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Chapter 2. Changing SELinux states and modes
When enabled, SELinux can run in one of two modes: enforcing or permissive. The following sections show how to permanently change into these modes.
2.1. Permanent changes in SELinux states and modes
As discussed in SELinux states and modes, SELinux can be enabled or disabled. When enabled, SELinux has two modes: enforcing and permissive.
Use the getenforce
or sestatus
commands to check in which mode SELinux is running. The getenforce
command returns Enforcing
, Permissive
, or Disabled
.
The sestatus
command returns the SELinux status and the SELinux policy being used:
$ sestatus
SELinux status: enabled
SELinuxfs mount: /sys/fs/selinux
SELinux root directory: /etc/selinux
Loaded policy name: targeted
Current mode: enforcing
Mode from config file: enforcing
Policy MLS status: enabled
Policy deny_unknown status: allowed
Memory protection checking: actual (secure)
Max kernel policy version: 31
When systems run SELinux in permissive mode, users and processes might label various file-system objects incorrectly. File-system objects created while SELinux is disabled are not labeled at all. This behavior causes problems when changing to enforcing mode because SELinux relies on correct labels of file-system objects.
To prevent incorrectly labeled and unlabeled files from causing problems, SELinux automatically relabels file systems when changing from the disabled state to permissive or enforcing mode. Use the fixfiles -F onboot
command as root to create the /.autorelabel
file containing the -F
option to ensure that files are relabeled upon next reboot.
Before rebooting the system for relabeling, make sure the system will boot in permissive mode, for example by using the enforcing=0
kernel option. This prevents the system from failing to boot in case the system contains unlabeled files required by systemd
before launching the selinux-autorelabel
service. For more information, see RHBZ#2021835.
2.2. Changing SELinux to permissive mode
When SELinux is running in permissive mode, SELinux policy is not enforced. The system remains operational and SELinux does not deny any operations but only logs AVC messages, which can be then used for troubleshooting, debugging, and SELinux policy improvements. Each AVC is logged only once in this case.
Prerequisites
-
The
selinux-policy-targeted
,libselinux-utils
, andpolicycoreutils
packages are installed on your system. -
The
selinux=0
orenforcing=0
kernel parameters are not used.
Procedure
Open the
/etc/selinux/config
file in a text editor of your choice, for example:# vi /etc/selinux/config
Configure the
SELINUX=permissive
option:# This file controls the state of SELinux on the system. # SELINUX= can take one of these three values: # enforcing - SELinux security policy is enforced. # permissive - SELinux prints warnings instead of enforcing. # disabled - No SELinux policy is loaded. SELINUX=permissive # SELINUXTYPE= can take one of these two values: # targeted - Targeted processes are protected, # mls - Multi Level Security protection. SELINUXTYPE=targeted
Restart the system:
# reboot
Verification
After the system restarts, confirm that the
getenforce
command returnsPermissive
:$ getenforce Permissive
2.3. Changing SELinux to enforcing mode
When SELinux is running in enforcing mode, it enforces the SELinux policy and denies access based on SELinux policy rules. In RHEL, enforcing mode is enabled by default when the system was initially installed with SELinux.
Prerequisites
-
The
selinux-policy-targeted
,libselinux-utils
, andpolicycoreutils
packages are installed on your system. -
The
selinux=0
orenforcing=0
kernel parameters are not used.
Procedure
Open the
/etc/selinux/config
file in a text editor of your choice, for example:# vi /etc/selinux/config
Configure the
SELINUX=enforcing
option:# This file controls the state of SELinux on the system. # SELINUX= can take one of these three values: # enforcing - SELinux security policy is enforced. # permissive - SELinux prints warnings instead of enforcing. # disabled - No SELinux policy is loaded. SELINUX=enforcing # SELINUXTYPE= can take one of these two values: # targeted - Targeted processes are protected, # mls - Multi Level Security protection. SELINUXTYPE=targeted
Save the change, and restart the system:
# reboot
On the next boot, SELinux relabels all the files and directories within the system and adds SELinux context for files and directories that were created when SELinux was disabled.
Verification
After the system restarts, confirm that the
getenforce
command returnsEnforcing
:$ getenforce Enforcing
Troubleshooting
After changing to enforcing mode, SELinux may deny some actions because of incorrect or missing SELinux policy rules.
To view what actions SELinux denies, enter the following command as root:
# ausearch -m AVC,USER_AVC,SELINUX_ERR,USER_SELINUX_ERR -ts today
Alternatively, with the
setroubleshoot-server
package installed, enter:# grep "SELinux is preventing" /var/log/messages
If SELinux is active and the Audit daemon (
auditd
) is not running on your system, then search for certain SELinux messages in the output of thedmesg
command:# dmesg | grep -i -e type=1300 -e type=1400
See Troubleshooting problems related to SELinux for more information.
2.4. Enabling SELinux on systems that previously had it disabled
To avoid problems, such as systems unable to boot or process failures, when enabling SELinux on systems that previously had it disabled, resolve Access Vector Cache (AVC) messages in permissive mode first.
