.TH XScreenSaver 1 "6.08 (10-Oct-2023)" "X Version 11"
.SH NAME
xscreensaver - extensible screen saver and screen locking framework
.SH SYNOPSIS
.B xscreensaver
[\-\-display \fIhost:display.screen\fP] \
[\-\-verbose] \
[\-\-version] \
[\-\-no\-splash] \
[\-\-log \fIfilename\fP]
.SH DESCRIPTION
XScreenSaver waits until the user is idle, and then runs graphics demos chosen
at random.  It can also lock your screen, and provides configuration and
control of display power management.

XScreenSaver is also available on macOS, iOS and Android.
.SH GETTING STARTED
XScreenSaver is a daemon that runs in the background.  You configure it
with the
.BR xscreensaver\-settings (1)
program.
.nf
.sp
	xscreensaver &
	xscreensaver-settings
.sp
.fi
.SH HOW IT WORKS
When it is time to activate the screensaver, a full-screen black window is
created that covers each monitor.  A sub-process is launched for each one
running a graphics demo, pointed at the appropriate window.  Because of this,
any program which can draw on a provided window can be used as a screensaver.
The various graphics demos are, in fact, just standalone programs that do
that.

When the user becomes active again, the screensaver windows are unmapped, and
the running subprocesses are killed.

The display modes are run at a low process priority, and spend most of their
time sleeping/idle by default, so they should not consume significant system
resources.
.SH COMMAND-LINE OPTIONS
.TP 8
.B \-\-display\fP \fIhost:display.screen\fP
The X display to use.  For displays with multiple screens, XScreenSaver
will manage all screens on the display simultaneously.
.TP 8
.B \-\-verbose
Print diagnostics to stderr.
.TP 8
.B \-\-version\fP
Print the version number and exit.
.TP 8
.B \-\-log\fP \fIfilename\fP
Append all diagnostic output to the given file.  This also 
implies \fI\-\-verbose\fP.  Use this when reporting bugs.
.TP 8
.B \-\-no\-splash
Don't display the splash screen at startup.
.SH POWER MANAGEMENT
The
.BR xscreensaver\-settings (1)
program is where you configure if and when your monitor should power off.
It saves the settings in your \fI~/.xscreensaver\fP file.
Do not use
.BR xset (1)
to manually change the power management settings, that won't work.

When the monitor is powered down, the display hacks will stop running
(though it may take a minute or two for XScreenSaver to notice).
.SH LAPTOP LIDS
If your system uses
.BR systemd (1)
or
.BR elogind (8),
then closing the lid of your laptop will cause the screen to lock immediately.

If not, then the screen might not lock until a few seconds \fIafter\fP you
re-open the lid.  Which is less than ideal.  So if you do not have
.BR systemd (1),
you might want to get in the habit of manually locking your screen
\fIbefore\fP closing the lid (\fIxscreensaver\-command\ \-\-lock\fP).
.SH PLAYING VIDEOS
Likewise, if you have
.BR systemd (1)
or
.BR elogind (8),
then all of the popular video players and web browsers will
prevent XScreenSaver from blanking the screen while video is playing.

Both of these features require that
.BR xscreensaver\-systemd (6)
be able connect to D-Bus.
.SH INSTALLATION
Each desktop environment has its own system for launching long-running
daemons like XScreenSaver, and since many of them come bundled with
their own (buggy, insecure, inferior) screen-locking frameworks, it is
also necessary to disable those other frameworks before XScreenSaver
can work.
.SS INSTALLING XSCREENSAVER ON GNOME OR UNITY
For many years, GNOME included XScreenSaver as-is, and everything just worked.
Not any more!
.RS 4
.TP 3
\fB1: Fully uninstall the other screen saver packages:\fP
.nf
.sp
	sudo apt remove gnome-screensaver
	sudo apt remove mate-screensaver
	sudo apt remove cinnamon-screensaver
	sudo apt remove light-locker
or
	sudo rpm -e gnome-screensaver
	sudo rpm -e mate-screensaver
	sudo rpm -e cinnamon-screensaver
	sudo rpm -e light-locker
.sp
.fi
Be careful that it doesn't try to uninstall all of GNOME.
.TP 3
\fB2: Turn off GNOME's built-in blanking.\fP
Set all of the following settings to "\fINever\fP" or "\fIOff\fP", as
these are all controlled by
.BR xscreensaver\-settings (1)
now:

"\fISettings / Privacy / Screen Lock / Blank Screen Delay\fP"
.br
"\fISettings / Privacy / Screen Lock / Automatic Screen Lock\fP"
.br
"\fISettings / Power / Blank Screen\fP"
.br
"\fISettings / Power / Automatic Suspend\fP"
.TP 3
\fB3: Launch XScreenSaver at login.\fP
Launch "\fITweaks\fP", select "\fIStartup Applications\fP", click the plus
sign, and select "\fIXScreenSaver\fP" (not "\fIXScreenSaver Settings\fP")
from the (very long) menu.

