Index: kern/kern_exec.c
===================================================================
--- kern/kern_exec.c
+++ kern/kern_exec.c
@@ -1194,7 +1194,7 @@
 
 	args->begin_argv = args->buf + length;
 	args->endp = args->begin_argv;
-	args->stringspace = ARG_MAX;
+	args->stringspace = argmax;
 
 	/*
 	 * extract arguments first
@@ -1264,14 +1264,14 @@
 
 	memset(args, '\0', sizeof(*args));
 	ofdp = td->td_proc->p_fd;
-	if (datalen >= ARG_MAX || fdslen > ofdp->fd_lastfile + 1)
+	if (datalen >= argmax || fdslen > ofdp->fd_lastfile + 1)
 		return (E2BIG);
 	error = exec_alloc_args(args);
 	if (error != 0)
 		return (error);
 
 	args->begin_argv = args->buf;
-	args->stringspace = ARG_MAX;
+	args->stringspace = argmax;
 
 	if (datalen > 0) {
 		/*
@@ -1484,7 +1484,7 @@
 	copyout(pagesizes, (void *)destp, szps);
 	imgp->pagesizeslen = szps;
 
-	destp -= ARG_MAX - imgp->args->stringspace;
+	destp -= argmax - imgp->args->stringspace;
 	destp = rounddown2(destp, sizeof(void *));
 
 	/*
@@ -1527,7 +1527,7 @@
 	/*
 	 * Copy out strings - arguments and environment.
 	 */
-	copyout(stringp, (void *)destp, ARG_MAX - imgp->args->stringspace);
+	copyout(stringp, (void *)destp, argmax - imgp->args->stringspace);
 
 	/*
 	 * Fill in "ps_strings" struct for ps, w, etc.
Index: kern/kern_mib.c
===================================================================
--- kern/kern_mib.c
+++ kern/kern_mib.c
@@ -112,8 +112,8 @@
 SYSCTL_INT(_kern, OID_AUTO, maxusers, CTLFLAG_RDTUN | CTLFLAG_NOFETCH,
     &maxusers, 0, "Hint for kernel tuning");
 
-SYSCTL_INT(_kern, KERN_ARGMAX, argmax, CTLFLAG_RD|CTLFLAG_CAPRD,
-    SYSCTL_NULL_INT_PTR, ARG_MAX, "Maximum bytes of argument to execve(2)");
+SYSCTL_INT(_kern, KERN_ARGMAX, argmax, CTLFLAG_RDTUN | CTLFLAG_NOFETCH,
+    &argmax, ARG_MAX, "Maximum bytes of argument to execve(2)");
 
 SYSCTL_INT(_kern, KERN_POSIX1, posix1version, CTLFLAG_RD|CTLFLAG_CAPRD,
     SYSCTL_NULL_INT_PTR, _POSIX_VERSION, "Version of POSIX attempting to comply to");
Index: kern/subr_param.c
===================================================================
--- kern/subr_param.c
+++ kern/subr_param.c
@@ -78,6 +78,12 @@
 #ifndef MAXFILES
 #define	MAXFILES (40 + 32 * maxusers)
 #endif
+#ifndef ARG_MAX
+#define ARG_MAX 262144
+#endif
+#ifndef _POSIX_ARG_MAX
+#define _POSIX_ARG_MAX 4096
+#endif
 
 static int sysctl_kern_vm_guest(SYSCTL_HANDLER_ARGS);
 
@@ -106,6 +112,7 @@
 u_long	dflssiz;			/* initial stack size limit */
 u_long	maxssiz;			/* max stack size */
 u_long	sgrowsiz;			/* amount to grow stack */
+int	argmax;				/* max bytes of argument to exec */
 
 SYSCTL_INT(_kern, OID_AUTO, hz, CTLFLAG_RDTUN | CTLFLAG_NOFETCH, &hz, 0,
     "Number of clock ticks per second");
@@ -294,6 +301,11 @@
 	if (maxpipekva > (VM_MAX_KERNEL_ADDRESS - VM_MIN_KERNEL_ADDRESS) / 64)
 		maxpipekva = (VM_MAX_KERNEL_ADDRESS - VM_MIN_KERNEL_ADDRESS) /
 		    64;
+
+	argmax = ARG_MAX;
+	TUNABLE_INT_FETCH("kern.argmax", &argmax);
+	if (argmax < _POSIX_ARG_MAX)
+		argmax = _POSIX_ARG_MAX;
 }
 
 /*
Index: sys/proc.h
===================================================================
--- sys/proc.h
+++ sys/proc.h
@@ -929,6 +929,7 @@
 extern int lastpid;
 extern int nprocs, maxproc;		/* Current and max number of procs. */
 extern int maxprocperuid;		/* Max procs per uid. */
+extern int argmax;			/* Max bytes of argument to exec. */
 extern u_long ps_arg_cache_limit;
 
 LIST_HEAD(proclist, proc);
Index: vm/vm_init.c
===================================================================
--- vm/vm_init.c
+++ vm/vm_init.c
@@ -277,7 +277,7 @@
 #else
 	exec_map_entries = 2 * mp_ncpus + 4;
 #endif
-	exec_map_entry_size = round_page(PATH_MAX + ARG_MAX);
+	exec_map_entry_size = round_page(PATH_MAX + argmax);
 	exec_map = kmem_suballoc(kernel_map, &minaddr, &maxaddr,
 	    exec_map_entries * exec_map_entry_size + 64 * PAGE_SIZE, FALSE);
 	pipe_map = kmem_suballoc(kernel_map, &minaddr, &maxaddr, maxpipekva,