### 1.3.3 Starting a Render Job

Starting POV-Ray rendering any scene file is as simple as running `povray` from a command-line with the scene file name as an argument. This will work with either a POV file or an INI file (as long as it has an associated POV file). See Understanding File Types. The scene is rendered with the current POV-Ray 3 options (see Understanding POV-Ray Options).

Note: One of the more common errors new users make is turning off the display option. The Display option (`+d`) is ON by default. If you turn this OFF in the INI file or on the command line, POV-Ray will not display the file as you render.

Please also note that POV-Ray for Unix will write the output file to a .png by default. There is no way to 'save the render window' after rendering is completed. If you turned file output off before starting the render, and change your mind, you will have to start the rendering all over again. We recommend that you just leave file output on all the time.

#### 1.3.3.1 X Window display

When the X Window display is used, the rendered image is displayed in a graphics window. During rendering, the window will be updated after every scanline has been rendered, or sooner if the rendering is taking a long time. To update it sooner you can click any mouse button in the window or press (almost) any key. Pressing `<CTRL-R>` or `<CTRL-L>` during rendering will refresh the whole screen. If you have the `Exit_Enable` or `+X` flag set, pressing 'q' or 'Q' at any time during the rendering will stop POV-Ray rendering and exit. The rendering will pause when complete if the `Pause_When_Done` (or `+P`) flag is set. To exit at this point, press the 'q' or 'Q' key or click any mouse button in the window.

POV-Ray 3.6 includes a color icon in the program if it was compiled with libXpm (which is available on most platforms where the X Window System is installed). If this icon is used for the render view window depends on the window manager being used (KDE, Gnome, fvwm, ...). POV-Ray also comes with a separate color icon (`xpovicon.xpm`) for use with the window managers that can use external icons. For instance, to have fvwm use this icon, copy the icon file to one of the directories pointed to by PixmapPath (or ImagePath) which is defined in your `$HOME/.fvwmrc`. Then, add the following line in `$HOME/.fvwmrc`:

    Style "Povray" Icon xpovicon.xpm

and re-start the X Window server (re-starting fvwm will not be enough). Using this icon with another window manager may use a different procedure.

Documentation of the special command line options to configure the X Window display can be found in Special Command-Line Options.

#### 1.3.3.2 SVGAlib display

For GNU/Linux systems that don't have the X Window System installed, or for those Linux users who prefer to run on the console, it is possible to use the SVGA library to display directly to the screen. For SVGAlib display, the `povray` binary must be installed as a setuid root executable. If POV-Ray does not use SVGAlib display, first try (as root):

    chown root.root povray
    chmod 4755 povray

Note: Doing this may have serious security implications. Running POV-Ray as root or through 'sudo' might be a better idea.

If it still doesn't work then make sure SVGAlib is installed on your machine and works properly. Anything that can at least use the 320x200x256 mode (ie regular VGA) should be fine, although modes up to 1280x1024x16M are possible. If you do not have root priviledges or can't have the system admin install POV-Ray, then you must use the X Window or text display which do not require any special system priviledges to run. If you are using a display resolution that is lower than what you are rendering, the display will be scaled to fit as much of the viewing window as possible.

#### 1.3.3.3 Output file formats

The default output file format of POV-Ray for Unix is PNG (+fn). This can be changed at runtime by setting the `Output_File_Type` or `+fx` option. Eventually, the default format can be changed at compile time by setting `DEFAULT_FILE_FORMAT` in the `config.h` file located in the unix/ directory.

Other convenient formats on Unix systems might be PPM (+fp) and TGA (+ft). For more information about output file formats see File Output Options.

If you are generating histogram files (See CPU Utilization Histogram) in the CSV format (comma separated values), then the units of time are in tens of microseconds (10 x 10-6 s), and each grid block can store times up to 12 hours.