BTRam: BTRFS auto-mounter

What is it?

btram was developed as a companion tool to btrbk for those of us who:

georeplicate datasets on multiple computers;
want the datasets to be easily accessible, and up to date, on more than one of those servers.

What does it do?

btram mounts the latest snapshot of each nominated dataset into a given location via a BTRFS subvolume mount, and can automatically remount the latest snapshot each time it’s run. For example, if you use btrbk to incremental-send updated snapshots each night, invoking btram -r will remount the newest snapshot. Because it inspects BTRFS subvolumes and uses mount, it must be run as root.

Where can I use it?

Linux / NAS

It should work on any *NIX system that supports BTRFS. It has been tested on Ubuntu GNU/Linux™.

License

btram is released under a “GPL3 or later” licence and, despite my best efforts to make it obviously defect-free, comes with absolutely no warranty whatsoever, express or implied; use it at your own risk. If you find bugs, please either report them to me so I can fast-track a fix or submit a pull request with a fix of your own. Feel free to log issues for bug reports and suggestions, or e-mail me at btram@luxagen.com .

Installation

Install Perl.
Clone or download this repository.
Install the dependencies:

Ubuntu:

sudo apt install libipc-run-perl libgetopt-lucid-perl

CPAN:

cpan -I IPC::Run Getopt::Lucid

Add to PATH (optional)

To facilitate addition to your $PATH, a bin/ directory is provided with a convenience symlink.

Configuration

btram’s configuration file must exist at /etc/btram.conf in order to work. This file consists of one line per subvolume mount, with 4 tab-separated columns. Multiple consecutive tabs count as a single column separator. The four columns are:

<mountpoint> <btrfs-vol-root> <snapshot-dir> <snapshot-prefix>

<btrfs-vol-root> is the filesystem location where the root subvolume is mounted; btram requires the root subvolume to be mounted and snapshots to live somewhere in that root subvolume. <snapshot-dir> is the relative path from the root mountpoint to the directory containing the snapshots, and <snapshot-prefix> is the equivalent of btrbk’s snapshot_name directive, i.e. the portion of the filename preceding the .$datestamp suffix.

Example

/My Data /btr/a .btrbk/server2 my-data

How to use

btram -h

…will tell you how to use the tool. Note that it won’t actually do any [re]mounting unless you invoke it with the -r option. A --verbose option exists that will print more diagnostic information, including the commands that btram -r will run.