Category: Linux

Troubleshooting Proxmox clusters and restoring the LXC container

Posted on by soban

Managing Proxmox clusters can sometimes present technical difficulties, such as inconsistencies in cluster configuration or issues with restoring LXC containers. Finding and resolving these issues is crucial for maintaining the stability and performance of the virtualization environment. In this article, I present a detailed guide on how to diagnose and resolve an issue with an unreachable node and how to successfully restore an LXC container.

Before you begin any actions, make sure you have a current backup of the system.

Diagnosing the State of the Proxmox Cluster

and:

To understand the state of the cluster, execute the following command on the node-up-page-04 node:

Expected output:

Then check the detailed cluster information with the following command:

Expected output:

Removing the Container Configuration File and Cleaning Data

I discovered that the configuration file for container 107 still exists on the cluster’s file system at the path:

Output:

To remove this file and any remaining data associated with the detached node, execute:

Restoring the Container

After removing the configuration file, I restored the LXC container on the node-up-page-04 node using the command:

Output:

The restoration process was successful, and the container was ready for use. This case illustrates the importance of thorough diagnostics and configuration file management in Proxmox when working with clusters. Regular reviews of configurations are advisable to avoid inconsistencies and operational issues in the future.

How to prevent hibernation and sleep on debian and proxmox laptops when the lid is closed

Posted on by soban

Virtualization servers based on Debian family systems, such as Proxmox, are often used in test environments where continuous availability is crucial. Sometimes these servers are installed on laptops, which serve as low-budget or portable solutions. However, the standard power management settings in laptops can lead to undesirable behaviors, such as sleeping or hibernating when the lid is closed. Below, I describe how to change these settings in an operating system based on Debian to ensure uninterrupted server operation.

Step 1: Accessing the Configuration File

Open the terminal and enter the following command to edit the /etc/systemd/logind.conf file using a text editor (e.g., nano):

Step 2: Modifying logind Settings

Find the line containing HandleLidSwitch and change its value to ignore. If the line is commented out (preceded by a # symbol), remove the #. You can also add this line to the end of the file if it does not exist.

Step 3: Applying and Restarting the Service

After making the changes and saving the file, you need to restart the systemd-logind service for the changes to take effect. Use the following command in the terminal:

With these changes, closing the laptop lid will no longer initiate hibernation or sleep, which is especially important when using Debian-based servers, including Proxmox, as server solutions.

Extending SWAP space on Proxmox using lvreduce

Posted on by soban

Introduction

Managing SWAP memory is a key element in administering Linux operating systems, especially in virtualization environments like Proxmox. SWAP acts as “virtual memory” that can be used when the system’s physical RAM is full. In this article, we will show how to increase SWAP space on a Proxmox server, using the lvresize tool to free up disk space that can then be allocated to SWAP.

Problem Overview

A user wants to increase SWAP space from 8 GB to 16 GB, but encounters the problem of lacking available space in the LVM volume group, which is required to increase SWAP.

Step 1: Checking Available Space

The command vgs displays the volume groups along with their sizes and available space.

Step 2: Reducing the Volume

Suppose there is a root volume of 457.26 GB, which can be reduced to free up an additional 8 GB for SWAP. Before reducing the volume, it is necessary to reduce the file system on this volume.

However, in the case of the XFS file system, reduction must occur offline or from a live CD.

Step 3: Using lvreduce

This command reduces the root volume by 8 GB, which is confirmed by a message about the volume size change.

Step 4: Deactivating SWAP

Before starting changes in SWAP size, SWAP must first be turned off using the above command.

Step 5: Expanding SWAP

The above commands first increase the SWAP space, then format it and reactivate it.

Finally, we verify the active SWAP areas using the above command to ensure everything is configured correctly.

This process shows how you can flexibly manage disk space on Proxmox servers, adjusting the size of SWAP depending on needs. Using lvreduce requires caution, as any operation on partitions and volumes carries the risk of data loss, therefore it is always recommended to make backups before proceeding with changes.

