Get current active desktop console user

Question

Hi,
I am googling for some time trying to find a way to determine UserID
of user using the physical console. I am after a command that can be
run from terminal, ssh, cron.
"who" shows all users logged in with Fast user switching,
all of them on 'console' but I see no way to figure out who is
the one using the desktop that time.
Many hits point to CGSession, but so far I was not able find the options
to get the ID of current console user. It is certain that this binary has
access to the value, because when trying -switchToUserID it can respond with:
Unable to Fast User Switch: User must be the current console user or root.
Is there any way to find out current console user? Would appreciate also
a pointer to some library I can call from C and printf the value.
Thanks in advance.
Andrej

Answer 1

Hi,
Your post was 100% to the point. Thanks a million. I was hoping there would be a binary in the system already to provide the info needed, so this forum appeared the most appropriate. So far I've never compiled my C program on a Mac but with the info from published documents it was a snap:
(how to paste code samples to this forum??)
mac40:timemgmt amk$ cat loguser.c
#include <stdio.h>
#include <SystemConfiguration/SystemConfiguration.h>
#include <CoreFoundation/CFString.h>
http://developer.apple.com/library/mac/#qa/qa2001/qa1133.html
http://developer.apple.com/library/mac/#documentation/MacOSX/Conceptual/BPMultip leUsers/Concepts/FastUserSwitching.html#//apple_ref/doc/uid/20002209-BAJDIHBJ
static CFStringRef CopyCurrentConsoleUsername(SCDynamicStoreRef store)
// Returns the name of the current console user, or NULL if there is
// none. store may be NULL, in which case a transient dynamic store
// session is used.
CFStringRef result;
result = SCDynamicStoreCopyConsoleUser(store, NULL, NULL);
// If the current console user is "loginwindow", treat that as equivalent
// to none.
if ( (result != NULL) && CFEqual(result, CFSTR("loginwindow")) ) {
CFRelease(result);
result = NULL;
return result;
main(int ac, char*av)
CFStringRef cf;
const char * s;
if ( ( cf = CopyCurrentConsoleUsername ( NULL ) ) != NULL )
if ( ( s = CFStringGetCStringPtr ( cf, CFStringGetFastestEncoding ( cf ) ) ) != NULL )
printf ( "%s\n", s );
exit ( 0 );
perror ( "Get current console user" );
exit ( 1 );
mac40:timemgmt amk$ cc -o loguser loguser.c -framework CoreFoundation -framework SystemConfiguration
mac40:timemgmt amk$ who | grep console
ivka console Nov 25 07:11
eyetv console Nov 22 12:31
mac40:timemgmt amk$ ./loguser
eyetv
mac40:timemgmt amk$
BTW, I am trying to implement a kind of distributed parental control with global time limits over multiple computers.
Thanks!