Accidently, I recursively destroyed access rights for /home/pi.
Since /home/pi/data is also affected MySQL stopped working.
I recovered functionaly by granting everyone full access (777) to /hoem/pi/data,
but I’m wondering what are correct settings.
Is there a description somewhere which access right are needed?
my /home/pi/data directory looks like it is 777 also.
pi@emonpi(ro):~$ ls -al
total 263
drwxr-xr-x 20 pi pi 4096 May 7 21:37 .
drwxr-xr-x 3 root root 4096 Nov 21 2015 ..
drwx------ 2 pi pi 4096 Nov 15 2016 .aptitude
drwxr-xr-x 3 pi pi 4096 Mar 16 2016 avrdude-rpi
drwxr-xr-x 4 pi pi 4096 Mar 26 14:05 backup
-rw-r--r-- 1 pi pi 70919 Nov 7 2016 backup_php.ini
-rw------- 1 pi pi 9300 May 7 22:09 .bash_history
-rw-r--r-- 1 pi pi 220 Nov 21 2015 .bash_logout
-rw-r--r-- 1 pi pi 3618 Nov 10 2016 .bashrc
drwxrwxrwx 11 pi pi 3072 May 15 11:21 data
drwxr-xr-x 7 pi pi 4096 Mar 26 11:00 emonhub
drwxr-xr-x 10 pi pi 4096 May 7 21:37 emonpi
drwxr-xr-x 6 pi pi 4096 Oct 31 2016 emonupload
drwxr-xr-x 3 pi pi 4096 May 15 11:36 huawei-hilink-status
-rw------- 1 pi pi 696 Mar 24 2016 .mysql_history
-rw------- 1 pi pi 31 Feb 27 16:57 .nano_history
@glyn.hudson might be able to tell you where it is documented.
Your best option would be to download a fresh emonSD, flash it to an SD card then use this as a template guide for restoring your image: