[xscreensaver] / driver / xscreensaver.man

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.TH XScreenSaver 1 "03-Feb-2003 (4.07)" "X Version 11"
.SH NAME
xscreensaver - extensible screen saver framework, plus locking
.SH SYNOPSIS
.B xscreensaver
[\-display \fIhost:display.screen\fP] \
[\-verbose] \
[\-no\-capture\-stderr] \
[\-no\-splash]
.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:
unlike
.BR xlock (1),
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.

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 paramter
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 tell the running xscreensaver process
to re-initialize itself, like so:
.EX
xscreensaver-command -restart
.EE
Note that if you changed the \fI.Xdefaults\fP file, you might also need to run
.BR xrdb (1):
.EX
xrdb < ~/.Xdefaults
.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.)
.PP
.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 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)
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.
.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 false.
.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 Netscape if it is already running,
otherwise, will launch a new Netscape 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 \fIxscreensaver\-demo\fP.
.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 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 memoryLimit\fP (class \fBMemoryLimit\fP)
The sub-processes created by \fIxscreensaver\fP will not be allowed to
allocate more than this much memory (more accurately, this is the maximum
size their address space may become.)  If any sub-process tries to allocate
more than this,
.BR malloc (3)
will fail, and the process will likely exit (or safely crash) rather than
going forth and hogging memory.  

The assumption here is that if one of the screenhacks is trying to use
a lot of memory, then something has gone wrong, and it's better to kill
that program than to overload the machine.

Default: 0, meaning "no limit."  30M is a good choice on most systems.
(But beware that setting this to a small value can cause OpenGL programs
to malfunction on certain systems.)
.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 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 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 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 at random, 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 simultaniously.)

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.)

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
Normally you won't 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 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 sgiSaverExtension\fP (class \fBBoolean\fP)
There are a number of different X server extensions which can make
xscreensaver's job easier.  The next few resources specify whether these
extensions should be utilized if they are available.

This resource controls whether the SGI \fBSCREEN_SAVER\fP server extension
will be used to decide whether the user is idle.  This is the default 
if \fIxscreensaver\fP has been compiled with support for this 
extension (which is the default on SGI systems.).  If it is available, 
the \fBSCREEN_SAVER\fP method is faster and more reliable than what will
be done otherwise, so use it if you can.  (This extension is only available
on Silicon Graphics systems, unfortunately.)
.TP 8
.B mitSaverExtension\fP (class \fBBoolean\fP)
This resource controls whether the \fBMIT\-SCREEN\-SAVER\fP server extension
will be used to decide whether the user is idle.  However, the default for
this resource is \fIfalse\fP, because even if this extension is available,
it is flaky (and it also makes the \fBfade\fP option not work properly.)
Use of this extension is not recommended.
.TP 8
.B xidleExtension\fP (class \fBBoolean\fP)
This resource controls whether the \fBXIDLE\fP server extension will be
used to decide whether the user is idle.  This is the default 
if \fIxscreensaver\fP has been compiled with support for this extension.
(This extension is only available for X11R4 and X11R5 systems, unfortunately.)
.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 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
Same as setting the \fIcaptureStderr\fP resource to \fIfalse\fP: 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.
.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.

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.

Before launching a subprocess, \fIxscreensaver\fP stores an appropriate value
for \fB$DISPLAY\fP in the environment that the child will receive.  (This is
so that if you start \fIxscreensaver\fP with a \fI-display\fP argument, the
programs which \fIxscreensaver\fP launches will draw on the same display;
and so that the child will end up drawing on the appropriate screen of a
multi-headed display.)

When the screensaver turns off, or is killed, care is taken to restore 
the ``real'' virtual root window if there is one.  Because of this, it is
important that you not kill the screensaver process with \fIkill -9\fP if
you are running a virtual-root window manager.  If you kill it with \-9,
you may need to restart your window manager to repair the damage.  This
isn't an issue if you aren't running a virtual-root window manager.

For all the gory details, see the commentary at the top of xscreensaver.c.

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.

As of version 3.28, 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 XDM(1)
You can run \fIxscreensaver\fP from your 
.BR xdm (1)
session, so that the screensaver will run even when nobody is logged 
in on the console.

The trick to using xscreensaver with \fIxdm\fP is this: keep in mind the 
two very different states in which xscreensaver will be running:
.RS 4
.TP 3
.B 1: Nobody logged in.

