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Dr Jackson
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Testing remote port connectivity - Linux hack
Testing remote port connectivity - BASH
On occasion, Telnet is not installed on a system, making it difficult to test if a remote port is connectable or not. If this is the case, the below method using simple Linux devices
can help diagnose a remote port connectivity issue.
Using bash
to test a remote port
Linux has a built in handler to test port connectivity in theĀ /dev/tcp/ directory. Using the below is a handy way to test remote port connectivity.
Connection successful
#> timeout 1 bash -c 'cat < /dev/null > /dev/tcp/google.com/80'
#> echo $?
0
Connection failure prior to the timeout
#> timeout 1 bash -c 'cat < /dev/null > /dev/tcp/sfsfdfdff.com/80'
bash: sfsfdfdff.com: Name or service not known
bash: /dev/tcp/sfsfdfdff.com/80: Invalid argument
$ echo $?
1
Connection not established before the timeout value of 1 second
#> timeout 1 bash -c 'cat < /dev/null > /dev/tcp/google.com/81'
#> echo $?
124