:0 . :1 , :2 all são nomes de exibição (também exibem nomes para um único motinor no mesmo host). Se vários servidores X estiverem em execução no host, suas exibições serão numeradas como valores incrementais, como :X , iniciando em :0 , para identificar uni e cada um deles.
Citando a seção DISPLAY NAMES de man 7 X :
Display Names
From the user's perspective, every X server has a display name of the form:
hostname:displaynumber.screennumber
This information is used by the application to determine how it should connect to the server and which screen it should use by default (on displays with multiple monitors):
hostname
The hostname specifies the name of the machine to which the display isphysically connected. If the hostname is not given, the most efficient way of communicating to a server on the same machine will be used.
displaynumber
The phrase "display" is usually used to refer to collection of monitors that share a common keyboard and pointer (mouse, tablet, etc.). Most workstations tend to only have one keyboard, and therefore, only one display. Larger, multi-user systems, however, frequently have several displays so that more than one person can be doing graphics work at once. To avoid confusion, each display on a machine is assigned a display number (beginning at 0) when the X server for that display is started. The display number must always be given in a display name.
screennumber
Some displays share a single keyboard and pointer among two or more monitors. Since each monitor has its own set of windows, each screen is assigned a screen number (beginning at 0) when the X server for that display is started. If the screen number is not given, screen 0 will be used.