What is selinux in redhat?

Answer 1

NSA Security-Enhanced Linux (SELinux) is an implementation of a flexi-

ble mandatory access control architecture in the Linux operating sys-

tem. The SELinux architecture provides general support for the

enforcement of many kinds of mandatory access control policies, includ-

ing those based on the concepts of Type Enforcement®, Role- Based

Access Control, and Multi-Level Security.

The /etc/selinux/config configuration file controls whether SELinux is

enabled or disabled, and if enabled, whether SELinux operates in per-

missive mode or enforcing mode. The SELINUX variable may be set to any

one of disabled, permissive, or enforcing to select one of these

options. The disabled option completely disables the SELinux kernel

and application code, leaving the system running without any SELinux

protection. The permissive option enables the SELinux code, but causes

it to operate in a mode where accesses that would be denied by policy

are permitted but audited. The enforcing option enables the SELinux

code and causes it to enforce access denials as well as auditing them.

Permissive mode may yield a different set of denials than enforcing

mode, both because enforcing mode will prevent an operation from pro-

ceeding past the first denial and because some application code will

fall back to a less privileged mode of operation if denied access.

The /etc/selinux/config configuration file also controls what policy is

active on the system. SELinux allows for multiple policies to be

installed on the system, but only one policy may be active at any given

time. At present, two kinds of SELinux policy exist: targeted and

strict. The targeted policy is designed as a policy where most pro-

cesses operate without restrictions, and only specific services are

placed into distinct security domains that are confined by the policy.

For example, the user would run in a completely unconfined domain while

the named daemon or apache daemon would run in a specific domain tai-

lored to its operation. The strict policy is designed as a policy

where all processes are partitioned into fine-grained security domains

and confined by policy. It is anticipated in the future that other

policies will be created (Multi-Level Security for example). You can

define which policy you will run by setting the SELINUXTYPE environment

variable within /etc/selinux/config. The corresponding policy configu-

ration for each such policy must be installed in the

/etc/selinux/SELINUXTYPE/ directories.

A given SELinux policy can be customized further based on a set of com-

pile-time tunable options and a set of runtime policy booleans. sys-

tem-config-securitylevel allows customization of these booleans and

tunables.