My notes on xinetd

1 Rocky and Centos8 sans xinetd

As of CentOS8 xinet.d is not needed nor used. Rather we use systemd and create a new service.

1.1 tftpd

Installing tftp-server creates a new service in /usr/lib/systemd/system, specifically

/usr/lib/systemd/system/tftp.socket
/usr/lib/systemd/system/tftp.service

You need to cp these files to /etc/systemd/system so that systemctl can systemctl can start and stop this daemon/service.

And rename them to tftp-server for both. i.e.

/etc/systemd/system/tftp-server.service
/etc/systemd/system/tftp-server.socket

They should be edited to look like this: tftp-server.service

[Unit]
Description=Tftp Server
Requires=tftp-server.socket
Documentation=man:in.tftpd

[Service]
ExecStart=/usr/sbin/in.tftpd -p -s /var/lib/tftpboot
StandardInput=socket

[Install]
WantedBy=multi-user.target
Also=tftp-server.socket

And tftp-server.socket

Description=Tftp Server Activation Socket

[Socket]
ListenDatagram=69
BindIPv6Only=both

[Install]
WantedBy=sockets.target

Start and stop with systemctl start tftp-server etc.

tftp runs on port 69. You will have to ensure that any firewalls allow port

See iptables file for details.

iptables -L -n
Chain INPUT (policy DROP)
target     prot opt source               destination         
ACCEPT     udp  --  0.0.0.0/0            0.0.0.0/0            udp dpt:53
ACCEPT     tcp  --  0.0.0.0/0            0.0.0.0/0            tcp dpt:53
ACCEPT     udp  --  0.0.0.0/0            0.0.0.0/0            udp dpt:67
ACCEPT     tcp  --  0.0.0.0/0            0.0.0.0/0            tcp dpt:67
ACCEPT     all  --  0.0.0.0/0            0.0.0.0/0            state RELATED,ESTABLISHED
ACCEPT     udp  --  0.0.0.0/0            0.0.0.0/0            udp dpt:69
MYICMP     icmp --  0.0.0.0/0            0.0.0.0/0            /* direct icmp rules to the MYICMP chain */
MYSSH      tcp  --  0.0.0.0/0            0.0.0.0/0            tcp dpt:22 /* direct ssh rules to the MYSSH chain */
ACCEPT     all  --  0.0.0.0/0            0.0.0.0/0           
LOG        all  --  0.0.0.0/0            0.0.0.0/0            LOG flags 0 level 6 prefix ">>> I N P U T  Dropped "

Chain FORWARD (policy DROP)

1.2 tftp root directory

For my setup the tftp daemon will serve files from /var/lib/tftpboot

1.3 Home

2 Extended Internet Daemon

Older Linux hosts typically run xinetd to control internet daemons, listen for incoming connections and keeping things secure. xinetd is the newer, more secure version of inetd which has not been obsoleted.

Why Xinetd? Why the need for xinetd? The xinetd daemon is a “super-daemon” or “super service” that listens for connection requests on behalf of other daemons and services. You can launch xinetd once and have it wake up other intended services as needed. Xinetd brings efficiency and security by being a single service that runs as needed– as opposed to having multiple, dormant services running needlessly in the background for most of their run time.

In this post, xinetd will be used to listen for any tftp requests that come in from clients. When the server receives a request, xinetd will launch tftp with the necessary options so that files can be downloaded by the tftp client as requested. Yes . . . you can run tftpd without xinetd; however, the xinetd config file keeps all the important tftpd options nice and tidy for you as we can see here:

  # sample /etc/xinet.d/tftp file
  service tftp
{    disable     = yes    
     socket_type     = dgram    
     protocol        = udp    
     wait            = yes 
     user            = root 
     server          = /usr/sbin/in.tftpd 
     server_args     = -s /var/lib/tftpboot 
     per_source      = 11 
     cps             = 100 2 
     flags           = IPv4
     }

If you still insist on running tftpd without xinetd, consult the man pages for in.tftpd. You’ll need to know how to use the correct options in order to get the tftpd server listening in stand-alone mode (that is to say, listening without xinetd).

2.1 tftpd managed through xinetd service

On some systems in.tftpd is managed through the xinetd service. /etc/xinetd.conf stores the default configuration of all services managed by xinetd, and also the default configuration of tftpd.

First off, you have to check if tftpd and xinetd have been installed on your system.

dnf list | grep -i inet 
dnf list | grep -i tftpd

# if not then install:

dnf install xinetd tftpd

in.tftpd is managed through the inetd service. /etc/xinetd.conf stores the default configuration of all services managed by xinetd, and also the default configuration of tftpd.