Issue Upgrading to Plesk Onyx 17.8.11 from 17.5.3 - warnings

[John S.]

Hi All,

I have just upgraded Plesk 17.5.3 to 17.8.11. Everything went smoothly, but I have received a few warnings:

which: no unrar in (/sbin:/bin:/usr/sbin:/usr/bin:/usr/local/sbin:/usr/local/bin)
 Trying to install sftp-server binary into chroot environment... cp: cannot stat `internal-sftp': No such file or directory
done
/var/www/vhosts/chrootinternal-sftp: application/x-directory; charset=binary
probably it will not work in chrooted accounts

WARNING!
Some problems are found during register /var/www/vhosts/chrootinternal-sftp in chrooted environment(see log file: /var/log/plesk/install/plesk_17.8.11_installation.log)

Continue...

What is the problem with 'internal-sftp'? How to fix that warning?

Thanks!