Provided by: polkitd_126-2_amd64 
NAME
polkit - Authorization Manager
OVERVIEW
polkit provides an authorization API intended to be used by privileged programs (“MECHANISMS”) offering
service to unprivileged programs (“SUBJECTS”) often through some form of inter-process communication
mechanism. In this scenario, the mechanism typically treats the subject as untrusted. For every request
from a subject, the mechanism needs to determine if the request is authorized or if it should refuse to
service the subject. Using the polkit APIs, a mechanism can offload this decision to a trusted party: The
polkit authority.
The polkit authority is implemented as an system daemon, polkitd(8), which itself has little privilege as
it is running as the polkitd system user. Mechanisms, subjects and authentication agents communicate with
the authority using the system message bus.
In addition to acting as an authority, polkit 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 polkit is comprised of the Authority (implemented as a service on the system
message bus) and an Authentication Agent per user session (provided and started by the user's graphical
environment). Actions are defined by applications. Vendors, sites and system administrators can control
authorization policy through Authorization Rules.
[IMAGE][1]
+-------------------+
| Authentication |
| Agent |
+-------------------+
| libpolkit-agent-1 |
+-------------------+
^ +---------+
| | Subject |
+--------------+ +---------+
| ^
| |
User Session | |
=======================|========================|=============
System Context | |
| |
| +---+
V |
/------------\ |
| System Bus | |
\------------/ |
^ ^ V
| | +---------------------+
+--------------+ | | Mechanism |
| | +---------------------+
V +----> | libpolkit-gobject-1 |
+------------------+ +---------------------+
| polkitd(8) |
+------------------+
| org.freedesktop. |
| PolicyKit1 |<---------+
+------------------+ |
^ |
| +--------------------------------------------+
| | /etc/polkit-1/actions/*.policy |
| | /run/polkit-1/actions/*.policy |
| | /usr/local/share/polkit-1/actions/*.policy |
| | /usr/share/polkit-1/actions/*.policy |
| +--------------------------------------------+
|
+--------------------------------------------+
| /etc/polkit-1/rules.d/*.rules |
| /run/polkit-1/rules.d/*.rules |
| /usr/local/share/polkit-1/rules.d/*.rules |
| /usr/share/polkit-1/rules.d/*.rules |
+--------------------------------------------+
For convenience, the libpolkit-gobject-1 library wraps the polkit D-Bus API and is usable from any C/C++
program as well as higher-level languages supporting GObjectIntrospection[2] such as JavaScript and
Python. 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 for registration and communication with the polkit D-Bus service.
See the developer documentation[3] for more information about writing polkit applications.
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 an
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][4]
+----------------------------------------------------------+
| |
| [Icon] Authentication required |
| |
| Authentication is required to format INTEL |
| SSDSA2MH080G1GC (/dev/sda) |
| |
| Administrator |
| |
| Password: [__________________________________] |
| |
| [Cancel] [Authenticate] |
+----------------------------------------------------------+
If the system is configured without a root account, it may prompt for a specific user designated as the
administrative user:
[IMAGE][5]
+----------------------------------------------------------+
| |
| [Icon] Authentication required |
| |
| Authentication is required to format INTEL |
| SSDSA2MH080G1GC (/dev/sda) |
| |
| [Icon] David Zeuthen |
| |
| Password: [__________________________________] |
| |
| [Cancel] [Authenticate] |
+----------------------------------------------------------+
Applications that do not run under a desktop environment (for example, if launched from an ssh(1) login)
may not 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 needs to declare a set of actions in order to use polkit. 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.
polkit actions are namespaced and can only contain the characters "[A-Z][a-z][0-9].-", e.g. 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 polkit Policy Configuration 1.0//EN"
"http://www.freedesktop.org/software/polkit/policyconfig-1.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[6]. Optional.
action
Declares an action. The action name is specified using the id attribute and can only contain the
characters "[A-Z][a-z][0-9].- ", e.g. ASCII, digits, period and hyphen.
Elements that can be used inside action include:
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 include:
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. Note that
this is not restrictive enough for most uses on multi-user systems; auth_admin* is generally
recommended.
auth_admin
Authentication by an administrative user is required.
auth_self_keep
Like auth_self but the authorization is kept for a brief period (e.g. five minutes). The warning
about auth_self above applies likewise.
auth_admin_keep
Like auth_admin but the authorization is kept for a brief period (e.g. five minutes).
annotate
Used for annotating an action with a key/value pair. The key is specified using 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 polkit actions, use the pkaction(1) command.
Known annotations
The org.freedesktop.policykit.exec.path annotation is used by the pkexec program shipped with polkit -
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.
AUTHORIZATION RULES
polkitd reads .rules files from the following directories in this order:
• /etc/polkit-1/rules.d
• /run/polkit-1/rules.d
• /usr/local/share/polkit-1/rules.d
• /usr/share/polkit-1/rules.d
These directories are processed in lexical order based on the basename of each file. If there's a tie,
files in directories earlier in the list are processed first. For example, for the following four files,
the order is:
• /etc/polkit-1/rules.d/10-auth.rules
• /run/polkit-1/rules.d/10-auth.rules
• /usr/local/share/polkit-1/rules.d/10-auth.rules
• /usr/share/polkit-1/rules.d/10-auth.rules
All of these directories are monitored, so if a rules file is changed, added, or removed, existing rules
are purged and all files are read and processed again. Rules files are written in the JavaScript[7]
programming language and interface with polkitd through the global polkit object (of type Polkit).
