Wiktionary
vb. 1 To affix a notice, announcement etc, to a post, board, wall or the like. 2 To enter any information, data etc (into a register, account, record etc). 3 (context basketball English) To establish a position in the frontcourt on one side or the other of the free throw lane, especially used against smaller defender.
Usage examples of "post up".
Penalty of death against the dealer who does not post up the contents of his warehouse, or who does not keep open shop.
Kirkwoods' phones wired and to get the command post up and running.
If I did not think that that resolution must fail, I would post up to Oxford immediately!
They overran the RSMP post up at the Velysen place, then hit here.
You're like a big lamp post up there, you berk, right in the open.
This great-grandfather, for several years when he was a young man, had run a trading post up on the Kickapoo, trading with the Sauks and Foxes who still were in the area.
There was a console call-post up over their heads, if anyone wanted to stand tall enough to try for it.