Upgrading Apache Cassandra from Version 3.1.15 and Higher to 4.1.x on Ubuntu 20.04.5 LTS: A Comprehensive Guide

Posted on by soban

Upgrading Apache Cassandra to a newer version is a significant task that database administrators undertake to ensure their systems benefit from new features, enhanced security measures, and improved performance. This guide provides a detailed walkthrough for upgrading Apache Cassandra from version 3.1.15 and higher to the latest 4.1.x version, specifically on Ubuntu 20.04.5 LTS, with an emphasis on pre-upgrade cleaning operations to manage disk space effectively.

Pre-upgrade Preparation

Backup Configuration Directory:

Before initiating the upgrade, it’s crucial to back up the Cassandra configuration directory. This precaution allows for a swift restoration of the configuration should any issues arise during the upgrade process. Utilize the following command to create a backup, incorporating the current date into the folder name for easy identification:

Pre-Cleanup Operations

Preparation is key to a smooth upgrade. Begin with maintenance commands to guarantee data integrity and optimize space usage, especially important for systems with limited disk space.

Scrub Data:

Execute nodetool scrub to clean and reorganize data on disk. Given that this operation may be time-consuming, particularly for databases with large amounts of data or limited disk space, it’s a critical step for a healthy upgrade process.

Clear Snapshots:

To further manage disk space, use nodetool clearsnapshot to remove existing snapshots, freeing up space for the upgrade process. To delete all snapshots on the node, simply use this method if you’re running out of space:

Cleanup Data:

Perform a nodetool cleanup to purge unnecessary data. In scenarios where disk space is a premium, it’s advisable to execute a scrub operation without generating a snapshot to conserve space:

Draining and Stopping Cassandra

Drain the Node:

Prior to halting the Cassandra service, ensure all data in memory is flushed to disk with nodetool drain.

Stop the Cassandra Service:

Cease the running Cassandra services to proceed with the upgrade safely:

Upgrading Cassandra

Update Source List:

Edit the repository sources to point to the new version of Cassandra by adjusting the cassandra.sources.list file:

Upgrade Packages:

With the repository sources updated, refresh the package list and upgrade the packages. When executing the apt upgrade command, you can keep pressing Enter as the default option is ‘N’ (No):

Modify Configuration:

Adjust the Cassandra configuration for version 4.1.x by commenting out or deleting deprecated options:

Update JAMM Library:

Ensure the Java Agent Memory Manager (JAMM) library is updated to enhance performance:

Backup and update the JVM options file:

It’s a good practice to back up configuration files before making changes. This step renames the existing jvm-server.options file to jvm-server.options.orig as a backup. Then, it copies the jvm.options file to jvm-server.options to apply the standard JVM options for Cassandra servers.

Optimization and Verification

Optimize Memory Usage:

Post-upgrade, it’s beneficial to evaluate and optimize memory usage and swap space to ensure efficient Cassandra operation:

Restart the Cassandra Service:

Apply the new version by restarting the Cassandra service:

Verify Upgrade:

Confirm the success of the upgrade by inspecting the cluster’s topology and state, ensuring all nodes are functional:

By adhering to this comprehensive guide, database administrators can effectively upgrade Apache Cassandra to version 4.1.x, capitalizing on the latest advancements and optimizations the platform has to offer, while ensuring data integrity and system performance through careful pre-upgrade preparations.

Optimization and Verification

After successfully upgrading Apache Cassandra to version 4.1.x and ensuring the cluster is fully operational, it’s crucial to conduct post-upgrade maintenance to optimize the performance and security of your database system. This section outlines essential steps and considerations to maintain a healthy and efficient Cassandra environment.

Monitor Performance and Logs

In the immediate aftermath of the upgrade, closely monitor the system’s performance, including CPU, memory usage, and disk I/O, to identify any unexpected behavior or bottlenecks. Additionally, review the Cassandra system logs for warnings or errors that may indicate potential issues requiring attention.

Tune and Optimize

Based on the performance monitoring insights, you may need to adjust Cassandra’s configuration settings for optimal performance. Consider tuning parameters related to JVM options, compaction, and read/write performance, keeping in mind the specific workload and data patterns of your application.

