TCP investigations

Network/Investigation/README.md

@@ -0,0 +1,77 @@
+
+# TCP investigation script
+
+**A bash script to get information about active TCP connections.**
+
+Some relevant key features:
+
+* The script lists the **TCP connections established** at the time it runs.
+* For each connection, it shows some statistics about the process involved, for example the **bytes read and written** by the process.
+* Regarding the process involved, it lists the **files and folders opened** by the process itself.
+* The information obtained is then processed into an **HTML report**, which is sent via **email**.
+* The script is **portable** and can run on any **GNU/Linux** system running [curl](https://curl.se/).
+
+## Screenshots
+
+![Example of report displayed in Claws Mail](claws.png)
+
+Example of report displayed in Claws Mail.
+
+## Install
+
+### Requirements
+
+* **net-tools**: NET-3 networking toolkit
+* **lsof**: Utility to list open files
+* **sysstat**: system performance tools for Linux
+* **dos2unix**: convert text file line endings between CRLF and LF
+* **curl**: command line tool for transferring data with URL syntax
+
+### Get the code
+
+You can use **git**.
+
+    git clone https://git.lattuga.net/netico/code-library.git
+
+And then look for the script **tcp-investigation.sh**.
+
+### Post installation
+
+Fill in these **configuration variables**, which you can find in the very first part of the script:
+
+    # Sender
+    SENDER="someone@domain.tld"
+    # Recipient
+    RECIPIENT="someone.else@domain.tld"
+    # Mail relay URL
+    RELAY="smtp://powerful.mail.server:587"
+
+If the mail server you have chosen to use requires **SMTP authentication**, you must enter the credentials in **/root/.netrc**. Read [this page](https://everything.curl.dev/usingcurl/netrc) carefully to learn how to do this.
+
+## Usage
+
+The script requires **root privileges**. Run
+
+    sudo ./tcp-investigation.sh
+
+...and wait for the email report.
+
+## Hacking
+
+### Sending e-mail messages
+
+Sending e-mail in a shell environment is not as easy as it sounds. It is even more complicated to send HTML instead of plain text. **mutt** and some versions of **mailx** support sending HTML, but require a working mail server.
+
+To work around these problems, the script attempts to build a standards-compliant message so that it can be passed to a **Sendmail** wrapper (there are wrappers for **Exim**, **Postfix**, **qmail**) or [sent by **curl](https://everything.curl.dev/usingcurl/smtp) (also read [Using curl to send email](https://stackoverflow.com/questions/14722556/using-curl-to-send-email)).
+
+Some recommended reading on email message format: [RFC822](https://datatracker.ietf.org/doc/html/rfc822), [RFC2822](https://www.rfc-editor.org/rfc/rfc2822).
+
+If you want to use the local email system, find the line that invokes **curl**
+
+    curl -s -n --ssl-reqd ...
+
+comment it out, and add something similar
+
+    cat $MSG | /usr/lib/sendmail -t
+
+Otherwise, use **curl**, which however must be configured (as explained) and requires a valid email account and an external mail server (the same one you would use in **Thunderbird** or other MUAs).

Network/README.md

@@ -0,0 +1,7 @@
+# Network
+
+**Things related to the Internet and networks in general.**
+
+## [TCP investigation](https://git.lattuga.net/netico/code-library/src/master/Network/Investigation)
+
+In the [Investigation](https://git.lattuga.net/netico/code-library/src/master/Network/Investigation) folder you can find a **bash** script to analyze **active TCP connections** on a **GNU/Linux** system.

README.md

@@ -2,8 +2,12 @@
 
 ## netico's Code Library
 
-This is a collection of code snippets, documentation, scattered notes, how-to's, proofs of concept and experiments, designed to be a learning tool for you who want to learn the art of programming.
+This is a collection of code snippets, documentation, scattered notes, how-to's, proofs of concept, and experiments, designed to be a useful tool for entering the world of computer programming.
 
 ### [OSM](https://git.lattuga.net/netico/code-library/src/master/OSM)
 
 Crazy fun with **OpenStreetMaps**.
+
+### [Network](https://git.lattuga.net/netico/code-library/src/master/Network)
+
+Things related to the Internet and **networks** in general.