First section non-systemd linux, second section systemd linux.
For non-systemd linux:
http://www.cyberciti.biz/tips/linux-audit-files-to-see-who-made-changes-to-a-file.html
install audit
start on boot
ntsysv
or
chkconfig auditd on
/etc/init.d/auditd start
auditctl -w "/media/Office-Files/Files/a-PI/Clients" -p rwxa
ausearch -f "/media/Office-Files/Files/a-PI/Clients" -i | less
For systemd linux:
https://www.linux.com/learn/linux-system-monitoring-and-more-auditd
https://www.linux.com/learn/customized-file-monitoring-auditd
With distribution install audit or auditd
sudo systemctl status auditd.service
sudo systemctl start auditd.service
sudo systemctl enable auditd.service #to run at boot sudo aureport