I want to allow a user to execute some privileged commands.

I setup the sudoer configurations as follows:
First configuration:
# sudoers file.
#
# This file MUST be edited with the 'visudo' command as root.
#
# See the sudoers man page for the details on how to write a sudoers file.
#

# User privilege specification
root ALL=(ALL) ALL

powah ALL = NOPASSWD: /usr/sbin/tethereal
powah ALL = NOPASSWD: /usr/local/sbin/iwconfig



Second configuration:

# sudoers file.
#
# This file MUST be edited with the 'visudo' command as root.
#
# See the sudoers man page for the details on how to write a sudoers file.
#

# User privilege specification
root ALL=(ALL) ALL
powah ALL=(ALL) ALL


Login as powah using the first and then the second configurations, the privileged command can not be executed:
$ /sbin/ifconfig ath0 up
SIOCSIFFLAGS: Permission denied


Login as root, then the privileged command can be executed:
$ su
Password:
# /sbin/ifconfig ath0 up

Try