If you're thinking of running xscreensaver from XDM at all, then it's 
probably because you want graphics demos to be running on the console
when nobody is logged in there.  In this case, xscreensaver will function
only as a screen saver, not a screen locker: it doesn't make sense
for xscreensaver to lock the screen, since nobody is logged in yet!
The only thing on the screen is the XDM login prompt.
.TP 3
.B 2: Somebody logged in.

Once someone has logged in through the XDM login window, the situation is
very different.  For example: now it makes sense to lock the screen (and
prompt for the logged in user's password); and now xscreensaver should
consult that user's \fI~/.xscreensaver\fP file; and so on.
.RE

The difference between these two states comes down to a question of,
which user is the \fIxscreensaver\fP process running as?  For the first
state, it doesn't matter.  If you start \fIxscreensaver\fP in the usual
XDM way, then xscreensaver will probably end up running as root, which 
is fine for the first case (the ``nobody logged in'' case.)

However, once someone is logged in, running as root is no longer fine:
because xscreensaver will be consulting root's \fI.xscreensaver\fP file
instead of that of the logged in user, and won't be prompting for the
logged in user's password, and so on.  (This is not a security problem,
it's just not what you want.)

So, once someone has logged in, you want xscreensaver to be running as that
user.  The way to accomplish this is to kill the old xscreensaver process
and start a new one (as the new user.)

The simplest way to accomplish all of this is as follows:
.RS 4
.TP 3
.B 1: Launch xscreensaver before anyone logs in.

To the file \fI/usr/lib/X11/xdm/Xsetup\fP, add the lines
.EX
xhost +localhost
xscreensaver-command -exit
xscreensaver &
.EE
This will run xscreensaver as root, over the XDM login window.
Moving the mouse will cause the screen to un-blank, and allow the user
to type their password at XDM to log in.
.TP 3
.B 2: Restart xscreensaver when someone logs in.

Near the top of the file \fI/usr/lib/X11/xdm/Xsession\fP, add those same lines:
.EX
xscreensaver-command -exit
xscreensaver &
.EE
When someone logs in, this will kill off the existing (root) xscreensaver
process, and start a new one, running as the user who has just logged in.
If the user's .xscreensaver file requests locking, they'll get it.  They
will also get their own choice of timeouts, and graphics demos, and so on.

Alternately, each user could just put those lines in their 
personal \fI~/.xsession\fP files.
.RE

Make sure you have \fB$PATH\fP set up correctly in the \fIXsetup\fP 
and \fIXsession\fP scripts, or \fIxdm\fP won't be able to 
find \fIxscreensaver\fP, and/or \fIxscreensaver\fP won't be able to 
find its graphics demos.

(If your system does not seem to be executing the \fIXsetup\fP file, you
may need to configure it to do so: the traditional way to do this is
to make that file the value of the \fIDisplayManager*setup\fP resource
in the \fI/usr/lib/X11/xdm/xdm-config\fP file.  See the man page for
.BR xdm (1)
for more details.)

It is safe to run \fIxscreensaver\fP as root (as \fIxdm\fP is likely to 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 \fIxdm\fP, then this probably means that you have
.BR xauth (1)
or some other security mechanism turned on.  One way around this is to
add \fB"xhost\ +localhost"\fP to \fIXsetup\fP, just before \fIxscreensaver\fP
is launched.  

Note that this will give access to the X server to anyone capable of logging
in to the local machine, so in some environments, this might not be 
appropriate.  If turning off file-system-based access control is not
acceptable, then running \fIxscreensaver\fP from the \fIXsetup\fP file
might not be possible, and xscreensaver will only work when running as
a normal, unprivileged user.

For more 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 USING GDM(1)
Using xscreensaver with
.BR gdm (1)
is easy, because gdm has a configuration tool.  Just fire up
.BR gdmconfig (1)
and on the \fIBackground\fP page, type \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.)

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.
.SH USING CDE (COMMON DESKTOP ENVIRONMENT)
The easiest way to use \fIxscreensaver\fP on a system with CDE is to simply
switch off the built-in CDE screensaver, and use \fIxscreensaver\fP instead;
and second, to tell the front panel to run 
.BR xscreensaver\-command (1)
with the \fI\-lock\fP option when the \fILock\fP icon is clicked.