Run nodetool upgradesstables

To ensure that all SSTables are updated to the latest format, execute nodetool upgradesstables on each node in the cluster. This operation will rewrite SSTables that are not already in the current format, which is essential for taking full advantage of the improvements and features in Cassandra 4.1.x (Check the space, and if required, delete all snapshots as shown above.):

This process can be resource-intensive and should be scheduled during off-peak hours to minimize impact on live traffic.

Implement Security Enhancements

Cassandra 4.1.x includes several security enhancements. Review the latest security features and best practices, such as enabling client-to-node encryption, node-to-node encryption, and advanced authentication mechanisms, to enhance the security posture of your Cassandra cluster.

Review and Update Backup Strategies

With the new version in place, reassess your backup strategies to ensure they are still effective and meet your recovery objectives. Verify that your backup and restore procedures are compatible with Cassandra 4.1.x and consider leveraging new tools or features that may have been introduced in this release for more efficient data management.

Proxy through nginx frontend to the second virtual server wordpress

Posted on by soban

In a situation where we have one public IP address and we have many domains directed to that IP address, it is worth considering spreading the traffic to other servers. Proxmox, which allows you to create a pair of virtual machines, is perfect in such a situation. In my case, each virtual machine is separated and the traffic is broken down by nginx, which distributes the traffic to other servers. The virtual machine on my website will redirect traffic, I have the IP address for wordpress: 10.10.11.105 on port 80. In this case, no encryption is required, but the frontend itself, which manages the traffic, will present itself with encryption and security on port 443.

Two machines with the following configuration will participate throughout the process:
up-page IP: 10.10.14.200
soban-pl IP: 10.10.11.105

So let’s move on to the frontend that distributes traffic to other machines.
The frontend is done by linux debian 11 (bullseye), in addition, I have the following entry in the repository (/etc/apt/sources.list):

To install nginx, run the following commands:

You should make sure that the traffic from the frontend has the appropriate port 80 transitions. You can read how to check the network transitions here: Check network connection and open TCP port via netcat.

Screenshot of a terminal window showing a successful telnet connection to the IP address 10.10.11.105 on port 80, followed by the user exiting the telnet session with the 'quit' command.

The configuration of the frontend that distributes the traffic is as follows (/etc/nginx/conf.d/soban.pl.ssl.conf):

Configuration of the above-mentioned wordpress, additional authorization is also set when you try to log in to wp-admin, you can read about it here: More security wp-admin in nginx.

In the next step, check if the nginx configuration is correct by:

Terminal output displaying a successful nginx configuration test with the messages: 'nginx: the configuration file /etc/nginx/nginx.conf syntax is ok' and 'nginx: configuration file /etc/nginx/nginx.conf test is successful'.

If everything is fine, restart nginx:

In a virtual machine with nginx it should also be installed. This is the same as debian linux 11 (bullseye), so the respository should look like this:

Just installing nginx looks the same as on a machine that acts as a proxy.

All configuration is in /etc/nginx/conf.d/soban.pl.conf:

Also in this case, check the correctness of the nginx service configuration:

Everything looks fine, so let’s move on to restarting the service:

If the whole configuration was done correctly, the page should be directed without encrypted traffic to the virtual machine with wordpress. A wordpress service with nginx is not the only one that can be hosted or proxied. We can direct traffic from nginx to e.g. jboss, apacha and all other web services. Of course, this requires a corresponding modification of the configuration presented above, but the general outline of the concept as an nginx proxy has been presented. You should also remember about the appropriate configuration of keys and certificates. In my case let’s encrypt works perfectly for this.

