Some of the minimal Linux distributions have no telnet client utility or similar utilities such as nc,ncat unless you install it. Most of time we need to do troubleshooting to check connection if server/service is accessible. Do not worry–You still have mechanism inside the Linux kernel without installing above utilities. Take a look at below examples and change it accordingly for your case.
Checking TCP connection:
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root@debian2:# echo > /dev/tcp/8.8.8.8/53 && echo "PORT IS OPEN" || echo "PORT IS NOT OPEN" PORT IS OPEN root@debian2:~# echo > /dev/tcp/google.com/80 && echo "PORT IS OPEN" || echo "PORT IS NOT OPEN" PORT IS OPEN root@debian2:~# echo > /dev/tcp/google.com/443 && echo "PORT IS OPEN" || echo "PORT IS NOT OPEN" PORT IS OPEN #I have to send signal SIGINT. root@debian2:~# echo > /dev/tcp/google.com/123 && echo "PORT IS OPEN" || echo "PORT IS NOT OPEN" ^C-su: connect: Network is unreachable |
Checking UDP Connection:
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root@debian2:~# echo > /dev/udp/0.pool.ntp.org/123 && echo "PORT IS OPEN" || echo "PORT IS NOT OPEN" PORT IS OPEN |