I am running an icinga supervision and have to start a command (perl script) wich need super user rights.
I added the user (nagios) and command (check_dhcp_relayed.pl) to the sudo file and switched of tty requirement (see below). I restarted the icinga service.
-------------------
#
# This file MUST be edited with the 'visudo' command as root.
#
# Please consider adding local content in /etc/sudoers.d/ instead of
# directly modifying this file.
#
# See the man page for details on how to write a sudoers file.
#
Defaults env_reset
Defaults mail_badpass
Defaults secure_path="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/lib/nagios/plugin"

# Host alias specification

# User alias specification

# Cmnd alias specification

# User privilege specification
root ALL=(ALL:ALL) ALL

# Allow members of group sudo to execute any command
%sudo ALL=(ALL:ALL) ALL
# See sudoers(5) for more information on "#include" directives:
Cmnd_Alias DHCPRELAY = /usr/lib/nagios/plugins/check_dhcp_relayed.pl
Defaults logfile="/var/log/sudo.log"
nagios ALL=NOPASSWDHCPRELAY
Defaults !requiretty
Defaults!DHCPRELAY !requiretty
Defaults:nagios !requiretty
Defaults:root !requiretty
-------------------------------------------
Still the command cannot be executed. Error message is:
"sudo: no tty present and no askpass program specified"
sudo.log holds the message:
"command not allowed TTY=unknown"
logging in as nagios and starting the script works, so it seems the tty is missing which should be handled with the !requiretty.
Linux distribution is debian 9.9.
Any solution?

you explicitely disabled tty by this: Defaults:nagios !requiretty

Sudo has to have some way of getting your password. Otherwise how does it know that you are who you claim to be? If you aren't using a terminal, you must specify another way of getting the password. That's what the askpass program is for.