From http://www.jwz.org/xscreensaver/xscreensaver-5.27.tar.gz

[xscreensaver] / driver / xscreensaver.man

.de EX          \"Begin example
.ne 5
.if n .sp 1
.if t .sp .5
.nf
.in +.5i
..
.de EE
.fi
.in -.5i
.if n .sp 1
.if t .sp .5
..
.TH XScreenSaver 1 "09-Nov-2013 (5.23)" "X Version 11"
.SH NAME
xscreensaver - extensible screen saver and screen locking framework
.SH SYNOPSIS
.B xscreensaver
[\-display \fIhost:display.screen\fP] \
[\-verbose] \
[\-no\-splash] \
[\-no\-capture\-stderr] \
[\-log \fIfilename\fP]
.SH DESCRIPTION
The \fIxscreensaver\fP program waits until the keyboard and mouse have been 
idle for a period, and then runs a graphics demo chosen at random.  It 
turns off as soon as there is any mouse or keyboard activity.

This program can lock your terminal in order to prevent others from using it,
though its default mode of operation is merely to display pretty pictures on
your screen when it is not in use.

It also provides configuration and control of your monitor's power-saving
features.
.SH GETTING STARTED
For the impatient, try this:
.EX
xscreensaver &
xscreensaver-demo
.EE
The
.BR xscreensaver-demo (1)
program pops up a dialog box that lets you configure the screen saver,
and experiment with the various display modes.

.B Note that xscreensaver has a client-server model:
the \fIxscreensaver\fP program is a daemon that runs in the background;
it is controlled by the foreground
.BR xscreensaver-demo (1)
and
.BR xscreensaver-command (1)
programs.
.SH CONFIGURATION
The easiest way to configure \fIxscreensaver\fP is to simply run the
.BR xscreensaver-demo (1)
program, and change the settings through the GUI.  The rest of this
manual page describes lower level ways of changing settings.

I'll repeat that because it's important:

.RS 4
The easy way to configure xscreensaver is to run the 
.BR xscreensaver-demo (1)
program.  You shouldn't need to know any of the stuff described 
in \fIthis\fP manual unless you are trying to do something tricky,
like customize xscreensaver for site-wide use or something.
.RE

Options to \fIxscreensaver\fP are stored in one of two places: in 
a \fI.xscreensaver\fP file in your home directory; or in the X resource
database.  If the \fI.xscreensaver\fP file exists, it overrides any settings
in the resource database.  

The syntax of the \fI.xscreensaver\fP file is similar to that of
the \fI.Xdefaults\fP file; for example, to set the \fItimeout\fP parameter
in the \fI.xscreensaver\fP file, you would write the following:
.EX
timeout: 5
.EE
whereas, in the \fI.Xdefaults\fP file, you would write
.EX
xscreensaver.timeout: 5
.EE
If you change a setting in the \fI.xscreensaver\fP file while xscreensaver
is already running, it will notice this, and reload the file.  (The file will
be reloaded the next time the screen saver needs to take some action, such as
blanking or unblanking the screen, or picking a new graphics mode.)

If you change a setting in your X resource database, or if you want
xscreensaver to notice your changes immediately instead of the next time
it wakes up, then you will need to reload your \fI.Xdefaults\fP file,
and then tell the running xscreensaver process to restart itself, like so:
.EX
xrdb < ~/.Xdefaults
xscreensaver-command -restart
.EE
If you want to set the system-wide defaults, then make your edits to
the xscreensaver app-defaults file, which should have been installed
when xscreensaver itself was installed.  The app-defaults file will
usually be named /usr/lib/X11/app-defaults/XScreenSaver, but different
systems might keep it in a different place (for example,
/usr/openwin/lib/app-defaults/XScreenSaver on Solaris.)

When settings are changed in the Preferences dialog box (see above)
the current settings will be written to the \fI.xscreensaver\fP file.
(The \fI.Xdefaults\fP file and the app-defaults file will never be
written by xscreensaver itself.)
.SH COMMAND-LINE OPTIONS
.I xscreensaver
also accepts a few command-line options, mostly for use when debugging:
for normal operation, you should configure things via the \fI~/.xscreensaver\fP
file.
.TP 8
.B \-display \fIhost:display.screen\fP
The X display to use.  For displays with multiple screens, XScreenSaver
will manage all screens on the display simultaniously.
.TP 8
.B \-verbose
Same as setting the \fIverbose\fP resource to \fItrue\fP: print diagnostics
on stderr and on the xscreensaver window.
.TP 8
.B \-no-capture-stderr
Do not redirect the stdout and stderr streams to the xscreensaver window
itself.  If xscreensaver is crashing, you might need to do this in order
to see the error message.
.TP 8
.B \-log \fIfilename\fP
This is exactly the same as redirecting stdout and stderr to the given
file (for append).  This is useful when reporting bugs.
.SH HOW IT WORKS
When it is time to activate the screensaver, a full-screen black window is
created on each screen of the display.  Each window is created in such a way
that, to any subsequently-created programs, it will appear to be a "virtual
root" window.  Because of this, any program which draws on the root 
window (and which understands virtual roots) can be used as a screensaver.
The various graphics demos are, in fact, just standalone programs that
know how to draw on the provided window.

