Index: numactl.1.lm       
===================================================================
--- numactl.1.lm       
+++ numactl.1.lm       
@@ -107,6 +107,15 @@
 .El
 .Sh EXIT STATUS
 .Ex -std
+.Sh ENVIRONMENT
+.Nm
+sets the environment variable
+.Va NUMACTL=YES
+before running
+.Ar cmd ...
+so programs that know they need to be run under
+.Nm
+can check.
 .Sh EXAMPLES
 Create a
 .Pa /bin/sh
Index: numactl.c.lm       
===================================================================
--- numactl.c.lm       
+++ numactl.c.lm       
@@ -231,6 +231,7 @@
                        (void) set_numa_domain_cpuaffinity(cpu_domain,
                            CPU_WHICH_PID, -1);

+               putenv("NUMACTL=YES");
                errno = 0;
                execvp(*argv, argv);
                err(errno == ENOENT ? 127 : 126, "%s", *argv);