As more and more businesses move to Linux servers, it’s important to know the best practices for securing these systems. Here are some of the most important things to keep in mind when it comes to Linux server security:

1. Keep your system up to date. This includes both the kernel and all of the applications that are running on the server. Regular updates will help ensure that any security vulnerabilities are patched in a timely manner.

2. Use a strong password policy. This means using long, complex passwords that are difficult to guess. Passwords should be changed regularly, and different passwords should be used for different accounts.

3. Limit access to the server. Only give users the permissions they need to perform their jobs, and no more. This will help reduce the chances of someone accidentally or maliciously damaging the system.

4. Use a firewall. A firewall can help protect your server from attacks by blocking unwanted traffic.

5. Backup your data regularly. This way, if something does happen to your server, you’ll have a copy of all your data that you can use to restore the system.

Following these best practices will help keep your Linux server secure.

Linux user permissions

Every Linux user has a user ID and a group ID. User IDs are used to identify individual users, while group IDs are used to identify groups of users. Every user belongs to at least one group, and every file on a Linux system is owned by a user and a group.

Linux permissions determine who can access a file or directory and what they can do with it. There are three types of permissions: read, write, and execute. Read permission allows a user to view the contents of a file. Write permission allows a user to modify the contents of a file. Execute permission allows a user to run a file as a program.

Permissions are set for three different types of users: the owner of the file, members of the file’s group, and all other users. The owner of a file can always read, write, and execute it. Members of a file’s group can read and execute the file, but they cannot write to it. All other users can only read the file.

To change the permissions of a file, you use the chmod command. The chmod command stands for “change mode”, and it is used to change the permissions of a file. The syntax for the chmod command is:

chmod [permissions] [filename]

For example, to give read, write, and execute permissions to the owner of a file named “file1”, you would use the following command:

chmod 700 file1

Linux file permissions

Linux file permissions are a way to control who can access and modify files on your computer. By default, only the owner of a file can read or write to it. However, you can change these permissions to allow others to read, write, or execute the file as well.

To do this, each file has a set of three permissions: read, write, and execute. Read permission allows a user to view the contents of a file. Write permission allows a user to modify the contents of a file. Execute permission allows a user to run a file as a program.

You can set these permissions for three different types of users: the owner of the file, members of the owner’s group, and all other users. To set permissions, you use the chmod command followed by the permission you want to set and the user or group you want to set it for.

For example, to give read and write permission to the owner of a file named “myfile”, you would use the following command:

chmod u+rw myfile

This would allow the owner of “myfile” to read and write to it, but not execute it. To give all users read and write permission, you would use:

chmod a+rw myfile

And to give everyone read, write, and execute permission, you would use:

chmod a+rwx myfile

Sudo and su commands

Sudo and su are two Linux commands that are used to execute a command as a superuser or substitute user, respectively.

Sudo allows a permitted user to execute a command as the superuser or another user, as specified in the sudoers file. The real and effective uids are set to match those of the target user as specified in the sudoers file. When sudo is configured to allow a user to run commands as any other user, the invoking user’s real uid is used to determine who they will run the command as.

Su allows a user to become another user, specified by the -l option, by default the superuser. It invokes a login shell for that user. If a command is specified, it is passed to the shell for execution. Otherwise, an interactive shell is executed.

Firewalls

A firewall is a network security system that filters and controls incoming and outgoing network traffic based on predetermined security rules. A firewall can be hardware- or software-based, and it is often used in conjunction with other security measures, such as anti-virus software.

Firewalls are used to protect networks from unauthorized access and can be used to control traffic between different network segments. Firewalls can also be used to block specific types of traffic, such as certain types of file transfers or incoming connections from specific IP addresses.

Secure Shell (SSH)

Secure Shell or SSH is a network protocol that allows for secure communication between two devices. This is done by encrypting all data that is sent between the devices. SSH is often used to access remote servers or devices in a secure manner.

Intrusion detection

An intrusion detection system (IDS) is a device or software application that monitors network or system activities for malicious or unauthorized behavior and produces reports to a Management Station.

There are three main types of intrusion detection:

Network intrusion detection looks at network traffic and monitors for suspicious activity.

Host-based intrusion detection looks at activity on individual hosts and can detect malicious activity, such as someone trying to gain access to a system or file.

Application-based intrusion detection looks at activity at the application level and can detect things like SQL injection attacks.

honeypots

A honeypot is a computer system that is specifically designed to attract and lure attackers. The honeypot entices attackers by appearing to be an easy target with vulnerabilities. Once an attacker takes the bait, the honeypot tracks and monitors their activity, providing information that can be used to improve security.

Honeypots can be used to detect attacks, study attackers and their techniques, and distract them from other systems. By observing the activity on a honeypot, organizations can learn about new attacks and develop ways to protect their systems.

Honeypots can be deployed in a few different ways, depending on the organization’s needs. Some honeypots are designed to mimic production systems, while others are designed to look like decoy systems. There are also honeypots that are designed to be part of a network of systems, and there are standalone honeypots.

Organizations can use honeypots to improve their security posture by luring attackers away from production systems, learning about new attacks, and developing countermeasures.

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