Visible bell mini-Howto
Alessandro Rubini, v2.3, 2001-12-03
This document explains how to use termcap to configure a visual bell on one's system and describes how to disable audible bells on demand.
This document is Copyright (c) 1997, Alessandro Rubini.
This document is distributed under the terms of the GNU Free Documentation License. You should have received a copy along with it. If not, it is available from http://www.fsf.org/licenses/fdl.html.
The Linux console driver beeps the audible bell whenever a BEL char is output (ASCII code 7). Though this is a right choice for the default behaviour, many users don't like their computer to beep. This mini-Howto is meant to explain how to tell applications not to output the BEL code. It also explain how to instruct the kernel and the X Window System to avoid beeping when a BEL is output. Note that most of this document refers to the text console, as configuring the X server is an easy catch-all for any user who works in a graphic environment.
In my opinion the best way to face a fussy computer is fixing the hardware, and my own computer doesn't even carry a loudspeaker.
Speakerectomy is by far the most brilliant solution to the audible bell problem. As its name implies, it consists in removing the beeps by removing the beeper. The operation is straightforward and you don't even need any anesthetic, but if you want there's room for refinement.
PC's are usually equipped with a silly switch to lower CPU clock. The switch is never used when you work in a multitasking environment, as you don't even need to slow the computer down to run games based on software loops. Unfortunately we can't use the switch to increase processor speed, but we can use it to enable/disable the loudspeaker. Sometimes the speaker is useful even if you enjoy a silent number cruncher, for example to signal the end of a lenghty compilation. To modify the switch functionality, just detatch it from the main board and connect its wires in series with the loudspeaker.
Owners of laptop boxes, unfortunately, don't have easy access to the loudspeaker, and neither they have a spare switch to turn to a different task. The preferred solution for such users is configuring their software to avoid beeping, as described below.
As of Linux 1.3.43, Martin Mares added the ability to configure the
pitch and duration of the beep, by modifying
console.c. Each console can be configured to feature a
different duration and/or pitch of the bell sound; the task is
accomplished by using escape sequences to the console device. You
can configure your own
~/.login file to select a different beep sound
associated to each console (or no beep at all, if needed).
The escape sequences work as follow:
]selects the bell frequency in Hertz. The value should be in the range 21-32766, otherwise the result is undefined. If the `xx' argument is missing, the default value (750Hz) will apply, as in `ESC-
]selects the bell duration, in milli-seconds. If you specify more than 2 seconds, the default applies (125ms). Once again, if the `xx' argument is missing (ESC-
) the default value will be used.
To select, for example, a 50Hz pitch for one-second duration, you
echo -e "\\33[10;50]\\33[11;1000]"" with
bash (where "-e" means `understand Escape sequences'.
If you use
tcsh the same command spells "
Although I don't know of any version of the
command that supports such configuration, a future version of the
command might well support a command-line option to configure the
If you run Linux-1.3.43 or newer, you may be satisfied with the escape sequences and avoid reading further. If you run an older kernel, or if you want the visual bell, you'll enjoy the rest of this document.
/etc/termcap is a text file that lists the
applications use the
termcap information to move the
cursor around the screen and do other screen-oriented tasks.
vi and all the
curses-based applications use the
The database describes several terminal types. The
TERM environment variable selects the right behaviour
at run-time, by naming a
termcap entry to be used by
Within the database, each capability of the terminal appears as a
two-letter code and a representation of the actual escape sequence
used to get the desired effect. The separator character between
different capabilities is the colon (":"). As an example, the
audible bell, with code "bl", usually appears as
bl=^G". This sequence tells that the bell sound is
obtained by printing the control-G character, the ASCII BEL.
In addition to the
bl capability, the
capability is recognized. It is used to represent the "visible
vb is usually missing in the
entry of the
Most modern applications and libraries use the
terminfo database instead of
This database uses one file per terminal-type and lives in
/usr/lib/terminfo; to avoid using huge directories,
the description of each terminal type is stored in a directory
named after its first letter; the
/usr/lib/terminfo/l/linux. To build a
terminfo entry you'll ``compile'' the
termcap description; refer to the
program and its manual page.
You can add the entry for the
vb capability in your
own termcap file, if it doesn't already define one. Dennis
) suggested to insert the following line in
termcap entry for
linux (note that
the entry is called
console in old distributions):
The trailing backslash is used to escape the newline in the database. Dennis' code does the following (his own words):
- Save the cursor position (uust a safety precaution).
- Change the background color several times between normal and reverse.
- Restore the cursor position.
If you want to force the visible bell on your console you can use
bl" entry in
termcap and define it
with the same string suggested for "
vb" above. This
approach is handy if you don't want to customize each application
(which is described below, anyway). I use this option on all the
machines where I can run Linux and I can't detach the speaker.
This is an incomplete list of applications that can be instrued to
vb entry for the current terminal type (using
termcap information or the
- The X server: use the "
xset b" command to select the bell's behaviour. The command takes three numeric arguments: volume, pitch and duration. "
xset -b" disables the bell altogether. Configuring the X server affects all the applications running on the display.
xterm: xterm can convert each bell to either a visible or audible signal. If you use the audible bell, the settings of "
xset" will apply. The bell in
xtermdefualts to be audible, but you can use the "
-vb" command line option and the "
xterm*visualBell: true" resource to turn it to a visible flash. You can toggle visible/audible signaling at run-time by using the menu invoked by control--left-mouse-button. If you run X you most likely won't need the following information.
tcsh(6.04 and later): "
set visiblebell". The instruction can be placed in
.cshrcor can be issued interactively. To reset the audible bell just "
unset visiblebell". To disable any notification issue use "
set nobeep" instead.
bash(any bash, as fas as I know): put "
set bell-style visible" in your
~/.bashrc. Possible bell-style's are also "none" or "audible".
readline, as well as other
readlinebased applications): put "
set prefer-visible-bell" in
elvis: put "
set flash" in
~/.exrcor tell "
:set flash" interactively (note the colon). To disable the visible bell use
noflashin place of
emacs: put "
(setq visible-bell t)" in your
~/.emacs. It is disabled by "
(setq visible-bell nil)".
less: use "
-q" on command line to use the visual bell, use "
-Q" to disable any reporting. Default options can be put in your environment variable "
screen: issue the CtrlA-CtrlG command. It changes the behaviour of all the virtual screens. Refer to the man page under "CUSTOMIZATION" for setting the default.
The bad news is that not every application uses
terminfo. Most small programs
feature 'backslash-a' (alarm) characters in the C source code. The
"alarm" code becomes a literal ASCII BEL in the strings as stored
in the executable binary. Real application don't usually fall in
this category, but be careful of C newcomers who give you their own
programs. Students of computer science are the worst of all,
The only way to make these programs silent applications is spekearectomy, or using the escape sequences by Martin Mares.