mergerfs/mkdocs/docs/pages/documentation/tips_notes.md

# TIPS / NOTES

- This document is literal and thorough. If a suspected feature isn't
  mentioned it doesn't exist. If certain libfuse arguments aren't
  listed they probably shouldn't be used.
- Ensure you're using the latest version.
- Run mergerfs as `root`. mergerfs is designed and intended to be run
  as `root` and may exibit incorrect behavior if run otherwise..
- If you don't see some directories and files you expect, policies
  seem to skip branches, you get strange permission errors, etc. be
  sure the underlying filesystems' permissions are all the same. Use
  `mergerfs.fsck` to audit the filesystem for out of sync permissions.
- If you still have permission issues be sure you are using POSIX ACL
  compliant filesystems. mergerfs doesn't generally make exceptions
  for FAT, NTFS, or other non-POSIX filesystem.
- Do **not** use `cache.files=off` if you expect applications (such as
  rtorrent) to use [mmap](http://linux.die.net/man/2/mmap)
  files. Shared mmap is not currently supported in FUSE w/ page
  caching disabled. Enabling `dropcacheonclose` is recommended when
  `cache.files=partial|full|auto-full`.
- [Kodi](http://kodi.tv), [Plex](http://plex.tv),
  [Subsonic](http://subsonic.org), etc. can use directory
  [mtime](http://linux.die.net/man/2/stat) to more efficiently
  determine whether to scan for new content rather than simply
  performing a full scan. If using the default **getattr** policy of
  **ff** it's possible those programs will miss an update on account
  of it returning the first directory found's **stat** info and it's a
  later directory on another mount which had the **mtime** recently
  updated. To fix this you will want to set
  **func.getattr=newest**. Remember though that this is just
  **stat**. If the file is later **open**'ed or **unlink**'ed and the
  policy is different for those then a completely different file or
  directory could be acted on.
- Some policies mixed with some functions may result in strange
  behaviors. Not that some of these behaviors and race conditions
  couldn't happen outside **mergerfs** but that they are far more
  likely to occur on account of the attempt to merge multiple sources
  of data which could be out of sync due to the different policies.
- For consistency it's generally best to set **category** wide policies
  rather than individual **func**'s. This will help limit the
  confusion of tools such as
  [rsync](http://linux.die.net/man/1/rsync). However, the flexibility
  is there if needed.