check_users: Use utmpx(5) only if available

For systems that don't provide an utmpx(5) interface, restore the code
that was replaced in commit 3e622f3a47bc7d31f22513a79892c3c52febd2d3.

configure.in

@@ -316,6 +316,10 @@ AS_IF([test "x$with_ldap" != "xno"], [
   LIBS="$_SAVEDLIBS"
 ])
 
+dnl Check for headers used by check_users
+AC_CHECK_HEADERS(utmpx.h)
+AM_CONDITIONAL([HAVE_UTMPX], [test "$ac_cv_header_utmpx_h" = "yes"])
+
 dnl Check for headers used by check_ide_smart
 case $host in
   *linux*)

plugins/Makefile.am

@@ -112,6 +112,10 @@ check_ide_smart_LDADD = $(BASEOBJS)
 negate_LDADD = $(BASEOBJS)
 urlize_LDADD = $(BASEOBJS)
 
+if !HAVE_UTMPX
+check_users_LDADD += popen.o
+endif
+
 ##############################################################################
 # secondary dependencies
 

plugins/check_users.c

@@ -36,7 +36,12 @@ const char *email = "nagiosplug-devel@lists.sourceforge.net";
 
 #include "common.h"
 #include "utils.h"
-#include <utmpx.h>
+
+#if HAVE_UTMPX_H
+# include <utmpx.h>
+#else
+# include "popen.h"
+#endif
 
 #define possibly_set(a,b) ((a) == 0 ? (b) : 0)
 
@@ -53,7 +58,11 @@ main (int argc, char **argv)
 	int users = -1;
 	int result = STATE_UNKNOWN;
 	char *perf;
+#if HAVE_UTMPX_H
 	struct utmpx *putmpx;
+#else
+	char input_buffer[MAX_INPUT_BUFFER];
+#endif
 
 	setlocale (LC_ALL, "");
 	bindtextdomain (PACKAGE, LOCALEDIR);
@@ -69,6 +78,7 @@ main (int argc, char **argv)
 
 	users = 0;
 
+#if HAVE_UTMPX_H
 	/* get currently logged users from utmpx */
 	setutxent ();
 
@@ -77,6 +87,39 @@ main (int argc, char **argv)
 			users++;
 
 	endutxent ();
+#else
+	/* run the command */
+	child_process = spopen (WHO_COMMAND);
+	if (child_process == NULL) {
+		printf (_("Could not open pipe: %s\n"), WHO_COMMAND);
+		return STATE_UNKNOWN;
+	}
+
+	child_stderr = fdopen (child_stderr_array[fileno (child_process)], "r");
+	if (child_stderr == NULL)
+		printf (_("Could not open stderr for %s\n"), WHO_COMMAND);
+
+	while (fgets (input_buffer, MAX_INPUT_BUFFER - 1, child_process)) {
+		/* increment 'users' on all lines except total user count */
+		if (input_buffer[0] != '#') {
+			users++;
+			continue;
+		}
+
+		/* get total logged in users */
+		if (sscanf (input_buffer, _("# users=%d"), &users) == 1)
+			break;
+	}
+
+	/* check STDERR */
+	if (fgets (input_buffer, MAX_INPUT_BUFFER - 1, child_stderr))
+		result = possibly_set (result, STATE_UNKNOWN);
+	(void) fclose (child_stderr);
+
+	/* close the pipe */
+	if (spclose (child_process))
+		result = possibly_set (result, STATE_UNKNOWN);
+#endif
 
 	/* check the user count against warning and critical thresholds */
 	if (users > cusers)