noble (1) pkexec.1.gz

Provided by: pkexec_124-2ubuntu1.24.04.2_amd64 bug

NAME

       pkexec - Execute a command as another user

SYNOPSIS

       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
       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.

       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 the section called “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[1] 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/catcommand_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
       https://gitlab.freedesktop.org/polkit/polkit/-/issues/ 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)