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=head1 NAME
squashfu - an incremental backup solution
=head1 SYNOPSIS
I<squashfu> <action> [options]
=head1 DESCRIPTION
I<squashfu> is a Bash based backup utility that uses the flexibility of rsync, squashfs,
and aufs to create incremental backups and offer limited compression.
=head1 ACTIONS
=over
=item B<-B>
Runs a regular backup, using the config file at F</etc/squashfu>.
=item B<-C>
Create a new squashed seed by merging old bins. This will leave you with a no more
than the number of bins specified by the I<MIN_BINS> setting in the config.
=item B<-D> I<BIN>
Delete the incremental backup with the number I<BIN>. This is done interactively and you
will have a chance to confirm before any files are deleted.
=item B<-G> I<path>
Directly restore a file or directory. This is an interactive operation and a list of
locations where the target is found will be presented.
=item B<-Q>
Displays usage statistics, including the size of the compressed seed and each incremental
backup with its creation date and bin number.
=item B<-R>
Cookies will be persistent and reused for logins. If you specify this option, you must
also provide a cookie file path with the B<-C> option or in the config file.
=item B<-U>
Unmount the squash and union. Although I<squashfu> will always check and unmount as
necessary before an operation, this is provided as a convenience.
=back
=head1 OPTIONS
=over
=item B<-c> F<PATH>
Specify an alternate config file as denoted by F<PATH>. The default config will still be
sourced, but options specified in this config will override the defaults. If your extra
config overrides the location of the backups, ensure that this config is always passed
for any operation.
=back
=head1 HOW IT WORKS
Goal: To create a backup solution which provides incremental backups and compression,
and which also provides an easy way to roll back.
Design:
A directory structure is created as follows (with some terminology included):
backup_root/
|- seed.sfs <-- squash, or seed
|- ro/ <-- squash mount point
|- rw/ <-- union mount point
|- .bins/ <-- incrementals
|-1/
| .....
| .....
| .....
| .....
| .....
|-n/
/var/
|- lib/
|- .squashfu.inv <-- bin inventory list (or binventory)
F<seed.sfs> is created from an initial backup and compressed using SquashFS, which is
simply a read only filesystem which focuses on compression. It's mounted, using a
loopback device, on ro/.
At the time of the backup, the next available bin is determined, created, and logged
to an inventory sheet with a timestamp. A union is created with all the available bins,
mounted in reverse chronological order on top of the seed (newest to oldest) on rw/.
At this point, the union represents the state of your files at the end of the last
backup. The newest branch is marked as read/write, and rsync is called. Because this
top branch is the only writable location in the union, the files rsync generates with
the -u (update) flag are placed into this branch. The backup finishes, and the union
and seed are unmounted.
At this point, Squashfu ensures compliance with the user's settings of MAX_BINS. If
the current number of used bins exceeds this value, a new seed is generated. The
number of old incrementals merged into the new seed is determined by the difference
between MAX_BINS and MIN_BINS in the config file. In this way, you always have
MIN_BINS available to roll back to, but you're not forced to recompress your seed
at every backup -- an operation that may take a long time depending on how big
your backup source is.
If and when you want to roll back, execute Squashfu with the -R action, and supply
the number of bins you want to roll back. The bins are ordered chronologically,
and the oldest "number_of_bins - bins_to_rollback" are mounted on the union mount
point.
B<WARNING:>
You should not, under any circumstances, add or remove files contained in the bins,
nor should you alter your binventory's time stamps. Doing so many result in your cat
being set on fire or your backups being destroyed.
=head1 INSTALLATION
~ On Arch Linux, build and install from the AUR.
~ On other distributions, use the included Makefile to run B<make install>, ensuring
that the I<DESTDIR> and I<MANPREFIX> are specified.
~ Read over each option in F</etc/squashfu.conf> and set it accordingly.
~ Create your first backup with I<squashfu> B<-B> and validate that the backup was
created successfully.
~ It may be a wise idea to make more changes, run a new backup and inspect the resulting
incremental.
=head1 FURTHER READING
L<http://en.wikipedia.org/wiki/Aufs>
L<http://en.wikipedia.org/wiki/UnionFS>
L<http://aufs.sourceforge.net/>
L<http://en.wikipedia.org/wiki/SquashFS>
L<http://en.wikipedia.org/wiki/Rsync>
=head1 SEE ALSO
B<aufs>(5), B<rsync>(1)
=head1 AUTHOR
Dave Reisner E<lt>d@falconindy.comE<gt>
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