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Merge pull request #1145 from trapexit/readme 

Lots of misc README updates
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trapexit 1 year ago
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@ -1,7 +1,7 @@
.\"t
.\" Automatically generated by Pandoc 2.9.2.1
.\"
.TH "mergerfs" "1" "2023-02-23" "mergerfs user manual" ""
.TH "mergerfs" "1" "" "mergerfs user manual" ""
.hy
.SH NAME
.PP
@ -74,12 +74,12 @@ A + B = C
\f[R]
.fi
.PP
mergerfs does \f[B]NOT\f[R] support the copy-on-write (CoW) or whiteout
mergerfs does \f[B]not\f[R] support the copy-on-write (CoW) or whiteout
behaviors found in \f[B]aufs\f[R] and \f[B]overlayfs\f[R].
You can \f[B]not\f[R] mount a read-only filesystem and write to it.
However, mergerfs will ignore read-only drives when creating new files
so you can mix read-write and read-only drives.
It also does \f[B]NOT\f[R] split data across drives.
It also does \f[B]not\f[R] split data across drives.
It is not RAID0 / striping.
It is simply a union of other filesystems.
.SH TERMINOLOGY
@ -110,6 +110,38 @@ start with one of the following option sets.
.SS You don\[cq]t need \f[C]mmap\f[R]
.PP
\f[C]cache.files=off,dropcacheonclose=true,category.create=mfs\f[R]
.SS Command Line
.PP
\f[C]mergerfs -o create.files=partial,dropcacheonclose=true,category.create=mfs /mnt/hdd0:/mnt/hdd1 /media\f[R]
.SS /etc/fstab
.PP
\f[C]/mnt/hdd0:/mnt/hdd1 /media fuse.mergerfs create.files=partial,dropcacheonclose=true,category.create=mfs 0 0\f[R]
.SS systemd mount
.PP
https://github.com/trapexit/mergerfs/wiki/systemd
.IP
.nf
\f[C]
[Unit]
Description=mergerfs service
[Service]
Type=simple
KillMode=none
ExecStart=/usr/bin/mergerfs \[rs]
-f \[rs]
-o create.files=partial \[rs]
-o dropcacheonclose=true \[rs]
-o category.create=mfs \[rs]
/mnt/hdd0:/mnt/hdd1 \[rs]
/media
ExecStop=/bin/fusermount -uz /media
Restart=on-failure
[Install]
WantedBy=default.target
\f[R]
.fi
.PP
See the mergerfs wiki for real world
deployments (https://github.com/trapexit/mergerfs/wiki/Real-World-Deployments)
@ -168,6 +200,11 @@ The request will succeed but do nothing.
Useful for benchmarking mergerfs.
(default: false)
.IP \[bu] 2
\f[B]lazy-umount-mountpoint=BOOL\f[R]: mergerfs will attempt to
\[lq]lazy umount\[rq] the mountpoint before mounting itself.
Useful when performing live upgrades of mergerfs.
(default: false)
.IP \[bu] 2
\f[B]ignorepponrename=BOOL\f[R]: Ignore path preserving on rename.
Typically rename and link act differently depending on the policy of
\f[C]create\f[R] (read below).
@ -364,11 +401,22 @@ Use \f[C]async_read=false\f[R] instead.
\f[B]splice_write\f[R]: deprecated - Does nothing.
.IP \[bu] 2
\f[B]splice_move\f[R]: deprecated - Does nothing.
.IP \[bu] 2
\f[B]allow_other\f[R]: deprecated - mergerfs always sets this FUSE
option as normal permissions can be used to limit access.
.IP \[bu] 2
\f[B]use_ino\f[R]: deprecated - mergerfs should always control inode
calculation so this is enabled all the time.
.PP
\f[B]NOTE:\f[R] Options are evaluated in the order listed so if the
options are \f[B]func.rmdir=rand,category.action=ff\f[R] the
\f[B]action\f[R] category setting will override the \f[B]rmdir\f[R]
setting.
.PP
\f[B]NOTE:\f[R] Always look at the documentation for the version of
mergerfs you\[cq]re using.
Not all features are available in older releases.
Use \f[C]man mergerfs\f[R] or find the docs as linked in the release.
.SS Value Types
.IP \[bu] 2
BOOL = `true' | `false'
@ -403,7 +451,7 @@ calculation and a individual minfreespace value.
The values are set by prepending an \f[C]=\f[R] at the end of a branch
designation and using commas as delimiters.
