secUser=`who am i | awk '{print $1}'` 
#echo $secUser 
su $secUser -c 指令> > /dev/null 2>1  #这一条命令的执行权限是临时的，只在本条语句起作用 
id -u # 结果为0，还是root用户权限 

 -c, --command COMMAND   pass COMMAND to the invoked shell
 -h, --help     display this help message and exit
 -, -l, --login    make the shell a login shell
 -m, -p,
 --preserve-environment  do not reset environment variables, and
        keep the same shell
 -s, --shell SHELL    use SHELL instead of the default in passwd