linux: added fingerprint readers on linux

wiki/linux/fingerprint_reader.md

@@ -0,0 +1,126 @@
+# Fingerprint Reader
+
+Fingerprint readers can be used for local authentication on
+[Linux](/wiki/linux.md) systems.
+
+## Setup
+
+Support for most fingerprint reader devices is provided by the `libfprint` library and the
+`fprintd` daemon, which in turn need to be installed.
+Many [Linux](/wiki/linux.md) distributions package both components directly under this name.
+
+After installation restart the daemon.
+
+```sh
+sudo systemctl restart fprintd
+```
+
+By default enrolling fingerprints may require administrative privileges.
+This can be changed using a `polkit` rule that allows members of the `wheel` group to enroll
+fingerprints without using `sudo`.
+
+Create the file `/etc/polkit-1/rules.d/49-fprint.rules`.
+
+```sh
+sudo vim /etc/polkit-1/rules.d/49-fprint.rules
+```
+
+Insert the following rule.
+
+```txt
+polkit.addRule(function(action, subject) {
+    if (action.id == "net.reactivated.fprint.device.enroll" &&
+        subject.isInGroup("wheel")) {
+        return polkit.Result.YES;
+    }
+});
+```
+
+## Usage
+
+This section addresses the usage of fingerprint readers.
+
+### Enrolling a Fingerprint
+
+A fingerprint can be registered using the following command.
+
+```sh
+fprintd-enroll
+```
+
+The program will repeatedly ask to place a finger on the reader until the fingerprint has been
+successfully recorded.
+
+### Listing Stored Fingerprints
+
+Stored fingerprints of the current user can be displayed with the following command.
+`<user>` describes the username to list fingerprints for.
+
+```sh
+fprintd-list <user>
+```
+
+Fingerprints of other users can be inspected using administrative privileges.
+
+```sh
+sudo fprintd-list root
+```
+
+### Removing Fingerprints
+
+Fingerprints can be deleted using `fprintd-delete`.
+The following displays the removal of a finger called `<finger>` (for example `right-index-finger`)
+for a user called `<user>`.
+
+```sh
+sudo fprintd-delete <user> <finger>
+```
+
+### Using Fingerprints with `sudo`
+
+Fingerprint authentication can be used with `sudo` through PAM.
+
+Edit the configuration file.
+
+```sh
+sudo vim /etc/pam.d/sudo
+```
+
+Add the following line near the top of the file.
+The line should be placed near the top of the file so that fingerprint authentication is attempted
+before password authentication.
+
+```txt
+auth sufficient pam_fprintd.so
+```
+
+With this configuration the fingerprint reader can be used for `sudo` authentication while the
+password remains available as a fallback.
+
+## Troubleshooting
+
+This section will focus on errors and the fixing of errors of fingerprint readers.
+
+### Permission denied when enrolling fingerprints
+
+When attempting to enroll a fingerprint the following error may occur:
+
+```txt
+EnrollStart failed: GDBus.Error:net.reactivated.Fprint.Error.PermissionDenied:
+Not Authorized: net.reactivated.fprint.device.enroll
+```
+
+In this case `fprintd` requires elevated privileges to enroll fingerprints.
+
+The issue can be solved by creating a `polkit` rule which allows members of the `wheel` group to
+enroll fingerprints.
+
+In this case the polkit rule `/etc/polkit-1/rules.d/49-fprint.rules` most likely was not set as
+described in the [setup section](#setup).
+
+After adding the rule the error should vanish.
+The rule fingerprint enrollment can then be executed without `sudo`.
+
+```sh
+fprintd-enroll
+```

wiki/linux/hardware_(linux).md

@@ -1,9 +1,9 @@
 # Hardware (Linux)
 
-This entry focusses on various hardware components of a [Linux](/wiki/linux.md) desktop PC or a
+This entry focuses on various hardware components of a [Linux](/wiki/linux.md) desktop PC or a
 laptop.
 For non-Linux specific or general topics in hardware see the
-[correspoding entry](/wiki/hardware_%28general%29.md)
+[corresponding entry](/wiki/hardware_%28general%29.md)
 
 ## Battery
 
@@ -11,22 +11,22 @@ The battery of a notebook can be inspected by using the `upower` command.
 To use it the tool needs to be installed.
 In most [Linux](/wiki/linux.md) distributions this is bundled in a package of the same name.
 
-This section is based on [a video by eKiwi](https://youtu.be/t9KMFDTb79E) which addresses battery
-health.
+This section is based on [a YouTube video by the user eKiwi](https://youtu.be/t9KMFDTb79E) which
+addresses battery health.
 
-To find out about a battery, its name needs to be known, which can be done using the following
+To find out about a battery, its name needs to be known which can be done using the following
 command.
 
 ```sh
 upower -e
 ```
 
-Afterwards different values like the state, voltage, percentage and many other can be displayed.
-Additionally it will show the original capacity (`energy-full-design`) and the current capacity
+Afterward different values like the state, voltage, percentage and much other can be displayed.
+Additionally, it will show the original capacity (`energy-full-design`) and the current capacity
 (`energy-full`), which can be used to determine the health of the battery.
 The following is an example command where `<battery-name>` is the name of the batter returned from
 the previous step.
-This might by similar to `/org/freedesktop/UPower/devices/battery_BAT0`.
+This might be similar to `/org/freedesktop/UPower/devices/battery_BAT0`.
 
 ```sh
 upower -i <battery-name>
@@ -62,7 +62,7 @@ like the RPM for fans.
 This section is based on a
 [Reddit comment by zedbraxmen](https://www.reddit.com/r/thinkpad/comments/wjb8qz/configuring_trackpoint_in_wayland/).
 
-The sensitivity and speed of the classic trackpoint on ThinkPads can be changed using UDEV rules.
+The sensitivity and speed of the classic TrackPoint on ThinkPads can be changed using UDEV rules.
 The following lines are an example for a potential file `.rules` located at `/etc/udev/rules.d/`.
 It could look something like the following.
 The values for sensitivity and speed could be adjusted.
@@ -74,3 +74,10 @@ ATTR{name}=="TPPS/2 IBM TrackPoint",
 ATTR{device/sensitivity}="275",
 ATTR{device/speed}="215",
 ```
+
+## Fingerprint Readers
+
+Many modern laptops include fingerprint sensors which can be used for authentication on
+[Linux](/wiki/linux.md).
+Setup and usage is described in the
+[entry regarding fingerprint reader](/wiki/linux/fingerprint_reader.md).