While the JavaScript interpreter used in particular versions of polkit may support non-standard features
(such as the let keyword), authorization rules must conform to ECMA-262 edition 5[8] (in other words, the
JavaScript interpreter used may change in future versions of polkit).
Authorization rules are intended for two specific audiences
• System Administrators
• Special-purpose Operating Systems / Environments
and those audiences only. In particular, applications, mechanisms and general-purpose operating systems
must never include any authorization rules.
The Polkit type
The following methods are available on the polkit object:
void addRule(polkit.Result function(action, subject) {...});
void addAdminRule(string[] function(action, subject) {...});
void log(string message);
string spawn(string[] argv);
The addRule() method is used for adding a function that may be called whenever an authorization check for
action and subject is performed. Functions are called in the order they have been added until one of the
functions returns a value. Hence, to add an authorization rule that is processed before other rules, put
it in a file in /etc/polkit-1/rules.d with a name that sorts before other rules files, for example
00-early-checks.rules. Each function should return a value from polkit.Result
polkit.Result = {
NO : "no",
YES : "yes",
AUTH_SELF : "auth_self",
AUTH_SELF_KEEP : "auth_self_keep",
AUTH_ADMIN : "auth_admin",
AUTH_ADMIN_KEEP : "auth_admin_keep",
NOT_HANDLED : null
};
corresponding to the values that can be used as defaults. If the function returns
polkit.Result.NOT_HANDLED, null, undefined or does not return a value at all, the next user function is
tried.
Keep in mind that if polkit.Result.AUTH_SELF_KEEP or polkit.Result.AUTH_ADMIN_KEEP is returned,
authorization checks for the same action identifier and subject will succeed (that is, return
polkit.Result.YES) for the next brief period (e.g. five minutes) even if the variables passed along with
the check are different. Therefore, if the result of an authorization rule depend on such variables, it
should not use the "*_KEEP" constants (if similar functionality is required, the authorization rule can
easily implement temporary authorizations using the Date[9] type for timestamps).
The addAdminRule() method is used for adding a function that may be called whenever administrator
authentication is required. The function is used to specify what identities may be used for administrator
authentication for the authorization check identified by action and subject. Functions added are called
in the order they have been added until one of the functions returns a value. Each function should return
an array of strings where each string is of the form "unix-group:<group>", "unix-netgroup:<netgroup>" or
"unix-user:<user>". If the function returns null, undefined or does not return a value at all, the next
function is tried.
There is no guarantee that a function registered with addRule() or addAdminRule() is ever called - for
example an early rules file could register a function that always returns a value, hence ensuring that
functions added later are never called.
If user-provided code takes a long time to execute, no exception will be thrown and the script will be
killed right away (the current limit is 15 seconds). This is used to catch runaway scripts.
The spawn() method spawns an external helper identified by the argument vector argv and waits for it to
terminate. If an error occurs or the helper doesn't exit normally with exit code 0, an exception is
thrown. If the helper does not exit within 10 seconds, it is killed. Otherwise, the program's standard
output is returned as a string. The spawn() method should be used sparingly as helpers may take a very
long or indeterminate amount of time to complete and no other authorization check can be handled while
the helper is running. Note that the spawned programs will run as the unprivileged polkitd system user.
The log() method writes the given message to the system logger prefixed with the JavaScript filename and
line number. Log entries are emitted using the LOG_AUTHPRIV flag meaning that the log entries usually
ends up in the file /var/log/secure. The log() method is usually only used when debugging rules. The
Action and Subject types has suitable toString() methods defined for easy logging, for example,
polkit.addRule(function(action, subject) {
if (action.id == "org.freedesktop.policykit.exec") {
polkit.log("action=" + action);
polkit.log("subject=" + subject);
}
});
will produce the following when the user runs 'pkexec -u bateman bash -i' from a shell:
May 24 14:28:50 thinkpad polkitd[32217]: /etc/polkit-1/rules.d/10-test.rules:3: action=[Action id='org.freedesktop.policykit.exec' command_line='/usr/bin/bash -i' program='/usr/bin/bash' user='bateman' user.gecos='Patrick Bateman' user.display='Patrick Bateman (bateman)']
May 24 14:28:50 thinkpad polkitd[32217]: /etc/polkit-1/rules.d/10-test.rules:4: subject=[Subject pid=1352 user='davidz' groups=davidz,wheel, seat='seat0' session='1' local=true active=true]
The Action type
The action parameter passed to user functions is an object with information about the action being
checked. It is of type Action and has the following attribute:
string id
The action identifier, for example org.freedesktop.policykit.exec.
The following methods are available on the Action type:
string lookup(string key);
The lookup() method is used to lookup the polkit variables passed from the mechanism. For example, the
pkexec(1) mechanism sets the variable program which can be obtained in JavaScript using the expression
action.lookup("program"). If there is no value for the given key, then undefined is returned.
