[sf-lug] system beep
a_kleider at yahoo.com
Mon Jan 18 01:04:26 PST 2010
I've learned a few things in my pursuit of this issue and am passing them on for anyone who might be interested:
The problem is that my initial method of making the alarm noise was
to send CTRL-A characters to standard output.
If the at utility is used, when the script is eventually run, there is no
attached terminal to which to send the output.
A workaround (suggested by Akkana) was to send output directly to /dev/console but to do so, its permissions have to be modified
(sudo chmod 602 /dev/console).
$ echo $'\a' >/dev/console
This ofcourse raises some security issues, but I can't think how that could
be much of a problem (on my personal laptop.) From a security point of view, having to change the setuid bit of the script or running it as root seemed even less desirable options to me.
The other thing I discovered is that the syntax of the at utility doesn't
seem to allow any parameters to be passed to the job(s). I got around this
by using its -f option. This didn't work until all paths were specified
as absolute paths, again, I assume, because when run, who knows what is the current working directory. By 'all paths' I mean (1) the file given to the -f option and (2) the script listed in that file.
$ cat time
/home/alex/Python/Alarm/hardwareTimer -s 3
$ at 06:00am -f /home/alex/Python/Alarm/time
By the way, my script happens to be written in Python, but that's a different matter.
--- On Fri, 1/8/10, Akkana Peck <akkana at shallowsky.com> wrote:
> From: Akkana Peck <akkana at shallowsky.com>
> Subject: Re: [sf-lug] system beep
> To: sf-lug at linuxmafia.com
> Date: Friday, January 8, 2010, 10:17 AM
> > On Thu, 2010-01-07 at 17:49
> -0800, Alex Kleider wrote:
> > > if at the linux command line (bash shell) I type
> > > $ echo $'\a'
> > > the bell rings
> jim writes:
> > when i use the command
> > $ echo $'\a'
> Another way is to tell bash to print the beep character
> (ctrl-G, ASCII 7):
> $ echo -e "\007"
> But when I put either one in a script and run it through
> at, the
> problem seems to be that at is redirecting the output, so
> the ctrl-G
> never goes to a terminal that can turn it into sound. Try
> some visible text in your script:
> echo BEEP $'\a'
> and you'll see that you never see the BEEP either if you
> call it
> from at.
> If you explicitly redirect it to a terminal, it works.
> For instance, type tty to find out what your current
> terminal is,
> then put that in the script:
> echo BEEP $'\a' >/dev/pts/1
> and call it from at, and it should work (it did for me).
> But that's not very convenient if you want to schedule a
> script to run
> days fom now, since you'd have to be sure what pty is there
> you can write to.
> If your script can run as root, you could use the console:
> echo $'\a' >/dev/console
> Or if you're pretty sure you'll be logged in on the console
> your own user, you could use tty0 or tty1:
> echo $'\a' >/dev/tty1
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