gnome-tweaks  Pomodoro . It helps you to manage time according to the pomodoro technique. You can install this app through Ubuntu Software Center. VLC . It is open source multimedia player with plenty...

How to run python or other scripts using PHP or other popular web programming languages in a Linux environment? Problem We want to access the PHP program through a web server application (Apache/Nginx). The PHP program needs to run other scripts stored in the same machine. Sample Problem PHP program is located in /var/www/html/index.php Python program is located in /var/www/html/capture.py Python program will access Pi Camera, capture an image, and store it in /var/www/html/assets/photo.jpg Solution index.php should access and run capture.py script. The script is as follows: $output = shell_exec("python /var/www/html/capture.py"); Execution of external program using shell_exec() or exec() will block the program. The next line of PHP codes will be run after the external program returns an output. So, we shouldn't run an excessive amount of external programs. Clients will wait too long on their browser. If our application actually needs ma...

When you have a domain, for example,  yourdomain.com , you can create your email address at that domain name like yourname@yourdomain.com . Several domain name records which I consider to be important for mail domain are: 1. MX Record Of course, it assigns a domain where the mail exchange server is located. For example: Name Priority Type Data yourdomain.com 10 MX mx.yourdomain.com 2. SPF Record SPF is a spam and phishing scam fighting method that uses DNS SPF records to define which hosts are permitted to send e-mails for a domain. See http://www.openspf.org . For example: Name Type Data yourdomain.com TXT "v=spf1 mx mx:yourdomain.com -all" This configuration means emails sent from all servers defined in the MX record of yourdomain.com are permitted by the sender organization 3. DKIM Record DKIM allows an organization to take responsibility for a message in a way t...

A webcam can not be accessed by two or more applications simultaneously. The solution is you can duplicate the video stream and make it available for any application. In short, you create a virtual webcam. First, a webcam is commonly detected on  /dev/video* . Before you go through the steps to duplicate video stream, you should check whether your webcam is working. You can try to capture video using VLC by this command. (For example, your webcam is on  /dev/video0 ) $ vlc v4l2:///dev/video0 If it doesn't work, you can try to change its mode to 0777 and make sure there are no other applications accessing it. If it still doesn't work, you can buy a new webcam. Seriously. Don't buy a cheap and unknown-brand webcam. I have $5 webcam and it had wasted my time. $ apt-get install ffmpeg linux-generic v4l2loopback-dkms FFmpeg is the main application that will access your webcam and duplicate its video stream. V4L2loopback is needed to create multiple virtual capture devic...

Sometimes, your web application is installed in a web server which is behind reverse proxy server like Cloudflare or other services. In that condition, your application will always read the reverse proxy server IP as client IP. In Nginx, you can use ngx_http_realip_module to get the real client IP ( see detail ). To enable this module, you need to make sure that you use latest Nginx server from repository or you can build it from source with --with-http_realip_module  configuration parameter. I  prefer to install it from repository as Nginx 1.10.0 in Ubuntu 16.04 has enabled this module by default. You can check whether it's enabled or not by following command. $ nginx -V Then, the reslut should be like: $ nginx version: nginx/1.10.0 (Ubuntu) ... ... --with-http_realip_module ... ... Now, you can put the module configuration in http block or server block of your Nginx configuration. For example, you use Cloudflare service for your web application. You should lis...

If you want to setup a site with HTTPS, you need a valid SSL certificate from Certificate Authority (CA). Let's Encrypt is a CA that can provide you a free valid SSL certificate by requesting it using certain software. The software which is recommended by Let's Encrypt is Certbot . From the main page of Certbot site, you can choose what web server and operating system you use then it will show you the installation steps. For example, I use Nginx on Ubuntu 16.04. $ sudo apt-get install software-properties-common $ sudo add-apt-repository ppa:certbot/certbot $ sudo apt-get update $ sudo apt-get install python-certbot-nginx $ certbot --nginx Last command will get a certificate for you and have Certbot edit your Nginx configuration automatically to serve it. Sometimes, you may get error notes. It is about failure of integration process to existing web server configuration. It's not crucial cause you can integrate manually with simple steps. If you only want to get cer...

PHP 7 comes with a new version of the Zend Engine, numerous improvements and new features such as: Improved performance: PHP 7 is up to twice as fast as PHP 5.6 Significantly reduced memory usage Abstract Syntax Tree Consistent 64-bit support Improved Exception hierarchy Many fatal errors converted to Exceptions Secure random number generator Removed old and unsupported SAPIs and extensions The null coalescing operator Return and Scalar Type Declarations Anonymous Classes Zero cost asserts Today (12 April 2016), latest Ubuntu release doesn't include PHP 7. You can install PHP 7 from third-party repository such as PPA. PPAs are not bound by the release schedules or policies of Ubuntu so they are free to change versions more frequently, among other things. Ondrey PPA is a popular way of staying more up to date with PHP. Ondrey is the official owner of the PHP tree in Debian, which is upstream from Ubuntu. To install PHP 7 in Ubuntu you can do the following: ...

Nowadays, an SSL certificate which is usually used for HTTPS connections become pretty important. Even Google starts to give a ranking boost to secure HTTPS/SSL sites . There are several cheap certificates that you can buy like Comodo PositiveSSL. I usually buy cheap certificates from Namecheap.com  which provides SSL certificates as low as $4/year. After you buy the certificate, you need to set up your server. Here are the steps to set up an SSL certificate on your server. 1. Purchase the certificate You can buy the certificate from Namecheap.com . After you buy it, you need to activate your certificate by providing your generated CSR file. 2. Generate private key and CSR file In a Linux server, you can run the following command on the terminal to generate a private key and CSR file. $ openssl req -new -newkey rsa:2048 -nodes -keyout mydomain.com.key -out mydoain.com.csr   When you run the command, you will be asked for Country ID, domain name, registrant...