Improving encryption on old red hat 5 by new Oracle Linux 7 using apache mod_proxy

Posted on by soban

There are situations when we need to increase the encryption level on the old system – according to the PCI audit requirements. However, the old system is no longer supported, so updating the encryption level is not possible. This is not a recommended solution, because we should try to transfer the application to a new system. After all, when we have little time, it is possible to hide the old version of the system and allow only the new machine to move to it. In this particular example, we will use mod_proxy as a proxy to redirect traffic to the old machine, while using iptables we will only allow communication with the new machine. It is not a recommended solution, but it works and I would like to present it here. The systems that I will be basing on in this example are the old red hat 5 and the new oracle linux 7. Recently, it has become very important to use a minimum of tls 1.2 and none below for banking transactions. Let’s start with the proxy server configuration oracle linux 7.

As of this writing, the addressing is as follows:
new_machine IP: 10.10.14.100
old_machine IP: 10.10.14.101
Traffic will be routed on port 443 from new_machine to old_machine.

Before we go to proxy configuration, please make sure there are network transitions from new_machine (10.10.14.100) to old_machine (10.10.14.101) to port 443. You can read how to verify network connections here: check network connection and open tcp port via netcat.

We go to the installation of apache and mod_proxy:

After installing apache, go to the edition:

Below are the news on the check level, what are the updates, and ip on the next service update:

In order to verify the correctness of apache configuration, you can issue a command that will check it:

If the apache configuration is correct, we can proceed to reloading apache:

At this point, we have a configured proxy connection. Before we move on to limiting traffic with iptables, I suggest you go to the site – with the new mod_proxy configured and test if everything is working properly and if there are any problems with the application.

Once everything is working fine, the network transitions are there, we can go to the iptables configuration for red hat 5. Let’s start by checking the system version:

Now we are going to prepare iptables so that the network traffic is available on port 443 from the new_machine (10.10.14.100). To do this, edit the file /etc/sysconfig/iptables:

After iptables settings are correct, we can reload the service:

In this way, we managed to cover up the weak encryption by proxying and diverting traffic to the new machine. This is not a recommended solution and you should try to transfer the application to a new environment compatible with the new system. However, in crisis situations, we can use this solution. Network traffic is not allowed by other IP addresses, so scanners will not be able to detect weak encryption on the old machine, and users using the old environment will not be able to use it. This does not change the fact that weak encryption is still set in the old environment and needs to be corrected. The example I gave is for the old red hat 5 and the new oracle linux 7, but it can be assumed that a similar solution and configuration is possible for other versions of the system.

Increasing the security of the ssh service

Posted on by soban

Nowadays, many bots or hackers look for port 22 on servers and try to log in. Usually, the login attempt is made as the standard linuxe root user. In this short article, I will describe how to create a user that will be able to log in as root and change the default ssh port 22 to 2222. Let’s go:

This way we created the user ‘soban’ and assigned it the default shell ‘/bin/bash’.

We still need to set a password for the user ‘soban’:

In the next step, let’s add it to ‘/etc/sudoers’ so that it can become root. Keep in mind that once the user can get root, he will be able to do anything on the machine!

Please add this entry below:

How can we test whether the user has the ability to log in as root? Nothing easier, first we’ll switch to the user we just created:

To list the possible sudo commands, just type the command:

Finally, to confirm whether it is possible to log in as root, you should issue the command:

Now that we have a root user ready, let’s try disabling ssh logon directly and change the default port. To do this, go to the default configuration of the ssh service, which is located in ‘/etc/ssh/sshd_config’:

We are looking for a line containing ‘Port’ – it can be hashed, so it should be unhashed and ‘PermitRootLogin’. Then set them as below:

In this way, we changed the default port 22 to 2222 and disallowed the possibility of logging in directly to the root user. However, the ssh service still needs to be reloaded, in debian or kali linux we do it like this:

In this way, we have managed to create a user who can safely log into the ssh service and become root. In addition, after changing the port, we will not go out on port 22 scans, which by default is set and scanned by a potential burglar. Installing the fail2ban service is also a very good improvement in security.

iftop as a good network traffic monitoring tool

Posted on by soban

iftop is a command-line tool used for real-time network bandwidth monitoring. It displays a continuously updated list of network connections and the amount of data transferred between them. The connections are listed in a table format and are sorted by either the amount of data transferred or the total number of packets sent or received.

iftop provides a variety of filtering options, allowing you to limit the display to specific hosts, networks, or ports. It also provides support for IPv6, and it can display information about the source and destination IP addresses, port numbers, and protocols.

iftop is particularly useful for monitoring network traffic in real-time and identifying which applications or services are consuming the most bandwidth. It can also help identify network performance issues and can assist in troubleshooting network problems.

