Solving under CentOS 6.5 command not found problem


Today, while CentOS system is turned on, and suddenly all the commands are in normal use, such as: shutdown reboot SSH SCP. Display all command not found.
To understand!!! A few days ago was fine.
Identify configuration file/root/.bash_profile to modify:
1, enter the root path
2,. bash_profile are hidden files, using the command: display
3, VI. bash_profile to read as follows:
# .bash_profile
# Get the aliases and functions
if [ -f ~/.bashrc ]; then
. ~/.bashrc
fi
# User specific environment and startup programs
PATH=$PATH:$HOME/bin:/sbin:/usr/bin:/usr/sbin
export PATH
unset USERNAME
4, save and exit
5, direct power off shutdown reboot (because the shutdown order execution. Directly off), after the restart problemsolving!