Disable FTP Server (proftpd) in Plesk

I don't need proftpd on my root server, I use sftp, so:

vi /etc/xinetd.d/ftp_psa

change

disable         = no

to 

disable         = yes

How to kill all cron jobs

kill $(pgrep cron)

BTW f.e.
kill $(pgrep php)
works as well

Delete empty mails from maildrop

I don't know why I have a bunch of empty mails on maildrop folder of postfix, but ...

find /var/spool/postfix/maildrop/ -size 0 -name '*' -exec rm {} +

Postfix. Delete some mails from the queue

Change "123@example" to something you need ...

mailq|grep '123@example'|awk {'print $1'}|grep -v "(host"|tr -d '*!'|postsuper -d -

Decrypt private key

I purchased today a Wildcard SSL certificate from RapidSSL. When I tried to insert it in Parallels Plesk, the private key was wrong. I found out that I must decrypt it first:

openssl rsa -in name_of_file.key -out decrypted.name_of_file.key