When the user becomes active again, the screensaver windows are unmapped, and
the running subprocesses are killed by sending them \fBSIGTERM\fP.  This is 
also how the subprocesses are killed when the screensaver decides that it's
time to run a different demo: the old one is killed and a new one is launched.

You can control a running screensaver process by using the
.BR xscreensaver\-command (1)
program (which see.)
.SH POWER MANAGEMENT
Modern X servers contain support to power down the monitor after an idle
period.  If the monitor has powered down, then \fIxscreensaver\fP will
notice this (after a few minutes), and will not waste CPU by drawing 
graphics demos on a black screen.  An attempt will also be made to
explicitly power the monitor back up as soon as user activity is detected.

The \fI~/.xscreensaver\fP file controls the configuration of your
display's power management settings: if you have used
.BR xset (1)
to change your power management settings, then xscreensaver will
override those changes with the values specified 
in \fI~/.xscreensaver\fP (or with its built-in defaults, if there
is no \fI~/.xscreensaver\fP file yet.)

To change your power management settings, run
.BR xscreensaver\-demo (1)
and change the various timeouts through the user interface.
Alternately, you can edit the \fI~/.xscreensaver\fP file directly.

If the power management section is grayed out in the
.BR xscreensaver\-demo (1)
window,  then that means that your X server does not support
the XDPMS extension, and so control over the monitor's power state
is not available.

If you're using a laptop, don't be surprised if changing the DPMS
settings has no effect: many laptops have monitor power-saving behavior
built in at a very low level that is invisible to Unix and X.  On such
systems, you can typically adjust the power-saving delays only by
changing settings in the BIOS in some hardware-specific way.

If DPMS seems not to be working with XFree86, make sure the "DPMS"
option is set in your \fI/etc/X11/XF86Config\fP file.  See the
.BR XF86Config (5)
manual for details.
.SH USING GNOME
For the better part of a decade, GNOME shipped xscreensaver as-is,
and everything just worked out of the box.  In 2005, however, they
decided to re-invent the wheel and ship their own replacement for
the \fIxscreensaver\fP daemon called "\fIgnome-screensaver\fP",
rather than improving xscreensaver and contributing their changes
back.  As a result, the "\fIgnome-screensaver\fP" program is insecure,
bug-ridden, and missing many features of xscreensaver.  You shouldn't
use it.

To replace gnome-screensaver with xscreensaver:
.RS 4
.TP 3
\fB1: Fully uninstall the gnome-screensaver package.\fP
.EX
sudo apt-get remove gnome-screensaver
.EE
.TP 3
\fB2: Launch xscreensaver at login.\fP
Select "\fIStartup Applications\fP" from the menu (or manually
launch "\fIgnome-session-properties\fP") and add "\fIxscreensaver\fP".
.TP 3
\fB3: Make "Lock Screen" use xscreensaver.\fP
.EX
sudo ln -sf /usr/bin/xscreensaver-command \\
            /usr/bin/gnome-screensaver-command
.EE
.SH USING KDE
Like GNOME, KDE also decided to invent their own screen saver framework
from scratch instead of simply using xscreensaver.  To replace the KDE
screen saver with xscreensaver, do the following:
.RS 4
.TP 3
\fB1: Turn off KDE's screen saver.\fP
Open the "\fIControl Center\fP" and
select the "\fIAppearance & Themes / Screensaver\fP" page.
Un-check "\fIStart Automatically\fP".
.TP 3
\fB2: Find your Autostart directory.\fP
Open the "\fISystem Administration / Paths\fP" page,
and see what your "Autostart path" is set to: it will
probably be \fI~/.kde/Autostart/\fP or something similar.
.TP 3
\fB3: Make xscreensaver be an Autostart program.\fP
Create a .desktop file in your autostart directory 
called \fIxscreensaver.desktop\fP that contains the following five lines:
.EX

