netcat hangs on sending udp packet

[Jeff Abrahamson]

On a Linux (Ubuntu 16.04) box with no listener on port 8095, I type this

    echo 1 | nc -u -w 1 127.0.0.1 8095

and the command does not return. On my workstation (Ubuntu 17.10), where also nothing listens on 8095, NC returns immediately, which is what I'd expect.

Adding the -v flag causes nc to return immediately (with status 1 rather than 0).

I would expect sending a UDP packet always to succeed quickly if a network interface exists.

Note that this behaviour does not exist in netcat 1.178 (on ubuntu 17.10), so this is only a bug against the version still running in 16.04.4 LTS.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: netcat (not installed)
ProcVersionSignature: Ubuntu 4.4.0-116.140-generic 4.4.98
Uname: Linux 4.4.0-116-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.15
Architecture: amd64
Date: Sun Feb 25 08:39:54 2018
JournalErrors:
 Error: command ['journalctl', '-b', '--priority=warning', '--lines=1000'] failed with exit code 1: Hint: You are currently not seeing messages from other users and the system.
       Users in the 'systemd-journal' group can see all messages. Pass -q to
       turn off this notice.
 No journal files were opened due to insufficient permissions.
SourcePackage: netcat
UpgradeStatus: No upgrade log present (probably fresh install)