-INSTALL_FILE=install -o root -g root -m 644
-INSTALL_PROGRAM=install -o root -g root -m 755 -s
-INSTALL_DIR=install -o root -g root -m 755 -d
+INSTALL_FILE ?= install -o root -g root -m 644
+INSTALL_PROGRAM ?= install -o root -g root -m 755 -s
+INSTALL_DIR ?= install -o root -g root -m 755 -d
+STRIP ?= strip