To accomplish this involves five steps:
.RS 4
.TP 3
\fB1: Switch off CDE's locker\fP
Do this by turning off ``\fIScreen Saver and Screen Lock\fP'' in the
Screen section of the Style Manager.
.TP 3
\fB2: Edit sessionetc\fP
Edit the file \fI~/.dt/sessions/sessionetc\fP and add to it the line
.EX
xscreensaver &
.EE
And make sure the sessionetc file is executable.
This will cause \fIxscreensaver\fP to be launched when you log in.
(As always, make sure that xscreensaver and the graphics demos are on
your \fB$PATH\fP; the path needs to be set in \fI.cshrc\fP 
and/or \fI.dtprofile\fP, not \fI.login\fP.)
.TP 3
\fB3: Create XScreenSaver.dt\fP
Create a file called \fI~/.dt/types/XScreenSaver.dt\fP with the following
contents:
.EX
ACTION XScreenSaver
{
  LABEL         XScreenSaver
  TYPE          COMMAND
  EXEC_STRING   xscreensaver-command -lock
  ICON          Dtkey
  WINDOW_TYPE   NO_STDIO
}
.EE
This defines a ``lock'' command for the CDE front panel, that knows how
to talk to \fIxscreensaver\fP.
.TP 3
\fB4: Create Lock.fp\fP
Create a file called \fI~/.dt/types/Lock.fp\fP with the following
contents:
.EX
CONTROL Lock
{
  TYPE             icon
  CONTAINER_NAME   Switch
  CONTAINER_TYPE   SWITCH
  POSITION_HINTS   1
  ICON             Fplock
  LABEL            Lock
  PUSH_ACTION      XScreenSaver
  HELP_TOPIC       FPOnItemLock
  HELP_VOLUME      FPanel
}
.EE
This associates the CDE front panel ``Lock'' icon with the lock command
we just defined in step 3.
.TP 3
\fB5: Restart\fP
Select ``\fIRestart Workspace Manager\fP'' from the popup menu to make
your changes take effect.  If things seem not to be working, check the
file \fI~/.dt/errorlog\fP for error messages.
.RE
.SH USING HP VUE (VISUAL USER ENVIRONMENT)
Since CDE is a descendant of VUE, the instructions for using xscreensaver
under VUE are similar to the above:
.RS 4
.TP 3
\fB1: Switch off VUE's locker\fP
Open the ``\fIStyle Manager\fP'' and select ``\fIScreen\fP.''
Turn off ``\fIScreen Saver and Screen Lock\fP'' option.
.TP 3
\fB2: Make sure you have a Session\fP
Next, go to the Style Manager's, ``\fIStartup\fP'' page.
Click on ``\fISet Home Session\fP'' to create a session, then 
on ``\fIReturn to Home Session\fP'' to select this session each
time you log in.
.TP 3
\fB3: Edit vue.session\fP
Edit the file \fI~/.vue/sessions/home/vue.session\fP and add to it
the line
.EX
vuesmcmd -screen 0 -cmd "xscreensaver"
.EE
This will cause \fIxscreensaver\fP to be launched when you log in.
(As always, make sure that xscreensaver and the graphics demos are on
your \fB$PATH\fP; the path needs to be set in \fI.cshrc\fP
and/or \fI.profile\fP, not \fI.login\fP.)
.TP 3
\fB3: Edit vuewmrc\fP
Edit the file \fI~/.vue/vuewmrc\fP and add (or change) the Lock control:
.EX
CONTROL Lock
{
  TYPE         button
  IMAGE        lock
  PUSH_ACTION  f.exec "xscreensaver-command -lock"
  HELP_TOPIC   FPLock
}
.EE
This associates the VUE front panel ``Lock'' icon with the xscreensaver 
lock command.
.RE
.PP
.SH USING KDE (K DESKTOP ENVIRONMENT)
I understand that KDE has invented their own wrapper around xscreensaver,
that is inferior to 
.BR xscreensaver-demo (1)
in any number of ways.  I've never actually seen it, but I'm told that
this is the way you disable it:
.RS 4
.TP 3
\fB1: Switch off KDE's screen saver.\fP
Open the ``\fIControl Center\fP'' and
select the ``\fILook and Feel / Screensaver\fP'' page.
Turn off the ``\fIEnable Screensaver\fP'' checkbox.
.TP 3
\fB2: Find your Autostart directory.\fP
Open the ``\fILook and Feel / Desktop / Paths\fP'' page,
and see what your ``Autostart'' directory is set to: it will
probably be \fI~/.kde3/Autostart/\fP or something similar.
.TP 3
\fB3: Make xscreensaver be an Autostart program.\fP
Create a 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
.RE
.PP
Now use xscreensaver normally, controlling it via the usual
.BR xscreensaver-demo (1)
and
.BR xscreensaver-command (1)
mechanisms.
.SH ADDING TO MENUS
The
.BR xscreensaver-command (1)
program is a perfect candidate for something to add to your window manager's
popup menus.  If you use 
.BR mwm (1),
.BR 4Dwm (1),
.BR twm (1),
or (probably) any of \fItwm\fP's many descendants, you can do it like this:
.RS 0
.TP 3
\fB1. Create ~/.mwmrc (or ~/.twmrc or ...)\fP
If you don't have a \fI~/.mwmrc\fP file (or, on SGIs, a \fI~/.4Dwmrc\fP file;
or, with twm, a \fI~/.twmrc\fP file) then create one by making a copy of
the \fI/usr/lib/X11/system.mwmrc\fP 
file (or \fI/usr/lib/X11/twm/system.twmrc\fP, and so on.)
.TP 3
\fB2. Add a menu definition.\fP
Something like this:
.EX
menu XScreenSaver
{
 "Blank Screen Now" !"sleep 3; xscreensaver-command -activate"
 "Lock Screen Now"  !"sleep 3; xscreensaver-command -lock"
 "Screen Saver Demo"         !"xscreensaver-demo"
 "Screen Saver Preferences"  !"xscreensaver-demo -prefs"
 "Reinitialize Screen Saver" !"xscreensaver-command -restart"
 "Kill Screen Saver"         !"xscreensaver-command -exit"
 "Launch Screen Saver"       !"xscreensaver &"
}
.EE
.TP 3
\fB3. Add the menu\fP
For
.BR mwm (1)
and
.BR 4Dwm (1),
find the section of the file that says \fIMenu DefaultRootMenu\fP.
For
.BR twm (1),
it will probably be \fImenu "defops"\fP.  If you add a line somewhere 
in that menu definition that reads
.EX
  "XScreenSaver"        f.menu XScreenSaver
.EE
then this will add an XScreenSaver sub-menu to your default root-window
popup menu.  Alternately, you could just put the xscreensaver menu items
directly into the root menu.
.RE

