The main window consists of a menu bar and two tabbed pages. The first page is for editing the list of demos, and the second is for editing various other parameters of the screensaver.

Blank Screen Now
Activates the background xscreensaver daemon, which will then run a demo at random. This is the same as running xscreensaver-command (1) with the --activate option.

Lock Screen Now
Just like Blank Screen Now, except the screen will be locked as well (even if it is not configured to lock all the time.) This is the same as running xscreensaver-command (1) with the --lock option.

Kill Daemon
If the xscreensaver daemon is running on this screen, kill it. This is the same as running xscreensaver-command (1) with the --exit option.

Restart Daemon
If the xscreensaver daemon is running on this screen, kill it. Then launch it again. This is the same as doing "xscreensaver-command --exit" followed by "xscreensaver".

Note that it is not the same as doing "xscreensaver-command --restart".

Exit
Exits the xscreensaver-settings program (this program) without affecting the background xscreensaver daemon, if any.

About...
Displays the version number of this program, xscreensaver-settings.

Documentation...
Opens up a web browser looking at the XScreenSaver web page, where you can find online copies of the xscreensaver (1), xscreensaver-settings (1), and xscreensaver-command (1) manuals.

This option menu controls the activation behavior of the screen saver. The options are:
Disable Screen Saver
Don't ever blank the screen, and don't ever allow the monitor to power down.

Blank Screen Only
When blanking the screen, just go black: don't run any graphics.

Only One Screen Saver
When blanking the screen, only ever use one particular display mode (the one selected in the list.)

Random Screen Saver
When blanking the screen, select a random display mode from among those that are enabled and applicable. If there are multiple monitors connected, run a different display mode on each one. This is the default.

Random Same Saver
This is just like Random Screen Saver, except that the same randomly-chosen display mode will be run on all monitors, instead of different ones on each.

Double-clicking in the list on the left will let you try out the indicated demo. The screen will go black, and the program will run in full-screen mode, just as it would if the xscreensaver daemon had launched it. Clicking the mouse again will stop the demo and un-blank the screen.

Single-clicking in the list will run it in the small preview pane on the right. (But beware: many of the display modes behave somewhat differently when running in full-screen mode, so the scaled-down view might not give an accurate impression.)

When Mode is set to Random Screen Saver, each name in the list has a checkbox next to it: this controls whether this display mode is enabled. If it is unchecked, then that mode will not be chosen. (Though you can still run it explicitly by double-clicking on its name.)

If the list has focus, you can type any character to search within it.

Beneath the list are a pair of up and down arrows. Clicking on the down arrow will select the next item in the list, and then run it in full-screen mode, just as if you had double-clicked on it. The up arrow goes the other way. This is just a shortcut for trying out all of the display modes in turn.

After the user has been idle this long, the xscreensaver daemon will blank the screen.

After the screensaver has been running for this long, the currently running graphics demo will be killed, and a new one started. If this is 0, then the graphics demo will never be changed: only one demo will run until the screensaver is deactivated by user activity.

If there are multiple screens, the savers are staggered slightly so that while they all change every cycle minutes, they don't all change at the same time.

When this is checked, the screen will be locked when it activates.

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 minutes, and Blank After is 10 minutes, 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, Lock Screen After 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.

This button, below the small preview window, runs the demo in full-screen mode so that you can try it out. This is the same thing that happens when you double-click an element in the list. Click the mouse to dismiss the full-screen preview.

This button will pop up a dialog where you can configure settings specific to the display mode selected in the list.

Some of the graphics hacks manipulate images. These settings control where those source images come from. The savers load images by running the xscreensaver-getimage (1) and xscreensaver-getimage-file (1) programs.
Grab Desktop Images
If this option is selected, then savers are allowed to manipulate the desktop image, that is, a display mode might draw a picture of your desktop melting, or being distorted in some way. The security-paranoid might want to disable this option, because if it is set, it means that the windows on your desktop will occasionally be visible while your screen is locked. Others will not be able to do anything, but they may be able to see whatever you left on your screen.