Overall, iftop is a powerful and flexible tool for network monitoring and analysis, and it can be a valuable addition to any network administrator’s toolkit.

One of the more useful network traffic monitoring tools I find is iftop. It is especially useful when the link’s throat is flooded. In my experience, it is easy to use it to catch all kinds of network attacks, especially DoS. In the example given below, I will send a larger file to the remote machine and limit its upload speed, in the meantime I will observe the traffic with the iftop tool. Let’s start by installing iftop on the local machine. In this case it is kali linux: 

The distribution doesn’t matter in this case, just like it installs on any other operating system, it may well be linux debian.

We will do the same on the remote machine, so let’s move on to installing iftop on linux debian:

To start monitoring network traffic, run iftop with parameters: ‘-PpNn’:

As I am ssh connected to the remote machine, I can see my network connection.

Now let’s go back to the local machine, create a large file:

Once we have created a 1GB file, let’s try to send it with a transfer limit to the remote machine:

In this case, I used scp with the limit of 800 to send the file. To calculate how many KB/sec this is, divide by 8. From a simple calculation it follows that 800/8 = 100. To see scp and how to send files I encourage you to read: Securely Copy Files (scp) tool to copying files by ssh.

When sending the file, the traffic on the local machine looked like this (outgoing traffic):

At the same time, it looked like this on the remote machine (incoming traffic):

As you can see, in this way you can catch both outgoing and incoming traffic. The iftop tool has more parameters, I encourage you to read the manual. It is a simple tool, however, thanks to it, we can easily observe live network traffic. In the case of bruteforce, a significant number of connections will be made, but in the case of a DoS attack, the attacker will try to saturate the bandwidth, therefore the incoming traffic on the machine will be large. There are situations when the machine is naturally overloaded with the network, then you should limit the connection speed, in this case iptables works perfectly.

Securely Copy Files (scp) tool to copying files by ssh

Posted on by soban

A very good tool for securely copying files via the ssh protocol between machines is scp. It allows you to transfer files to the target machine as well as download from a given source. The tool is usually built into the system so it works on many distributions. Below I will present how you can send and download files. For correct file transfer, running ssh service is required, because it is the basis of scp operation. Of course, when using the tool, you can specify the port as the parameter, provided that it has been changed. The standard port used by the ssh daemon is 22. 

In Linux, scp (Secure Copy) is a command-line utility used for securely transferring files between local and remote systems. It is a secure alternative to cp, which is not secure when transferring files over a network.

The scp command is commonly used for copying files to or from a remote server. It uses the SSH protocol to securely transfer files and provides the same level of security as SSH. The syntax of the scp command is as follows:

Here, [source] is the file or directory you want to copy, and [destination] is the location where you want to copy the file or directory.

Some common options used with the scp command are:

  • -r: Copies directories recursively
  • -P: Specifies the port number to use for the SSH connection
  • -i: Specifies the path to the identity file used for authentication

For example, to copy a file named file.txt from a remote server to the local machine, you would use the following command:

This command will copy the file from the remote server to the local machine at the specified directory.

Similarly, to copy a directory named dir from the local machine to a remote server, you would use the following command:

This command will copy the directory and its contents from the local machine to the remote server at the specified directory.

Let’s start by creating an example file that we will transfer: 

in the next step, let’s move on to uploading the file. In my case, the port from ssh has been changed to 2222:

The first time you connect, you will be asked for a fingerprint. 
As you can see, the file has been sent correctly. 

