The X font server — a legacy daemon that hands rasterized fonts to X11 clients over the network.
IANA registers 7100 as font-service, and the xfs man page confirms the daemon's default port number is 7100. In the X11 model an X server or client with FontPath set to tcp/host:7100 fetches font metrics and glyphs from xfs rather than from local files. Modern desktops render fonts client-side through fontconfig and Xft, so xfs is effectively obsolete; distributions that still ship it default to a local socket or -nolisten tcp. An open 7100 today is either a very old X installation or an unrelated application on the number.
Do not expose
xfs has no meaningful authentication and is unmaintained legacy code with a history of remote overflow bugs; there is no reason to have it reachable off the host.
$ fslsfonts -server TARGET:7100Seen this on your network? Beige Box scans your Wi-Fi and shows every open port on every device — and its Ports tool links straight back here.
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Corrections or a missing port? Reply @rimrocksystems.