mergerfs/mkdocs/docs/tips_notes.md
Antonio SJ Musumeci 75d7a93724 Rework mkdocs based documentation
Lots of restructoring and extra information.
2025-01-03 12:17:26 -06:00

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# Tips and Notes
* This document is literal and reasonably 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. Especially before submitting
bug reports.
* Run mergerfs as `root`. mergerfs is designed and intended to be run
as `root` and may exhibit incorrect behavior if run otherwise.
* If you do not 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.
* Unless using Linux v6.6 or above do **not** use `cache.files=off` if
you expect applications (such as rtorrent) to use
[mmap](http://linux.die.net/man/2/mmap). Enabling `dropcacheonclose`
is recommended when `cache.files=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 is 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.