Re: serial communication

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On Thu, 2012-04-05 at 14:25 -0500, ron r wrote:
> I am using Fedora 16.   Using "ls -l /dev/ttyS*" shows 4 "devices"
> with "crw-rw----" for each one.   So then I looked on google for
> setting serial permissions, and entered "chmod a+rw /dev/ttyS0" as
> root and the serial port now works!
> That was a nice victory, but the line must be entered at each boot.
> (Is there a solution to that?)
> 
I have this file:
==============File 99-local.rules start===============
#
# Locally defined rules.
#

#
# Give world read/write access to ttyS* and ttyUSB* serial devices
#
KERNEL=="tty[A-Z]*", GROUP="uucp", MODE="0666"
===============File 99-local.rules end================
installed in /etc/udev/rules.d/

There was no file with that name installed by default in my system but
check your system before dropping it in so you don't accidentally
clobber anything. I use the 99 prefix because these rules files are
applied in name sort order and I want to be sure that the device files
have been created before trying to override their access permissions. 

Another thing to check: the group assignments for serial port devices
may have changed since I wrote that file, which was for the first Fedora
that used UDEV serial port management, possibly Fedora 12 but could be
earlier. Before you install it, run "ls -l /dev/ttyS*" and, if the group
isn't "uucp" (it may be "tty"), replace that string with the group name
F16 is using. 

I know that this time round I just dropped 99-local.rules in without
checking the group name and appended " 8250.nr_uarts=5" to the
GRUB_CMDLINE_LINUX parameter in /etc/default/grub so the kernel knew it
was dealing with five serial ports: I have one on the motherboard and
another four on a multiport serial card. Then I rebooted so the kernel
parameter took effect and it all worked.


Martin






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