Or, see the "\fILAUNCHING XSCREENSAVER FROM SYSTEMD\fP" section below.
That works too.
.TP 3
\fB4: Make GNOME's "Lock" icon use XScreenSaver.\fP
This used to work, but no longer does with GNOME 3.38.  If you figure it out,
let me know!  This still works for Cinnamon 4.8 and MATE 1.24:
.nf
.sp
	sudo ln -sf /usr/bin/xscreensaver-command \\
	       /usr/bin/gnome-screensaver-command
	sudo ln -sf /usr/bin/xscreensaver-command \\
	    /usr/bin/cinnamon-screensaver-command
	sudo ln -sf /usr/bin/xscreensaver-command \\
	        /usr/bin/mate-screensaver-command
	sudo ln -sf /usr/bin/xscreensaver-command \\
	       /usr/bin/xfce4-screensaver-command
	sudo ln -sf /usr/bin/xscreensaver-command \\
	            /usr/bin/light-locker-command
.sp
.fi
This change will get blown away when you upgrade.
.SS INSTALLING XSCREENSAVER ON KDE
Like GNOME, KDE also decided to re-invent the wheel.  To replace the KDE
screen saver with XScreenSaver, do the following:
.RS 4
.TP 3
\fB1: Turn off KDE's built-in blanking.\fP
In \fISystem Settings\fP, un-check the following items, as these are
controlled by
.BR xscreensaver\-settings (1)
now:

"\fIWorkspace Behavior / Screen Locking / Lock automatically\fP"
.br
"\fIWorkspace Behavior / Screen Locking / After waking from sleep\fP"
.br
"\fIWorkspace Behavior / Screen Locking / Keyboard shortcut\fP"
.br
"\fIHardware / Power Management / Screen Energy Saving\fP"
.br
"\fIHardware / Power Management / Suspend session\fP"
.br
"\fIHardware / Power Management / Laptop lid closed" = Do Nothing\fP

If there are multiple tabs, you may need to change these settings on all
three of them: "On AC power", "Battery" and "Low Battery".
.TP 3
\fB2: Launch XScreenSaver at login.\fP
Copy the file \fI/usr/share/applications/xscreensaver.desktop\fP into
the directory \fI~/.config/autostart/\fP
.TP 3
\fB3: Make KDE's "Lock" icon use XScreenSaver.\fP
Find the "\fIkscreenlocker_greet\fP" program.  It might be in 
"\fI/usr/lib/*/libexec/\fP", or it might be somewhere else.
Delete that file and replace it with a file containing these two lines.
Make it executable (chmod a+x).
.nf
.sp
	#!/bin/sh
	xscreensaver-command \-\-lock &
.sp
.fi
This change will get blown away when you upgrade.
.TP 3
\fB4: Turn off KDE's built-in locking on suspend, even harder.\fP
Even after disabling KDE's screen locking, above, it is \fIpossible\fP that
KDE will still use its built-in locker when you close your laptop's lid.  If
that is happening, double-check the settings above, but if those are correct,
try the following.  First, ensure you are running KDE 5.21 or newer.  Next,
enable \fI"systemd user sessions"\fP for KDE so that you can edit the
parameters for \fIksmserver:\fP
.nf
.sp
	kwriteconfig5 \-\-file startkderc \-\-group General \\
	  \-\-key systemdBoot true
.sp
.fi
Log out and back in.

Next, edit the \fIplasma-ksmserver\fP service to change how \fIksmserver\fP
is launched:
.nf
.sp
	systemctl edit --user plasma-ksmserver.service
.sp
.fi
Replace the contents of the file that lets you edit with this:
.nf
.sp
	[Service]
	ExecStart=
	ExecStart=/usr/bin/ksmserver \-\-no\-lockscreen
.sp
.fi
Then log out and back in \fIagain\fP.
.SS LAUNCHING XSCREENSAVER FROM LXDE
Add the line \fI@xscreensaver\fP to
\fI/etc/xdg/lxsession/LXDE/autostart\fP or
\fI/etc/xdg/lxsession/LXDE-pi/autostart\fP.
.SS LAUNCHING XSCREENSAVER FROM SYSTEMD
If you are not using GNOME, KDE or LXDE, the way to launch XScreenSaver
at login is probably
.BR systemd (1).

