Think of SELinux as a glorified labeling system. It adds labels, known as security contexts, to files and directories through extended file attributes. It also adds the same type of label, known as domains, to system processes. To see these contexts and domains on your CentOS machines, use the -Z option with either ls or ps. For example, files and directories in my own home directory would look like the following:
[donnie@localhost ~]$ ls -Z
drwxrwxr-x. donnie donnie unconfined_u:object_r:user_home_t:s0 acl_demo_dir
-rw-rw-r--. donnie donnie unconfined_u:object_r:user_home_t:s0 yum_list.txt
[donnie@localhost ~]$
Processes on my system would look something like the following:
[donnie@localhost ~]$ ps -Z
LABEL PID TTY TIME CMD
unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 1322 pts/0 00:00...