devices are up but graphs empty (nan)

[nour]

i used this link for cacti installation: https://www.linuxhelp.com/how-to-instal ... -in-linux/

now devices are up but no graph since two days.

Log file in the attachments


so need help please
and for your information i'm new in centos 7 and cacti ,so please any help should be with the commands.

thanks alot