# pkexec

pkexec

1

pkexec

Execute a command as another user

          pkexec
          --version
          --disable-internal-agent
          --help

          pkexec

    		--keep-cwd

              --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 pkexec-action) 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.

`pkexec` will run `PROGRAM` in `username`'s home directory, unless `--keep-cwd` is used to override this behavior

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 pkexec-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 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@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 on how to subscribe.

## SEE ALSO

polkit

8,

polkitd

8,

pkaction

1,

pkcheck

1,

pkttyagent

1