Copy the file \fI/usr/share/xscreensaver/xscreensaver.service\fP into
the directory \fI~/.config/systemd/user/\fP.  Create that directory first
if it doesn't exist.  Then enable it with:
.nf
.sp
	systemctl \-\-user enable xscreensaver
.sp
.fi
.SS LAUNCHING XSCREENAVER FROM UPSTART
If you are not using GNOME, KDE or LXDE, and your system uses
.BR upstart (7)
instead of
.BR systemd (1),
launch the \fI"Startup Applications"\fP applet, click \fI"Add"\fP, and enter
these lines:
.nf
.sp
	Name: XScreenSaver
	Command: xscreensaver
	Comment: XScreenSaver
.sp
.fi
.SS LAPTOP LIDS WITHOUT SYSTEMD
BSD systems or other systems without
.BR systemd (1)
or
.BR elogind (8)
might have luck by adding "\fIxscreensaver\-command \-\-suspend\fP" to
some appropriate spot in \fI/etc/acpi/events/anything\fP or in
\fI/etc/acpi/handler.sh\fP, if those files exist.
.SS LAUNCHING XSCREENSAVER FROM 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).

On the \fIGeneral\fP page set the \fILocal Greeter\fP to
\fIStandard Greeter\fP.

On the \fIBackground\fP page, type the
command \fI"xscreensaver \-\-no\-splash"\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.)

If that doesn't work, you can edit the config file directly. Edit
\fI/etc/X11/gdm/gdm.conf\fP to include:
.nf
.sp
	Greeter=/usr/bin/gdmlogin
	BackgroundProgram=xscreensaver \-\-no\-splash
	RunBackgroundProgramAlways=true
.sp
.fi
In this situation, the \fIxscreensaver\fP process will be running as user
\fIgdm\fP.  You can configure the settings for this nobody-logged-in
state (timeouts, DPMS, etc.) by editing the \fI~gdm/.xscreensaver\fP file.

If you get "connection refused" errors when running \fIxscreensaver\fP
from \fIgdm\fP, then this probably means that you are having
.BR xauth (1)
problems.  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).

There might be a way to accomplish this with other display managers.
It's a mystery!
.SH THE WAYLAND PROBLEM
Wayland is a completely different window system that is intended to replace
X11.  After 14+ years of trying, some Linux distros have finally begun
enabling it by default.  Most deployments of it also include XWayland, which
is a compatibility layer that allows \fIsome\fP X11 programs to continue to
work within a Wayland environment.

Unfortunately, XScreenSaver is not one of those programs.

If your system is running XWayland, XScreenSaver will malfunction in two
ways:
.RS 0
.TP 3
\fB1:\fP It will be unable to detect user activity in non-X11 programs.

This means that while a native Wayland program is selected, XScreenSaver will
think that you are idle, and may blank the screen prematurely.
.TP 3
\fB2:\fP It will be unable to lock the screen.

This is because X11 grabs don't work properly under XWayland, so there is no
way for XScreenSaver to prevent the user from switching away from the screen
locker to another application.
.RE

In short, for XScreenSaver to work properly, you will need to switch off
Wayland and use the X Window System like in the "good old days".
.SS TO DISABLE WAYLAND UNDER GNOME
The login screen should have a gear-icon menu that lets you change the session
type from "GNOME" (the Wayland session) to "GNOME on Xorg" (the X11 session).

Alternately, edit \fI/etc/gdm/custom.conf\fP and make sure it includes this
line:
.nf
.sp
	WaylandEnable=false
.fi
.SS TO DISABLE WAYLAND UNDER KDE
The login screen should have a menu that lets you change the session type to
"Plasma (X11)".