For Fvwm2, the process is similar: first create a \fI~/.fvwm2rc\fP file
if you don't already have one, by making a copy of
the \fI/etc/X11/fvwm2/system.fvwm2rc\fP file.  Then, add a menu definition
to it:
.EX
AddToMenu XScreenSaver "XScreenSaver" Title
+ "Blank Screen Now"          Exec xscreensaver-command -activate
+ "Lock Screen Now"           Exec xscreensaver-command -lock
+ "Screen Saver Demo"         Exec xscreensaver-command -demo
+ "Screen Saver Preferences"  Exec xscreensaver-command -prefs
+ "Reinitialize Screen Saver" Exec xscreensaver-command -restart
+ "Kill Screen Saver"         Exec xscreensaver-command -exit
+ "Launch Screen Saver"       Exec xscreensaver
+ "Run Next Demo"             Exec xscreensaver-command -next
+ "Run Previous Demo"         Exec xscreensaver-command -prev

# To put the XScreenSaver sub-menu at the end of the root menu:
AddToMenu RootMenu "XScreenSaver" Popup XScreenSaver
.EE
The Enlightenment window manager keeps each of its menus in a separate
file. So, you need to create a file 
named \fI~/.enlightenment/xscreensaver.menu\fP with the contents:
.EX
"XScreenSaver Commands"
 "Blank Screen Now"    NULL exec "xscreensaver-command -activate"
 "Lock Screen Now"     NULL exec "xscreensaver-command -lock"
 "Screen Saver Demo"   NULL exec "xscreensaver-command -demo"
 "Screen Saver Prefs"  NULL exec "xscreensaver-command -prefs"
 "Reinitialize Saver"  NULL exec "xscreensaver-command -restart"
 "Kill Screen Saver"   NULL exec "xscreensaver-command -exit"
 "Launch Screen Saver" NULL exec "xscreensaver"
.EE
then add
.EX
 "XScreenSaver"        NULL menu "xscreensaver.menu"
.EE
to \fI~/.enlightenment/file.menu\fP to put the XScreenSaver submenu on 
your left-button root-window menu.

