At start-up a message explaining that the a font is missing may occur. i.e.
WARNING: Cannot open required font
This message can in principle appear later on, but this is at least rare.
The missing font message is relatively normal, and means that a standard X-11 font will be used instead of a times roman font. (The times roman font family is available in PostScript, so is used to give a close match between the screen and hard copy output.)
Ideally the graphics system uses one of the following fonts to provide text in a wide variety of scaled sizes:
clR4x6, timR08, timR10, timR12, timR14, timR18, timR24
If the nearest smaller times roman font is not available then, the above warning message is output, and one of the following list of X-11 fonts will be used if available:
5x7, 5x8, 6x9, 6x10, 6x12, 7x13, 7x14, 9x15, 8x16, 10x20, 12x24
If the requested font is not found then FIT2D will try to use either the 6x10 or the 9x15 font. If neither of these is found, then the font selection has really failed, no text will be output for the required size, and the following message will be output:
ERROR: Cannot open 6x10 nor 9x15 fonts, text cannot be
output to the X-11 screen. You may be able to 'load'
the necessary fonts, or change the font path. See
your system administrator or local X-11 guru. Ideally
the TIMES-ROMAN series of fonts should be available.
It may be possible to alter the font path, or to add extra fonts to the server to overcome these problems. This is however a job for the system administrator.