centos找不到环境变量 -bash: ls: command not found

#在系统中输入命令，报如下错误：

[root@a1 work]# ll
-bash: ls: command not found

#昨时解决办法：
export PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

#永久解决办法：
echo "export PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/roobo/server/mysql/bin:/root" >>/etc/profile
source /etc/profile