updated 'Keep system updated'; TOC

- signed-off-by: trimstray <trimstray@gmail.com>

README.md

@@ -93,6 +93,9 @@
     + [Disk quotas](lib/post_install_tasks/disk_partitions.md#eight_pointed_black_star-disk-quotas)
     + [Summary checklist](lib/post_install_tasks/disk_partitions.md#ballot_box_with_check-summary-checklist)
   * **[Keep system updated](#keep-system-updated)**
+    + [Introduction](lib/post_install_tasks/keep_system_updated.md#information_source-introduction)
+    + [Make sure that the system is up to date](lib/post_install_tasks/keep_system_updated.md#eight_pointed_black_star-make-sure-that-the-system-is-up-to-date)
+    + [Summary checklist](lib/post_install_tasks/keep_system_updated.md#ballot_box_with_check-summary-checklist)
   * **[Package management](#package-management)**
     + [Automatic security updates](#automatic-security-updates)
     + [Remove packages with known issues](#remove-packages-with-known-issues)

lib/post_install_tasks/keep_system_updated.md

@@ -0,0 +1,54 @@
+## Post install tasks
+
+### Keep system updated
+
+#### :information_source: Introduction
+
+Software updates offer plenty of benefits. It’s all about revisions. These might include repairing security holes that have been discovered and fixing or removing computer bugs.
+
+Some benefits:
+
+- close up problems of security that has been discovered
+- it can improve the stability of the system
+- improvements the system stacks, e.g. network stack
+
+#### :eight_pointed_black_star: Make sure that the system is up to date
+
+For CentOS:
+
+```bash
+# Check for updates
+yum check-update
+
+# Install updates
+yum update
+```
+
+For Debian:
+
+```bash
+# Check for updates
+apt-get update -qq ; apt-get upgrade -duyq
+
+# Install updates
+apt-get upgrade && apt-get dist-upgrade
+```
+
+###### Useful resources
+
+- [How Often Should I Update our Linux Server?](https://serverfault.com/questions/9490/how-often-should-i-update-our-linux-server)
+
+###### Policies
+
+| <b><u>Policy</u></b> | <b><u>ID/Description</u></b> | <b><u>Severity</u></b> |
+| :---         | :---         |
+| <b>STIG</b> | [V-71999](https://www.stigviewer.com/stig/red_hat_enterprise_linux_7/2017-12-14/finding/V-71999) | Severity: <b>Medium</b> |
+| <b>CIS</b> | 1.2, 1.8 |  |
+| <b>OpenSCAP</b> | CCI-002605, CCI-002607 | CAT II |
+
+#### :ballot_box_with_check: Summary checklist
+
+| <b>Item</b> | <b>True</b> | <b>False</b> |
+| :---        | :---:       | :---:        |
+| Regulary update your system | :black_square_button: | :black_square_button: |
+| Automatic check system updates | :black_square_button: | :black_square_button: |