feat(notes): add guide for OCR and PDF manipulation on Linux

- Added instructions for setting up Tesseract with language support.
- Documented steps for converting PDFs to images using `pdftoppm` and alternatives like `ImageMagick`.
- Included examples for single and multi-page OCR processing.
- Detailed methods for merging extracted text into a single file.
- Added troubleshooting tips for improving OCR results and handling selectable PDFs with `pdftotext`.

notes/debian_setup_aptly.md

@@ -343,7 +343,7 @@ chown -R aptly:aptly /home/aptly/.ssh/
     **Adding Packages**
 
     ```bash
-    sudo su -l aptly
+    sudo -iu aptly
     mkdir /home/aptly/packages/
     ```
 
@@ -372,6 +372,14 @@ chown -R aptly:aptly /home/aptly/.ssh/
     rm ~/<hostname-internet>.private-key.asc
     ```
 
+    **Register keys with public keyservers**
+
+    ```bash
+    gpg --send-keys <gpg-repository-key-id>
+    gpg --keyserver hkp://keyserver.ubuntu.com --send-keys <gpg-repository-key-id>
+    gpg --keyserver hkp://pgp.mit.edu --send-keys <gpg-repository-key-id>
+    ```
+
     **Import GPG Key**
 
     ```bash

notes/dns.md

@@ -0,0 +1,64 @@
+# DNS
+
+## Table of Contents
+
+- [DNS](#dns)
+  - [Table of Contents](#table-of-contents)
+  - [Flush DNS Cache](#flush-dns-cache)
+  - [systemctl](#systemctl)
+  - [dig](#dig)
+  - [nslookup](#nslookup)
+
+## Flush DNS Cache
+
+- Clear the DNS cache to ensure that the system resolves domain names with the most up-to-date information.
+
+```bash
+resolvectl flush-caches
+systemd-resolve --flush-caches
+```
+
+- Use `resolvectl` for newer systems or `systemd-resolve` for older systems (pre-2020).
+
+## systemctl
+
+- This command enables the `systemd-resolved` service if it is not already running, ensuring DNS resolution through `systemd`.
+
+```bash
+systemctl enable systemd-resolved.service
+```
+
+**Explanation of the command:**
+
+- `systemd-resolve --flush-caches`: This command clears the DNS cache maintained by `systemd-resolved`, which can help resolve issues with outdated or incorrect DNS entries.
+- After flushing the cache, it may be necessary to restart the `systemd-resolved` service to ensure proper operation.
+
+```bash
+systemctl restart systemd-resolved
+service systemd-resolved restart
+```
+
+- To restart the service, use `systemctl restart systemd-resolved` (preferred). The `service` command is available but is considered legacy.
+
+## dig
+
+```bash
+dig domain.com
+dig +short NS domain.com
+```
+
+## nslookup
+
+- `nslookup` is a legacy tool but still useful for querying DNS. You can also specify custom DNS servers, such as `1.1.1.1` (Cloudflare) or `8.8.8.8` (Google), to query DNS directly without using the system’s default resolver.
+
+```bash
+nslookup domain.com
+nslookup -q=cname domain.com
+nslookup -q=cname domain.com 1.1.1.1
+nslookup -q=cname domain.com 8.8.8.8
+```
+
+```bash
+nslookup -q=mx domain.com
+nslookup -q=txt domain.com
+```

notes/linux.md

@@ -7,6 +7,7 @@
   - [System Information](#system-information)
     - [Hardware Information](#hardware-information)
     - [Software Information](#software-information)
+- [Commands to Get Information About Linux Version, Kernel Version, and Release](#commands-to-get-information-about-linux-version-kernel-version-and-release)
   - [User Management](#user-management)
     - [User Information](#user-information)
     - [Super User Management](#super-user-management)
@@ -42,6 +43,17 @@ To gather detailed information about your hardware, use the following commands:
 
