A program to send a character to another tty fails in 64-bit
 

I wrote a small program to send a character to a terminal other than my own. I moved to 64-bit recently and the program fails.

I open a terminal with:
then send a character with:
The open succeeds but the ioctl fails with errno=1, Operation not permitted.

If I send to its own tty it works. Ownership and permissions of the target terminal don't matter. If I do it as root it works.
What's the difference between 32 and 64 bit?

Most likely you are hitting capabilities. My guess would be you need CAP_SYS_TTYCONFIG.

http://man7.org/linux/man-pages/man7...ilities.7.html

Thanks. I didn't know about this; BTW it's CAP_SYS_TTY_CONFIG. I wrote the program a few years ago. I worked until I switched to 64-bit, same kernel version.

You updated system to 64 bits keeping same group settings for user?

Yes.

Setting the sticky bit makes it work.