SELinux (Security-Enhanced Linux) is a critical component of security policy in Linux-based systems, including the CentOS distribution. Its main task is to restrict access of applications and processes to system resources based on security policies. In this article, we will focus on basic SELinux setup on the CentOS 7 operating system.
Overview of SELinux
SELinux can operate in three modes: Enforcing, Permissive, and Disabled. In Enforcing mode, SELinux enforces security policies and logs attempts to violate them. Permissive mode is used for debugging, where SELinux does not block any operations but logs them as policy violations. Disabled mode completely deactivates SELinux.
Checking the Current SELinux Status
To check the current status of SELinux on your system, use the command:
sestatus
This command will show whether SELinux is enabled and in which mode it is operating.
Changing SELinux Mode
To change the SELinux mode, you can use the setenforce tool as follows:
- To switch to Permissive mode:
setenforce 0 - To switch to Enforcing mode:
setenforce 1
Persistently Changing SELinux Mode
If you want to change the SELinux mode permanently, you need to edit the /etc/selinux/config file. Open this file in any text editor and change the value of SELINUX to enforcing, permissive, or disabled.
Setting SELinux Policies
SELinux offers various policies for different security needs. These policies define which operations are allowed for applications and services. You can manage these policies using the semanage tool. For example, to allow the Apache web server access to user home directories, use the command:
semanage boolean -m --on httpd_enable_homedirs
Troubleshooting
When configuring and operating SELinux, you may encounter issues with application access to certain resources. For analyzing and resolving these issues, the audit2why tool is useful, which helps you analyze SELinux logs and determine why access was denied.
Properly configuring SELinux is crucial for securing your system. Although its configuration may be challenging initially, it provides an important layer of protection against unauthorized access and activities. With the help of this guide and available tools, you can effectively set up and manage SELinux on your CentOS 7 system.
