Provided by: policykit-1_0.105-20ubuntu0.18.04.6_amd64 
NAME
polkit - Authorization Framework
OVERVIEW
PolicyKit provides an authorization API intended to be used by privileged programs
(“MECHANISMS”) offering service to unprivileged programs (“CLIENTS”) through some form of
IPC mechanism such as D-Bus or Unix pipes. In this scenario, the mechanism typically
treats the client as untrusted. For every request from a client, the mechanism needs to
determine if the request is authorized or if it should refuse to service the client. Using
the PolicyKit API, a mechanism can offload this decision to a trusted party: The PolicyKit
Authority.
In addition to acting as an authority, PolicyKit allows users to obtain temporary
authorization through authenticating either an administrative user or the owner of the
session the client belongs to. This is useful for scenarios where a mechanism needs to
verify that the operator of the system really is the user or really is an administrative
user.
SYSTEM ARCHITECTURE
The system architecture of PolicyKit is comprised of the Authority (implemented as a
service on the system message bus) and a Authentication Agent per user session (provided
and started by the user session e.g. GNOME or KDE). Additionally, PolicyKit supports a
number of extension points – specifically, vendors and/or sites can write extensions to
completely control authorization policy. In a block diagram, the architecture looks like
this:
[IMAGE][1]
+-------------------+
| Authentication |
| Agent |
+-------------------+
| libpolkit-agent-1 |
+-------------------+
^ +--------+
| | Client |
+--------------+ +--------+
| ^
| |
User Session | |
=======================|========================|=============
System Context | |
| |
| +---+
V |
/------------\ |
| System Bus | |
\------------/ |
^ ^ V
| | +---------------------+
+--------------+ | | Mechanism |
| | +---------------------+
V +----> | libpolkit-gobject-1 |
+------------------+ +---------------------+
| org.freedesktop. |
| PolicyKit1 |
+------------------+
| Backends and |
| Extensions |
+------------------+
For convenience, the libpolkit-gobject-1 library wraps the PolicyKit D-Bus API using
GObject. However, a mechanism can also use the D-Bus API or the pkcheck(1) command to
check authorizations.
The libpolkit-agent-1 library provides an abstraction of the native authentication system,
e.g. pam(8) and also facilities registration and communication with the PolicyKit D-Bus
service.
PolicyKit extensions and authority backends are implemented using the libpolkit-backend-1
library.
See the developer documentation[2] for more information about using and extending
PolicyKit.
See pklocalauthority(8) for information about the Local Authority - the default authority
implementation shipped with PolicyKit.
AUTHENTICATION AGENTS
An authentication agent is used to make the user of a session prove that the user of the
session really is the user (by authenticating as the user) or an administrative user (by
authenticating as a administrator). In order to integrate well with the rest of the user
session (e.g. match the look and feel), authentication agents are meant to be provided by
the user session that the user uses. For example, an authentication agent may look like
this:
[IMAGE][3]
+----------------------------------------------------------+
| Authenticate [X] |
+----------------------------------------------------------+
| |
| [Icon] Authentication is required to run ATA SMART |
| self tests |
| |
| An application is attempting to perform an |
| action that requires privileges. Authentication |
| as the super user is required to perform this |
| action. |
| |
| Password for root: [_________________________] |
| |
| [V] Details: |
| Drive: ATA INTEL SSDSA2MH08 (045C) |
| Device: /dev/sda |
| Action: org.fd.devicekit.disks.drive-ata-smart-selftest |
| Vendor: The DeviceKit Project |
| |
| [Cancel] [Authenticate] |
+----------------------------------------------------------+
If the system is configured without a root account it may allow you to select the
administrative user who is authenticating:
[IMAGE][4]
+----------------------------------------------------------+
| Authenticate [X] |
+----------------------------------------------------------+
| |
| [Icon] Authentication is required to run ATA SMART |
| self tests |
| |
| An application is attempting to perform an |
| action that requires privileges. Authentication |
| as one of the users below is required to |
| perform this action. |
| |
| [[Face] Patrick Bateman (bateman) [V]] |
| |
| Password for bateman: [______________________] |
| |
| [V] Details: |
| Drive: ATA INTEL SSDSA2MH08 (045C) |
| Device: /dev/sda |
| Action: org.fd.devicekit.disks.drive-ata-smart-selftest |
| Vendor: The DeviceKit Project |
| |
| [Cancel] [Authenticate] |
+----------------------------------------------------------+
See pklocalauthority(8) on how to set up the local authority implemention for systems
without a root account.
Applications that do not run under a desktop environment (for example, if launched from a
ssh(1) login) may not have have an authentication agent associated with them. Such
applications may use the PolkitAgentTextListener type or the pkttyagent(1) helper so the
user can authenticate using a textual interface.
