Enrico Zini: shops
Shops
Christmas songs should only ever be played on Christmas day.
In church.
At midnight.
Unless I happen to be there.
BackupPC is a pretty good backup system. Its configuration is rather
flexible, it has nice expiry policies, and it can store duplicated
file contents only once (for files that are shared across hosts or
don't change in time) within a compressed pool of data. However, it
doesn't do much to help pushing the data to off-site storage, or at
least not very efficiently. So if you have a BackupPC instance
running on a Raspberry Pi or a plug computer at home, it's a bit
tricky to protect your data against loss due to burglary or home fire.
The obvious solution would be to rsync the storage pool to a remote
site. However, the current pooling system relies heavily on
hardlinks, and rsync is notoriously inefficient with those. In the
home backup server scenario, this means that even if the computer is
more powerful than a Pi and can handle the memory requirements of
rsync, you'll often end up transferring way too much data.
So, since the obvious solution doesn't work straight away, what do we
do? Why, we fix it, of course. With a little look into the storage
pool, we notice that the bulk of the data is stored in files with an
abstract name (related to the contents) within a $prefix/pool
directory; the files with concrete names looking much like their
original are stored within $prefix/pc, and they're actually the same
files because they're hardlinks. Knowing this (that rsync doesn't),
we can make a smarter replication tool, by
- pushing only the pool with standard rsync;
- storing locally, and recreating remotely, the structure of hardlinks;
- pushing everything again with standard rsync.
rsync -aH; step 2 can be
implemented using the following two scripts. Run
store-hardlinks.pl locally, push the links file, then run
restore-hardlinks.pl on the remote server. This will ensure that
files already present in the pool are also hardlinked in their natural
location.
store-hardlinks.pl:
#! /usr/bin/perl -w use strict; use Storable qw(nstore); use File::Find; use vars qw/$prefix $poolpath $pcpath %i2cpool %todo $store/; $prefix = '/var/lib/backuppc'; $poolpath = '$prefix/cpool'; $pcpath = '$prefix/pc'; $store = '$prefix/links'; # for the convenience of &wanted calls, including -eval statements: use vars qw/*name *dir *prune/; *name = *File::Find::name; *dir = *File::Find::dir; *prune = *File::Find::prune; # Scan pool File::Find::find( wanted => \&wanted_pool , $poolpath); # Scan PC dirs File::Find::find( wanted => \&wanted_pc , $pcpath); nstore \%todo, $store; exit; sub wanted_pc my ($dev,$ino,$mode,$nlink,$uid,$gid); (($dev,$ino,$mode,$nlink,$uid,$gid) = lstat($_)) && -f _ && ($nlink > 1) && do $name =~ s,$pcpath/,,; if (defined $i2cpool $ino ) $todo $name = $i2cpool $ino ; sub wanted_pool my ($dev,$ino,$mode,$nlink,$uid,$gid); (($dev,$ino,$mode,$nlink,$uid,$gid) = lstat($_)) && -f _ && ($nlink > 1) && do $name =~ s,$poolpath/,,; $i2cpool $ino = $name;
restore-hardlinks.pl:
The initial transfer can still take forever if the pool is large (and if you're pushing it through the small end of an ADSL link ), but at least the files are only transferred once. Note: This is only useful for current versions of BackupPC. Apparently BackupPC 4 will have a different pooling system without hardlinks, and the following hack will no longer be required. For now, though, here it is.#! /usr/bin/perl -w use strict; use Storable; use File::Path qw/make_path/; use vars qw/$prefix $poolpath $pcpath %todo $store/; $prefix = '/srv/backuppc-mirror'; $poolpath = "$prefix/cpool"; $pcpath = "$prefix/pc"; $store = "$prefix/links"; %todo = % retrieve ($store) ; my ($dev,$ino,$mode,$nlink,$uid,$gid); foreach my $src (keys %todo) my $inode; my $dest = $todo $src ; my $dpath = "$poolpath/$dest"; my $spath = "$pcpath/$src"; my $sdir = $spath; $sdir =~ s,/[^/]*?$,,; make_path ($sdir); next unless -e $dpath; if (! -e $spath) link $dpath, $spath; next; (($dev,$ino,$mode,$nlink,$uid,$gid) = lstat($spath)); $inode = $ino; (($dev,$ino,$mode,$nlink,$uid,$gid) = lstat($dpath)); if ($ino != $inode) unlink $spath; link $dpath, $spath;
In early October, I had an opportunity to talk about
Replacing my phone
My first Android phone was
a 
This is my monthly summary of my free software related activities. If you re among the people who 
I recently bought a Cubieboard to replace my old Sheevaplug which has finally blown a power supply capacitor (this appears to be a common defect of Sheevaplugs), so I am publishing these instructions which show how to install Debian on 
Blogging from a phone... first time ever. I don't want to forget some specifics for this :)
I have just completed an exam to try to enter a postgraduate program (I'll talk more about it once it becomes real ). The exam is administered by CENEVAL, the same evaluation agency Where I presented my graduation equivalency exam some years ago - Only this exam is for all of the postgraduate studies on many national universities and is thus basically just a psychometric test.
The exam had 162 questions, all to be filled in a optical reader sheet, on five subjects: mathematical reasoning, Spanish grammar and comprehension, Project management, Computers and technology, And English reading and understanding.
It was all in all a fun exam to take, mostly due to the math reasoning part. But... on the Subject I Know I am an expert, I have to complain (and intend to find a easy to do so formally). First, I spotted two absolute mistakes (and answered based on What I knew others would, but knowing the answer is wrong technically). One was a subtlety, on how and why have hard drives should be defragmented (and part of my quip is that it's an obsolete habit, but besides, the answers were all erroneous), but a second one was... just wrong. It asked on what should not be part of an "Internet link" (can only guess they meant An URL). The 4 options were valid parts of a URL - including one very seldom used by most people, but very often by many of us: the @ sign.
Anyway, answered it, but my other main gripe is that most of the section was in specific use of Office software. Not only In Office-like, which would be bad enough to begin with, but on specific ways of using Mainly Excel And PowerPoint. Syntax issues, or the name of the menu under which to look for specific functions.
Backups are fun and exciting! Restores are exciting, in a terrifying
and stressful way. Fixing serious bugs is gratifying, in a depressing
way.
I am glad to announce two software releases: 
Following up on my 
Today was my last day working at 
Appointed to the Debian Tech Committee
I m pleased to announce that I ve been appointed to serve on the
Debain Technical Committee.
I d like to thank the other committee members and the Debian project
leader, Lucas Nussbaum, for giving me this opportunity to serve. I
look forward to working within the committee to further Debian s goals
as the universal operating system.
I'm running a local unbound instance on my laptop to get working
DNSSEC. It turns out that with the captive portal NSB (the Norwegian
national rail company), this doesn't work too well and you get into an
endless series of redirects. Changing 
probably just not as default.
I do agree 