2 bup: It backs things up
3 =======================
5 bup is a program that backs things up. It's short for "backup." Can you
6 believe that nobody else has named an open source program "bup" after all
9 Despite its unassuming name, bup is pretty cool. To give you an idea of
10 just how cool it is, I wrote you this poem:
13 What rhymes with awesome?
15 But that's irrelevant.
17 Hmm. Did that help? Maybe prose is more useful after all.
20 Reasons bup is awesome
21 ----------------------
23 bup has a few advantages over other backup software:
25 - It uses a rolling checksum algorithm (similar to rsync) to split large
26 files into chunks. The most useful result of this is you can backup huge
27 virtual machine (VM) disk images, databases, and XML files incrementally,
28 even though they're typically all in one huge file, and not use tons of
29 disk space for multiple versions.
31 - It uses the packfile format from git (the open source version control
32 system), so you can access the stored data even if you don't like bup's
35 - Unlike git, it writes packfiles *directly* (instead of having a separate
36 garbage collection / repacking stage) so it's fast even with gratuitously
37 huge amounts of data. bup's improved index formats also allow you to
38 track far more filenames than git (millions) and keep track of far more
39 objects (hundreds or thousands of gigabytes).
41 - Data is "automagically" shared between incremental backups without having
42 to know which backup is based on which other one - even if the backups
43 are made from two different computers that don't even know about each
44 other. You just tell bup to back stuff up, and it saves only the minimum
45 amount of data needed.
47 - You can back up directly to a remote bup server, without needing tons of
48 temporary disk space on the computer being backed up. And if your backup
49 is interrupted halfway through, the next run will pick up where you left
50 off. And it's easy to set up a bup server: just install bup on any
51 machine where you have ssh access.
53 - Bup can use "par2" redundancy to recover corrupted backups even if your
54 disk has undetected bad sectors.
56 - Even when a backup is incremental, you don't have to worry about
57 restoring the full backup, then each of the incrementals in turn; an
58 incremental backup *acts* as if it's a full backup, it just takes less
61 - You can mount your bup repository as a FUSE filesystem and access the
62 content that way, and even export it over Samba.
64 - It's written in python (with some C parts to make it faster) so it's easy
65 for you to extend and maintain.
68 Reasons you might want to avoid bup
69 -----------------------------------
71 - This is a very early version. Therefore it will most probably not work
72 for you, but we don't know why. It is also missing some
73 probably-critical features.
75 - It requires python >= 2.4, a C compiler, and an installed git version >=
78 - It currently only works on Linux, MacOS X >= 10.4,
79 NetBSD, Solaris, or Windows (with Cygwin). Patches to support
80 other platforms are welcome.
90 - Check out the bup source code using git:
92 git clone git://github.com/apenwarr/bup
94 - Install the needed python libraries (including the development
97 On Debian/Ubuntu this is usually sufficient (run as root):
99 apt-get install python2.6-dev python-fuse
100 apt-get install python-pyxattr python-pylibacl
101 apt-get install linux-libc-dev
103 Substitute python2.5-dev or python2.4-dev if you have an older
104 system. Alternately, on newer Debian/Ubuntu versions, you can try
107 apt-get build-dep bup
109 On CentOS (for CentOS 6, at least), this should be sufficient (run
112 yum groupinstall "Development Tools"
113 yum install python python-dev
114 yum install fuse-python pyxattr pylibacl
115 yum install perl-Time-HiRes
117 In addition to the default CentOS repositories, you may need to add
118 RPMForge (for fuse-python) and EPEL (for pyxattr and pylibacl).
120 - Build the python module and symlinks:
128 (The tests should pass. If they don't pass for you, stop here and send
131 - You can install bup via "make install", and override the default
132 destination with DESTDIR and PREFIX.