[Desktop Entry]
Exec=xscreensaver
Name=XScreenSaver
Type=Application
X-KDE-StartupNotify=false
.EE
.TP 3
\fB4: Make the various "lock session" buttons call xscreensaver.\fP
The file you want to replace next has moved around over the years. It
might be called \fI/usr/libexec/kde4/kscreenlocker\fP,
or it might be called "\fIkdesktop_lock\fP" or "\fIkrunner_lock\fP"
or "\fIkscreenlocker_greet\fP", and
it might be in \fI/usr/lib/kde4/libexec/\fP
or in \fI/usr/kde/3.5/bin/\fP or even in \fI/usr/bin/\fP,
depending on the distro and phase of the moon.  Replace the contents
of that file with these two lines:
.EX

#!/bin/sh
xscreensaver-command -lock

.EE
Make sure the file is executable (chmod a+x).
.RE
.PP
Now use xscreensaver normally, controlling it via the usual
.BR xscreensaver-demo (1)
and
.BR xscreensaver-command (1)
mechanisms.
.SH USING UNITY
Guess what, they did it again!  Ubuntu Unity's screen-locking
framework is \fIyet another\fP rewrite, and it is completely broken,
bug-ridden and insecure. At this time I don't have any information on
how to turn it off and use xscreensaver instead.  If you do, let me
know.
.SH USING GDM
You can run \fIxscreensaver\fP from your 
.BR gdm (1)
session, so that the screensaver will run even when nobody is logged 
in on the console.  To do this, run
.BR gdmconfig (1)
and on the \fIBackground\fP page, type the 
command \fB"xscreensaver -nosplash"\fP into the \fIBackground Program\fP
field.  That will cause gdm to run xscreensaver while nobody is logged
in, and kill it as soon as someone does log in.  (The user will then
be responsible for starting xscreensaver on their own, if they want.)

Another way to accomplish the same thing is to edit the
file \fI/etc/X11/gdm/gdm.conf\fP to include:
.EX
BackgroundProgram=xscreensaver -nosplash
RunBackgroundProgramAlways=true
.EE
In this situation, the \fIxscreensaver\fP process will probably be running
as user \fIgdm\fP instead of \fIroot\fP.  You can configure the settings
for this nobody-logged-in state (timeouts, DPMS, etc.) by editing
the \fI~gdm/.xscreensaver\fP file.

To get gdm to run the BackgroundProgram, you may need to switch it from
the "Graphical Greeter" to the "Standard Greeter".

It is safe to run \fIxscreensaver\fP as root (as \fIxdm\fP or \fIgdm\fP may do.)
If run as root, \fIxscreensaver\fP changes its effective user and group ids 
to something safe (like \fI"nobody"\fP) before connecting to the X server
or launching user-specified programs.

An unfortunate side effect of this (important) security precaution is that
it may conflict with cookie-based authentication.

If you get "connection refused" errors when running \fIxscreensaver\fP
from \fIgdm\fP, then this probably means that you have
.BR xauth (1)
or some other security mechanism turned on.  For information on the
X server's access control mechanisms, see the man pages for
.BR X (1),
.BR Xsecurity (1),
.BR xauth (1),
and
.BR xhost (1).
.SH BUGS
Bugs?  There are no bugs.  Ok, well, maybe.  If you find one, please let
me know.  http://www.jwz.org/xscreensaver/bugs.html explains how to
construct the most useful bug reports.
.PP
.TP 4
.B Locking and root logins
In order for it to be safe for xscreensaver to be launched by \fIxdm\fP,
certain precautions had to be taken, among them that xscreensaver never
runs as \fIroot\fP.  In particular, if it is launched as root (as \fIxdm\fP
is likely to do), xscreensaver will disavow its privileges, and switch 
itself to a safe user id (such as \fInobody\fP.)

An implication of this is that if you log in as \fIroot\fP on the console, 
xscreensaver will refuse to lock the screen (because it can't tell
the difference between \fIroot\fP being logged in on the console, and a
normal user being logged in on the console but xscreensaver having been 
launched by the
.BR xdm (1)
.I Xsetup
file.)

The solution to this is simple: you shouldn't be logging in on the console
as \fIroot\fP in the first place!  (What, are you crazy or something?)  

Proper Unix hygiene dictates that you should log in as yourself, and
.BR su (1)
to \fIroot\fP as necessary.  People who spend their day logged in
as \fIroot\fP are just begging for disaster.
.TP 4
.B XAUTH and XDM
For xscreensaver to work when launched by
.BR xdm (1)
or
.BR gdm (1),
programs running on the local machine as user \fI"nobody"\fP must be
able to connect to the X server.  This means that if you want to run
xscreensaver on the console while nobody is logged in, you may need
to disable cookie-based access control (and allow all users who can log
in to the local machine to connect to the display.)  

