Month: April 2023

Troubleshooting a Mysterious Networking Issue in Windows 11 (NOT!)

Networking issues can be frustrating and time-consuming to troubleshoot. This was just one of my many experiences troubleshooting an interesting network issue that took me a while to solve.

The Problem: One day, I noticed that my computer’s network connection was acting up. The network interface card (NIC) was sending packets just fine, but it was receiving very few packets, and eventually, it would stop receiving packets altogether. At first, I suspected that the issue happened after I installed the Insider Preview of Windows 11, so I reset Windows. I updated the Realtek NIC driver to the latest version, hoping that it might help. The problem persisted.

The Troubleshooting: Next, I decided to reinstall Windows 11 from scratch, thinking that it might fix the issue. The problem still persisted even after the fresh install. Now I knew that the issue was likely to be hardware.

I boot into Linux from a USB drive. To my surprise, the issue persisted even in Linux. This ruled out any software or driver issues with Windows.

The Solution: I started to suspect that the issue might be with my Wi-Fi access point. I have a TP-Link Deco 6E mesh Wi-Fi system, and one of the access points acts as the main router. I decided to swap the problematic access point with another one, and to my relief, the issue disappeared instantly. My NIC was now sending and receiving packets normally, and I was back online.

Conclusion: Networking issues can be tricky to troubleshoot, and it’s easy to get lost in a sea of software and driver issues. Sometimes, the problem might not even be with your computer at all, but with your network equipment. If you’re experiencing a similar networking issue, try ruling out all software and driver issues first, and then focus on your network equipment. Hopefully, my experience will save you some time and frustration.

Watch out for Apparmor!

I’ve been hit by Apparmor a couple of times now. First with Samba, then with Openldap. AppArmor is a mandatory access control (MAC) system that restricts the capabilities of applications on a Linux system. While it can enhance the security of a Linux system, it can also cause issues with certain applications. Here are some apps that AppArmor can break and workarounds for each.

  1. Docker

Docker is a popular containerization technology that allows users to package and run applications in isolated environments. AppArmor can cause issues with Docker by blocking access to certain system resources required by Docker containers. To work around this issue, you can create a custom AppArmor profile for Docker that allows it to access the necessary resources.

To create a custom AppArmor profile for Docker, you can create a new profile file in the /etc/apparmor.d/ directory with the following contents:

# Profile for Docker
profile docker-container {
  # Allow access to necessary system resources
  /var/lib/docker/** rw,
  /var/run/docker.sock rw,
  /sys/fs/cgroup/** rw,
  /proc/sys/** rw,
  /etc/hostname r,
  /etc/hosts r,
  /etc/resolv.conf r,
  /etc/passwd r,
  /etc/group r,
  /etc/shadow r,
  /etc/gshadow r,
}

After creating the profile file, you can load it into the AppArmor kernel by running the following command:

sudo apparmor_parser -r /etc/apparmor.d/docker-container
  1. Apache

Apache is a widely used web server that can also be affected by AppArmor. If Apache is running in a restricted environment, it may not be able to access certain files or directories. To resolve this issue, you can modify the AppArmor profile for Apache to allow access to the necessary resources.

To modify the AppArmor profile for Apache, you can edit the existing profile file located in /etc/apparmor.d/usr.sbin.apache2 and add the necessary permissions. For example, to allow Apache to access the /var/www/html/ directory, you can add the following line to the profile:

/var/www/html/** r,

After making the necessary changes, you can reload the AppArmor profile by running the following command:

sudo service apparmor reload
  1. MySQL

MySQL is a popular open-source relational database management system that can be affected by AppArmor. If AppArmor is blocking access to MySQL, you may experience issues with database connectivity. To work around this issue, you can modify the AppArmor profile for MySQL to allow access to the necessary resources.

To modify the AppArmor profile for MySQL, you can edit the existing profile file located in /etc/apparmor.d/usr.sbin.mysqld and add the necessary permissions. For example, to allow MySQL to access the /var/lib/mysql/ directory, you can add the following line to the profile:

/var/lib/mysql/** rwk,

After making the necessary changes, you can reload the AppArmor profile by running the following command:

sudo service apparmor reload
  1. Nginx

Nginx is a high-performance web server that can also be affected by AppArmor. If Nginx is running in a restricted environment, it may not be able to access certain files or directories required for its operation. To resolve this issue, you can modify the AppArmor profile for Nginx to allow access to the necessary resources.

