Linux Platform Security: Practical Tools and Methods

This page contains course information for students taking the SELinux short course, offered September 16 and 18, 2014 through Merit. This information will be available before and during the course.

Hints and Tips

• Connect the network

  CentOS by default starts user sessions with the network disconnected. To connect your session to the network, click the network icon on the upper right of your guest's (not the host's) screen and set the wired network's System entry to "On."

• VMware Tools

If cut/paste into or out of the virtual lab environment's window doesn't seem to work, or the desktop wallpaper doesn't redraw to fill the window after you resize it, try one or more of these:

1. Manually start /usr/bin/vmware-user
2. Log out and log back into your desktop session; and,
3. Restart your X session.
• Screensaver timeout

  To lengthen your virtual lab environment's screensaver timeout, visit System | Preferences | Screensaver and adjust the "Regard the computer as idle after" value.

• Screen resolution

  To increase the virtual lab environment's screen resolution from 1280x768, visit System | Preferences | Display, and choose the desired resolution from the dropdown list.

• Default terminal window attributes

  To change terminal default attributes such as the window size or the character size:

  1. Start a terminal window (by selecting Applications | System Tools | Terminal).
  2. Select Edit | Profile Preferences from the terminal window menubar to pop up the default terminal profile.
  3. In the profile editing window popup, under the General tab, to change the default text size, uncheck the "Use the system fixed width font" checkbox, then select the Monospace font and the desired point size.
  4. Similarly, to change the default terminal window size, check the "Use custom default terminal size" checkbox and set the desired number of rows and columns.
  5. Click Close to close the profile.
• NAT vs. Bridged VMware guest

  As shipped, the virtual lab environment shares your host platform's network connection by using a NAT service running on your host platform. While this is the most scalable and unobtrusive way to run a VMware guest, some operations will not work as expected, such as traceroute commands. To switch your guest over to bridged mode, in which it obtains a network address via DHCP directly from the same network provider that your host platform uses, follow these steps:

  1. Click on the <...> symbol at the top or bottom of your host's (not the guest's) screen, or look under Network Adapter in your host's VM Settings menu.
  2. Select the Bridged option.
  3. Wait for the network icon on the upper right of your guest's screen to disconnect and re-connect.
  4. Sometimes the network icon will not re-connect, but will continue to show as disconnected (small red X). In this case, click the network icon and manually set the wired network's System entry to "On."

• Boot into the BIOS

  To enter the VMware guest's BIOS, say for changing boot devices, you'll need to hit F2 at the right time during boot. This is often difficult to do reliably, so use the following strategy instead:

  1. Add the following line to the end of your .vmx file:
     bios.forceSetupOnce = "TRUE"
  2. Boot up your virtual lab environment. You'll see a conventional BIOS screen, from which you can make BIOS-level changes and boot your guest.
     Note: VMware will change the value of this option to FALSE in your .vmx file after a successful boot. This means you'll need to re-enable this trigger each time you want to use it.

• Change password hashing algorithm

  To change your virtual lab environment's password hashing algorithm from SHA512 to MD5, change the string "sha512" to "md5" in /etc/pam.d/system-auth. Any passwords you set or modify after this change has been made will use the new hashing algorithm; existing password hashes are not affected.
  Note: MD5 is a weaker hashing algorithm than SHA-512 and should not be used except in designated experiments in this course.

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