I am working on a project which requires opening a serial port and write/read data with an external device.

'Cutecom' returned error "could not open serial port"

'Terminal' returned error "permission denied" when I tried to execute "stty -F /dev/ttyS0 57600 parodd" command.

I am loged in the box with administrative previleges.

The command "chmod o+rw /dev/ttyS0", which I found in this forum also returns "Operation not permitted" error. Terminal output is given below:

Please Help to resolve this.

------------------------------------------------
"user@ubuntu:~$ dmesg | grep tty
[ 0.000000] console [tty0] enabled
[ 0.990934] 00:06: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A
[ 88.941050] cdc_acm 1-7:1.1: ttyACM0: USB ACM device
[ 88.944660] cdc_acm 1-7:1.3: ttyACM1: USB ACM device
user@ubuntu:~$ stty -F /dev/ttyS0 57600 parodd
stty: /dev/ttyS0: Permission denied
user@ubuntu:~$ chmod o+rw /dev/ttyS0
chmod: changing permissions of ‘/dev/ttyS0’: Operation not permitted
--------------------------------------------------

thanks.
GRams.

What is the output of this command?
This is what my system gives:
jdk

Hi JDK,

command 'ls -l /dev/ttyS0' give following output:
crw-rw---- 1 root dialout 4, 64 May 2 14:21 /dev/ttyS0.
/dev/ttyS0 is given a yellow background.
'/dev# ls -l ttyS0' - does not appear in the terminal.

thanks
GRams.

I wouldn't expect it to. That was just to show you what command I gave, what folder I gave it from and that I was logged in as root when I gave it. /dev#
is just the prompt.
jdk

I am getting to know the command structure & appreciate your exlanation.

'ls -l /dev/ttyS0' throws following output for me. My ID has admin rights.
crw-rw---- 1 root dialout 4, 64 May 2 14:21 /dev/ttyS0.

is there a way to fix the issue and get the port open?.

thanks.
grams.

I think you have to use "sudo" in Ubuntu. Have you tried the command: Then you will be prompted for your own password and then that should solve the permissions issue.
jdk

Hi Jdkaye,
I found a solution (from another forum) for this problem by adding my id to the group the tty's belong to. I didn't try sudo. Anyways, thanks for your time and help
-grams.

Code:
user@ubuntu:~$ id -Gn
user adm cdrom sudo dip plugdev lpadmin sambashare
user@ubuntu:~$ sudo adduser user dialout
[sudo] password for user:
Adding user `user' to group `dialout' ...
Adding user user to group dialout
Done.
user@ubuntu:~$ id -Gn
user adm cdrom sudo dip plugdev lpadmin sambashare
//*adduser is not reflected
//*log out and log in for adduser to take effect
user@ubuntu:~$ id -Gn
user adm dialout cdrom sudo dip plugdev lpadmin sambashare

Now I am able to send commands and receive data.

You're quite welcome. As a service to others please mark this thread as [SOLVED]. You use the Thread Tools menu just above your first post on this thread. Thanks.
jdk