Example: /mnt/drive=RW,1234
.SS branch type
.SS branch mode
.IP \[bu] 2
RW: (read/write) - Default behavior.
Will be eligible in all policy categories.
@ -417,7 +465,7 @@ NC: (no-create) - Will be excluded from \f[C]create\f[R] policies.
You can\[cq]t create on that branch but you can change or delete.
.SS minfreespace
.PP
Same purpose as the global option but specific to the branch.
Same purpose and syntax as the global option but specific to the branch.
If not set the global value is used.
.SS globbing
.PP
@ -428,12 +476,12 @@ the shell itself will apply the glob itself.\f[R]
.IP
.nf
\f[C]
# mergerfs /mnt/disk\[rs]*:/mnt/cdrom /media/drives
# mergerfs /mnt/hdd\[rs]*:/mnt/ssd /media
\f[R]
.fi
.PP
The above line will use all mount points in /mnt prefixed with
\f[B]disk\f[R] and the \f[B]cdrom\f[R].
\f[B]hdd\f[R] and \f[B]ssd\f[R].
.PP
To have the pool mounted at boot or otherwise accessible from related
tools use \f[B]/etc/fstab\f[R].
@ -441,7 +489,7 @@ tools use \f[B]/etc/fstab\f[R].
.nf
\f[C]
# <file system> <mount point> <type> <options> <dump> <pass>
/mnt/disk*:/mnt/cdrom /mnt/pool fuse.mergerfs minfreespace=16G 0 0
/mnt/hdd*:/mnt/ssd /media fuse.mergerfs minfreespace=16G 0 0
\f[R]
.fi
.PP
@ -532,7 +580,7 @@ This tuple is not client facing.
The inode that is presented to the client is passed through the kernel
uninterpreted.
.PP
From FUSE docs regarding \f[C]use_ino\f[R]:
From FUSE docs for \f[C]use_ino\f[R]:
.IP
.nf
\f[C]
@ -879,7 +927,7 @@ a branch.
\f[B]ENOENT\f[R] will be returned if no eligible branch is found.
.SS Path Preservation
.PP
Policies, as described below, are of two basic types.
Policies, as described below, are of two basic classifications.
\f[C]path preserving\f[R] and \f[C]non-path preserving\f[R].
.PP
All policies which start with \f[C]ep\f[R] (\f[B]epff\f[R],
@ -897,8 +945,6 @@ With the \f[C]msp\f[R] or \f[C]most shared path\f[R] policies they are
defined as \f[C]path preserving\f[R] for the purpose of controlling
\f[C]link\f[R] and \f[C]rename\f[R]\[cq]s behaviors since
\f[C]ignorepponrename\f[R] is available to disable that behavior.
In mergerfs v3.0 the path preserving behavior of rename and link will
likely be separated from the policy all together.
.SS Policy descriptions
.PP
A policy\[cq]s behavior differs, as mentioned above, based on the
@ -906,7 +952,6 @@ function it is used with.
Sometimes it really might not make sense to even offer certain policies
because they are literally the same as others but it makes things a bit
more uniform.
In mergerfs 3.0 this might change.
.PP
.TS
tab(@);
@ -1249,10 +1294,99 @@ For create functions \f[C]mkdir\f[R], \f[C]mknod\f[R], and
\f[C]symlink\f[R] which don\[cq]t return a file descriptor and therefore
can have \f[C]all\f[R] or \f[C]epall\f[R] policies it will return
success if any of the calls succeed and an error otherwise.
.SH BUILD / UPDATE
.SH INSTALL
.PP
https://github.com/trapexit/mergerfs/releases
.PP
If your distribution\[cq]s package manager includes mergerfs check if
the version is up to date.
If out of date it is recommended to use the latest release found on the
release page.
Details for common distros are below.
.SS Debian
.PP
Most Debian installs are of a stable branch and therefore do not have
the most up to date software.
While mergerfs is available via \f[C]apt\f[R] it is suggested that uses
install the most recent version available from the releases
page (https://github.com/trapexit/mergerfs/releases).
.SS prebuilt deb
.IP
.nf
\f[C]
wget https://github.com/trapexit/mergerfs/releases/download/<ver>/mergerfs_<ver>.debian-<rel>_<arch>.deb
dpkg -i mergerfs_<ver>.debian-<rel>_<arch>.deb
\f[R]
.fi
.SS apt
.IP
.nf
\f[C]
sudo apt install -y mergerfs
\f[R]
.fi
.SS Ubuntu
.PP
Most Ubuntu installs are of a stable branch and therefore do not have
the most up to date software.