Alternately, edit \fI/etc/sddm.conf\fP and change the \fISessionDir\fP line
under the \fI[Wayland]\fP section to say:
.nf
.sp
	SessionDir=/dev/null
.fi
.SH SECURITY CONCERNS
XScreenSaver has a decades-long track record of securely locking your screen.
However, there are many things that can go wrong.  X11 is a very old system,
and has a number of design flaws that make it susceptible to foot-shooting.
.SS MAGIC BACKDOOR KEYSTROKES
The Xorg and XFree86 X servers, as well as the Linux kernel, both trap
certain magic keystrokes before X11 client programs ever see them.
If you care about keeping your screen locked, this is a big problem.
.TP 3
.B Ctrl+Alt+Backspace
This keystroke kills the X server, and on some systems, leaves you at
a text console.  If the user launched X11 manually, that text console
will still be logged in.  To disable this keystroke globally and
permanently, you need to set the \fBDontZap\fP flag in your
.BR xorg.conf (5)
or
.BR XF86Config (5)
file.
.TP 3
.B Ctrl-Alt-F1, Ctrl-Alt-F2, etc.
These keystrokes will switch to a different virtual console, while leaving the
console that X11 is running on locked.  If you left a shell logged in on
another virtual console, it is unprotected.  So don't leave yourself logged in
on other consoles.  You can disable VT switching globally and permanently by
setting \fBDontVTSwitch\fP in your
.BR xorg.conf (5),
but that might make your system harder to use, since VT switching is an actual
useful feature.

There is no way to disable VT switching only when the screen is
locked.  It's all or nothing.
.TP 3
.B Ctrl-Alt-KP_Multiply
This keystroke kills any X11 app that holds a lock, so typing this will kill
XScreenSaver and unlock the screen.  You can disable it by turning off
\fBAllowClosedownGrabs\fP in
.BR xorg.conf (5).
.TP 3
.B Alt-SysRq-F
This is the Linux kernel "OOM-killer" keystroke.  It shoots down random
long-running programs of its choosing, and so might target and kill
XScreenSaver.  You can disable this keystroke globally with:
.nf
.sp
	echo 176 > /proc/sys/kernel/sysrq
.sp
.fi
There's little that I can do to make the screen locker be secure so long
as the kernel and X11 developers are \fIactively\fP working against
security like this.  The strength of the lock on your front door
doesn't matter much so long as someone else in the house insists on
leaving a key under the welcome mat.
.SS THE OOM-KILLER
Even if you have disabled the \fBAlt-SysRq-F\fP OOM-killer keystroke, the
OOM-killer might still decide to assassinate XScreenSaver at random, which
will unlock your screen.  If the
.BR xscreensaver\-auth (6)
program is installed setuid, it attempts to tell the OOM-killer to leave
the XScreenSaver daemon alone, but that may or may not work.

You would think that the OOM-killer would pick the process using the most
memory, but most of the time it seems to pick the process that would be most
comically inconvenient, such as your screen locker, or
.BR crond (8).
You can disable the OOM-killer entirely with:
.nf
.sp
	echo 2 > /proc/sys/vm/overcommit_memory
	echo vm.overcommit_memory = 2 >> /etc/sysctl.conf
.sp
.fi
In addition to the kernel's OOM-killer, 
.BR systemd (1)
has its own.  The included \fIxscreensaver.service\fP file attempts to
evade it, but you may want to just turn it off anyway:
.nf
.sp
	sudo systemctl disable --now systemd-oomd
	sudo systemctl mask systemd-oomd
.sp
.fi
.SS X SERVER ACCESS IS GAME OVER
X11's security model is all-or-nothing.  If a program can connect to your X
server at all, either locally or over the network, it can log all of your
keystrokes, simulate keystrokes, launch arbitrary programs, and change the
settings of other programs.  Assume that anything that can connect to your X
server can execute arbitrary code as the logged-in user.  See
.BR Xsecurity (1)
and 
.BR xauth (1).
.SS PAM PASSWORDS
If your system uses PAM (Pluggable Authentication Modules), then PAM must be
configured for XScreenSaver.  If it is not, then you \fImight\fP be in a
situation where you can't unlock.  Probably the file you need 
is \fI/etc/pam.d/xscreensaver\fP.
.SS DON'T LOG IN AS ROOT
Never log in as root.  Log in as a normal user and use
.BR sudo (1)
as necessary.  If you are logged in as root, XScreenSaver will not lock your
screen or run display modes, for numerous good and proper reasons.
.SH MULTI-USER OR SITE-WIDE CONFIGURATION
For a single user, the proper way to configure XScreenSaver is to simply
run the
.BR xscreensaver\-settings (1)
program, and change the settings through the GUI.  Changes are written
to the \fI~/.xscreensaver\fP file.

