Filestat plugin reports file exists on permission denied

[lastsky]

Bug report

filestat plugin not working

Relevant telegraf.conf (for any server - the same):

[[outputs.prometheus_client]]
  listen = "192.168.22.1:9126"

[[inputs.filestat]]
  files = ["/root/test.txt"]
  md5 = false

[[outputs.prometheus_client]]
  listen = "192.168.22.1:9126"

[[inputs.filestat]]
  files = ["/root/test.txt"]
  md5 = true

System info:

from: telegraf-1.2.1-1.x86_64
up to: telegraf-1.3.4-1.x86_64
any centos kernel.

% uname -a
Linux server1 3.10.0-514.26.2.el7.x86_64 #1 SMP Tue Jul 4 15:04:05 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux

Steps to reproduce:

server1 % touch test.txt
server1 % ls test.txt 
test.txt

server2 % ls test.txt 
ls: cannot access test.txt: No such file or directory

monitoring % curl -s server1:9126/metrics | grep filestat_exists
# HELP filestat_exists Telegraf collected metric
# TYPE filestat_exists untyped
filestat_exists{file="/root/test.txt",host="server1"} 1

monitoring % curl -s server2:9126/metrics | grep filestat_exists
# HELP filestat_exists Telegraf collected metric
# TYPE filestat_exists untyped
filestat_exists{file="/root/test.txt",host="server2"} 1

Expected behavior:

As documented here:
https://github.com/influxdata/telegraf/tree/master/plugins/inputs/filestat

exists (int, 0 | 1)
size_bytes (int, bytes)
md5 (optional, string)

Actual behavior:

exist == 1 and it doesnt depends upon file presence
no size_bytes (expected: 0 bytes)
no md5 (expected: string)

Use case: [Why is this important (helps with prioritizing requests)]

I need:
monitor pid files presence
monitor lock files presence
monitor log files presense and size
monitor files changes
monitor unwanted special files presence

What I do: use telegraf
What colleagues think I do: developing something magic
What I actually do: writing ugly shell scripts :)

[lastsky]

@danielnelson Thank You! 👍 🤝