134 Files are normally installed to "$DESTDIR/$PREFIX" where DESTDIR is
135 empty by default, and PREFIX is set to /usr. So if you wanted to
136 install bup to /opt/bup, you might do something like this:
138 make install DESTDIR=/opt/bup PREFIX=''
144 Binary packages of bup are known to be built for the following OSes:
147 http://packages.debian.org/search?searchon=names&keywords=bup
149 http://packages.ubuntu.com/search?searchon=names&keywords=bup
150 - pkgsrc (NetBSD, Dragonfly, and others)
151 http://pkgsrc.se/sysutils/bup
152 http://cvsweb.netbsd.org/bsdweb.cgi/pkgsrc/sysutils/bup/
158 - Try making a local backup as a tar file:
160 tar -cvf - /etc | bup split -n local-etc -vv
162 - Try restoring your backup tarball:
164 bup join local-etc | tar -tf -
166 - Look at how much disk space your backup took:
170 - Make another backup (which should be mostly identical to the last one;
171 notice that you don't have to *specify* that this backup is incremental,
172 it just saves space automatically):
174 tar -cvf - /etc | bup split -n local-etc -vv
176 - Look how little extra space your second backup used on top of the first:
180 - Restore your old backup again (the ~1 is git notation for "one older than
183 bup join local-etc~1 | tar -tf -
185 - Get a list of your previous backups:
187 GIT_DIR=~/.bup git log local-etc
189 - Make a backup on a remote server (which must already have the 'bup' command
190 somewhere in the server's PATH (see /etc/profile, etc/environment,
191 ~/.profile, or ~/.bashrc), and be accessible via ssh.
192 Make sure to replace SERVERNAME with the actual hostname of your server):
194 tar -cvf - /etc | bup split -r SERVERNAME: -n local-etc -vv
196 - Try restoring the remote backup tarball:
198 bup join -r SERVERNAME: local-etc | tar -tf -
200 - Try using the new (slightly experimental) 'bup index' and 'bup save'
201 style backups, which bypass 'tar' but have some missing features (see
202 "Things that are stupid" below):
205 bup save -n local-etc /etc
207 - Do it again and see how fast an incremental backup can be:
210 bup save -n local-etc /etc
212 (You can also use the "-r SERVERNAME:" option to 'bup save', just like
213 with 'bup split' and 'bup join'. The index itself is always local,
214 so you don't need -r there.)
216 That's all there is to it!
222 - FreeBSD's default 'make' command doesn't like bup's Makefile. In order to
223 compile the code, run tests and install bup, you need to install GNU Make
224 from the port named 'gmake' and use its executable instead in the commands
225 seen above. (i.e. 'gmake test' runs bup's test suite)
227 - Python's development headers are automatically installed with the 'python'
228 port so there's no need to install them separately.
230 - To use the 'bup fuse' command, you need to install the fuse kernel module
231 from the 'fusefs-kmod' port in the 'sysutils' section and the libraries from
232 the port named 'py-fusefs' in the 'devel' section.
234 - The 'par2' command can be found in the port named 'par2cmdline'.
236 - In order to compile the documentation, you need pandoc which can be found in
237 the port named 'hs-pandoc' in the 'textproc' section.
240 Notes on NetBSD/pkgsrc
241 ----------------------
243 - See pkgsrc/sysutils/bup, which should be the most recent stable
244 release and includes man pages. It also has a reasonable set of
245 dependencies (git, par2, py-fuse-bindings).
247 - The "fuse-python" package referred to is hard to locate, and is a
248 separate tarball for the python language binding distributed by the
249 fuse project on sourceforge. It is available as
250 pkgsrc/filesystems/py-fuse-bindings and on NetBSD 5, "bup fuse"
253 - "bup fuse" presents every directory/file as inode 0. The directory
254 traversal code ("fts") in NetBSD's libc will interpret this as a
255 cycle and error out, so "ls -R" and "find" will not work.
257 - It is not clear if extended attribute and POSIX acl support does
266 bup stores its data in a git-formatted repository. Unfortunately, git
267 itself doesn't actually behave very well for bup's use case (huge numbers of
268 files, files with huge sizes, retaining file permissions/ownership are
269 important), so we mostly don't use git's *code* except for a few helper
270 programs. For example, bup has its own git packfile writer written in
273 Basically, 'bup split' reads the data on stdin (or from files specified on
274 the command line), breaks it into chunks using a rolling checksum (similar to
275 rsync), and saves those chunks into a new git packfile. There is one git
278 When deciding whether to write a particular chunk into the new packfile, bup
279 first checks all the other packfiles that exist to see if they already have that
280 chunk. If they do, the chunk is skipped.
282 git packs come in two parts: the pack itself (*.pack) and the index (*.idx).
283 The index is pretty small, and contains a list of all the objects in the
284 pack. Thus, when generating a remote backup, we don't have to have a copy
285 of the packfiles from the remote server: the local end just downloads a copy
286 of the server's *index* files, and compares objects against those when
287 generating the new pack, which it sends directly to the server.
289 The "-n" option to 'bup split' and 'bup save' is the name of the backup you
290 want to create, but it's actually implemented as a git branch. So you can
291 do cute things like checkout a particular branch using git, and receive a
292 bunch of chunk files corresponding to the file you split.
