I try to update periodically, but pi-hole hasn't worked for many months. Updating the raspberry itself never seems to give errors obvious to me. Here's sudo mount:
> pi@raspberrypi:/etc/.pihole $ sudo mount
> /dev/mmcblk0p7 on / type ext4 (rw,noatime,data=ordered)
> devtmpfs on /dev type devtmpfs (rw,relatime,size=87784k,nr_inodes=21946,mode=755)
> sysfs on /sys type sysfs (rw,nosuid,nodev,noexec,relatime)
> proc on /proc type proc (rw,relatime)
> tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev)
> devpts on /dev/pts type devpts (rw,nosuid,noexec,relatime,gid=5,mode=620,ptmxmode=000)
> tmpfs on /run type tmpfs (rw,nosuid,nodev,mode=755)
> tmpfs on /run/lock type tmpfs (rw,nosuid,nodev,noexec,relatime,size=5120k)
> tmpfs on /sys/fs/cgroup type tmpfs (ro,nosuid,nodev,noexec,mode=755)
> cgroup on /sys/fs/cgroup/systemd type cgroup (rw,nosuid,nodev,noexec,relatime,xattr,release_agent=/lib/systemd/systemd-cgroups-agent,name=systemd)
> cgroup on /sys/fs/cgroup/blkio type cgroup (rw,nosuid,nodev,noexec,relatime,blkio)
> cgroup on /sys/fs/cgroup/net_cls type cgroup (rw,nosuid,nodev,noexec,relatime,net_cls)
> cgroup on /sys/fs/cgroup/cpu,cpuacct type cgroup (rw,nosuid,nodev,noexec,relatime,cpu,cpuacct)
> cgroup on /sys/fs/cgroup/devices type cgroup (rw,nosuid,nodev,noexec,relatime,devices)
> cgroup on /sys/fs/cgroup/freezer type cgroup (rw,nosuid,nodev,noexec,relatime,freezer)
> systemd-1 on /proc/sys/fs/binfmt_misc type autofs (rw,relatime,fd=27,pgrp=1,timeout=0,minproto=5,maxproto=5,direct)
> debugfs on /sys/kernel/debug type debugfs (rw,relatime)
> sunrpc on /run/rpc_pipefs type rpc_pipefs (rw,relatime)
> mqueue on /dev/mqueue type mqueue (rw,relatime)
> configfs on /sys/kernel/config type configfs (rw,relatime)
> /dev/mmcblk0p6 on /boot type vfat (rw,relatime,fmask=0022,dmask=0022,codepage=437,iocharset=ascii,shortname=mixed,errors=remount-ro)
> tmpfs on /run/user/1000 type tmpfs (rw,nosuid,nodev,relatime,size=18420k,mode=700,uid=1000,gid=1000)
> tmpfs on /run/user/999 type tmpfs (rw,nosuid,nodev,relatime,size=18420k,mode=700,uid=999,gid=996)
> gvfsd-fuse on /run/user/1000/gvfs type fuse.gvfsd-fuse (rw,nosuid,nodev,relatime,user_id=1000,group_id=1000)
> fusectl on /sys/fs/fuse/connections type fusectl (rw,relatime)
> /dev/mmcblk0p5 on /media/pi/SETTINGS type ext4 (rw,nosuid,nodev,relatime,data=ordered,uhelper=udisks2)