If you want to set the system-wide defaults, then make your edits to
\fI/etc/X11/app-defaults/XScreenSaver\fP instead.  The two files have
similar (but not identical) syntax.

You can also make changes via the X Resource Database and
.BR xrdb (1),
but that can be very confusing and is not really recommended. 

Options in \fI~/.xscreensaver\fP override any settings in the resource
database or app-defaults file.

If you change a setting in the \fI.xscreensaver\fP file while XScreenSaver
is already running, it will notice this, and reload the file as needed.
But if you change a setting in the X Resource Database, you will need to
restart XScreenSaver for those changes to take effect:
.nf
.sp
	xrdb < ~/.Xdefaults
	xscreensaver-command \-\-restart
.sp
.fi
.SH X RESOURCES
These are the X resources use by XScreenSaver program.  You probably won't
need to change these manually: that's what the
.BR xscreensaver\-settings (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.

If there are multiple screens, the savers are staggered slightly so
that while they all change every \fIcycle\fP minutes, they don't all
change at the same time.
.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.
.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 \fItimeout\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, \fIlockTimeout\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).  A few
seconds are added each time you type a character.
.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 verbose\fP (class \fBBoolean\fP)
Whether to print diagnostics.  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.
.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\-settings (1).
.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),
.BR kdmctl (1),
.BR lxdm (1)
or
.BR dm-tool (1).
.TP 8
.B nice\fP (class \fBNice\fP)
The sub-processes launched by XScreenSaver 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 desktop will fade to
black instead of simply winking out.  Default: true.
.TP 8
.B unfade\fP (class \fBBoolean\fP)
If this is true, then when the screensaver deactivates, desktop will fade back
ininstead of appearing immediately.  This is only done if \fIfade\fP is true
as well.  Default: true.
.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 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\-settings (1)
program will suppress the non-existent programs from the list if this
is true.  Default: false.
.TP 8
.B authWarningSlack\fP (class \fBInteger\fP)
After you successfully unlock the screen, a dialog may pop up informing
you of previous failed login attempts.  If all of those login attemps
were within this amount of time, they are ignored.  The assumption
is that incorrect passwords entered within a few seconds of a correct
one are user error, rather than hostile action.  Default 20 seconds.
.TP 8
.B mode\fP (class \fBMode\fP)
Controls the screen-saving behavior.  Valid 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\-settings (1)
do it for you!
.TP 8
.B programs\fP (class \fBPrograms\fP)
The graphics hacks which XScreenSaver 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\-settings (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.

The default XScreenSaver hacks directory (typically
\fI/usr/libexec/xscreensaver/\fP) is prepended to \fB$PATH\fP
before searching for these programs.

To use a program as a screensaver, it must be able to render onto
the window provided to it in the \fB$XSCREENSAVER_WINDOW\fP environment
variable.  If it creates and maps its own window instead, it won't work.
It must render onto the provided window.

.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:
.nf
.sp
	mono:   mono-program  -root        \\n\\
	color:  color-program -root        \\n\\
.sp
.fi
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:
.nf
.sp
	PseudoColor: cmap-program  -root   \\n\\
	TrueColor:   24bit-program -root   \\n\\
.sp
.fi
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.
.RE
.PP
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
.TP 8
.B visualID\fP (class \fBVisualID\fP)
This is an historical artifact left over from when 8-bit
displays were still common.  You should probably ignore this.

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.)

Valid 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 N
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
.PP
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, above.
.RE
.TP 8
.B installColormap\fP (class \fBBoolean\fP)
This is an historical artifact left over from when 8-bit displays were still
common.  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.
(Which, in this century, you do.)
.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.

A single pixel of motion will still cause the monitor to power back on,
but not un-blank. This is because the X11 server itself unfortunately handles
power-management-related activity detection rather than XScreenSaver.
.SH BUGS
https://www.jwz.org/xscreensaver/bugs.html explains how to write the most
useful bug reports.  If you find a bug, please let me know!
.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.
.TP 8
.B PATH
to find the sub-programs to run, including the display modes.
.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 https://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 systemd (1),
.BR elogind (8),
.BR xscreensaver\-settings (1),
.BR xscreensaver\-command (1),
.BR xscreensaver\-systemd (6),
.BR xscreensaver\-gl\-helper (6),
.BR xscreensaver\-getimage (6),
.BR xscreensaver\-text (6).
.SH COPYRIGHT
Copyright \(co 1991-2022 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>

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
three decades!