--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/progs/read2.c	Tue Dec 30 21:59:47 2014 +0000
@@ -0,0 +1,47 @@
+#include <stdio.h>
+#include <unistd.h>
+#include <errno.h>
+
+FILE *f; //file pointer
+
+//tests return errno = 13 for permission denied
+void read_test(char *name) 
+{
+    if ((f = fopen(name, "r")) == NULL) {
+      printf("%s is not readable, errno = %d\n", name, errno);
+    } else {
+      printf("%s is readable\n", name); fclose(f);
+    }
+}
+
+void write_test(char *name) 
+{
+    if ((f = fopen(name, "r+")) == NULL) {
+      printf("%s is not writable, errno = %d\n", name, errno);
+    } else {
+      printf("%s is writable\n", name); fclose(f);
+    }
+}
+
+int main(int argc, char *argv[])
+{   
+    printf("Real UID = %d\n", getuid());
+    printf("Effective UID = %d\n", geteuid());
+    
+    read_test(argv[1]);
+    write_test(argv[1]);
+
+    //lowering the access rights to the caller
+    if (setuid(getuid())) {  
+      printf("could not reset setuid, errno = %d\n", errno); 
+      return 1;
+    }
+        
+    printf("Real UID = %d\n", getuid());
+    printf("Effective UID = %d\n", geteuid());      
+
+    read_test(argv[1]);
+    write_test(argv[1]);
+
+    return 0;
+}