Upgrade 9.6 to 9.7 "Warning: session_start() ..."
Upgrade does not work:
"Warning: session_start() function.session-start: open(/var/www/vhosts/www.peter5.com/tmp/www.peter5.com/tmp/sess_ea5150d536b51e0760613214ef2287f7, O_RDWR) failed: No such file or directory (2) in /vdir/www.peter5.com/var/www/vhosts/www.peter5.com/web/alphayaya_tw0907/tiki-install.php on line 60
...
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Warning: Unknown: open(/var/www/vhosts/www.peter5.com/tmp/www.peter5.com/tmp/sess_ea5150d536b51e0760613214ef2287f7, O_RDWR) failed: No such file or directory (2) 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/www/vhosts/www.peter5.com/tmp/www.peter5.com/tmp) in Unknown on line 0"
What causes this and what to do?