write/mesg default settings

[jason_m]

To use the write command, I believe both the sender and the recipient need to have write access enabled to their terminal. The write man page says to do this with the command 'mesg y'.

It seems to me that depending on how I start my terminal session, the default value of whether write access is enabled or disabled is different. Neither the write or mesg man pages describe where this value is stored or where the default comes from.

A search of this forum and of google seems to just either return the man pages for the commands or end the discussion with "you can enable it with mesg".

Does anyone know where the default/initial setting for that access comes from?

Just playing around, appreciate your responses,

Jason

[gemlin]

Hi,
you are telling correct ,maybe internally its defined as a yes option for mesg command.Any more solutions pls welcome for this issue...
mesg
The mesg command controls messages received on a terminal.
-n does not allow messages to be displayed on screen
-y allows messages to be displayed on screen

write
The write command allows inter-user communication. A user can send messages by addressing the other user’s terminal or login id.
write user-name [terminal number]


rgds
gemlin

[jason_m]

I got a little adventurous last night and went straight to the mesg source code to see how this works. It is quite simple really, it all depends on the terminal device file permissions.

When I log in at the console, I can check which tty device I am using with the ps command:

  PID TTY          TIME CMD
14751 tty3     00:00:00 bash
14826 tty3     00:00:00 ps

So I'm using tty3. Let's see if terminal messages are enabled or not with the mesg command:

jason@compy ~ $ mesg
is n

Lets see what the file permissions are on my tty device:

jason@compy ~ $ ls -l /dev/tty3
crw------- 1 jason tty 4, 3 2008-11-06 07:45 /dev/tty3

Looks like only I have access to the device. This is consistent with the output of mesg. Thus any other user attempting to write to my terminal will be denied.

After running 'mesg y', lets check out the permissions again:

jason@compy ~ $ ls -l /dev/tty3
crw--w---- 1 jason tty 4, 3 2008-11-06 07:45 /dev/tty3

Now any other user in the tty group will be able to write to my terminal. So there you have it

I'm not familiar with how to configure udev, but i believe that I see different file permission modes between tty and pty devices which I think explains the different initial permissions for terminal write access.

[gemlin]

well dude...