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 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
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 <[email protected]> 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)
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