As you see, every window manager does this stuff gratuitously differently,
just to make your life difficult.  You are in a maze of twisty menu
configuration languages, all alike.
.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.
.TP 8
.B Locking and XDM
If xscreensaver has been launched from 
.BR xdm (1)
before anyone has logged in, you will need to kill and then restart the
xscreensaver daemon after you have logged in, or you will be confused by
the results.  (For example, locking won't work, and your \fI~/.xscreensaver\fP
file will be ignored.)

When you are logged in, you want the \fIxscreensaver\fP daemon to be 
running under \fIyour\fP user id, not as root or some other user.

If it has already been started by \fIxdm\fP, you can kill it by sending
it the \fBexit\fP command, and then re-launching it as you, by putting
something like the following in your personal X startup script:
.EX
xscreensaver-command -exit
xscreensaver &
.EE
The ``\fIUsing XDM(1)\fP'' section, above, goes into more detail, and explains
how to configure the system to do this for all users automatically.
.TP 8
.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 8
.B XAUTH and XDM
For xscreensaver to work when launched by
.BR xdm (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 XDM(1)\fP'' section, 
above, for more details.

If anyone has suggestions on how xscreensaver could be made to work with
.BR xdm (1)
without first turning off \fI.Xauthority\fP-based access control, please
let me know.
.TP 8
.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.  So, after you change your password, you'll have to do
.EX
xscreensaver-command -restart
.EE
to make \fIxscreensaver\fP notice.
.TP 8
.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 8
.B Colormap lossage: TWM
The \fBinstallColormap\fP option doesn't work very well with the
.BR twm (1)
window manager and its descendants.  

There is a race condition between the screensaver and this window manager,
which can result in the screensaver's colormap not getting installed
properly, meaning the graphics hacks will appear in essentially random
colors.  (If the screen goes white instead of black, this is probably why.)

The
.BR mwm (1)
and
.BR olwm (1)
window managers don't have this problem.  The race condition exists
because X (really, ICCCM) does not provide a way for an OverrideRedirect 
window to have its own colormap, short of grabbing the server (which is 
neither a good idea, nor really possible with the current design.)  What 
happens is that, as soon as xscreensaver installs its colormap, \fBtwm\fP 
responds to the resultant \fBColormapNotify\fP event by re-instaling the 
default colormap.  Apparently, \fBtwm\fP doesn't \fIalways\fP do this; it 
seems to do it regularly if the screensaver is activated from a menu item, 
but seems to not do it if the screensaver comes on of its own volition, or 
is activated from another console.  
.RS 8
.TP 4
.B Attention, window manager authors!
You should only call
.BR XInstallColormap (3)
in response to user events.  That is, it is appropriate to install a colormap
in response to \fBFocusIn\fP, \fBFocusOut\fP, \fBEnterNotify\fP, 
and \fBLeaveNotify\fP events; but it is not appropriate to call it in
response to \fBColormapNotify\fP events.  If you install colormaps in
response to \fIapplication\fP actions as well as in response to \fIuser\fP
actions, then you create the situation where it is impossible for 
override-redirect applications (such as xscreensaver) to display their
windows in the proper colors.
.RE
.TP 8
.B Colormap lossage: XV, XAnim, XEarth
Some programs don't operate properly on visuals other than the default one,
or with colormaps other than the default one.  See the discussion of the
magic "default-n" visual name in the description of the \fBprograms\fP 
resource in the \fIConfiguration\fP section.  When programs only work with
the default colormap, you need to use a syntax like this:
.EX
   default-n: xv -root image-1.gif -quit  \\n\\
   default-n: xearth -nostars -wait 0     \\n\\
.EE
It would also work to turn off the \fBinstallColormap\fP option altogether,
but that would deny extra colors to those programs that \fIcan\fP take
advantage of them.
.TP 8
.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 suck a lot of 
cycles.  Care should be taken to slow down programs intended for use as 
screensavers by inserting strategic calls to
.BR sleep (3)
or
.BR usleep (3)
(or making liberal use of any \fI\-delay\fP options which the programs 
may provide.)

Note that the OpenGL-based graphics demos are real pigs on machines that
don't have texture hardware.

Also, an active screensaver will cause your X server to be pretty much 
permanently swapped in; but the same is true of any program that draws
periodically, like 
.BR xclock (1)
or
.BR xload (1).
.TP 8
.B Latency and Responsiveness
If the subprocess is drawing too quickly and the connection to the X
server is a slow one (such as an X terminal running over a phone line) then 
the screensaver might not turn off right away when the user becomes active
again (the
.BR ico (1)
demo has this problem if being run in full-speed mode).  This can be
alleviated by inserting strategic calls to
.BR XSync (3)
in code intended for use as a screensaver.  This prevents too much graphics
activity from being buffered up.
.TP 8
.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.