While mergerfs is available via \f[C]apt\f[R] it is suggested that uses
install the most recent version available from the releases
page (https://github.com/trapexit/mergerfs/releases).
.SS prebuilt deb
.IP
.nf
\f[C]
wget https://github.com/trapexit/mergerfs/releases/download/<version>/mergerfs_<ver>.ubuntu-<rel>_<arch>.deb
dpkg -i mergerfs_<ver>.ubuntu-<rel>_<arch>.deb
\f[R]
.fi
.SS apt
.IP
.nf
\f[C]
sudo apt install -y mergerfs
\f[R]
.fi
.SS Raspberry Pi OS
.PP
Effectively the same as Debian or Ubuntu.
.SS Fedora
.IP
.nf
\f[C]
wget https://github.com/trapexit/mergerfs/releases/download/<ver>/mergerfs-<ver>.fc<rel>.<arch>.rpm
sudo rpm -i mergerfs-<ver>.fc<rel>.<arch>.rpm
\f[R]
.fi
.SS CentOS / Rocky
.IP
.nf
\f[C]
wget https://github.com/trapexit/mergerfs/releases/download/<ver>/mergerfs-<ver>.el<rel>.<arch>.rpm
sudo rpm -i mergerfs-<ver>.el<rel>.<arch>.rpm
\f[R]
.fi
.SS ArchLinux
.IP "1." 3
Setup AUR
.IP "2." 3
Install \f[C]mergerfs\f[R]
.SS Other
.PP
Static binaries are provided for situations where native packages are
unavailable.
.IP
.nf
\f[C]
wget https://github.com/trapexit/mergerfs/releases/download/<ver>/mergerfs-static-linux_<arch>.tar.gz
sudo tar xvf mergerfs-static-linux_<arch>.tar.gz -C /
\f[R]
.fi
.SH BUILD
.PP
\f[B]NOTE:\f[R] Prebuilt packages can be found at and recommended for
most users: https://github.com/trapexit/mergerfs/releases
.PP
\f[B]NOTE:\f[R] Only tagged releases are supported.
\f[C]master\f[R] and other branches should be considered works in
progress.
@ -1276,7 +1410,7 @@ $ make deb
$ sudo dpkg -i ../mergerfs_<version>_<arch>.deb
\f[R]
.fi
.SS RHEL / CentOS /Fedora
.SS RHEL / CentOS / Rocky / Fedora
.IP
.nf
\f[C]
@ -1287,7 +1421,7 @@ $ su -
# rpm -i rpmbuild/RPMS/<arch>/mergerfs-<version>.<arch>.rpm
\f[R]
.fi
.SS Generically
.SS Generic
.PP
Have git, g++, make, python installed.
.IP
@ -1339,6 +1473,8 @@ continue to run even if the software using it stop or are restarted.
To work around this you can use a \[lq]lazy umount\[rq].
Before mounting over top the mount point with the new instance of
mergerfs issue: \f[C]umount -l <mergerfs_mountpoint>\f[R].
Or you can let mergerfs do it by setting the option
\f[C]lazy-umount-mountpoint=true\f[R].
.SH RUNTIME CONFIG
.SS .mergerfs pseudo file
.IP
@ -1825,8 +1961,6 @@ enable (or disable) page caching (\f[C]cache.files\f[R])
.IP \[bu] 2
enable \f[C]cache.writeback\f[R]
.IP \[bu] 2
enable \f[C]cache.open\f[R]
.IP \[bu] 2
enable \f[C]cache.statfs\f[R]
.IP \[bu] 2
enable \f[C]cache.symlinks\f[R]
@ -1856,6 +1990,8 @@ increase readahead on all devices:
.PP
If you come across a setting that significantly impacts performance
please contact trapexit so he may investigate further.
Please test both against your normal setup, a singular branch, and with
\f[C]nullrw=true\f[R]
.SH BENCHMARKING
.PP
Filesystems are complicated.
@ -1959,19 +2095,16 @@ echo 3 | sudo tee /proc/sys/vm/drop_caches
.fi
.SH TIPS / NOTES
.IP \[bu] 2
This document is very literal and thorough.
Unless there is a bug things work as described.
This document is literal and thorough.
If a suspected feature isn\[cq]t mentioned it doesn\[cq]t exist.
If certain libfuse arguments aren\[cq]t listed they probably
shouldn\[cq]t be used.
.IP \[bu] 2
Ensure you\[cq]re using the latest version.
Few distros have the latest version.