You should be sure that this is an acceptable thing to do in your
environment before doing it.  See the "\fIUsing GDM\fP" section, 
above, for more details.
.TP 4
.B Passwords
If you get an error message at startup like "couldn't get password
of \fIuser\fP" then this probably means that you're on a system in which 
the
.BR getpwent (3)
library routine can only be effectively used by root.  If this is the case, 
then \fIxscreensaver\fP must be installed as setuid to root in order for
locking to work.  Care has been taken to make this a safe thing to do.  

It also may mean that your system uses shadow passwords instead of the standard
.BR getpwent (3)
interface; in that case, you may need to change some options 
with \fIconfigure\fP and recompile.

If you change your password after xscreensaver has been launched, it will
continue using your old password to unlock the screen until xscreensaver
is restarted.  On some systems, it may accept \fIboth\fP your old and new
passwords.  So, after you change your password, you'll have to do
.EX
xscreensaver-command -restart
.EE
to make \fIxscreensaver\fP notice.
.TP 4
.B PAM Passwords
If your system uses PAM (Pluggable Authentication Modules), then in order
for xscreensaver to use PAM properly, PAM must be told about xscreensaver.
The xscreensaver installation process should update the PAM data (on Linux,
by creating the file \fI/etc/pam.d/xscreensaver\fP for you, and on Solaris, 
by telling you what lines to add to the \fI/etc/pam.conf\fP file.)  

If the PAM configuration files do not know about xscreensaver, then 
you \fImight\fP be in a situation where xscreensaver will refuse to ever
unlock the screen.

This is a design flaw in PAM (there is no way for a client to tell the
difference between PAM responding "I have never heard of your module",
and responding, "you typed the wrong password".)  As far as I can tell,
there is no way for xscreensaver to automatically work around this, or
detect the problem in advance, so if you have PAM, make sure it is
configured correctly!
.TP 4
.B Machine Load
Although this program "nices" the subprocesses that it starts, 
graphics-intensive subprograms can still overload the machine by causing
the X server process itself (which is not "niced") to consume many
cycles.  Care has been taken in all the modules shipped with xscreensaver
to sleep periodically, and not run full tilt, so as not to cause
appreciable load.

However, if you are running the OpenGL-based screen savers on a machine
that does not have a video card with 3D acceleration, they \fIwill\fP
make your machine slow, despite
.BR nice (1).

Your options are: don't use the OpenGL display modes; or, collect the
spare change hidden under the cushions of your couch, and use it to
buy a video card manufactured after 1998.  (It doesn't even need to be
\fIfast\fP 3D hardware: the problem will be fixed if there is any
3D hardware \fIat all.\fP)
.TP 4
.B XFree86's Magic Keystrokes
The XFree86 X server traps certain magic keystrokes before client programs ever
see them.  Two that are of note are Ctrl+Alt+Backspace, which causes 
the X server to exit; and Ctrl+Alt+F\fIn\fP, which switches virtual consoles.
The X server will respond to these keystrokes even if xscreensaver has the
screen locked.  Depending on your setup, you might consider this a problem.

