Accessing SELinux policy documentation
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There are many excellent man pages for the confined domains included with SELinux policy. These man pages describe booleans and context types for each domain. They also include sample
semanage commands for adding context mappings, changing booleans, and more.
Unfortunately for the sysadmin getting started with SELinux configuration, these man pages are often not installed by default. The SELinux policy man pages are available from two locations. The upstream Reference Policy repo has a handful of pre-built man pages. The rest can be generated from the policy content with a tool found in the
Install from a distribution package
Some distributions pre-generate the man pages and package them to make the documentation easy to add to your system. Fedora, CentOS, and Red Hat Enterprise Linux 8 all include an
selinux-policy-doc.noarch package in their base repositories. This package is not installed by default, but is easy to add with a
$ sudo yum install selinux-policy-doc.noarch
Red Hat Enterprise Linux 7 has this package as well, but it is in the "Optional" repo which is not enabled by default. Either enable the repo permanently with
$ sudo subscription-manager repo --enable=rhel-7-server-optional-rpms
or just add the repo temporarily during the installation:
$ sudo yum --enablerepo=rhel-7-server-optional-rpms install selinux-policy-doc.noarch
Now that the SELinux domain documentation is available, search for the relevant pages with:
$ man -k _selinux
Note: After installing the docs package you may also need to update the man page index cache before seeing the results from search:
$ sudo mandb
Generate man pages from the policy
If the docs package is not available, or if you only want to generate a man page for a specific domain, you can also build the man pages from the policy. First, install the
devel packages and their dependencies:
$ sudo yum install policycoreutils-devel
Then, use the
sepolicy command to generate a specific man page by specifying the domain type (the SELinux context type associated with the running process that is being contained). For example:
$ sepolicy manpage -d httpd_t
The resulting man page will be generated in the
/tmp directory and can be viewed by name:
$ man /tmp/httpd_selinux.8
There are options for the
sepolicy manpage command to override the output location (
--path), generate an html version (
--web), or generate all (
--all) pages. To see these and other options, use:
$ man sepolicy-manpage
As long as a user has write privileges to the output path, they can generate and view a man page.
Preview the magic of these man pages
The SELinux man pages for domain types all have a common layout. As with any set of man pages, the more man pages you read, the easier it is to scan or speed read the next one.
Each man page starts with the expected NAME and DESCRIPTION fields of any man page. The SELinux domain man pages then include the sections ENTRYPOINTS and PROCESS TYPES. (Entrypoints are the types assigned to the executable files, which when launched as daemons transition to the confined process types.)
Not all process types are daemons though, some may be interactive executables. For example,
sshd_exec_t is an entrypoint which transitions to the
sshd_t process type. In addition,
ssh_keygen_t and are also examples of process types.
Process types are also known as domain types and are the types that can be placed into permissive mode with the
After any entrypoint and process type sections, the SELinux domain man page has sections for any BOOLEANS, PORT TYPES, MANAGED FILES, and FILE CONTEXTS that apply to that domain. These sections define keywords and provide samples for modifications that can be made with the
semanage command. Enabling a boolean allows a different rule set for different use cases. File and port context modifications allow a system to be configured to hold data in a non-default location or run on a non-default port.
Each man page ends with a list of COMMANDS referenced in the man page and the traditional man page AUTHOR and SEE ALSO sections.
targeted policy, the
httpd domain page is probably the longest, since that domain has the most booleans and file types to describe. It was also one of the first domains confined in the history of the SELinux
Start with a domain that is familiar to you such as
ntpd. Then search for domains that are relevant to your environment. After installing the
selinux-docs package, I have over 850 man pages to explore on my system!
And remember, keep SELinux enforcing! (Here's how.)