polkit (formerly PolicyKit) is an authorization API intended to be used by privileged programs (e.g. system daemons) offering services to unprivileged programs.
Privileged programs (in the following called daemons) with polkit support offload the decision as to whether a program is allowed to use some function of the daemon. The daemon keeps an incoming request on hold, asks polkit if the program is authorized, and then allows or denies the request based on polkit's return. The requesting program is not aware of polkit and so needs no polkit support itself. The communication is handled over D-Bus.
Daemons come with polkit action files, which offer some function and define who is authorized. This can be any user, either the active or inactive user. Also they can specify that the user needs to authenticate by entering a password as himself or as admin. These actions do not grant root permission to an entire process, but rather allows a finer level of control of centralized system policy.
The authorization defaults defined by the action files can be refined by rules files. Here you can define who's admin (root or any user in a special group) and add special handling for an action.
The USE flags of policykit are:
|examples||No||Install examples, usually source code|
|gtk||Yes||Adds support for x11-libs/gtk+ (The GIMP Toolkit)|
|introspection||Yes||Use dev-libs/gobject-introspection for introspection|
|kde||Yes||Adds support for KDE (K Desktop Environment)|
|nls||Yes||Adds Native Language Support (using gettext - GNU locale utilities)|
|pam||Yes||Adds support for PAM (Pluggable Authentication Modules) - DANGEROUS to arbitrarily flip|
|selinux||No||!!internal use only!! Security Enhanced Linux support, this must be set by the selinux profile or breakage will occur|
|systemd||No||Use sys-apps/systemd instead of sys-auth/consolekit for session tracking|
After setting this you want to update your system so the changes take effect:
The actions files are in /usr/share/polkit-1/actions, the rules files are in /usr/share/polkit-1/rules.d and /etc/polkit-1/rules.d.
Rules redefine who's authorized for an action. The rules files begin with a number and are processed in lexical order. The first file with a matching rule is used. Own files should have a low number, like 10. The filenames have the .rules suffix.
For example, to let the users of the "wheel" group also perform functions as administrators, create the following file:
To allow user "larry" to mount disks, create the following file:
See the polkit man page for more information.
If you installed KDE with the policykit USE flag, there are system settings modules in the "System Administration" section:
- Actions Policy: Rules configuration.
- Global Policy Configuration: Administrator configuration.
- Show all available actions:
- Show details about the given action:
- List all temporary authorizations for the current session:
- Runs the given program with the user rights of the given user:
For more information see the man pages, e.g. for pkaction: man pkaction