Anyway

I was upgrad­ing the Word­Press site for someone and had a few moments of pan­ic when, after upgrad­ing, all I could see were blank pages. Vis­ions of hav­ing to go through the pain of rein­stalling the data­base from the backup, and upload­ing all the files from the backup, were dan­cing through my head, which would turn a quick upgrade into a long mara­thon. The upgrade here was from 2.6.something to 3.0.1, and I had­n’t bothered doing all the inter­me­di­ate upgrades, so that made the pro­spect even worse.

Pok­ing around the vari­ous sup­port pages encour­aged me to try a couple of dif­fer­ent things first. The fact that all the pages were blank, both the admin site and the pub­licly-vis­ible site, made the prob­lem seem worse than it ended up being. And the solu­tions turned out to be rel­at­ively simple.

Step 1: get the admin site going. I’d made all the plu­gins inact­ive, but fol­low­ing the advice on the WP FAQ troubleshoot­ing page, I renamed the plu­gins dir­ect­ory to plugins.hold, and cre­ated a new empty plu­gins dir­ect­ory. This worked, and I could see the admin site. It turns out that one par­tic­u­lar plu­gin cre­ated hav­oc even when it was­n’t activ­ated. I could then rein­stall all the needed plu­gins cleanly from the auto­mat­ic install one at a time, test­ing to make sure each one worked.

Step 2: go to the Appear­ance page and turn on the default theme (one thing I’d for­got­ten to do before upgrad­ing). It turns out that the old theme was­n’t com­pat­ible with 3.0.1, and showed only blank pages. 

Now the site works again, albeit not look­ing quite the same as it did due to the theme, but that prob­lem is tract­able and does­n’t cre­ate any­where near the same “oh, no” prob­lem that the oth­ers did.