php - Ubuntu sendmail spam -

i have installed sendmail in ubuntu send mails , works fine, have detected every 30' receive e-mail subject:

cron [ -x /usr/lib/php5/maxlifetime ] && [ -x /usr/lib/php5/sessionclean ] && [ -d /var/lib/php5 ] && /usr/lib/php5/sessionclean /var/lib/php5 $(/usr/lib/php5/maxlifetime)

and every 20 minutes receive other e-amil subject:

cron test -x /etc/init.d/sendmail && /usr/share/sendmail/sendmail cron-msp

what happened? how can avoid send e-mails?