Unfortunately, there is no way for xscreensaver itself to override the
interpretation of these keys.  If you want to disable Ctrl+Alt+Backspace
globally, you need to set the \fIDontZap\fP flag in 
your \fI/etc/X11/XF86Config\fP file.  To globally disable VT switching,
you can set the \fIDontVTSwitch\fP flag.  See the
.BR XF86Config (5)
manual for details.
.SH X RESOURCES
These are the X resources use by the \fIxscreensaver\fP program.
You probably won't need to change these manually (that's what the
.BR xscreensaver\-demo (1)
program is for).
.TP 8
.B timeout\fP (class \fBTime\fP)
The screensaver will activate (blank the screen) after the keyboard and
mouse have been idle for this many minutes.  Default 10 minutes.
.TP 8
.B cycle\fP (class \fBTime\fP)
After the screensaver has been running for this many minutes, the currently
running graphics-hack sub-process will be killed (with \fBSIGTERM\fP), and a
new one started.  If this is 0, then the graphics hack will never be changed:
only one demo will run until the screensaver is deactivated by user activity.
Default 10 minutes.
.TP 8
.B lock\fP (class \fBBoolean\fP)
Enable locking: before the screensaver will turn off, it will require you 
to type the password of the logged-in user (really, the person who ran
xscreensaver), or the root password.  (\fBNote:\fP this doesn't work if the
screensaver is launched by
.BR xdm (1)
because it can't know the user-id of the logged-in user.  See 
the "\fIUsing XDM(1)\fP" section, below.
.TP 8
.B lockTimeout\fP (class \fBTime\fP)
If locking is enabled, this controls the length of the "grace period"
between when the screensaver activates, and when the screen becomes locked.
For example, if this is 5, and \fI\-timeout\fP is 10, then after 10 minutes,
the screen would blank.  If there was user activity at 12 minutes, no password
would be required to un-blank the screen.  But, if there was user activity
at 15 minutes or later (that is, \fI\-lock\-timeout\fP minutes after 
activation) then a password would be required.  The default is 0, meaning
that if locking is enabled, then a password will be required as soon as the 
screen blanks.
.TP 8
.B passwdTimeout\fP (class \fBTime\fP)
If the screen is locked, then this is how many seconds the password dialog box
should be left on the screen before giving up (default 30 seconds.)  This
should not be too large: the X server is grabbed for the duration that the
password dialog box is up (for security purposes) and leaving the server 
grabbed for too long can cause problems.
.TP 8
.B dpmsEnabled\fP (class \fBBoolean\fP)
Whether power management is enabled.
.TP 8
.B dpmsStandby\fP (class \fBTime\fP)
If power management is enabled, how long until the monitor goes solid black.
.TP 8
.B dpmsSuspend\fP (class \fBTime\fP)
If power management is enabled, how long until the monitor goes into
power-saving mode.
.TP 8
.B dpmsOff\fP (class \fBTime\fP)
If power management is enabled, how long until the monitor powers down
completely.  Note that these settings will have no effect unless both
the X server and the display hardware support power management; not 
all do.  See the \fIPower Management\fP section, below, for more 
information.
.TP 8
.B dpmsQuickOff\fP (class \fBBoolean\fP)
If \fImode\fP is \fIblank\fP and this is true, then the screen will be
powered down immediately upon blanking, regardless of other
power-management settings.
.TP 8
.B visualID\fP (class \fBVisualID\fP)
Specify which X visual to use by default.  (Note carefully that this resource
is called \fBvisualID\fP, not merely \fBvisual\fP; if you set the \fBvisual\fP
resource instead, things will malfunction in obscure ways for obscure reasons.)

Legal values for the \fBVisualID\fP resource are:
.RS 8
.TP 8
.B default
Use the screen's default visual (the visual of the root window.)  
This is the default.
.TP 8
.B best
Use the visual which supports the most colors.  Note, however, that the
visual with the most colors might be a TrueColor visual, which does not
support colormap animation.  Some programs have more interesting behavior
when run on PseudoColor visuals than on TrueColor.
.TP 8
.B mono
Use a monochrome visual, if there is one.
.TP 8
.B gray
Use a grayscale or staticgray visual, if there is one and it has more than
one plane (that is, it's not monochrome.)
.TP 8
.B color
Use the best of the color visuals, if there are any.
.TP 8
.B GL
Use the visual that is best for OpenGL programs.  (OpenGL programs have
somewhat different requirements than other X programs.)
.TP 8
.I class
where \fIclass\fP is one of \fBStaticGray\fP, \fBStaticColor\fP, 
\fBTrueColor\fP, \fBGrayScale\fP, \fBPseudoColor\fP, or \fBDirectColor\fP.
Selects the deepest visual of the given class.
.TP 8
.I number
where \fInumber\fP (decimal or hex) is interpreted as a visual id number, 
as reported by the
.BR xdpyinfo (1)
program; in this way you can have finer control over exactly which visual
gets used, for example, to select a shallower one than would otherwise
have been chosen.

.RE
.RS 8
Note that this option specifies only the \fIdefault\fP visual that will
be used: the visual used may be overridden on a program-by-program basis.
See the description of the \fBprograms\fP resource, below.
.RE
.TP 8
.B installColormap\fP (class \fBBoolean\fP)
On PseudoColor (8-bit) displays, install a private colormap while the
screensaver is active, so that the graphics hacks can get as many
colors as possible.  This is the default.  (This only applies when the
screen's default visual is being used, since non-default visuals get
their own colormaps automatically.)  This can also be overridden on a
per-hack basis: see the discussion of the \fBdefault\-n\fP name in the
section about the \fBprograms\fP resource.

