Serial port appears to be controlled by another program.

There is a Linux program called "fuser". It lists those processes that have an open file descriptor to a file  you list on the commandline.

tree:~> sleep 5 < /dev/ttyAMA0 &

[1] 15354

tree:~> fuser /dev/ttyAMA0

/dev/ttyAMA0:        15354

tree:~> fuser /dev/ttyAMA0

tree:~>

Then you can list the process using ps. In my case, if I hadn't known what that 15354 process was, I would have typed "ps auxww |grep 15354".

To find the process name of a pid you can also use "ps -a 15354".

I found this at RasPi Wiki at elinux.org:

S/W: Preventing Linux from using the serial port

 

By default Linux will grab the serial port and use it as a terminal. If you want to use it for other purposes you must prevent this. Here are the methods you can use: ...

Maybe this is what's going on.

You may be correct. There is a file in the boot partition/directory on the SD card called cmdline.txt. The file has one line in it:

dwc_otg.lpm_enable=0 console=serial0,115200 console=tty1 root=/dev/mmcblk0p2 rootfstype=ext4 elevator=deadline fsck.repair=yes rootwait

As you can see "console=serial0,115200" tells Linux to use the serial port as a console. If you remove that part of the command line (you probably

want to save the original file in the boot directory first), Linux will no longer use the serial port. Since the boot partition uses a Microsoft FAT partition

the file can be edited using either Windows or Linux.

Thanks for all the help.  I decided to take another SD card and rebuild the system I had and save it as a starting point in case I have any other problems.  When I get finished, I'll go back to the original OS and figure out what caused the problem using the help you guys have given me.  I'm sure someone else might eventually have the same problem and would like to know what the resolution was.  Give me a day or so as I have other things to attend to.

I pulled the SD card and looked at it.  There is no file called "cmdline.txt" on the disk.  Here is the contents of the SD card:

I went back to this pointer and did what it said.  I executed "raspi-config", selected #9, "Advanced Options", selected "Serial" and then disabled the serial.  Then selected "Finish" and that took care of it after a reboot.  Thanks a million for the help.

Terry

Not sure what OS you are using other than it is not Raspbian. I see the riscos-boot.bin file but the fact that you used raspi-config which is I believe a BASH

script program to fix it has gotten me really confused.

Good to see that you got it working !

Actually, it's what came with the Pi I got from Element 14 along with the preconfigured SD card. I had two SD cards and they were both the same.