Dovecot v2.2.22 (fe789d2) starting up for imap, pop3 (core dumps disabled)

[baskar anand]

 Always I have the following lines in my mail.log (at startup and service restart)

dovecot: master: Warning: Killed with signal 15 (by pid=3156 uid=0 code=kill)
dovecot: log: Warning: Killed with signal 15 (by pid=1 uid=0 code=kill)
dovecot: master: Dovecot v2.2.22 (fe789d2) starting up for imap, pop3 (core dumps disabled)

dovecot -n output is below:

# 2.2.22 (fe789d2): /etc/dovecot/dovecot.conf
# Pigeonhole version 0.4.13 (7b14904)
# OS: Linux 4.4.0-31-generic x86_64 Ubuntu 16.04.1 LTS 
auth_mechanisms = plain login
mail_location = mbox:~/mail:INBOX=/var/mail/%u
mail_privileged_group = mail
namespace inbox {
  inbox = yes
  location = 
  mailbox Drafts {
    special_use = \Drafts
  }
  mailbox Junk {
    special_use = \Junk
  }
  mailbox Sent {
    special_use = \Sent
  }
  mailbox "Sent Messages" {
    special_use = \Sent
  }
  mailbox Trash {
    special_use = \Trash
  }
  prefix = 
}
passdb {
  driver = pam
}
protocols = " imap pop3"
service auth-worker {
  user = root
}
service auth {
  unix_listener /var/spool/postfix/private/auth {
    group = postfix
    mode = 0660
    user = postfix
  }
}
ssl_cert =