I wish to change selinux mode from permissive to enforcing on ubuntu 12.04 LTS.
i edit the /etc/selinux/config file .
Original file content:

# 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:
# default - equivalent to the old strict and targeted policies
# mls - Multi-Level Security (for military and educational use)
# src - Custom policy built from source
SELINUXTYPE=ubuntu

# SETLOCALDEFS= Check local definition changes
SETLOCALDEFS=0


After i change it:

# 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:
# default - equivalent to the old strict and targeted policies
# mls - Multi-Level Security (for military and educational use)
# src - Custom policy built from source
SELINUXTYPE=targeted

# SETLOCALDEFS= Check local definition changes
SETLOCALDEFS=0

Basically i change permissive to enforcing and ubuntu to targeted. But when i reboot after this ubuntu doesn't boot. All i get is a blank screen.
I then have to boot in the recovery mode and reedit the file to its original contents to boot into ubuntu normally again.

Hi Alan,

Sorry for replying late, also I'm not a SELinux expert.

When,

SELINUX=permissive

Have you check the audit log file to see what are the denied? if the system boots in SELINUX=permissive mode, you might have the denied in the log file and you can find out what is causing the problem.