commands: Add AddUserSubGroupRange and AddUserSubUserRange

To write /etc/sub{g,u}id files.

commands/main.go

@@ -108,6 +108,18 @@ func AddGroup(root, groupName string, groupID int) error {
 	return ChrootExec(root, cmd)
 }
 
+// AddUserSubUserRange will write /etc/subuid with a subordinate UID range for a user
+func AddUserSubUserRange(root, userName string, rangeMin, rangeMax int) error {
+	cmd := fmt.Sprintf("/usr/sbin/usermod --add-subuids %d-%d \"%s\"", rangeMin, rangeMax, userName)
+	return ChrootExec(root, cmd)
+}
+
+// AddUserSubUserRange will write /etc/subgid with a subordinate GID range for a user
+func AddUserSubGroupRange(root, userName string, rangeMin, rangeMax int) error {
+	cmd := fmt.Sprintf("/usr/sbin/usermod --add-subgids %d-%d \"%s\"", rangeMin, rangeMax, userName)
+	return ChrootExec(root, cmd)
+}
+
 // AddUser will chroot into the given root and add a user
 func AddUser(root, userName, gecos, home, shell string, uid, gid int) error {
 	cmd := fmt.Sprintf("/usr/sbin/useradd -m -d \"%s\" -s \"%s\" -u %d -g %d \"%s\" -c \"%s\"",