Tail plugin does not respect parameter "read_from_head true"

Wanted to read logs from “/var/log/yum.log” as an example, with fluentd’s tail plugin, and input it to solr collection1. When I tried with default config, solr displayed only logs that where read during the plugin was running. But i wanted to read the whole file from the beginning with all past logs. So as fluentd documentation suggested, I used “read_from_head true” parameter in “source” section. However it had no effect, the tail plugin still worked the same way, just reading the last logs.

Could you please suggest what am i doing wrong? Thank you!

This is my config file:

<source>
  @type tail
  <parse>
      @type none
  </parse>
  path /var/log/yum.log
  pos_file positions.pos
  tag varlog.*
  path_key filename
  read_from_head true
</source>

<match varlog.**>
  @type solr

  # The Solr base url (for example http://localhost:8983/solr).
  base_url http://localhost:8983/solr

  # The Solr collection/core name (default collection1).
  collection collection1
</match>
 pos_file positions.pos

It seems that last log position is respected in that case.
If positions.pos is removed, then fluentd is restarted, it will work as you expected.