|  |  |  |  | 
| pkexecpkexec — Execute a command as another user | 
pkexec  [--version] [--disable-internal-agent] [--help]
pkexec  [ 
          --user
          username
         ]  PROGRAM  [ ARGUMENTS ...]
      pkexec allows an authorized user to execute
      PROGRAM as another user. If
      PROGRAM is not specified, the default
      shell will be run.  If username is
      not specified, then the program will be executed as the
      administrative super user, root.
    
      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. If the authorization could not
      be obtained because the user dismissed the authentication
      dialog, pkexec exits with a return value of
      126.
    
      pkexec, like any other polkit application,
      will use the authentication agent registered for the calling
      process or session. However, if no authentication agent is
      available, then pkexec will register its own
      textual authentication agent. This behavior can be turned off by
      passing the --disable-internal-agent option.
    
Executing a program as another user is a privileged operation. By default the action to check for (see the section called “ACTION AND 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.
      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 by default allow you to run
      X11 applications as another user since
      the $DISPLAY and $XAUTHORITY
      environment variables are not set. These two variables will be retained
      if the org.freedesktop.policykit.exec.allow_gui annotation
      on an action is set to a nonempty value; this is discouraged, though, and
      should only be used for legacy programs.
    
      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) 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).
By default, the org.freedesktop.policykit.exec action is used. To use another action, use the org.freedesktop.policykit.exec.path annotation on an action with the value set to the full path of the program. In addition to specifying the program, the authentication message, description, icon and defaults can be specified. If the org.freedesktop.policykit.exec.argv1 annotation is present, the action will only be picked if the first argument to the program matches the value of the annotation.
      Note that authentication messages may reference variables (see
      the section called “VARIABLES”), for example
      $(user) will be expanded to the value of the
      user variable.
    
To avoid modifying existing software to prefix their command-line invocations with pkexec, it's possible to use pkexec in a she-bang wrapper like this:
#!/usr/bin/pkexec /usr/bin/python
import os
import sys
print "Hello, I'm running as uid %d"%(os.getuid())
for n in range(len(sys.argv)):
    print "arg[%d]=`%s'"%(n, sys.argv[n])
      If this script is installed into /usr/bin/my-pk-test,
      then the following annotations
    
[...] <annotate key="org.freedesktop.policykit.exec.path">/usr/bin/python</annotate> <annotate key="org.freedesktop.policykit.exec.argv1">/usr/bin/my-pk-test</annotate> [...]
      can be used to select the appropriate polkit action. Be careful
      to get the latter annotation right, otherwise it will match any
      pkexec invocation of
      /usr/bin/python scripts.
    
The following variables are set by pkexec. They can be used in authorization rules and messages shown in authentication dialogs:
| program | Fully qualified path to the program to be executed. Example: “/bin/cat” | 
| command_line | The requested command-line (do not use this for any security checks, it is not secure). Example: “cat /srv/xyz/foobar” | 
| user | The user name of the user to execute the program as. Example: “davidz” | 
| user.gecos | The full name of the user to execute the program as. Example: “David Zeuthen” | 
| user.display | A representation of the user to execute the program as that is suitable for display in an authentication dialog. Is typically set to a combination of the user name and the full name. Example: “David Zeuthen (davidz)” | 
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.