may simply not appear that you do not have execute permissions or should do it as root.
example: ubuntu 8.04 on the command you mentioned,
ifconfig
works for me normally, you can now if you are in Debian, happened to me, I can only run it as root:
su -
password:> do not see what you write <
ifconfig
on the other hand know that more help gnu-linux distribution you are using.
for root pass, or you can usually try:
sudo su
or
su -
Greetings.