could not write to the log file

1566774858 SQL: SELECT Count(*) as NumRows FROM LkupSyn;
>1566774858 -1 rows affected
Warning: Unknown: open(/var/lib/php/session/sess_lnfjib4kr19b1qa4iqh69ga8u4, O_RDWR) failed: No space left on device (28) in Unknown on line 0

Warning: Unknown: Failed to write session data (files). Please verify that the current setting of session.save_path is correct (/var/lib/php/session) in Unknown on line 0