Hacker News Reader

Comment by Y_Y | Hacker News Reader

Can't one just

    sudo echo -e "\7”

anyway? Or if you're trying to do something fancier there is snd-pcsp which lets use use the piezo as a normal ALSA device (quality may vary). Not that many modern machines even include such a useful device.

View on HN

If you're connected to a remote server, `echo` will annoy you and your cat, but `beep` will annoy the server administrator :)

I have long wished servers had functioning speakers.

And that virtio-beep existed.

I wonder what would happen if I pushed to get the support into KVM and the kernel. Best case scenario, the videos accompanying the too-bemused-to-really-be-angry bug reports would be legendary.

Why would that need root? Is it not up to your terminal emulator to interpret the \7 and trigger the actual beep?

See the "A note about ioctl" section of the README: https://github.com/johnath/beep

That section says:

> there's only one file opening, and while there is a potential race condition there, it's with /dev/console. If someone can exploit this race by replacing /dev/console, you've got bigger problems. :)

However, by reading the source one can see that you can now tell beep where it should direct its output (-e, which is not documented anywhere), so the note above is no longer accurate.

I would guess that this is the crux of the problem – the patch that fixes the security issue basically changes "open the output device once for each beep" to "open the output device on startup", greatly reducing the number of races. (It also zeroes out the buffer that's being written to certain output devices, but I have no idea if that is also to patch this security hole or to proactively prevent uninitialized bytes from leaking.)

But echo doesn't do any ioctls. The only thing it does is writing bytes on stdout.

I guess the whole point of setuid is that no, you can't always "just sudo" :-)

    #include <curses.h>
    main() { beep(); }

In fairness, the beep command does more https://linux.die.net/man/1/beep

Nitpick: on my machine, that's:

    sudo echo -e "\07"

Simply displaying a character doesn't need sudo at all anyway, so just

    echo -e "\07"

`sudo` isn't there for displaying the character, it's there for ioctl to have permissions to play the beep on remote terminals[1].

I think some terminal emulators (eg Konsole) will just read char 7 and play a system defined WAV or other workaround but your more classic terminals (eg xterm) would potentially have difficulties calling the system bell.

[1] for reference: Xorg terminals are also classed as remote terminals (eg check the TTY column in `w` to see how Linux assigns pseudo-tty's to terminal emulators inside X).

Even in that case, you'd have to run the terminal as root. Running echo as root won't do anything. X11 also has beep functionality built in, which is what I'd expect xterm to use.

> Even in that case, you'd have to run the terminal as root. Running echo as root won't do anything.

To be honest that was my assumption as well but I didn't test that theory so was only reporting on the rationale of the GPs post

> X11 also has beep functionality built in, which is what I'd expect xterm to use

X11 runs as root though (that said Xorg may not anymore now as there were talks about patching Linux so it didn't have to be) so Xorg could easily still use the standard ioctl bell (that's possibly all Xorg is doing behind the scenes in fact?)

But as I said earlier, some GUI terminal emulators avoid ioctl entirely and play a WAV tone instead.

"echo -e" is not portable, and neither are any escape sequences for echo.

The portable way to print ASCII BEL is:

    printf '\a'

Yes, it tries to do fancy things with ioctl().

Reply on news.ycombinator.com