Some Linux systems come with a VT_LOCKSWITCH ioctl, that one could 
theoretically use to prevent VT-switching while the screen is locked; 
but unfortunately, this ioctl can only be used by root, which means
that xscreensaver can't use it (since xscreensaver disavows its privileges
shortly after startup, for security reasons.)

Any suggestions for other solutions to this problem are welcome.
.TP 8
.B XView Clients
Apparently there are some problems with XView programs getting confused
and thinking that the screensaver window is the real root window even when
the screensaver is not active: ClientMessages intended for the window manager
are sent to the screensaver window instead.  This could be solved by making
xscreensaver forward all unrecognised ClientMessages to the real root window,
but there may be other problems as well.  If anyone has any insight on the
cause of this problem, please let me know.  (XView is an X11 toolkit that 
implements the (quite abominable) Sun OpenLook look-and-feel.)
.TP 8
.B MIT Extension and Fading
The \fBMIT-SCREEN-SAVER\fP extension is junk.  Don't use it.

When using the \fBMIT-SCREEN-SAVER\fP extension in conjunction with 
the \fBfade\fP option, you'll notice an unattractive flicker just before 
the fade begins.  This is because the server maps a black window just before 
it tells the \fIxscreensaver\fP process to activate.  The \fIxscreensaver\fP 
process immediately unmaps that window, but this results in a flicker.  I 
haven't figured a way  to get around this; it seems to be a fundamental
property of the (mis-) design of this server extension.

It sure would be nice if someone would implement the \fBSGI SCREEN_SAVER\fP
extension in XFree86; it's dead simple, and works far better than the
overengineered and broken \fBMIT-SCREEN-SAVER\fP extension.
.TP 8
.B SGI Power Saver
If you're running Irix 6.3, you might find that your monitor is powering down
after an hour or two even if you've told it not to.  This is fixed by SGI
patches 2447 and 2537.

If you're running Irix 6.5, this bug is back.  I don't know a fix.
.TP 8
.B MesaGL and Voodoo Cards
If you have a 3Dfx/Voodoo card, the default settings for xscreensaver will
run the GL-based graphics demos in such a way that they will not take 
advantage of the 3D acceleration hardware.  The solution is to change
the \fBprograms\fP entries for the GL hacks from this:
.EX
       gears -root                        \\n\\
.EE
to this:
.EX
       MESA_GLX_FX=fullscreen  gears      \\n\\
.EE
That is, make sure that \fB$MESA_GLX_FX\fP is set to \fIfullscreen\fP, and
don't tell the program to draw on the root window.  This may seem strange,
but the setup used by Mesa and these kinds of cards \fIis\fP strange!

For those who don't know, these cards work by sitting between your normal
video card and the monitor, and seizing control of the monitor when it's 
time to do 3D.  But this means that accelerated 3D only happens in full-screen
mode (you can't do it in a window, and you can't see the output of 3D and 2D
programs simultaniously), and that 3D will probably drive your monitor at a
lower resolution, as well.  It's bizarre.

This probably isn't ever necessary on more modern cards; I'm not sure.

If you find that GL programs only work properly when run as root, and not
as normal users, then the problem is that your \fI/dev/3dfx\fP file is not
configured properly.  Check the Linux 3Dfx FAQ.
.TP 8
.B Keyboard LEDs
If \fIprocInterrupts\fP is on (which is the default on Linux systems) and
you're using some program that toggles the state of your keyboard LEDs,
xscreensaver won't work right: turning those LEDs on or off causes a 
keyboard interrupt, which xscreensaver will interpret as user activity.
So if you're using such a program, set the \fIprocInterrupts\fP resource
to False.
.TP 8
.B Extensions
If you are not making use of one of the server extensions (\fBXIDLE\fP,
\fBSGI SCREEN_SAVER\fP, or \fBMIT-SCREEN-SAVER\fP), then it is possible, in 
rare situations, for \fIxscreensaver\fP to interfere with event propagation 
and make another X program malfunction.  For this to occur, that other
application would need to \fInot\fP select \fBKeyPress\fP events on its 
non-leaf windows within the first 30 seconds of their existence, but then 
select for them later.  In this case, that client \fImight\fP fail to receive 
those events.  This isn't very likely, since programs generally select a
constant set of events immediately after creating their windows and then 
don't change them, but this is the reason that it's a good idea to install 
and use one of the server extensions instead, to work around this shortcoming
in the X protocol.

