kazulog@sv1:~$ cat /etc/os-release | head -2
PRETTY_NAME="Ubuntu 26.04 LTS"
NAME="Ubuntu"
kazulog@sv1:~$ grep -vE '^(#|$)' /etc/inetd.conf
daytime		stream	tcp6	nowait	root	internal
kazulog@sv1:~$ ls -l /etc/inetd.d/
total 8
-rw-r--r-- 1 root root  90 Sep 12 09:47 echo
-rw-r--r-- 1 root root 160 Sep 12 09:47 hello
kazulog@sv1:~$ cat /etc/inetd.d/echo /etc/inetd.d/hello
# echo サービス（inetd の内蔵サービス）
echo	stream	tcp	nowait	root	internal
# 自作サービス: 10013 番につながると /usr/local/bin/hello.sh を実行する
hello	stream	tcp	nowait	nobody	/usr/sbin/tcpd	/usr/local/bin/hello.sh
kazulog@sv1:~$ cat /etc/hosts.allow
# /etc/hosts.allow: list of hosts that are allowed to access the system.
#                   See the manual pages hosts_access(5) and hosts_options(5).
#
# Example:    ALL: LOCAL @some_netgroup
#             ALL: .foobar.edu EXCEPT terminalserver.foobar.edu
#
# If you're going to protect the portmapper use the name "rpcbind" for the
# daemon name. See rpcbind(8) and rpc.mountd(8) for further information.
#
# SSH は必ず許可する（締め出し防止）
sshd: ALL
kazulog@sv1:~$ cat /etc/hosts.deny
# /etc/hosts.deny: list of hosts that are _not_ allowed to access the system.
#                  See the manual pages hosts_access(5) and hosts_options(5).
#
# Example:    ALL: some.host.name, .some.domain
#             ALL EXCEPT in.fingerd: other.host.name, .other.domain
#
# If you're going to protect the portmapper use the name "rpcbind" for the
# daemon name. See rpcbind(8) and rpc.mountd(8) for further information.
#
# The PARANOID wildcard matches any host whose name does not match its
# address.
#
# You may wish to enable this to ensure any programs that don't
# validate looked up hostnames still leave understandable logs. In past
# versions of Debian this has been the default.
# ALL: PARANOID
# 自作サービスは 192.168.100.20 からの接続を拒否する
hello.sh: 192.168.100.20
kazulog@sv1:~$ systemctl is-enabled inetutils-inetd; systemctl is-active inetutils-inetd
enabled
active
kazulog@sv1:~$ systemctl is-active hello-socket.socket
active
kazulog@sv1:~$ sudo ss -tlnp | grep -E ":(7|13|10013|10014) "
LISTEN 0      10           0.0.0.0:10013      0.0.0.0:*    users:(("inetutils-inetd",pid=4189,fd=7))
LISTEN 0      10           0.0.0.0:7          0.0.0.0:*    users:(("inetutils-inetd",pid=4189,fd=6))              
LISTEN 0      4096               *:10014            *:*    users:(("systemd",pid=1,fd=79))                        
LISTEN 0      10                 *:13               *:*    users:(("inetutils-inetd",pid=4189,fd=4))