For example  #ls 2>&1 > ls.log What is actually mean by 2>&1?? Since every shell process has there own descriptor :: 0 (stdin), 1 (stdout) and 2 (stderr) :: and & in the front of &1 indicated that 1 is not a file or folder, it is a descriptor. The > mean redirect the out put to another descriptors or  files. in this case 2>&1 > ls.log means that stderr(2) and stdout(1) put is redirected to the ls.log file. normally, for example #ls […]

When you try to umount the regular way, if a device is busy you’ll get the following : dev:/# umount /dev/sda1 umount2: Device or resource busy umount: /boot: device is busy This can be solver very easy by entering this : dev:/# umount -l /dev/sda1