294 If you use '-b' or '-t' or '-c' instead of '-n', bup split will output a
295 list of blobs, a tree containing that list of blobs, or a commit containing
296 that tree, respectively, to stdout. You can use this to construct your own
297 scripts that do something with those values.
301 'bup index' walks through your filesystem and updates a file (whose name is,
302 by default, ~/.bup/bupindex) to contain the name, attributes, and an
303 optional git SHA1 (blob id) of each file and directory.
305 'bup save' basically just runs the equivalent of 'bup split' a whole bunch
306 of times, once per file in the index, and assembles a git tree
307 that contains all the resulting objects. Among other things, that makes
308 'git diff' much more useful (compared to splitting a tarball, which is
309 essentially a big binary blob). However, since bup splits large files into
310 smaller chunks, the resulting tree structure doesn't *exactly* correspond to
311 what git itself would have stored. Also, the tree format used by 'bup save'
312 will probably change in the future to support storing file ownership, more
313 complex file permissions, and so on.
315 If a file has previously been written by 'bup save', then its git blob/tree
316 id is stored in the index. This lets 'bup save' avoid reading that file to
317 produce future incremental backups, which means it can go *very* fast unless
318 a lot of files have changed.
321 Things that are stupid for now but which we'll fix later
322 --------------------------------------------------------
324 Help with any of these problems, or others, is very welcome. Join the
325 mailing list (see below) if you'd like to help.
327 - 'bup save' and 'bup restore' have immature metadata support.
329 On the plus side, they actually do have support now, but it's new,
330 and not remotely as well tested as tar/rsync/whatever's. If you'd
331 like to help test, please do; something like 'rsync -niaHAX src/
332 restore/' may be useful on that front.
334 In addition, at the moment, if any strip or graft-style options
335 are specified to 'bup save', then no metadata will be written for
336 the root directory. That's obviously less than ideal.
338 - 'bup index' is slower than it should be.
340 It's still rather fast: it can iterate through all the filenames on my
341 600,000 file filesystem in a few seconds. But it still needs to rewrite
342 the entire index file just to add a single filename, which is pretty
343 nasty; it should just leave the new files in a second "extra index" file
346 - bup could use inotify for *really* efficient incremental backups.
348 You could even have your system doing "continuous" backups: whenever a
349 file changes, we immediately send an image of it to the server. We could
350 give the continuous-backup process a really low CPU and I/O priority so
351 you wouldn't even know it was running.
353 - bup currently has no features that prune away *old* backups.
355 Because of the way the packfile system works, backups become "entangled"
356 in weird ways and it's not actually possible to delete one pack
357 (corresponding approximately to one backup) without risking screwing up
360 git itself has lots of ways of optimizing this sort of thing, but its
361 methods aren't really applicable here; bup packfiles are just too huge.
362 We'll have to do it in a totally different way. There are lots of
363 options. For now: make sure you've got lots of disk space :)
365 - bup has never been tested on anything but Linux, MacOS, and Windows+Cygwin.
367 There's nothing that makes it *inherently* non-portable, though, so
368 that's mostly a matter of someone putting in some effort. (For a
369 "native" Windows port, the most annoying thing is the absence of ssh in
370 a default Windows installation.)
372 - bup needs better documentation.
374 According to a recent article about git in Linux Weekly News
375 (https://lwn.net/Articles/380983/), "it's a bit short on examples and
376 a user guide would be nice." Documentation is the sort of thing that
377 will never be great unless someone from outside contributes it (since
378 the developers can never remember which parts are hard to understand).
380 - bup is "relatively speedy" and has "pretty good" compression.
382 ...according to the same LWN article. Clearly neither of those is good
383 enough. We should have awe-inspiring speed and crazy-good compression.
384 Must work on that. Writing more parts in C might help with the speed.
388 Actually, that's not stupid, but you might consider it a limitation.
389 There are a bunch of Linux GUI backup programs; someday I expect someone
390 will adapt one of them to use bup.
396 bup has an extensive set of man pages. Try using 'bup help' to get
397 started, or use 'bup help SUBCOMMAND' for any bup subcommand (like split,
398 join, index, save, etc.) to get details on that command.
400 For further technical details, please see ./DESIGN.
406 bup is a work in progress and there are many ways it can still be improved.
407 If you'd like to contribute patches, ideas, or bug reports, please join the
410 You can find the mailing list archives here:
412 http://groups.google.com/group/bup-list
414 and you can subscribe by sending a message to:
416 bup-list+subscribe@googlegroups.com