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diff --git a/README b/README new file mode 100644 index 0000000..c13b2a9 --- /dev/null +++ b/README @@ -0,0 +1,62 @@ +LISTENING(1) General Commands Manual LISTENING(1) + +NAME + listening – check if a TCP server is listening + +SYNOPSIS + listening [-t connect-timeout] [-w wait-timeout] [host:]port + +DESCRIPTION + The listening utility performs a TCP scan against the given host + (defaulting to localhost) and port. + + This can be used to detect if a slowly starting service is ready to + accept connections. + + The options are as follows: + + -t connect-timeout + Wait at most connect-timeout seconds per connection attempt + (default: 0.2s, decimal fractions are allowed). + + -w wait-timeout + Wait at most wait-timeout seconds total (decimal fractions are + allowed), and keep trying to connecting when connection has been + refused. + +DETAILS + listening implements a TCP SYN scan (half-open scan), which has several + benefits: + + • As the target program does not accept(2) the connection, there's no + trace of testing. + + • It's possible to do in unprivileged Linux userspace, thanks to + TCP_QUICKACK and SO_LINGER (but also Linux specific). + + Note that firewalls may block this kind of scan, so for reliable results + listening should be used on localhost only or within a DMZ. + +EXIT STATUS + listening returns one of the following status codes: + + 0 when the port is up + 1 when the port refuses connection + 2 when timeout was reached + 99 if some other error occurred + +SEE ALSO + nc(1), nmap(1) + +AUTHORS + Leah Neukirchen <leah@vuxu.org> + +LICENSE + listening is in the public domain. + + To the extent possible under law, the creator of this work has waived all + copyright and related or neighboring rights to this work. + + http://creativecommons.org/publicdomain/zero/1.0/ + +Void Linux August 8, 2023 Void Linux |