.IP \[bu] 2
Run mergerfs as \f[C]root\f[R] unless you\[cq]re merging paths which are
owned exclusively and fully by the same user otherwise strange
permission issues may arise.
mergerfs is designed and intended to be run as \f[C]root\f[R].
Run mergerfs as \f[C]root\f[R].
mergerfs is designed and intended to be run as \f[C]root\f[R] and may
exibit incorrect behavior if run otherwise..
.IP \[bu] 2
If you don\[cq]t see some directories and files you expect, policies
seem to skip branches, you get strange permission errors, etc.
@ -2077,8 +2210,8 @@ noforget
inodecalc=path-hash
.SS rtorrent fails with ENODEV (No such device)
.PP
Be sure to set \f[C]cache.files=partial|full|auto-full\f[R] or turn off
\f[C]direct_io\f[R].
Be sure to set \f[C]cache.files=partial|full|auto-full|per-processe\f[R]
or turn off \f[C]direct_io\f[R].
rtorrent and some other applications use
mmap (http://linux.die.net/man/2/mmap) to read and write to files and
offer no fallback to traditional methods.
@ -2232,45 +2365,6 @@ There might be a hack to work around this (make mergerfs read the
would be limited to Linux and the /etc/group DB.
Preferably users would mount in the host group file into the containers
or use a standard shared user & groups technology like NIS or LDAP.
.SS mergerfs or libfuse crashing
.PP
First\&... always upgrade to the latest version unless told otherwise.
.PP
If using mergerfs below 2.22.0:
.PP
If suddenly the mergerfs mount point disappears and
\f[C]Transport endpoint is not connected\f[R] is returned when
attempting to perform actions within the mount directory \f[B]and\f[R]
the version of libfuse (use \f[C]mergerfs -v\f[R] to find the version)
is older than \f[C]2.9.4\f[R] its likely due to a bug in libfuse.
Affected versions of libfuse can be found in Debian Wheezy, Ubuntu
Precise and others.
.PP
In order to fix this please install newer versions of libfuse.
If using a Debian based distro (Debian,Ubuntu,Mint) you can likely just
install newer versions of
libfuse (https://packages.debian.org/unstable/libfuse2) and
fuse (https://packages.debian.org/unstable/fuse) from the repo of a
newer release.
.PP
If using mergerfs at or above 2.22.0:
.PP
First upgrade if possible, check the known bugs section, and contact
trapexit.
.SS mergerfs appears to be crashing or exiting
.PP
There seems to be an issue with Linux version \f[C]4.9.0\f[R] and above
in which an invalid message appears to be transmitted to libfuse (used
by mergerfs) causing it to exit.
No messages will be printed in any logs as it\[cq]s not a proper crash.
Debugging of the issue is still ongoing and can be followed via the
fuse-devel
thread (https://sourceforge.net/p/fuse/mailman/message/35662577).
.SS rm: fts_read failed: No such file or directory
.PP
Please update.
This is only happened to mergerfs versions at or below v2.25.x and will
not occur in more recent versions.
.SH FAQ
.SS How well does mergerfs scale? Is it \[lq]production ready?\[rq]
.PP
@ -2352,7 +2446,7 @@ the documentation will be improved.
.PP
That said, for the average person, the following should be fine:
.PP
\f[C]-o cache.files=off,dropcacheonclose=true,category.create=mfs\f[R]
\f[C]cache.files=off,dropcacheonclose=true,category.create=mfs\f[R]
.SS Why are all my files ending up on 1 drive?!
.PP
Did you start with empty drives?
@ -2470,7 +2564,7 @@ Some of these also affect the use of mergerfs from container platforms
such as Docker.
.SS Why use FUSE? Why not a kernel based solution?
.PP
As with any two solutions to a problem there are advantages and
As with any solutions to a problem there are advantages and
disadvantages to each one.
.PP
A FUSE based solution has all the downsides of FUSE:
@ -2497,8 +2591,6 @@ Allows more flexibility in design and features
.IP \[bu] 2
Overall easier to write, secure, and maintain
.IP \[bu] 2
Ability to run without root access or need to change the kernel
.IP \[bu] 2
Much lower barrier to entry (getting code into the kernel takes a lot of
time and effort initially)
.PP
@ -2517,33 +2609,6 @@ to using \f[C]fuse.mergerfs\f[R] as the type in \f[C]/etc/fstab\f[R].
If \f[C]mergerfs\f[R] doesn\[cq]t work as a type it could be due to how
the \f[C]mount.mergerfs\f[R] tool was installed.
