PKEXEC(1) pkexec PKEXEC(1)
pkexec - 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
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.
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:
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
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
The following variables are set by pkexec. They can be used in authorization rules and
messages shown in authentication dialogs:
Fully qualified path to the program to be executed. Example: "/bin/cat"
The requested command-line (do not use this for any security checks, it is not
secure). Example: "cat /srv/xyz/foobar"
The user name of the user to execute the program as. Example: "davidz"
The full name of the user to execute the program as. Example: "David Zeuthen"
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)"
Written by David Zeuthen <email@example.com> with a lot of help from many others.
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.
polkit(8), polkitd(8), pkaction(1), pkcheck(1), pkttyagent(1)
1. she-bang wrapper
polkit May 2009 PKEXEC(1)