let principals-command.sh work for noexec /var/run
diff --git a/regress/principals-command.sh b/regress/principals-command.sh
index 9006437..b90a8cf 100644
--- a/regress/principals-command.sh
+++ b/regress/principals-command.sh
@@ -14,15 +14,15 @@
 
 # Establish a AuthorizedPrincipalsCommand in /var/run where it will have
 # acceptable directory permissions.
-PRINCIPALS_COMMAND="/var/run/principals_command_${LOGNAME}"
-cat << _EOF | $SUDO sh -c "cat > '$PRINCIPALS_COMMAND'"
+PRINCIPALS_CMD="/var/run/principals_command_${LOGNAME}"
+cat << _EOF | $SUDO sh -c "cat > '$PRINCIPALS_CMD'"
 #!/bin/sh
 test "x\$1" != "x${LOGNAME}" && exit 1
 test -f "$OBJ/authorized_principals_${LOGNAME}" &&
 	exec cat "$OBJ/authorized_principals_${LOGNAME}"
 _EOF
 test $? -eq 0 || fatal "couldn't prepare principals command"
-$SUDO chmod 0755 "$PRINCIPALS_COMMAND"
+$SUDO chmod 0755 "$PRINCIPALS_CMD"
 
 # Create a CA key and a user certificate.
 ${SSHKEYGEN} -q -N '' -t ed25519  -f $OBJ/user_ca_key || \
@@ -33,109 +33,113 @@
     -z $$ -n ${USER},mekmitasdigoat $OBJ/cert_user_key || \
 	fatal "couldn't sign cert_user_key"
 
-# Test explicitly-specified principals
-for privsep in yes no ; do
-	_prefix="privsep $privsep"
+if [ -x $PRINCIPALS_CMD ]; then
+	# Test explicitly-specified principals
+	for privsep in yes no ; do
+		_prefix="privsep $privsep"
 
-	# Setup for AuthorizedPrincipalsCommand
-	rm -f $OBJ/authorized_keys_$USER
-	(
-		cat $OBJ/sshd_proxy_bak
-		echo "UsePrivilegeSeparation $privsep"
-		echo "AuthorizedKeysFile none"
-		echo "AuthorizedPrincipalsCommand $PRINCIPALS_COMMAND %u"
-		echo "AuthorizedPrincipalsCommandUser ${LOGNAME}"
-		echo "TrustedUserCAKeys $OBJ/user_ca_key.pub"
-	) > $OBJ/sshd_proxy
+		# Setup for AuthorizedPrincipalsCommand
+		rm -f $OBJ/authorized_keys_$USER
+		(
+			cat $OBJ/sshd_proxy_bak
+			echo "UsePrivilegeSeparation $privsep"
+			echo "AuthorizedKeysFile none"
+			echo "AuthorizedPrincipalsCommand $PRINCIPALS_CMD %u"
+			echo "AuthorizedPrincipalsCommandUser ${LOGNAME}"
+			echo "TrustedUserCAKeys $OBJ/user_ca_key.pub"
+		) > $OBJ/sshd_proxy
 
-	# XXX test missing command
-	# XXX test failing command
+		# XXX test missing command
+		# XXX test failing command
 
-	# Empty authorized_principals
-	verbose "$tid: ${_prefix} empty authorized_principals"
-	echo > $OBJ/authorized_principals_$USER
-	${SSH} -2i $OBJ/cert_user_key \
-	    -F $OBJ/ssh_proxy somehost true >/dev/null 2>&1
-	if [ $? -eq 0 ]; then
-		fail "ssh cert connect succeeded unexpectedly"
-	fi
+		# Empty authorized_principals
+		verbose "$tid: ${_prefix} empty authorized_principals"
+		echo > $OBJ/authorized_principals_$USER
+		${SSH} -2i $OBJ/cert_user_key \
+		    -F $OBJ/ssh_proxy somehost true >/dev/null 2>&1
+		if [ $? -eq 0 ]; then
+			fail "ssh cert connect succeeded unexpectedly"
+		fi
 
-	# Wrong authorized_principals
-	verbose "$tid: ${_prefix} wrong authorized_principals"
-	echo gregorsamsa > $OBJ/authorized_principals_$USER
-	${SSH} -2i $OBJ/cert_user_key \
-	    -F $OBJ/ssh_proxy somehost true >/dev/null 2>&1
-	if [ $? -eq 0 ]; then
-		fail "ssh cert connect succeeded unexpectedly"
-	fi
+		# Wrong authorized_principals
+		verbose "$tid: ${_prefix} wrong authorized_principals"
+		echo gregorsamsa > $OBJ/authorized_principals_$USER
+		${SSH} -2i $OBJ/cert_user_key \
+		    -F $OBJ/ssh_proxy somehost true >/dev/null 2>&1
+		if [ $? -eq 0 ]; then
+			fail "ssh cert connect succeeded unexpectedly"
+		fi
 
-	# Correct authorized_principals
-	verbose "$tid: ${_prefix} correct authorized_principals"
-	echo mekmitasdigoat > $OBJ/authorized_principals_$USER
-	${SSH} -2i $OBJ/cert_user_key \
-	    -F $OBJ/ssh_proxy somehost true >/dev/null 2>&1
-	if [ $? -ne 0 ]; then
-		fail "ssh cert connect failed"
-	fi
+		# Correct authorized_principals
+		verbose "$tid: ${_prefix} correct authorized_principals"
+		echo mekmitasdigoat > $OBJ/authorized_principals_$USER
+		${SSH} -2i $OBJ/cert_user_key \
+		    -F $OBJ/ssh_proxy somehost true >/dev/null 2>&1
+		if [ $? -ne 0 ]; then
+			fail "ssh cert connect failed"
+		fi
 
