lsof faulty output while using -F option

[Manik Jain]

After upgrading to xenial, the -F option returns faulty output especially when used with field character 'n'.

OS version --> xenial, lsof --> 4.89 :

# lsb_release -rd
Description: Ubuntu 16.04.2 LTS
Release: 16.04

# uname -a
Linux some-hostname.com 4.4.0-1020-aws #29-Ubuntu SMP Wed Jun 14 15:54:52 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux

# dpkg -l lsof
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name Version Architecture Description
+++-=============================================-===========================-===========================-===============================================================================================
ii lsof 4.89+dfsg-0.1 amd64 Utility to list open files

Running lsof with '-Fn' lists some entries starting with 'f' for e.g. f5, f8, f11 below: (hostnames/port no. changed below)

# lsof -a -iTCP -sTCP:ESTABLISHED -P -Fn
p11628
f5
nsome-hostname.com:59612->ec2-x-x-x-x.xxxx.amazonaws.com:443
f8
nlocalhost:29896->localhost:80
f11
nlocalhost:12150->localhost:80
p25352

-------

While on precise it still seems to work fine:

OS version --> precise, lsof --> 4.81

# lsb_release -rd
Description: Ubuntu 12.04.5 LTS
Release: 12.04

# uname -a
Linux some-hostname.com 3.13.0-117-generic #164~precise1-Ubuntu SMP Mon Apr 10 16:16:25 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux

# dpkg -l lsof
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name Version Description
+++-=============================================-=============================================-==========================================================================================================
ii lsof 4.81.dfsg.1-1build1 List open files

Running lsof with '-Fn' option in precise doesn't show anything like 'f10,f8,f5,f11' that's seen for xenial as put above. (hostnames/port no. changed below)

# lsof -a -iTCP -sTCP:ESTABLISHED -P -Fn

p23957
nsome-hostname.com:22375->some-domain-address:7483
p22118
nlocalhost:12346->localhost:80
nlocalhost:32121->localhost:80
nsome-hostname.com:13380->ec2-x-x-x-x.xxxx.amazonaws.com:443
p15128