Must be in \f[C]/sbin/\f[R] with proper permissions.
.SS Why was libfuse embedded into mergerfs?
.IP "1." 3
A significant number of users use mergerfs on distros with old versions
of libfuse which have serious bugs.
Requiring updated versions of libfuse on those distros isn\[cq]t
practical (no package offered, user inexperience, etc.).
The only practical way to provide a stable runtime on those systems was
to \[lq]vendor\[rq] / embed the library into the project.
.IP "2." 3
mergerfs was written to use the high level API.
There are a number of limitations in the HLAPI that make certain
features difficult or impossible to implement.
While some of these features could be patched into newer versions of
libfuse without breaking the public API some of them would require hacky
code to provide backwards compatibility.
While it may still be worth working with upstream to address these
issues in future versions, since the library needs to be vendored for
stability and compatibility reasons it is preferable / easier to modify
the API.
Longer term the plan is to rewrite mergerfs to use the low level API.
.SS Why did support for system libfuse get removed?
.PP
See above first.
.PP
If/when mergerfs is rewritten to use the low-level API then it\[cq]ll be
plausible to support system libfuse but till then it\[cq]s simply too
much work to manage the differences across the versions.
.SS Why was splice support removed?
.PP
After a lot of testing over the years splicing always appeared to be at
@ -2733,11 +2798,6 @@ Disable file caching.
If you aren\[cq]t using applications which use \f[C]mmap\f[R] it\[cq]s
probably simpler to just disable it all together.
The kernel won\[cq]t send the requests when caching is disabled.
.SS What are these .fuse_hidden files?
.PP
Please upgrade.
mergerfs >= 2.26.0 will not have these temporary files.
See the notes on \f[C]unlink\f[R].
.SS It\[cq]s mentioned that there are some security issues with mhddfs. What are they? How does mergerfs address them?
.PP
mhddfs (https://github.com/trapexit/mhddfs) manages running as
@ -2789,11 +2849,11 @@ previously encountered questions/issues.
\f[B]Please make sure you are using the latest
release (https://github.com/trapexit/mergerfs/releases) or have tried it
in comparison. Old versions, which are often included in distros like
Debian and Ubuntu, are not ever going to be updated and your bug may
have been addressed already.\f[R]
Debian and Ubuntu, are not ever going to be updated and the issue you
are encountering may have been addressed already.\f[R]
.PP
\f[B]For commercial support or feature requests please contact me
directly.\f[R]
directly. (mailto:support@spawn.link)\f[R]
.SS Information to include in bug reports
.IP \[bu] 2
Information about the broader problem along with any attempted
@ -2801,7 +2861,7 @@ solutions. (https://xyproblem.info)
.IP \[bu] 2
Solution already ruled out and why.
.IP \[bu] 2
Version of mergerfs: \f[C]mergerfs -V\f[R]
Version of mergerfs: \f[C]mergerfs --version\f[R]
.IP \[bu] 2
mergerfs settings / arguments: from fstab, systemd unit, command line,
OMV plugin, etc.
@ -2848,21 +2908,26 @@ etc.
.IP \[bu] 2
github.com: https://github.com/trapexit/mergerfs/issues
.IP \[bu] 2
email: trapexit\[at]spawn.link
.IP \[bu] 2
discord: https://discord.gg/MpAr69V
.IP \[bu] 2
twitter: https://twitter.com/_trapexit
.IP \[bu] 2
reddit: https://www.reddit.com/user/trapexit
.SS Support development
reddit: https://www.reddit.com/r/mergerfs
.SS Donations
.PP
This software is released under the very liberal ISC license and is
https://github.com/trapexit/support
.PP
Development and support of a project like mergerfs requires a
significant amount of time and effort.
The software is released under the very liberal ISC license and is
therefore free to use for personal or commercial uses.
That said if you like this software and have the means please consider
supporting its development.
.PP
https://github.com/trapexit/support
If you are a personal user and find mergerfs and its support valuable
and would like to support the project financially it would be very much
appreciated.
.PP
If you are using mergerfs commercially please consider sponsoring the
project to ensure it continues to be maintained and receive updates.
If custom features are needed feel free to contact me
directly (mailto:support@spawn.link).
.SH LINKS
.IP \[bu] 2
https://spawn.link
@ -2876,5 +2941,3 @@ https://github.com/trapexit/mergerfs-tools
https://github.com/trapexit/scorch
.IP \[bu] 2
https://github.com/trapexit/bbf
.SH AUTHORS
Antonio SJ Musumeci <trapexit@spawn.link>.
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