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PKEXEC(1)                           pkexec                           PKEXEC(1)



NAME
       pkexec - Execute a command as another user

SYNOPSIS
       pkexec [--version] [--help]

       pkexec [--user username] PROGRAM [ARGUMENTS...]

DESCRIPTION
       pkexec allows an authorized user to execute PROGRAM as another user. If username is not specified, then the
       program will be executed as the administrative super user, root.

RETURN VALUE
       Upon successful completion, the return value is the return value of PROGRAM. If the calling process is not
       authorized or an authorization could not be obtained through authentication or an error occured, pkexec exits
       with a return value of 127.

SECURITY NOTES
       Executing a program as another user is a privileged operation. By default the required authorization (See the
       section called "REQUIRED AUTHORIZATIONS") requires administrator authentication. In addition, the
       authentication dialog presented to the user will display the full path to the program to be executed so the
       user is aware of what will happen:

           [IMAGE][1]

               +----------------------------------------------------------+
               |                     Authenticate                     [X] |
               +----------------------------------------------------------+
               |                                                          |
               |  [Icon]  Authentication is needed to run '/bin/bash?     |
               |          as the super user                               |
               |                                                          |
               |          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:                                             |
               |  Command: /bin/bash                                      |
               |  Run As:  Super User (root)                              |
               |  Action:  org.freedesktop.policykit.exec                 |
               |  Vendor:  The PolicyKit Project                          |
               |                                                          |
               |                                  [Cancel] [Authenticate] |
               +----------------------------------------------------------+

       The environment that PROGRAM will run it, will be set to a minimal known and safe environment in order to avoid
       injecting code through LD_LIBRARY_PATH or similar mechanisms. In addition the PKEXEC_UID environment variable
       is set to the user id of the process invoking pkexec. As a result, pkexec will not allow you to run e.g. X11
       applications as another user since the $DISPLAY environment variable is not set.

REQUIRED AUTHORIZATIONS
       By default, the org.freedesktop.policykit.exec authorization is required unless an action definition file is
       present for the program in question. To require another authorization, it can be specified using the
       org.freedesktop.policykit.exec.path annotation on an action (See the section called "EXAMPLE" for details).

EXAMPLE
       To specify what kind of authorization is needed to execute the program /usr/bin/pk-example-frobnicate as
       another user, simply write an action definition file like this

           <?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/policyconfig.dtd">
           <policyconfig>

             <vendor>Examples for the PolicyKit Project</vendor>
             <vendor_url>http://hal.freedesktop.org/docs/PolicyKit/</vendor_url>;

             <action id="org.freedesktop.policykit.example.pkexec.run-frobnicate">
               <description>Run the PolicyKit example program Frobnicate</description>
               <description xml:lang="da">K?r PolicyKit eksemplet Frobnicate</description>
               <message>Authentication is required to run the PolicyKit example program Frobnicate</message>
               <message xml:lang="da">Autorisering er pakraevet for at afvikle PolicyKit eksemplet Frobnicate</message>
               <icon_name>audio-x-generic</icon_name>
               <defaults>
                 <allow_any>no</allow_any>
                 <allow_inactive>no</allow_inactive>
                 <allow_active>auth_self_keep</allow_active>
               </defaults>
               <annotate key="org.freedesktop.policykit.exec.path">/usr/bin/pk-example-frobnicate</annotate>
             </action>

           </policyconfig>

       and drop it in the /usr/share/polkit-1/actions directory under a suitable name (e.g. matching the namespace of
       the action). Note that in addition to specifying the program, the authentication message, description, icon and
       defaults can be specified. For example, for the action defined above, the following authentication dialog will
       be shown:

           [IMAGE][2]

               +----------------------------------------------------------+
               |                     Authenticate                     [X] |
               +----------------------------------------------------------+
               |                                                          |
               |  [Icon]  Authentication is required to run the PolicyKit |
               |          example program Frobnicate                      |
               |                                                          |
               |          An application is attempting to perform an      |
               |          action that requires privileges. Authentication |
               |          is required to perform this action.             |
               |                                                          |
               |          Password: [__________________________________]  |
               |                                                          |
               | [V] Details:                                             |
               |  Command: /usr/bin/pk-example-frobnicate                 |
               |  Run As:  Super User (root)                              |
               |  Action:  org.fd.pk.example.pkexec.run-frobnicate        |
               |  Vendor:  Examples for the PolicyKit Project             |
               |                                                          |
               |                                  [Cancel] [Authenticate] |
               +----------------------------------------------------------+

       If the user is using the da_DK locale, the dialog looks like this:

           [IMAGE][3]

               +----------------------------------------------------------+
               |                     Autorisering                     [X] |
               +----------------------------------------------------------+
               |                                                          |
               |  [Icon]  Autorisering er pakraevet for at afvikle         |
               |          PolicyKit eksemplet Frobnicate                  |
               |                                                          |
               |          Et program fors?ger at udf?re en handling der   |
               |          kraever privilegier. Autorisering er pakraevet.   |
               |                                                          |
               |          Kodeord: [___________________________________]  |
               |                                                          |
               | [V] Detaljer:                                            |
               |  Bruger:   Super User (root)                             |
               |  Program:  /usr/bin/pk-example-frobnicate                |
               |  Handling: org.fd.pk.example.pkexec.run-frobnicate       |
               |  Vendor:   Examples for the PolicyKit Project            |
               |                                                          |
               |                                [Annuller] [Autorisering] |
               +----------------------------------------------------------+

       Note that pkexec does no validation of the ARGUMENTS passed to PROGRAM. In the normal case (where administrator
       authentication is required every time pkexec is used), this is not a problem since if the user is an
       administrator he might as well just run pkexec bash to get root.

       However, if an action is used for which the user can retain authorization (or if the user is implicitly
       authorized), such as with pk-example-frobnicate above, this could be a security hole. Therefore, as a rule of
       thumb, programs for which the default required authorization is changed, should never implicitly trust user
       input (e.g. like any other well-written suid program).

AUTHOR
       Written by David Zeuthen davidzATredhat.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
       polkit(8), pkaction(1), pkcheck(1)

NOTES
        1. /usr/share/gtk-doc/html/polkit-1/pkexec-bash.png

        2. /usr/share/gtk-doc/html/polkit-1/pkexec-frobnicate.png

        3. /usr/share/gtk-doc/html/polkit-1/pkexec-frobnicate-da.png



polkit                             May 2009                          PKEXEC(1)