This does nothing if you have a TrueColor (16-bit or deeper) display.
.TP 8
.B verbose\fP (class \fBBoolean\fP)
Whether to print diagnostics.  Default false.
.TP 8
.B timestamp\fP (class \fBBoolean\fP)
Whether to print the time of day along with any other diagnostic messages.
Default true.
.TP 8
.B splash\fP (class \fBBoolean\fP)
Whether to display a splash screen at startup.  Default true.
.TP 8
.B splashDuration\fP (class \fBTime\fP)
How long the splash screen should remain visible; default 5 seconds.
.TP 8
.B helpURL\fP (class \fBURL\fP)
The splash screen has a \fIHelp\fP button on it.  When you press it, it will
display the web page indicated here in your web browser.
.TP 8
.B loadURL\fP (class \fBLoadURL\fP)
This is the shell command used to load a URL into your web browser.
The default setting will load it into Mozilla/Netscape if it is already
running, otherwise, will launch a new browser looking at the \fIhelpURL\fP.
.TP 8
.B demoCommand\fP (class \fBDemoCommand\fP)
This is the shell command run when the \fIDemo\fP button on the splash window
is pressed.  It defaults to
.BR xscreensaver\-demo (1).
.TP 8
.B prefsCommand\fP (class \fBPrefsCommand\fP)
This is the shell command run when the \fIPrefs\fP button on the splash window
is pressed.  It defaults to \fIxscreensaver\-demo\ \-prefs\fP.
.TP 8
.B newLoginCommand\fP (class \fBNewLoginCommand\fP)
If set, this is the shell command that is run when the "New Login" button
is pressed on the unlock dialog box, in order to create a new desktop
session without logging out the user who has locked the screen.
Typically this will be some variant of
.BR gdmflexiserver (1)
or
.BR kdmctl (1).
.TP 8
.B nice\fP (class \fBNice\fP)
The sub-processes created by \fIxscreensaver\fP will be "niced" to this
level, so that they are given lower priority than other processes on the
system, and don't increase the load unnecessarily.  The default is 10.  
(Higher numbers mean lower priority; see 
.BR nice (1)
for details.)
.TP 8
.B fade\fP (class \fBBoolean\fP)
If this is true, then when the screensaver activates, the current contents
of the screen will fade to black instead of simply winking out.  This only
works on certain systems.  A fade will also be done when switching graphics
hacks (when the \fIcycle\fP timer expires.)  Default: true.  
.TP 8
.B unfade\fP (class \fBBoolean\fP)
If this is true, then when the screensaver deactivates, the original contents
of the screen will fade in from black instead of appearing immediately.  This
only works on certain systems, and if \fIfade\fP is true as well.
Default false.
.TP 8
.B fadeSeconds\fP (class \fBTime\fP)
If \fIfade\fP is true, this is how long the fade will be in 
seconds (default 3 seconds.)
.TP 8
.B fadeTicks\fP (class \fBInteger\fP)
If \fIfade\fP is true, this is how many times a second the colormap will
be changed to effect a fade.  Higher numbers yield smoother fades, but
may make the fades take longer than the specified \fIfadeSeconds\fP if
your server isn't fast enough to keep up.  Default 20.
.TP 8
.B captureStderr\fP (class \fBBoolean\fP)
Whether \fIxscreensaver\fP should redirect its stdout and stderr streams to
the window itself.  Since its nature is to take over the screen, you would not
normally see error messages generated by xscreensaver or the sub-programs it
runs; this resource will cause the output of all relevant programs to be
drawn on the screensaver window itself, as well as being written to the
controlling terminal of the screensaver driver process.  Default true.
.TP 8
.B ignoreUninstalledPrograms\fP (class \fBBoolean\fP)
There may be programs in the list that are not installed on the system,
yet are marked as "enabled."  If this preference is true, then such 
programs will simply be ignored.  If false, then a warning will be printed
if an attempt is made to run the nonexistent program.  Also, the
.BR xscreensaver-demo (1)
program will suppress the non-existent programs from the list if this
is true.  Default: false.
.TP 8
.B GetViewPortIsFullOfLies\fP (class \fBBoolean\fP)
Set this to true if the xscreensaver window doesn't cover the whole screen.
This works around a longstanding XFree86 bug #421.  See the 
xscreensaver FAQ for details.
.TP 8
.B font\fP (class \fBFont\fP)
The font used for the stdout/stderr text, if \fBcaptureStderr\fP is true.
Default \fB*\-medium\-r\-*\-140\-*\-m\-*\fP (a 14 point fixed-width font.)
.TP 8
.B mode\fP (class \fBMode\fP)
Controls the behavior of xscreensaver.  Legal values are:
.RS 8
.TP 8
.B random
When blanking the screen, select a random display mode from among those
that are enabled and applicable.  This is the default.
.TP 8
.B random-same
Like \fIrandom\fP, but if there are multiple screens, each screen
will run the \fIsame\fP random display mode, instead of each screen
running a different one.
.TP 8
.B one
When blanking the screen, only ever use one particular display mode (the
one indicated by the \fIselected\fP setting.)
.TP 8
.B blank
When blanking the screen, just go black: don't run any graphics hacks.
.TP 8
.B off
Don't ever blank the screen, and don't ever allow the monitor to power down.