DECLARING ACTIONS
A mechanism need to declare a set of “ACTIONS” in order to use PolicyKit. Actions
correspond to operations that clients can request the mechanism to carry out and are
defined in XML files that the mechanism installs into the /usr/share/polkit-1/actions
directory.
PolicyKit actions are namespaced and can only contain the characters [a-z][0-9].- e.g.
lower-case ASCII, digits, period and hyphen. Each XML file can contain more than one
action but all actions need to be in the same namespace and the file needs to be named
after the namespace and have the extension .policy.
The XML file must have the following doctype declaration
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE policyconfig PUBLIC "-//freedesktop//DTD PolicyKit Policy Configuration 1.0//EN"
"http://www.freedesktop.org/standards/PolicyKit/1.0/policyconfig.dtd">
The policyconfig element must be present exactly once. Elements that can be used inside
policyconfig includes:
vendor
The name of the project or vendor that is supplying the actions in the XML document.
Optional.
vendor_url
A URL to the project or vendor that is supplying the actions in the XML document.
Optional.
icon_name
An icon representing the project or vendor that is supplying the actions in the XML
document. The icon name must adhere to the Freedesktop.org Icon Naming
Specification[5]. Optional.
action
Declares an action. The action name is specified using the id attribute and can only
contain the characters [a-z][0-9].- e.g. lower-case ASCII, digits, period and hyphen.
Elements that can be used inside action includes:
description
A human readable description of the action, e.g. “Install unsigned software”.
message
A human readable message displayed to the user when asking for credentials when
authentication is needed, e.g. “Installing unsigned software requires
authentication”.
defaults
This element is used to specify implicit authorizations for clients.
Elements that can be used inside defaults includes:
allow_any
Implicit authorizations that apply to any client. Optional.
allow_inactive
Implicit authorizations that apply to clients in inactive sessions on local
consoles. Optional.
allow_active
Implicit authorizations that apply to clients in active sessions on local
consoles. Optional.
Each of the allow_any, allow_inactive and allow_active elements can contain the
following values:
no
Not authorized.
yes
Authorized.
auth_self
Authentication by the owner of the session that the client originates from is
required.
auth_admin
Authentication by an administrative user is required.
auth_self_keep
Like auth_self but the authorization is kept for a brief period.
auth_admin_keep
Like auth_admin but the authorization is kept for a brief period.
annotate
Used for annotating an action with a key/value pair. The key is specified using the
the key attribute and the value is specified using the value attribute. This element
may appear zero or more times. See below for known annotations.
vendor
Used for overriding the vendor on a per-action basis. Optional.
vendor_url
Used for overriding the vendor URL on a per-action basis. Optional.
icon_name
Used for overriding the icon name on a per-action basis. Optional.
For localization, description and message elements may occur multiple times with different
xml:lang attributes.
To list installed PolicyKit actions, use the pkaction(1) command.
Known annotations
The org.freedesktop.policykit.exec.path annotation is used by the pkexec program shipped
with PolicyKit - see the pkexec(1) man page for details.
The org.freedesktop.policykit.imply annotation (its value is a string containing a space
separated list of action identifiers) can be used to define meta actions. The way it works
is that if a subject is authorized for an action with this annotation, then it is also
authorized for any action specified by the annotation. A typical use of this annotation is
when defining an UI shell with a single lock button that should unlock multiple actions
from distinct mechanisms.
The org.freedesktop.policykit.owner annotation can be used to define a set of users who
can query whether a client is authorized to perform this action. If this annotation is not
specified then only root can query whether a client running as a different user is
authorized for an action. The value of this annotation is a string containing a space
separated list of PolkitIdentity entries, for example "unix-user:42 unix-user:colord". A
typical use of this annotation is for a daemon process that runs as a system user rather
than root.
AUTHOR
Written by David Zeuthen <davidz@redhat.com> with a lot of help from many others.
BUGS
Please send bug reports to either the distribution or the polkit-devel mailing list, see
the link http://lists.freedesktop.org/mailman/listinfo/polkit-devel on how to subscribe.
SEE ALSO
pklocalauthority(8) polkitd(8) pkaction(1), pkcheck(1), pkexec(1), pkttyagent(1)
NOTES
1. /usr/share/gtk-doc/html/polkit-1/polkit-architecture.png
2. developer documentation
file:///usr/share/gtk-doc/html/polkit-1/index.html
3. /usr/share/gtk-doc/html/polkit-1/polkit-authentication-agent-example.png
4. /usr/share/gtk-doc/html/polkit-1/polkit-authentication-agent-example-wheel.png
5. Freedesktop.org Icon Naming Specification
http://standards.freedesktop.org/icon-naming-spec/icon-naming-spec-latest.html