Grab Video Frames
If your system has a camera or other video input, selecting this option may allow the image-manipulating modes to grab a still-frame of video to operate on.

Choose Random Image
If this option is set, then the image-manipulating modes will select a random image file to operate on, from the specified source. That source may be a local directory, which will be recursively searched for images. Or, it may be the URL of an RSS or Atom feed (e.g., a Flickr gallery), in which case a random image from that feed will be selected instead. The contents of the feed will be cached locally and refreshed periodically as needed.

If more than one of the above image-related options are selected, then one will be chosen at random. If none of them are selected, then an image of video colorbars will be used instead.

Text Manipulation

Some of the display modes display and manipulate text. The following options control how that text is generated. The savers load text by running the xscreensaver-text (1) program.
Host Name and Time
If this checkbox is selected, then the text used by the screen savers will be the local host name, OS version, date, time, and system load.

Text
If this checkbox is selected, then the literal text typed in the field to its right will be used. If it contains % escape sequences, they will be expanded as per strftime (2).

Text File
If this checkbox is selected, then the contents of the corresponding file will be displayed.

Program
If this checkbox is selected, then the given program will be run, repeatedly, and its output will be displayed.

URL
If this checkbox is selected, then the given web page will be downloaded and displayed repeatedly. If the document contains HTML, RSS, or Atom, it will be converted to plain-text first.

Note: this re-downloads the document every time the screen saver runs out of text, so it will probably be hitting that web server multiple times a minute.

Power Management Settings

These settings control whether, and when, your monitor powers down.
Power Management Enabled
Whether the monitor should be powered down after a period of inactivity.

If this option is grayed out, it means your X server does not support the XDPMS extension, and so control over the monitor's power state is not available.

Standby After
If Power Management Enabled is selected, the monitor will go black after this much idle time. (Graphics demos will stop running, also.)

Suspend After
If Power Management Enabled is selected, the monitor will go into power-saving mode after this much idle time. This duration should be greater than or equal to Standby.

Off After
If Power Management Enabled is selected, the monitor will fully power down after this much idle time. This duration should be greater than or equal to Suspend.

Quick Power-off in "Blank Only" Mode
If the display mode is set to Blank Screen Only and this is checked, then the monitor will be powered off immediately upon blanking, regardless of the other power-management settings. In this way, the power management idle-timers can be completely disabled, but the screen will be powered off when black.

These options control how the screen fades to or from black when a screen saver begins or ends.
Fade To Black When Blanking
If selected, then when the screensaver activates, the current contents of the screen will fade to black instead of simply winking out.

Unfade From Black When Unblanking
The opposite: if selected, then when the screensaver deactivates, the original contents of the screen will fade in from black instead of appearing immediately. This is only done if Fade To Black is also selected.

Fade Duration
When fading or unfading are selected, this controls how long the fade will take.

This option menu lists the color schemes available for use on the unlock dialog.

There are more settings than these available, but these are the most commonly used ones; see the manual for xscreensaver (1) for other parameters that can be set by editing the ~/.xscreensaver file, or the X resource database.

--display host:display.screen
The X display to use. The xscreensaver-settings program will open its window on that display, and also control the xscreensaver daemon that is managing that same display.

--debug
Causes lots of diagnostics to be printed on stderr.

The xscreensaver and xscreensaver-settings processes must run on the same machine, or at least, on two machines that share a file system. When xscreensaver-settings writes a new version of the ~/.xscreensaver file, xscreensaver needs to see that same file, or it won't work.

DISPLAY
to get the default host and display number.

PATH
to find the sub-programs to run. However, note that the sub-programs actually launched by xscreensaver-settings for display in the inline preview pane, but are launched by the xscreensaver daemon when run full screen, so the $PATH setting in both processes matters.

HOME
for the directory in which to read and write the .xscreensaver file.

XENVIRONMENT
to get the name of a resource file that overrides the global resources stored in the RESOURCE_MANAGER property.

HTTP_PROXY, HTTPS_PROXY, http_proxy, or https_proxy
to get the default proxy host and port.

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