To modify the AppArmor profile for Nginx, you can edit the existing profile file located in /etc/apparmor.d/usr.sbin.nginx and add the necessary permissions. For example, to allow Nginx to access the /var/www/html/ directory, you can add the following line to the profile:

/var/www/html/** r,

After making the necessary changes, you can reload the AppArmor profile by running the following command:

sudo service apparmor reload
  1. OpenSSH

OpenSSH is a widely used remote access tool that can also be affected by AppArmor. If AppArmor is blocking access to OpenSSH, you may not be able to establish a remote connection to your Linux system. To work around this issue, you can modify the AppArmor profile for OpenSSH to allow access to the necessary resources.

To modify the AppArmor profile for OpenSSH, you can edit the existing profile file located in /etc/apparmor.d/usr.sbin.sshd and add the necessary permissions. For example, to allow OpenSSH to access the /var/log/auth.log file, you can add the following line to the profile:

/var/log/auth.log rw,

After making the necessary changes, you can reload the AppArmor profile by running the following command:

sudo service apparmor reload
  1. Samba

To modify the AppArmor profile for Samba, you can edit the existing profile file located in /etc/apparmor.d/usr.sbin.smbd and add the necessary permissions. For example, to allow Samba to access the /mnt/share/ directory, you can add the following line to the profile:

/mnt/share/** rw,

After making the necessary changes, you can reload the AppArmor profile by running the following command:

sudo service apparmor reload
  1. OpenLDAP

To modify the AppArmor profile for OpenLDAP, you can create a new profile file in the /etc/apparmor.d/ directory with the following contents:

# Profile for OpenLDAP
profile slapd {
  # Allow access to necessary system resources
  /var/lib/ldap/ r,
  /var/lib/ldap/** rw,
  /var/run/slapd/** rw,
  /etc/ldap/slapd.conf r,
  /etc/ldap/slapd.d/ r,
  /etc/ldap/slapd.d/** r,
  /usr/sbin/slapd mr,
  /usr/sbin/slapd.debug mr,
  /usr/sbin/slapd-{slave,monitor} ix,
  /usr/sbin/slapd.dbg mr,
  /usr/sbin/slapd-sock rw,
  /usr/sbin/slapd-sock-debug rw,
  /usr/sbin/slaptest mr,
}

After creating the profile file, you can load it into the AppArmor kernel by running the following command:

sudo apparmor_parser -r /etc/apparmor.d/slapd

By modifying AppArmor profiles for specific applications in this way, you can ensure that your applications have the necessary permissions to function correctly while still maintaining the security benefits of AppArmor.

AppArmor can cause issues with various applications on a Linux system, but these issues can usually be resolved by modifying the AppArmor profile for the affected application. By following the steps outlined above, you can ensure that your applications are functioning correctly while still maintaining the security benefits of AppArmor.

Loading up Active Directory with lots of groups

Loading up Active Directory with lots of groups can be a tedious task, but it can be made easier by following some steps. I recently had to do this to test a product to make sure that it can handle a large amount of data. I started with a list of job titles. Found that those titles were not enough groups and so ended up using a list of animals as the groups input to provide the script to automate the process of creating groups in Active Directory.

First, let’s assume that you already have Active Directory set up and that you have the necessary permissions to create groups. We will use the ldif template provided in the question to create groups in Active Directory.

Here is the step-by-step process to load up Active Directory with lots of groups:

  1. Prepare the list of groups: In our example, the list of animals is provided in the question. You can create your own list of groups based on your requirements.
  2. Create an ldif file: Use the ldif template provided in the question to create an ldif file that contains the group details. Make sure to replace {groupname} in the template with the actual name of the group.
  3. Run a for loop: To automate the process of creating groups, we can use a while loop that reads the list of groups and creates the groups in Active Directory using the ldif file. Here’s an example script:
#!/bin/bash

# Read the list of groups from a file
while read -r group; do
  # Replace {groupname} in the ldif file with the actual group name
  sed "s/{groupname}/$group/" group.ldif >> temp.ldif
  # Create the group in Active Directory using ldapadd command
  ldapadd -x -D "CN=Administrator,CN=Users,DC=mydomain,DC=com" -w password -f temp.ldif
done < groups.txt

In the above script, replace the following:

  • group.ldif with the name of the ldif file that you created in step 2.
  • groups.txt with the name of the file that contains the list of groups.
  • CN=Administrator,CN=Users,DC=mydomain,DC=com with the actual Distinguished Name (DN) of the user account that you want to use to create the groups.
  • password with the password for the user account.
  1. Run the script: Save the script to a file (e.g., create-groups.sh) and make it executable using the command chmod +x create-groups.sh. Then run the script using the command ./create-groups.sh.

That’s it! The script will create all the groups in the list and add them to Active Directory. You can modify the ldif template and the script as per your requirements to create groups with different attributes and properties.