Instead of the sign at the end of ‘~‘ we can specify where the target file should be placed (/tmp/example-path): 

There are many combinations, you can send, for example, all files containing the ending (*.tar.gz) to the user’s home directory, which is just symbolized by ‘~‘: 

An interesting parameter is the ‘-r‘ in scp where we can transfer entire folders, example using copying a folder from local machine to remote machine: 

OK, after the file has been successfully sent to the target machine, let’s delete the local file we created above and try to download it back: 

Next, let’s move on to downloading the file from the remote server to the local machine: 

Above I gave an example of how to send an entire folder from a local machine to a remote machine. The other way around, of course, we can also do it. To download a remote folder to a local machine, use the ‘-r‘ parameter:

The scp utility has more parameters, you can get them by reading the man page: 

It is worth paying attention to the ‘-l‘ parameter where we can set the limit of transferred files. This is useful when transferring larger files so as not to overload your connection. 

If you are tired of constantly entering your password, I encourage you to read how you can connect to ssh without providing a password. Then copying files using scp will become more: generate ssh key pair in linux.

In my opinion, scp is good for transferring files quickly one time. However, as often you exchange files between machines a more convenient way is to use sshfs as described here: sshfs great tool to mount remote file system.

sshfs great tool to mount remote file system

Posted on by soban

SSHFS (SSH File System) is a secure file transfer system that enables users to remotely access and manage files on a remote server over an encrypted SSH (Secure Shell) connection. SSHFS uses the SSH protocol to establish a secure connection between the local and remote systems, which enables users to securely transfer files between the two systems.

To use SSHFS, the user needs to have SSHFS installed on their local system as well as the remote system that they want to connect to. Once SSHFS is installed, the user can mount the remote system as a local directory on their system, and access the remote files as if they were stored locally.

SSHFS provides a secure and convenient way to access and manage files on remote systems, without the need for additional software or complicated configuration. It also enables users to access files on remote systems using standard file operations, such as copying, moving, and deleting, making it a simple and effective way to manage files on remote systems.

SSH Filesystem (sshfs) is a very useful tool for remotely transferring files over the ssh protocol. An additional advantage of the whole is encryption. This is a convenient way to mount a remote folder to delete files. Below I will try to briefly introduce how to install sshfs and how to mount the folder remotely. Additionally, we will make an entry in /etc/fstab at the end, so that the resource itself is mounted after restarting the system. Let’s move on to installing the tool itself:

In this case, as you can see, the installation was done on kali linuxe, however the procedure is the same on debian.

Let’s move on to the file mounting itself, at this point I will point out that the default port is 22. In my case, however, the port has been changed to 2222. For services such as ssh, I try to change the default ports so as not to get caught by bots and not end up in the database such as shodan.io. The command itself in this case is very simple, but first we need to create a folder:

Let’s try to mount a remote folder:

During mounting, we will be asked if the fingerprint is correct. Then for the system password. The command itself can be disassembled into ‘soban‘ – this is the username. Then ‘soban.pl‘ is the domain name, you can also put the IP address here. The next ‘/home/soban‘ element is the folder that will be mounted. And after the space ‘/home/kali/myremotedir‘ we give the folder where the remote folder should be mounted. If everything went as planned, we can list ‘/home/kali/myremotedir‘ and it should list the contents of the remotely mounted folder ‘/home/soban‘. Let’s list the contents of the ‘/home/kali/myremotedir‘ folder:

Let’s create a remote file:

Now let’s unmount the remote folder and try listing it again:

As expected, the folder is empty and the file we created was created on a remotely mounted drive. After unmounting as you can see the file ‘/home/kali/myremotedir/example‘.

The next step is to create a private key to mount the folder without entering a password. It is very important not to send nikmou your private key. How we can generate and add a public key to a remote server can be read here: “Generate SSH key pair in Linux“.

Now we will try to add an entry to /etc/fstab which will allow automatic mounting on startup of the remote folder system.
To do this, edit the /etc/fstab entry and add this entry:

It is important that all data is correct, in order to verify the parameters, you can use the command for this ‘id‘:

Now we can move on to mounting the resource:

When mounting for the first time, we may be asked to accept and confirm that the fingerprint is correct. After verifying the correctness of mounting the remote resource, we can restart the system. One note here, the system may get up longer.