-	# authorized_principals with bad key option
-	verbose "$tid: ${_prefix} authorized_principals bad key opt"
-	echo 'blah mekmitasdigoat' > $OBJ/authorized_principals_$USER
-	${SSH} -2i $OBJ/cert_user_key \
-	    -F $OBJ/ssh_proxy somehost true >/dev/null 2>&1
-	if [ $? -eq 0 ]; then
-		fail "ssh cert connect succeeded unexpectedly"
-	fi
+		# authorized_principals with bad key option
+		verbose "$tid: ${_prefix} authorized_principals bad key opt"
+		echo 'blah mekmitasdigoat' > $OBJ/authorized_principals_$USER
+		${SSH} -2i $OBJ/cert_user_key \
+		    -F $OBJ/ssh_proxy somehost true >/dev/null 2>&1
+		if [ $? -eq 0 ]; then
+			fail "ssh cert connect succeeded unexpectedly"
+		fi
 
-	# authorized_principals with command=false
-	verbose "$tid: ${_prefix} authorized_principals command=false"
-	echo 'command="false" mekmitasdigoat' > \
-	    $OBJ/authorized_principals_$USER
-	${SSH} -2i $OBJ/cert_user_key \
-	    -F $OBJ/ssh_proxy somehost true >/dev/null 2>&1
-	if [ $? -eq 0 ]; then
-		fail "ssh cert connect succeeded unexpectedly"
-	fi
+		# authorized_principals with command=false
+		verbose "$tid: ${_prefix} authorized_principals command=false"
+		echo 'command="false" mekmitasdigoat' > \
+		    $OBJ/authorized_principals_$USER
+		${SSH} -2i $OBJ/cert_user_key \
+		    -F $OBJ/ssh_proxy somehost true >/dev/null 2>&1
+		if [ $? -eq 0 ]; then
+			fail "ssh cert connect succeeded unexpectedly"
+		fi
 
+		# authorized_principals with command=true
+		verbose "$tid: ${_prefix} authorized_principals command=true"
+		echo 'command="true" mekmitasdigoat' > \
+		    $OBJ/authorized_principals_$USER
+		${SSH} -2i $OBJ/cert_user_key \
+		    -F $OBJ/ssh_proxy somehost false >/dev/null 2>&1
+		if [ $? -ne 0 ]; then
+			fail "ssh cert connect failed"
+		fi
 
-	# authorized_principals with command=true
-	verbose "$tid: ${_prefix} authorized_principals command=true"
-	echo 'command="true" mekmitasdigoat' > \
-	    $OBJ/authorized_principals_$USER
-	${SSH} -2i $OBJ/cert_user_key \
-	    -F $OBJ/ssh_proxy somehost false >/dev/null 2>&1
-	if [ $? -ne 0 ]; then
-		fail "ssh cert connect failed"
-	fi
+		# Setup for principals= key option
+		rm -f $OBJ/authorized_principals_$USER
+		(
+			cat $OBJ/sshd_proxy_bak
+			echo "UsePrivilegeSeparation $privsep"
+		) > $OBJ/sshd_proxy
 
-	# Setup for principals= key option
-	rm -f $OBJ/authorized_principals_$USER
-	(
-		cat $OBJ/sshd_proxy_bak
-		echo "UsePrivilegeSeparation $privsep"
-	) > $OBJ/sshd_proxy
+		# Wrong principals list
+		verbose "$tid: ${_prefix} wrong principals key option"
+		(
+			printf 'cert-authority,principals="gregorsamsa" '
+			cat $OBJ/user_ca_key.pub
+		) > $OBJ/authorized_keys_$USER
+		${SSH} -2i $OBJ/cert_user_key \
+		    -F $OBJ/ssh_proxy somehost true >/dev/null 2>&1
+		if [ $? -eq 0 ]; then
+			fail "ssh cert connect succeeded unexpectedly"
+		fi
 
-	# Wrong principals list
-	verbose "$tid: ${_prefix} wrong principals key option"
-	(
-		printf 'cert-authority,principals="gregorsamsa" '
-		cat $OBJ/user_ca_key.pub
-	) > $OBJ/authorized_keys_$USER
-	${SSH} -2i $OBJ/cert_user_key \
-	    -F $OBJ/ssh_proxy somehost true >/dev/null 2>&1
-	if [ $? -eq 0 ]; then
-		fail "ssh cert connect succeeded unexpectedly"
-	fi
-
-	# Correct principals list
-	verbose "$tid: ${_prefix} correct principals key option"
-	(
-		printf 'cert-authority,principals="mekmitasdigoat" '
-		cat $OBJ/user_ca_key.pub
-	) > $OBJ/authorized_keys_$USER
-	${SSH} -2i $OBJ/cert_user_key \
-	    -F $OBJ/ssh_proxy somehost true >/dev/null 2>&1
-	if [ $? -ne 0 ]; then
-		fail "ssh cert connect failed"
-	fi
-done
+		# Correct principals list
+		verbose "$tid: ${_prefix} correct principals key option"
+		(
+			printf 'cert-authority,principals="mekmitasdigoat" '
+			cat $OBJ/user_ca_key.pub
+		) > $OBJ/authorized_keys_$USER
+		${SSH} -2i $OBJ/cert_user_key \
+		    -F $OBJ/ssh_proxy somehost true >/dev/null 2>&1
+		if [ $? -ne 0 ]; then
+			fail "ssh cert connect failed"
+		fi
+	done
+else
+	echo "SKIPPED: $PRINCIPALS_COMMAND not executable " \
+	    "(/var/run mounted noexec?)"
+fi