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PKEXEC(1)                           pkexec                           PKEXEC(1)
NAME
       pkexec - Execute a command as another user
SYNOPSIS
       pkexec [--version] [--disable-internal-agent] [--help]
       pkexec [--user username] PROGRAM [ARGUMENTS...]
DESCRIPTION
       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.
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. If the authorization could not
       be obtained because the user dismissed the authentication dialog,
       pkexec exits with a return value of 126.
AUTHENTICATION AGENT
       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.
SECURITY NOTES
       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).
ACTION AND AUTHORIZATIONS
       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.
WRAPPER USAGE
       To avoid modifying existing software to prefix their command-line
       invocations with pkexec, it's possible to use pkexec in a she-bang
       wrapper[1] 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.
VARIABLES
       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)"
AUTHOR
       Written by David Zeuthen <davidz AT 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
       polkit(8), polkitd(8), pkaction(1), pkcheck(1), pkttyagent(1)
NOTES
        1. she-bang wrapper
           http://en.wikipedia.org/wiki/Shebang_(Unix)
polkit                             May 2009                          PKEXEC(1)