Why is / read-only?

Good people,

I have two Cubox-i4pros running Volumio. About a month ago, one of them appeared to have / mounted as read-only.

I cannot determine why this is. The MicroSD card fsck’s fine, including checking for bad blocks (none are found).

But it seems to be a problem. For instance, no log files are being written; and PHP doesn’t seem to be serving the application.

I have done some apt-get update / upgrades, in the hopes of getting a newer kernel which actually works with my AudioQuest DragonFly (but no luck there either). The last set of updates that applied were in mid-December 2015.

I have looked for others having a similar problem but they generally seem to have bad SD cards.

Any suggestions? Thanks in advance!