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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 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.
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.
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.