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Most device files will already be created and will be there
ready to use after you install your Linux system. If by some chance
you need to create one which is not provided then you should first
try to use the MAKEDEV script. This script is
usually located in
/dev/MAKEDEV but might also
have a copy (or a symbolic link) in
/sbin/MAKEDEV. If it turns out not to be in
your path then you will need to specify the path to it
/dev/ttyS0with major node 4 and minor node 64 as a character device with access permissions 0660 with owner root and group dialout.
ttyS0 is a serial port. The major and
minor node numbers are numbers understood by the kernel. The kernel
refers to hardware devices as numbers, this would be very difficult
for us to remember, so we use filenames. Access permissions of 0660
means read and write permission for the owner (root in this case)
and read and write permission for members of the group (dialout in
this case) with no access for anyone else.
MAKEDEV is the preferred way of creating
device files which are not present. However sometimes the
MAKEDEV script will not know about the device
file you wish to create. This is where the mknod
command comes in. In order to use mknod you need
to know the major and minor node numbers for the device you wish to
devices.txt file in the kernel
source documentation is the canonical source of this
/dev/ttyS0device file. We need to use mknod to create it. We know from looking at the
devices.txtthat it should be a character device with major number 4 and minor number 64. So we now know all we need to create the file.
More information on what hardware resources the kernel is using
can be found in the
/proc directory. Refer to
Section 3.7 in chapter 3.