.RE
.TP 8
.B selected\fP (class \fBInteger\fP)
When \fImode\fP is set to \fIone\fP, this is the one, indicated by its
index in the \fIprograms\fP list.  You're crazy if you count them and
set this number by hand: let
.BR xscreensaver\-demo (1)
do it for you!
.TP 8
.B programs\fP (class \fBPrograms\fP)
The graphics hacks which \fIxscreensaver\fP runs when the user is idle.
The value of this resource is a multi-line string, one \fIsh\fP-syntax
command per line.  Each line must contain exactly one command: no
semicolons, no ampersands.

When the screensaver starts up, one of these is selected (according to
the \fBmode\fP setting), and run.  After the \fIcycle\fP period
expires, it is killed, and another is selected and run.

If a line begins with a dash (-) then that particular program is
disabled: it won't be selected at random (though you can still select
it explicitly using the
.BR xscreensaver\-demo (1)
program.)

If all programs are disabled, then the screen will just be made blank,
as when \fImode\fP is set to \fIblank\fP.

To disable a program, you must mark it as disabled with a dash instead
of removing it from the list.  This is because the system-wide (app-defaults)
and per-user (.xscreensaver) settings are merged together, and if a user
just \fIdeletes\fP an entry from their programs list, but that entry still
exists in the system-wide list, then it will come back.  However, if the
user \fIdisables\fP it, then their setting takes precedence.

If the display has multiple screens, then a different program will be run
for each screen.  (All screens are blanked and unblanked simultaneously.)

Note that you must escape the newlines; here is an example of how you
might set this in your \fI~/.xscreensaver\fP file:

.RS 8
.EX
programs:  \\
       qix -root                          \\n\\
       ico -r -faces -sleep 1 -obj ico    \\n\\
       xdaliclock -builtin2 -root         \\n\\
       xv -root -rmode 5 image.gif -quit  \\n
.EE
.RE
.RS 8
Make sure your \fB$PATH\fP environment variable is set up correctly
\fIbefore\fP xscreensaver is launched, or it won't be able to find the
programs listed in the \fIprograms\fP resource.

To use a program as a screensaver, two things are required: that that
program draw on the root window (or be able to be configured to draw on
the root window); and that that program understand "virtual root"
windows, as used by virtual window managers such as
.BR tvtwm (1).
(Generally, this is accomplished by just including the \fI"vroot.h"\fP 
header file in the program's source.)

.B Visuals:

Because xscreensaver was created back when dinosaurs roamed the earth,
it still contains support for some things you've probably never seen,
such as 1-bit monochrome monitors, grayscale monitors, and monitors
capable of displaying only 8-bit colormapped images.

If there are some programs that you want to run only when using a color
display, and others that you want to run only when using a monochrome
display, you can specify that like this:
.EX
       mono:   mono-program  -root        \\n\\
       color:  color-program -root        \\n\\
.EE
.RE
.RS 8
More generally, you can specify the kind of visual that should be used for
the window on which the program will be drawing.  For example, if one 
program works best if it has a colormap, but another works best if it has
a 24-bit visual, both can be accommodated:
.EX
       PseudoColor: cmap-program  -root   \\n\\
       TrueColor:   24bit-program -root   \\n\\
.EE
.RE
.RS 8
In addition to the symbolic visual names described above (in the discussion
of the \fIvisualID\fP resource) one other visual name is supported in
the \fIprograms\fP list:
.RS 1
.TP 4
.B default-n
This is like \fBdefault\fP, but also requests the use of the default colormap,
instead of a private colormap.  (That is, it behaves as if 
the \fI\-no\-install\fP command-line option was specified, but only for
this particular hack.)  This is provided because some third-party programs
that draw on the root window (notably: 
.BR xv (1),
and
.BR xearth (1))
make assumptions about the visual and colormap of the root window: 
assumptions which xscreensaver can violate.

