umount2: Device or resource busy
umount: /u01/mount: device is busy.
(In some cases useful info about processes that use
the device is found by lsof(8) or fuser(1))
umount -f /u01/mount/
fuser -km /u01/mount/
fuser 命令显示访问某个文件的进程的PID. 。-k 是kill 访问这个文件的进程。 没有进程访问，就可以成功umount了。
c 当前路径(current directory.)我的理解是表示这个资源的占用是以文件目录方式，也就是进进入了需要释放的资源的路径，这是最常用的资源占用方式。
e 正在运行可执行文件（executable being run.），比如运行了光盘上的某个程序
f 打开文件（ open file），缺省模式下f忽略。所以上面的例子中，虽然是开打了光盘上的Autorun.inf文件，但是给出的标识是c，而不是f。
r root目录（root directory）.不太清楚？
m mmap文件或者共享库( mmap’ed file or shared library).这应该是说某个进程使用了你要释放的资源的某个共享文件
FUSER(1) User Commands FUSER(1)
fuser - identify processes using files or sockets
fuser [-a|-s|-c] [-4|-6] [-n space ] [-k [-i] [-signal ] ] [-muvf] name
fuser displays the PIDs of processes using the specified files or file systems. In the default display mode, each file name is followed by a letter denoting the type
c current directory.
e executable being run.
f open file. f is omitted in default display mode.
F open file for writing. F is omitted in default display mode.
r root directory.
m mmap'ed file or shared library.
fuser returns a non-zero return code if none of the specified files is accessed or in case of a fatal error. If at least one access has been found, fuser returns zero.
In order to look up processes using TCP and UDP sockets, the corresponding name space has to be selected with the -n option. By default fuser will look in both IPv6 and IPv4 sockets. To change the default, behavior, use the -4 and -6 options. The socket(s) can be specified by the local and remote port, and the remote address. All fields are optional, but commas in front of missing fields must be present:
Either symbolic or numeric values can be used for IP addresses and port numbers.
fuser outputs only the PIDs to stdout, everything else is sent to stderr.
-a Show all files specified on the command line. By default, only files that are accessed by at least one process are shown.
-c Same as -m option, used for POSIX compatibility.
-f Silently ignored, used for POSIX compatibility.
-k Kill processes accessing the file. Unless changed with -signal, SIGKILL is sent. An fuser process never kills itself, but may kill other fuser processes. The effective user ID of the process executing fuser is set to its real user ID before attempting to kill.
-i Ask the user for confirmation before killing a process. This option is silently ignored if -k is not present too.
-l List all known signal names.
-m name specifies a file on a mounted file system or a block device that is mounted. All processes accessing files on that file system are listed. If adirectory file is specified, it is automatically changed to name/. to use any file system that might be mounted on that directory.
-n space Select a different name space. The name spaces file (file names, the default), udp (local UDP ports), and tcp (local TCP ports) are supported. For ports, either the port number or the symbolic name can be specified. If there is no ambiguity, the shortcut notation name/Ispace (e.g. 80/tcp ) can be used.
-s Silent operation. -u and -v are ignored in this mode. -a must not be used with -s.
-signal Use the specified signal instead of SIGKILL when killing processes. Signals can be specified either by name (e.g. -HUP) or by number (e.g. -1). This option is silently ignored if the -k option is not used.
-u Append the user name of the process owner to each PID.
-v Verbose mode. Processes are shown in a ps-like style. The fields PID, USER and COMMAND are similar to ps. ACCESS shows how the process accesses the file. If the access is by the kernel (e.g. in the case of a mount point, awap file, etc.), kernel is shown instead of the PID.
-V Display version information.
-4 Search only for IPv4 sockets. This option must not be used with the -6 option and only has an effect with the tcp and udp namespaces.