In all these years, I've not heard of even a single case of this happening,
but it is theoretically possible, so I'm mentioning it for completeness...
.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 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 xscreensaver\-demo (1),
.BR xscreensaver\-command (1),
.BR xscreensaver\-gl\-helper (1),
.BR xdm (1),
.BR xset (1),
.BR Xsecurity (1),
.BR xauth (1),
.BR xhost (1).
.BR ant (1),
.BR atlantis (1),
.BR attraction (1),
.BR blitspin (1),
.BR bouboule (1),
.BR braid (1),
.BR bsod (1),
.BR bubble3d (1),
.BR bubbles (1),
.BR cage (1),
.BR compass (1),
.BR coral (1),
.BR critical (1),
.BR crystal (1),
.BR cynosure (1),
.BR decayscreen (1),
.BR deco (1),
.BR deluxe (1),
.BR demon (1),
.BR discrete (1),
.BR distort (1),
.BR drift (1),
.BR epicycle (1),
.BR fadeplot (1),
.BR flag (1),
.BR flame (1),
.BR flow (1),
.BR forest (1),
.BR galaxy (1),
.BR gears (1),
.BR glplanet (1),
.BR goop (1),
.BR grav (1),
.BR greynetic (1),
.BR halo (1),
.BR helix (1),
.BR hopalong (1),
.BR hypercube (1),
.BR ifs (1),
.BR imsmap (1),
.BR interference (1),
.BR jigsaw (1),
.BR julia (1),
.BR kaleidescope (1),
.BR kumppa (1),
.BR lament (1),
.BR laser (1),
.BR lightning (1),
.BR lisa (1),
.BR lissie (1),
.BR lmorph (1),
.BR loop (1),
.BR maze (1),
.BR moebius (1),
.BR moire (1),
.BR moire2 (1),
.BR morph3d (1),
.BR mountain (1),
.BR munch (1),
.BR noseguy (1),
.BR pedal (1),
.BR penetrate (1),
.BR penrose (1),
.BR petri (1),
.BR phosphor (1),
.BR pipes (1),
.BR pulsar (1),
.BR pyro (1),
.BR qix (1),
.BR rd-bomb (1),
.BR rocks (1),
.BR rorschach (1),
.BR rotor (1),
.BR rubik (1),
.BR sierpinski (1),
.BR slidescreen (1),
.BR slip (1),
.BR sonar (1),
.BR sphere (1),
.BR spiral (1),
.BR spotlight (1),
.BR sproingies (1),
.BR squiral (1),
.BR stairs (1),
.BR starfish (1),
.BR strange (1),
.BR superquadrics (1),
.BR swirl (1),
.BR t3d (1),
.BR triangle (1),
.BR truchet (1),
.BR vines (1),
.BR wander (1),
.BR worm (1),
.BR xflame (1),
.BR xjack (1),
.BR xlyap (1),
.BR xmatrix (1),
.BR bongo (1),
.BR ico (1),
.BR xaos (1),
.BR xbouncebits (1),
.BR xcthugha (1),
.BR xdaliclock (1),
.BR xfishtank (1),
.BR xmountains (1),
.BR xsplinefun (1),
.BR xswarm (1),
.BR xtacy (1),
.BR xv (1),
.BR chbg (1),
.BR xwave (1).
.SH COPYRIGHT
Copyright \(co 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
2000, 2001, 2002 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.
.SH ACKNOWLEDGEMENTS
Thanks to Angela Goodman for the XScreenSaver logo.

Thanks to the many people who have contributed graphics demos to the package.

Thanks to David Wojtowicz for implementing \fIlockTimeout\fP.

Thanks to Martin Kraemer for adding support for shadow passwords and
locking-disabled diagnostics.

Thanks to Patrick Moreau for the VMS port.

Thanks to Mark Bowyer for figuring out how to hook it up to CDE.

Thanks to Nat Lanza for the Kerberos support.

Thanks to Bill Nottingham for the initial PAM support.

And thanks to Jon A. Christopher for implementing the Athena dialog
support, back in the days before Lesstif or Gtk were viable alternatives
to Motif.