When systems run SELinux in permissive mode, users and processes might label various file-system objects incorrectly. File-system objects created while SELinux is disabled are not labeled at all. This behavior causes problems when changing to enforcing mode because SELinux relies on correct labels of file-system objects.
To prevent incorrectly labeled and unlabeled files from causing problems, SELinux automatically relabels file systems when changing from the disabled state to permissive or enforcing mode.
Before rebooting the system for relabeling, make sure the system will boot in permissive mode, for example by using the enforcing=0
kernel option. This prevents the system from failing to boot in case the system contains unlabeled files required by systemd
before launching the selinux-autorelabel
service. For more information, see RHBZ#2021835.
Procedure
- Enable SELinux in permissive mode. For more information, see Changing to permissive mode.
Restart your system:
# reboot
- Check for SELinux denial messages. For more information, see Identifying SELinux denials.
Ensure that files are relabeled upon the next reboot:
# fixfiles -F onboot
This creates the
/.autorelabel
file containing the-F
option.WarningAlways switch to permissive mode before entering the
fixfiles -F onboot
command.By default,
autorelabel
uses as many threads in parallel as the system has available CPU cores. To use only a single thread during automatic relabeling, use thefixfiles -T 1 onboot
command.- If there are no denials, switch to enforcing mode. For more information, see Changing SELinux modes at boot time.
Verification
After the system restarts, confirm that the
getenforce
command returnsEnforcing
:$ getenforce Enforcing
Next steps
To run custom applications with SELinux in enforcing mode, choose one of the following scenarios:
-
Run your application in the
unconfined_service_t
domain. - Write a new policy for your application. See the Writing a custom SELinux policy section for more information.
Additional resources
- SELinux states and modes section covers temporary changes in modes.
2.5. Disabling SELinux
When you disable SELinux, your system does not load your SELinux policy. As a result, the system does not enforce the SELinux policy and does not log Access Vector Cache (AVC) messages. Therefore, all benefits of running SELinux are lost.
Do not disable SELinux except in specific scenarios, such as performance-sensitive systems where the weakened security does not impose significant risks.
If your scenario requires to perform debugging in a production environment, temporarily use permissive mode instead of permanently disabling SELinux. See Changing to permissive mode for more information about permissive mode.
Prerequisites
The
grubby
package is installed:$ rpm -q grubby grubby-<version>
Procedure
Configure your boot loader to add
selinux=0
to the kernel command line:$ sudo grubby --update-kernel ALL --args selinux=0
Restart your system:
$ reboot
Verification
After the reboot, confirm that the
getenforce
command returnsDisabled
:$ getenforce Disabled
Alternative method
In RHEL 8, you can still use the deprecated method for disabling SELinux by using the SELINUX=disabled
option in the /etc/selinux/config
file. This results the kernel booting with SELinux enabled and switching to disabled mode later in the boot process. Consequently, memory leaks and race conditions might occur that cause kernel panics. To use this method:
Open the
/etc/selinux/config
file in a text editor of your choice, for example:# vi /etc/selinux/config
Configure the
SELINUX=disabled
option:# This file controls the state of SELinux on the system. # SELINUX= can take one of these three values: # enforcing - SELinux security policy is enforced. # permissive - SELinux prints warnings instead of enforcing. # disabled - No SELinux policy is loaded. SELINUX=disabled # SELINUXTYPE= can take one of these two values: # targeted - Targeted processes are protected, # mls - Multi Level Security protection. SELINUXTYPE=targeted
Save the change, and restart your system:
# reboot
2.6. Changing SELinux modes at boot time
On boot, you can set the following kernel parameters to change the way SELinux runs:
- enforcing=0
Setting this parameter causes the system to start in permissive mode, which is useful when troubleshooting issues. Using permissive mode might be the only option to detect a problem if your file system is too corrupted. Moreover, in permissive mode, the system continues to create the labels correctly. The AVC messages that are created in this mode can be different than in enforcing mode.
In permissive mode, only the first denial from a series of the same denials is reported. However, in enforcing mode, you might get a denial related to reading a directory, and an application stops. In permissive mode, you get the same AVC message, but the application continues reading files in the directory and you get an AVC for each denial in addition.
- selinux=0
This parameter causes the kernel to not load any part of the SELinux infrastructure. The init scripts notice that the system booted with the
selinux=0
parameter and touch the/.autorelabel
file. This causes the system to automatically relabel the next time you boot with SELinux enabled.ImportantDo not use the
selinux=0
parameter in a production environment. To debug your system, temporarily use permissive mode instead of disabling SELinux.- autorelabel=1
This parameter forces the system to relabel similarly to the following commands:
# touch /.autorelabel # reboot
If a file system contains a large amount of mislabeled objects, start the system in permissive mode to make the autorelabel process successful.
Additional resources
For additional SELinux-related kernel boot parameters, such as
checkreqprot
, see the/usr/share/doc/kernel-doc-<KERNEL_VER>/Documentation/admin-guide/kernel-parameters.txt
file installed with thekernel-doc
package. Replace the <KERNEL_VER> string with the version number of the installed kernel, for example:# yum install kernel-doc $ less /usr/share/doc/kernel-doc-4.18.0/Documentation/admin-guide/kernel-parameters.txt