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If there is an error reading from a disk, cdrom etc; then that is a kernel
driver error. The kernel driver may or may not display an error message.
Even if the kernel driver does display an error message, you may not see the
message because it may scroll off the display, or it may be displayed to a
different console. The kernel will NOT report the error to the program which
requested the data. Some programs like gzip may realize that something is
wrong with the data. Other programs like cp will never know that something
is wrong with the data. I do not know how to make a shell script which can
detect such errors.