# umount /dev/dsk/c0t2d0s7  umount: /dev/dsk/c0t2d0s7: device is busy

The fuser command
can take two types of arguments:

• normal filename: You can pass a normal filename or directory to the fuser
  command. In this case, it reports on that file or directory alone.
• special disk: You can also pass in a special disk name as an argument to
  fuser. In this case, it reports on all files and directories within the
  corresponding filesystem.

You can use the -u option to the fuser statement to display the user ID’s
as well as PID’s in its output.

Lets look at a few examples. The following command will display all processes and their
associated users that are using files/directories on a specified disk on a Sun Solaris
system:

# fuser -u /dev/dsk/c0t2d0s7
/dev/dsk/c0t2d0s7: 1313co(oracle) 1223c(root)

lsof /media/cdrom --> worked for me.

http://www.idevelopment.info/data/Unix/General_UNIX/GENERAL_Troubleshootingthedeviceisbusy.shtml

http://wiki.linuxquestions.org/wiki/Umount