Consult the documentation for each mechanism for what variables are available for each action.
The Subject type
The subject parameter passed to user functions is an object with information about the process being
checked. It is of type Subject and has the following attributes
int pid
The process id.
string user
The user name.
string[] groups
Array of groups that user user belongs to.
string seat
The seat that the subject is associated with - blank if not on a local seat.
string session
The session that the subject is associated with.
string system_unit
The systemd unit that the subject's process is part of (if any). Note that this can only match on
system units, as user units can be created with any name without privileges (unlike system units
which require root to create). A process running in a user unit will return the user session unit in
this attribute (e.g.: user-1000.service).
boolean local
Set to true only if seat is local.
boolean no_new_privileges
Set only if system_unit is not empty, and set to true only if the referenced systemd service unit has
the NoNewPrivileges= setting enabled. This ensures that the process cannot gain any new privileges
via executing setuid binaries.
boolean active
Set to true only if the session is active.
The following methods are available on the Subject type:
boolean isInGroup(string groupName);
boolean isInNetGroup(string netGroupName);
The isInGroup() method can be used to check if the subject is in a given group and isInNetGroup() can be
used to check if the subject is in a given netgroup.
Authorization Rules Examples
Allow all users in the admin group to perform user administration without changing policy for other
users:
polkit.addRule(function(action, subject) {
if (action.id == "org.freedesktop.accounts.user-administration" &&
subject.isInGroup("admin")) {
return polkit.Result.YES;
}
});
Define administrative users to be the users in the wheel group:
polkit.addAdminRule(function(action, subject) {
return ["unix-group:wheel"];
});
Forbid users in group children to change hostname configuration (that is, any action with an identifier
starting with org.freedesktop.hostname1.) and allow anyone else to do it after authenticating as
themselves:
polkit.addRule(function(action, subject) {
if (action.id.indexOf("org.freedesktop.hostname1.") == 0) {
if (subject.isInGroup("children")) {
return polkit.Result.NO;
} else {
return polkit.Result.AUTH_SELF_KEEP;
}
}
});
Run an external helper to determine if the current user may reboot the system:
polkit.addRule(function(action, subject) {
if (action.id.indexOf("org.freedesktop.login1.reboot") == 0) {
try {
// user-may-reboot exits with success (exit code 0)
// only if the passed username is authorized
polkit.spawn(["/opt/company/bin/user-may-reboot",
subject.user]);
return polkit.Result.YES;
} catch (error) {
// Nope, but do allow admin authentication
return polkit.Result.AUTH_ADMIN;
}
}
});
The following example shows how the authorization decision can depend on variables passed by the
pkexec(1) mechanism:
polkit.addRule(function(action, subject) {
if (action.id == "org.freedesktop.policykit.exec" &&
action.lookup("program") == "/usr/bin/cat") {
return polkit.Result.AUTH_ADMIN;
}
});
The following example shows another use of variables passed from the mechanism. In this case, the
mechanism is UDisks[10] which defines a set of actions and variables[11] that is used to match on:
// Allow users in group 'engineers' to perform any operation on
// some drives without having to authenticate
//
polkit.addRule(function(action, subject) {
if (action.id.indexOf("org.freedesktop.udisks2.") == 0 &&
action.lookup("drive.vendor") == "SEAGATE" &&
action.lookup("drive.model") == "ST3300657SS" &&
subject.isInGroup("engineers")) {
return polkit.Result.YES;
}
}
});
Allow all processes running as part of the admin.service systemd system unit to perform user
administration, as long as they cannot gain new privileges:
polkit.addRule(function(action, subject) {
if (action.id == "org.freedesktop.accounts.user-administration" &&
subject.system_unit == "admin.service" &&
subject.no_new_privileges) {
return polkit.Result.YES;
}
});
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
https://gitlab.freedesktop.org/polkit/polkit/-/issues/ on how to subscribe.
SEE ALSO
polkitd(8), pkaction(1), pkcheck(1), pkexec(1), pkttyagent(1)
NOTES
1. /usr/share/gtk-doc/html/polkit-1/polkit-architecture.png
2. GObjectIntrospection
https://live.gnome.org/GObjectIntrospection
3. developer documentation
http://www.freedesktop.org/software/polkit/docs/latest/
4. /usr/share/gtk-doc/html/polkit-1/polkit-authentication-agent-example.png
5. /usr/share/gtk-doc/html/polkit-1/polkit-authentication-agent-example-wheel.png
6. Freedesktop.org Icon Naming Specification
http://standards.freedesktop.org/icon-naming-spec/icon-naming-spec-latest.html
7. JavaScript
http://en.wikipedia.org/wiki/JavaScript
8. ECMA-262 edition 5
http://en.wikipedia.org/wiki/ECMAScript#ECMAScript.2C_5th_Edition
9. Date
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date
10. UDisks
http://udisks.freedesktop.org/docs/latest/udisks.8.html
11. actions and variables
http://udisks.freedesktop.org/docs/latest/udisks-polkit-actions.html
polkit February 2021 POLKIT(8)