root user can call the command directly;
if non root user want to call the command he should use the total path /sbin/ifconfig
or
add /sbin to the $PATH variable.
or
do like as: http://www.linuxdiyf.com/viewarticle.php?id=110316
"Fedora 9 -解决ifconfig无法于一般使用者状态下使用"