GNU/Linux

5 packages can be upgraded. Run ‘apt list –upgradable’ to see them.

 in Bash / GNU/Linux  tagged apt / bash / GNU/Linux / list / packages / ubuntu / upgradable by

Updating an operating system is a critical task that ensures the system’s security, stability, and performance. In Ubuntu, updating the system involves running several commands in the terminal. In this technical post, we will explain the process of updating an Ubuntu Server installation and how to fix the issue of pending package upgrades.

The first command that needs to be executed is sudo apt update. This command updates the list of available packages from the Ubuntu repositories. The -y option instructs the system to answer “yes” to prompts, ensuring the process runs uninterrupted.

The second command is sudo apt upgrade. This command upgrades all installed packages to their latest versions. Again, the -y option is used to answer “yes” to any prompts.

The third command, sudo apt autoremove, removes any unnecessary dependencies that are no longer required by the system.

After executing these three commands, the system displayed a warning message that says that five packages can be upgraded. To see the list of upgradable packages, we needed to execute the command apt list --upgradable. This command lists all the upgradable packages along with their versions.

The following command we executed was sudo apt-get dist-upgrade. This command upgrades the system to the latest distribution release, including kernel upgrades. However, the command failed to upgrade the pending packages in this case.

To fix the issue, we executed the command sudo apt-get install --only-upgrade $PACKAGE for each pending package. This command upgrades the specified package to its latest version. The $PACKAGE variable should be replaced with the package name that needs to be upgraded.

In summary, updating an Ubuntu Server installation involves running the sudo apt update, sudo apt upgrade, and sudo apt autoremove commands in the terminal. If there are any pending package upgrades, we can use the apt list --upgradable command to see the list of upgradable packages. If the sudo apt-get dist-upgrade command fails to upgrade the pending packages, we can use the sudo apt-get install --only-upgrade $PACKAGE command to upgrade each package individually.

Using nmap to scan a network and identify which hosts are alive

 in GNU/Linux  tagged GNU/Linux / network / nmap / scan / scanning by

The command “nmap -sP 192.168.100.0/24” scans a network and identifies which hosts are alive (i.e., which IP addresses are being used) within the specified range.

In more detail, the “nmap” command is a widely used network exploration tool that can be used for tasks such as host discovery, port scanning, and service enumeration.

The “-sP” option tells nmap to perform a “ping scan,” where it sends an ICMP echo request to each host in the specified IP range and checks for responses. This method is typically faster than other scanning techniques because it only determines whether a host is up or not without gathering additional information about the host’s ports or services.

The “192.168.100.0/24” argument specifies the IP range to be scanned, specifically the subnet mask “255.255.255.0,” which corresponds to the range of IP addresses from 192.168.100.0 to 192.168.100.255. The “/24” suffix is a shorthand notation for the subnet mask.

Overall, the command “nmap -sP 192.168.100.0/24” is a helpful tool for network administrators or security professionals who need to identify which hosts are active on a particular network quickly. It can help to identify potential security vulnerabilities or unauthorized devices connected to the network.

Unable to negotiate with IP port 22: no matching host key type found. Their offer: ssh-rsa

 in Bash / GNU/Linux  tagged bash / GNU/Linux / HostKeyAlgorithms / PubkeyAcceptedKeyTypes / ssh-rsa by

Secure Shell (SSH) is a cryptographic network protocol that is commonly used for secure data communication, remote command-line login, and other network services. The SSH command is used to remotely connect to a server or device and execute commands on that device. In this blog post, we will explain the following SSH command and when the extra parameters are needed.

ssh -p 22 -o HostKeyAlgorithms=+ssh-rsa -o PubkeyAcceptedKeyTypes=+ssh-rsa user@host;

Breakdown of the SSH command

  • ssh: The command to initiate a Secure Shell connection to a remote host.
  • -p 22: The -p option specifies the port number that SSH should use to connect to the remote host. In this case, the port number is 22, which is the default SSH port number.
  • -o HostKeyAlgorithms=+ssh-rsa: The -o option allows the user to set SSH options. In this case, the option HostKeyAlgorithms specifies the key exchange algorithm that should be used for the connection. The +ssh-rsa parameter adds the ssh-rsa algorithm to the list of acceptable algorithms.
  • -o PubkeyAcceptedKeyTypes=+ssh-rsa: Similar to the previous parameter, this option specifies the type of public key that will be accepted for authentication purposes. The +ssh-rsa parameter adds the ssh-rsa key type to the list of acceptable key types.
  • user@host: Specifies the username and hostname of the remote machine to connect to.

When are the extra parameters needed?

The extra parameters in this SSH command are used to specify the key exchange and authentication algorithms that are acceptable for the SSH connection. This is important because older, less secure algorithms can be vulnerable to attacks. By specifying only the more secure algorithms, you can help ensure that your connection is as secure as possible.

The specific parameters used in this command are not always necessary, but they can be useful in certain situations. For example, if you are connecting to an older SSH server that uses weaker encryption algorithms, you may want to specify only the stronger algorithms that are supported by both the server and your client. Similarly, if you are connecting to a server that requires a specific type of public key for authentication, you can specify that key type using the PubkeyAcceptedKeyTypes option.

In general, it’s a good idea to use the most secure algorithms that are supported by both your client and the remote server. This can help ensure that your connection is as secure as possible and minimize the risk of unauthorized access or data breaches.

In conclusion, the SSH command is a powerful tool for remotely connecting to and managing servers and devices. By understanding the different parameters and options available, you can customize your SSH connections to meet your specific needs and ensure that your connections are as secure as possible.

Splitting a zip file (or any file) into smaller parts

 in Bash / GNU/Linux  tagged bash / cat / GNU/Linux / split / unzip / zip by

In this post, we will explain the following commands:

  1. zip Original.zip Original/
  2. split -b 5M -d Original.zip Parts.zip.
  3. cat Parts.zip* > Final.zip
  4. unzip Final.zip -d Final

These commands are commonly used in Linux/Unix systems and can be very helpful when working with large files or transferring files over a network.

Command 1: zip Original.zip Original/

The zip command is used to compress files and create a compressed archive. In this command, we are compressing the directory named Original and creating an archive named Original.zip. The -r option is used to recursively include all files and directories inside the Original directory in the archive.

Command 2: split -b 5M -d Original.zip Parts.zip.

The split command is used to split a large file into smaller files. In this command, we are splitting the file Original.zip into smaller files with a size of 5 MB each. The -b option specifies the size of each split file, and the -d option is used to create numeric suffixes for the split files. The Parts.zip is the prefix for the split files.

Command 3: cat Parts.zip* > Final.zip

The cat command is used to concatenate files and print the output to the standard output. In this command, we are concatenating all the split files (which have the prefix Parts.zip) into a single file named Final.zip. The * is a wildcard character that matches any file with the specified prefix.

Command 4: unzip Final.zip -d Final

The unzip command is used to extract files from a compressed archive. In this command, we extract the files from the archive Final.zip and store them in a directory named Final. The -d option is used to specify the destination directory for the extracted files.

In conclusion, these commands can be beneficial when working with large files or transferring files over a network. By using the zip and split commands, we can compress and split large files into smaller ones, making them easier to transfer. Then, using the cat command, we can concatenate the split files into a single file. Finally, we can use the unzip command to extract the files from the compressed archive.