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Getting Started

Setting up pam_usb requires the following, once pam_usb is installed:

  1. Set up devices and users
  2. Configuring PAM for system authentication
  3. (Optional) Configuring pamusb-agent to run programs when the device is inserted or removed

Setting up Devices and Users

Once you've connected your USB device to the computer, use pamusb-conf to add it to the configuration file:

# pamusb-conf --add-device MyDevice
Please select the device you wish to add.
* Using "SanDisk Corp. Cruzer Titanium (SNDKXXXXXXXXXXXXXXXX)" (only option)
Which volume would you like to use for storing data ?
* Using "/dev/sda1 (UUID: <6F6B-42FC>)" (only option)
Name            : MyDevice
Vendor          : SanDisk Corp.
Model           : Cruzer Titanium
Serial          : SNDKXXXXXXXXXXXXXXXX
Volume UUID     : 6F6B-42FC (/dev/sda1)
Save to /etc/pamusb.conf ?
[Y/n] y
Done.

Note that MyDevice can be any arbitrary name you'd like. Also, you can add as many devices as you want.

Next, configure users you want to be able to authenticate with pam_usb:

# pamusb-conf --add-user root      
Which device would you like to use for authentication ?
* Using "MyDevice" (only option)
User            : root
Device          : MyDevice
Save to /etc/pamusb.conf ?
[Y/n] y
Done.

Check the configuration

You can run pamusb-check anytime to check if everything is correctly worked. This tool will simulate an authentication request (requires your device to be connected, otherwise it will fail).

# pamusb-check root
* Authentication request for user "root" (pamusb-check)
* Device "MyDevice" is connected (good).
* Performing one time pad verification...
* Verification match, updating one time pads...
* Access granted.

Setting up the PAM module

To add pam_usb into the system authentication process, we need to edit /etc/pam.d/common-auth

NOTE: If you are using RedHat or Fedora this file can be known as /etc/pam/system-auth.

Your default PAM common-auth configuration should include the following line:

auth    required        pam_unix.so nullok_secure

This is a current standard which uses passwords to authenticate a user.

Alter your /etc/pam.d/common-auth configuration to:

auth    sufficient      pam_usb.so
auth    required        pam_unix.so nullok_secure

The sufficient keyword means that if pam_usb allows the authentication, then no password will be asked. If the authentication fails, then the default password-based authentication will be used as fallback.

If you change it to required, it means that both the USB flash drive and the password will be required to grant access to the system.

At this point, you should be able to authenticate with the relevant USB device plugged-in.

scox $ su
* pam_usb v.SVN
* Authentication request for user "root" (su)
* Device "MyDevice" is connected (good).
* Performing one time pad verification...
* Verification match, updating one time pads...
* Access granted.

Agent

The pam_usb agent (pamusb-agent) allows you to automatically execute commands upon locking and unlocking events. Those events are generated when you insert or remove your authentication device. To configure the commands, you have to edit pam_usb's configuration file (/etc/pamusb.conf) and add agent entries into your user section.

For instance, you could automatically start your screensaver as soon as you remove the device, and deactivate it when you plug the device back.

DBUS (FreeDesktop.org specification):

<user id="scox">
  <device>MyDevice</device>
  <agent event="lock">dbus-send --session --dest=org.freedesktop.ScreenSaver --type=method_call --print-reply /ScreenSaver org.freedesktop.ScreenSaver.Lock</agent>
  <agent event="unlock">dbus-send --session --dest=org.freedesktop.ScreenSaver --type=method_call --print-reply /ScreenSaver org.freedesktop.ScreenSaver.SetActive boolean:false</agent>
</user>

GNOME (gnome-screensaver):

<user id="scox">
  <device>MyDevice</device>
  <agent event="lock">gnome-screensaver-command --lock</agent>
  <agent event="unlock">gnome-screensaver-command --deactivate</agent>
</user>

KDE (kscreensaver):

<user id="scox">
  <device>MyDevice</device>
  <agent event="lock">dcop kdesktop KScreensaverIface lock</agent>
  <agent event="unlock">dcop kdesktop KScreensaverIface quit</agent>
</user>

You can execute more commands by adding extra <agent> entries.

$ pamusb-agent
pamusb-agent[18329]: pamusb-agent up and running.
pamusb-agent[18329]: Watching device "MyDevice" for user "scox"
pamusb-agent[18329]: Device "MyDevice" has been removed, locking down user
"scox"...
pamusb-agent[18329]: Running "gnome-screensaver-command --lock"
pamusb-agent[18329]: Locked.
pamusb-agent[18329]: Device "MyDevice" has been inserted. Performing
verification...
pamusb-agent[18329]: Executing "/usr/bin/pamusb-check --quiet
--config=/etc/pamusb.conf --service=pamusb-agent scox"
pamusb-agent[18329]: Authentication succeeded. Unlocking user "scox"...
pamusb-agent[18329]: Running "gnome-screensaver-command --deactivate"
pamusb-agent[18329]: Unlocked.

Depending on your desktop environment, you have to add pamusb-agent to the list of autostarted applications so it will be started automatically.

GNOME:

  • Open System -> Preferences -> Sessions
  • Select Startup Programs and press Add
  • Enter pamusb-agent and press OK
  • Press Close

KDE:

cd ~/.kde/Autostart
ln -s /usr/bin/pamusb-agent pamusb-agent

Fine Tuning

There are many options available configure pam_usb.

Check out the configuration reference.

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