.RE
If you specify a particular visual for a program, and that visual does not
exist on the screen, then that program will not be chosen to run.  This
means that on displays with multiple screens of different depths, you can
arrange for appropriate hacks to be run on each.  For example, if one screen
is color and the other is monochrome, hacks that look good in mono can be 
run on one, and hacks that only look good in color will show up on the other.
.RE
.PP
.PP
You shouldn't ever need to change the following resources:
.PP
.TP 8
.B pointerPollTime\fP (class \fBTime\fP)
When server extensions are not in use, this controls how 
frequently \fIxscreensaver\fP checks to see if the mouse position or buttons
have changed.  Default 5 seconds.
.TP 8
.B pointerHysteresis\fP (class \fBInteger\fP)
If the mouse moves less than this-many pixels in a second, ignore it
(do not consider that to be "activity.")  This is so that the screen
doesn't un-blank (or fail to blank) just because you bumped the desk.
Default: 10 pixels.
.TP 8
.B windowCreationTimeout\fP (class \fBTime\fP)
When server extensions are not in use, this controls the delay between when 
windows are created and when \fIxscreensaver\fP selects events on them.
Default 30 seconds.
.TP 8
.B initialDelay\fP (class \fBTime\fP)
When server extensions are not in use, \fIxscreensaver\fP will wait this many
seconds before selecting events on existing windows, under the assumption that 
\fIxscreensaver\fP is started during your login procedure, and the window 
state may be in flux.  Default 0.  (This used to default to 30, but that was
back in the days when slow machines and X terminals were more common...)
.TP 8
.B procInterrupts\fP (class \fBBoolean\fP)
This resource controls whether the \fB/proc/interrupts\fP file should be
consulted to decide whether the user is idle.  This is the default
if \fIxscreensaver\fP has been compiled on a system which supports this
mechanism (i.e., Linux systems.)  

The benefit to doing this is that \fIxscreensaver\fP can note that the user
is active even when the X console is not the active one: if the user is 
typing in another virtual console, xscreensaver will notice that and will
fail to activate.  For example, if you're playing Quake in VGA-mode, 
xscreensaver won't wake up in the middle of your game and start competing 
for CPU.

The drawback to doing this is that perhaps you \fIreally do\fP want idleness
on the X console to cause the X display to lock, even if there is activity
on other virtual consoles.  If you want that, then set this option to False.
(Or just lock the X console manually.)

The default value for this resource is True, on systems where it works.
.TP 8
.B overlayStderr\fP (class \fBBoolean\fP)
If \fBcaptureStderr\fP is True, and your server supports "overlay" visuals,
then the text will be written into one of the higher layers instead of into
the same layer as the running screenhack.  Set this to False to disable 
that (though you shouldn't need to.)
.TP 8
.B overlayTextForeground\fP (class \fBForeground\fP)
The foreground color used for the stdout/stderr text, if \fBcaptureStderr\fP
is true.  Default: Yellow.
.TP 8
.B overlayTextBackground\fP (class \fBBackground\fP)
The background color used for the stdout/stderr text, if \fBcaptureStderr\fP
is true.  Default: Black.
.TP 8
.B bourneShell\fP (class \fBBourneShell\fP)
The pathname of the shell that \fIxscreensaver\fP uses to start subprocesses.
This must be whatever your local variant of \fB/bin/sh\fP is: in particular,
it must not be \fBcsh\fP.
.SH ENVIRONMENT
.PP
.TP 8
.B DISPLAY
to get the default host and display number, and to inform the sub-programs
of the screen on which to draw.
.TP 8
.B XSCREENSAVER_WINDOW
Passed to sub-programs to indicate the ID of the window on which they
should draw.  This is necessary on Xinerama/RANDR systems where
multiple physical monitors share a single X11 "Screen".
.TP 8
.B PATH
to find the sub-programs to run.
.TP 8
.B HOME
for the directory in which to read the \fI.xscreensaver\fP file.
.TP 8
.B XENVIRONMENT
to get the name of a resource file that overrides the global resources
stored in the RESOURCE_MANAGER property.
.SH UPGRADES
The latest version of xscreensaver, an online version of this manual,
and a FAQ can always be found at http://www.jwz.org/xscreensaver/
.SH SEE ALSO
.BR X (1),
.BR Xsecurity (1),
.BR xauth (1),
.BR xdm (1),
.BR gdm (1),
.BR xhost (1),
.BR xscreensaver\-demo (1),
.BR xscreensaver\-command (1),
.BR xscreensaver\-gl\-helper (1),
.BR xscreensaver\-getimage (1),
.BR xscreensaver\-text (1).
.SH COPYRIGHT
Copyright \(co 1991-2014 by Jamie Zawinski.
Permission to use, copy, modify, distribute, and sell this software
and its documentation for any purpose is hereby granted without fee,
provided that the above copyright notice appear in all copies and that
both that copyright notice and this permission notice appear in
supporting documentation.  No representations are made about the
suitability of this software for any purpose.  It is provided "as is"
without express or implied warranty.
.SH AUTHOR
Jamie Zawinski <jwz@jwz.org>.  Written in late 1991; version 1.0 posted
to comp.sources.x on 17-Aug-1992.

Please let me know if you find any bugs or make any improvements.

And a huge thank you to the hundreds of people who have contributed, in
large ways and small, to the xscreensaver collection over the past
two decades!