polkit Reference Manual |
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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 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 PolicyKit application,
will use the authentication agent registered for the calling
process. 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 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:
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
X11 applications as another user since
the $DISPLAY
and $XAUTHORITY
environment variables are not set. These two variables will be retained
if the org.freedesktop.policykit.exec.allow_gui annotation
on an action is set to a nonempty value; this is discouraged, though, and
should only be used for legacy programs.
By default, the org.freedesktop.policykit.exec authorization is required unless an action definition file is present for the program in question. To require another authorization, it can be specified using the org.freedesktop.policykit.exec.path annotation on an action (See the section called “EXAMPLE” for details).
To specify what kind of authorization is needed to execute the
program /usr/bin/pk-example-frobnicate
as
another user, simply write an action definition file like this
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE policyconfig PUBLIC "-//freedesktop//DTD PolicyKit Policy Configuration 1.0//EN" "http://www.freedesktop.org/standards/PolicyKit/1/policyconfig.dtd"> <policyconfig> <vendor>Examples for the PolicyKit Project</vendor> <vendor_url>http://hal.freedesktop.org/docs/PolicyKit/</vendor_url> <action id="org.freedesktop.policykit.example.pkexec.run-frobnicate"> <description>Run the PolicyKit example program Frobnicate</description> <description xml:lang="da">Kør PolicyKit eksemplet Frobnicate</description> <message>Authentication is required to run the PolicyKit example program Frobnicate (user=$(user), program=$(program), command_line=$(command_line))</message> <message xml:lang="da">Autorisering er påkrævet for at afvikle PolicyKit eksemplet Frobnicate (user=$(user), program=$(program), command_line=$(command_line))</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. Note that occurences of the strings
$(user)
, $(program)
and
$(command_line)
in the message will be
replaced with respectively the user (of the form "Real Name
(username)" or just "username" if there is no real name for the
username), the binary to execute (a fully-qualified path,
e.g. "/usr/bin/pk-example-frobnicate
") and
the command-line, e.g. "pk-example-frobnicate foo
bar
". For example, for the action defined above, the
following authentication dialog will be shown:
If the user is using the da_DK
locale, the
dialog looks like this:
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).
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.