[metapost] ! MetaPost capacity exceeded

[Karl Berry]

    > If you want your change to affect only metapost, add or change
    > main_memory.mpost only

I'm curious what kind of graph you are generating that the current
main_memory is insufficient for!  My knee-jerk reaction to such reports
is always to just increase the defaults, since if you're running into
it, probably others are too.  It's not just an infinite recursion or
some such?

    texlive ...and therefore I am uncertain what the 'best' command is.

Er, well, it all depends on what one wants to do :).  It's already done,
but for the record ...

As you already mentioned, fmtutil generates stuff per-user; fmtutils-sys
generates it for the "system" install.  In this case, I gather there was
no permission to write in the system dirs.

As for the options, here are the principal ones:
  --all                      recreate all format files
  --missing                  create all missing format files
  --refresh                  recreate only existing format files
  --byfmt formatname         (re)create format for `formatname'

So,  fmtutil --byfmt mpost  would have been my first suggestion, 
since it didn't seem desired to remake the tex or metafont formats here.

Happy formatting,
karl