 ### Software Information
 
+**Finding information on the Linux distribution**
+
+# Commands to Get Information About Linux Version, Kernel Version, and Release
+
+- **`lsb_release -a`**: Displays detailed information about the Linux distribution, including the distributor ID, description, release number, and codename.
+- **`cat /etc/debian_version`**: Displays the version of the Debian distribution if you're running a Debian-based system (like Ubuntu).
+- **`cat /etc/os-release`**: Displays information about the operating system, such as the name, version, and ID of the distribution.
+- **`cat /etc/*release`**: Searches for any files in the `/etc/` directory that contain the word `release` and displays their contents. This typically includes more detailed distribution information.
+- **`cat /etc/*version`**: Similar to `cat /etc/*release`, but it looks for files containing the word `version`. It can provide additional version-related details.
+- **`hostnamectl`**: Displays system information related to the hostname and other metadata about the system. This may include the operating system, kernel version, and architecture.
+
 **Finding Path to Binary**
 
 To find the location of an executable binary, use:

notes/pdf.md

@@ -0,0 +1,104 @@
+# PDF
+
+## Table of Contents
+
+- [PDF](#pdf)
+  - [Table of Contents](#table-of-contents)
+  - [OCR](#ocr)
+
+## OCR
+
+**Install necessary tools**
+Update the package list and install Tesseract with support for the desired language. Replace `fra` with your desired language code (e.g., `eng` for English).
+
+```bash
+apt update
+apt install tesseract-ocr tesseract-ocr-fra
+```
+
+**Verify the installation**
+
+Check the installed version of Tesseract and list available languages to ensure your chosen language is installed (e.g., `fra` for French).
+
+```bash
+tesseract --version
+tesseract --list-langs
+```
+
+**Install a utility to convert PDF pages into images**
+
+For PDFs that require OCR, you need a utility to convert PDF pages into images. Install `poppler-utils`, which includes `pdftoppm`.
+
+```bash
+apt install poppler-utils
+```
+
+**Convert PDF to images**
+
+Convert the PDF into JPEG images, with each page saved as a separate file. Each page will be named sequentially (e.g., `output-1.jpg`, `output-2.jpg`, etc.).
+
+```bash
+pdftoppm -jpeg your_file.pdf output
+```
+
+- **Tip**: Use a dedicated output directory to avoid overwriting existing files.
+- **Alternative tools**: If `poppler-utils` isn’t available, consider using `ImageMagick`:
+
+  ```bash
+  convert -density 300 your_file.pdf output-%04d.jpg
+  ```
+
+**Perform OCR on a single image**
+
+Run Tesseract OCR on an image to extract text. Specify the language using the `-l` option.
+
+```bash
+tesseract output-1.jpg output-text -l fra
+```
+
+The extracted text will be saved in `output-text.txt`.
+
+**Perform OCR on multiple images**
+
+For multi-page PDFs, process all images in a loop. This extracts text from each image and saves it to a separate `.txt` file.
+
+```bash
+for img in output-*.jpg; do
+    tesseract "$img" "${img%.jpg}" -l fra
+done
+```
+
+- **Note**: The `${img%.jpg}` syntax removes the `.jpg` extension, ensuring each `.txt` file matches its corresponding image.
+
+**Combine all text files**
+
+Merge the text from all processed pages into a single file. This is useful for assembling the full content of the PDF.
+
+```bash
+cat output-*.txt > complete_text.txt
+```
+
+If filenames are out of order, use a sorting approach before merging:
+
+```bash
+ls output-*.txt | sort -V | xargs cat > complete_text.txt
+```
+
+**Troubleshooting and Tips**
+
+**If Tesseract doesn’t recognize text**:
+
+- Ensure the images have sufficient quality and resolution. Use `-r` with `pdftoppm` to increase the DPI (e.g., `-r 300` for 300 DPI).
+- Try additional Tesseract language packs for better recognition of specific text styles.
+
+**Using `pdftotext` for simpler PDFs**:  
+ If the PDF contains selectable text (not just images), `pdftotext` from `poppler-utils` can extract text directly without OCR.
+
+```bash
+pdftotext your_file.pdf output.txt
+```
+
+Replace `convert` with `magick` for newer versions.
+
+**Verify language codes for Tesseract**:  
+ You can find a list of supported languages on the [Tesseract GitHub page](https://github.com/tesseract-ocr/tesseract).