READ-ONLY FS

After the fix, </dev/mmcblk0p1> was left in a read-only state;
this was explained in dmesg:

[ 55.107116] slide (GPIO 71) is now open
[ 82.010894] FAT: Filesystem error (dev mmcblk0p1)
[ 82.010925] fat_get_cluster: invalid cluster chain (i_pos 0)
[ 82.010955] File system has been set read-only
[ 82.107360] FAT: Filesystem error (dev mmcblk0p1)
[ 82.107421] fat_get_cluster: invalid cluster chain (i_pos 0)
[ 104.927398] slide (GPIO 71) is now closed,

an open-and-shut case.

Unmounting the partition and running fsck cleared this up (apparently,
a couple of files had 'EOF errors').