1 bup: It backs things up
2 =======================
4 bup is a program that backs things up. It's short for "backup." Can you
5 believe that nobody else has named an open source program "bup" after all
8 Despite its unassuming name, bup is pretty cool. To give you an idea of
9 just how cool it is, I wrote you this poem:
12 What rhymes with awesome?
14 But that's irrelevant.
16 Hmm. Did that help? Maybe prose is more useful after all.
19 Reasons bup is awesome
20 ----------------------
22 bup has a few advantages over other backup software:
24 - It uses a rolling checksum algorithm (similar to rsync) to split large
25 files into chunks. The most useful result of this is you can backup huge
26 virtual machine (VM) disk images, databases, and XML files incrementally,
27 even though they're typically all in one huge file, and not use tons of
28 disk space for multiple versions.
30 - It uses the packfile format from git (the open source version control
31 system), so you can access the stored data even if you don't like bup's
34 - Unlike git, it writes packfiles *directly* (instead of having a separate
35 garbage collection / repacking stage) so it's fast even with gratuitously
36 huge amounts of data. bup's improved index formats also allow you to
37 track far more filenames than git (millions) and keep track of far more
38 objects (hundreds or thousands of gigabytes).
40 - Data is "automagically" shared between incremental backups without having
41 to know which backup is based on which other one - even if the backups
42 are made from two different computers that don't even know about each
43 other. You just tell bup to back stuff up, and it saves only the minimum
44 amount of data needed.
46 - You can back up directly to a remote bup server, without needing tons of
47 temporary disk space on the computer being backed up. And if your backup
48 is interrupted halfway through, the next run will pick up where you left
49 off. And it's easy to set up a bup server: just install bup on any
50 machine where you have ssh access.
52 - Bup can use "par2" redundancy to recover corrupted backups even if your
53 disk has undetected bad sectors.
55 - Even when a backup is incremental, you don't have to worry about
56 restoring the full backup, then each of the incrementals in turn; an
57 incremental backup *acts* as if it's a full backup, it just takes less
60 - You can mount your bup repository as a FUSE filesystem and access the
61 content that way, and even export it over Samba.
63 - It's written in python (with some C parts to make it faster) so it's easy
64 for you to extend and maintain.
67 Reasons you might want to avoid bup
68 -----------------------------------
70 - This is a very early version. Therefore it will most probably not work
71 for you, but we don't know why. It is also missing some
72 probably-critical features.
74 - It requires python >= 2.5, a C compiler, and an installed git version >=
77 - It currently only works on Linux, MacOS X >= 10.4,
78 NetBSD, Solaris, or Windows (with Cygwin). Patches to support
79 other platforms are welcome.
89 - Check out the bup source code using git:
91 git clone git://github.com/bup/bup
93 - Install the needed python libraries (including the development
96 On Debian/Ubuntu this is usually sufficient (run as root):
98 apt-get install python2.6-dev python-fuse
99 apt-get install python-pyxattr python-pylibacl
100 apt-get install linux-libc-dev
102 Substitute python2.5-dev if you have an older system. Alternately,
103 on newer Debian/Ubuntu versions, you can try this:
105 apt-get build-dep bup
107 On CentOS (for CentOS 6, at least), this should be sufficient (run
110 yum groupinstall "Development Tools"
111 yum install python python-devel
112 yum install fuse-python pyxattr pylibacl
113 yum install perl-Time-HiRes
115 In addition to the default CentOS repositories, you may need to add
116 RPMForge (for fuse-python) and EPEL (for pyxattr and pylibacl).
118 On Cygwin, install python, make, rsync, and gcc4.
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 - Initialize the default BUP_DIR:
162 - Try making a local backup as a tar file:
164 tar -cvf - /etc | bup split -n local-etc -vv
166 - Try restoring your backup tarball:
168 bup join local-etc | tar -tf -
170 - Look at how much disk space your backup took:
174 - Make another backup (which should be mostly identical to the last one;
175 notice that you don't have to *specify* that this backup is incremental,
176 it just saves space automatically):
178 tar -cvf - /etc | bup split -n local-etc -vv
180 - Look how little extra space your second backup used on top of the first:
184 - Restore your old backup again (the ~1 is git notation for "one older than
187 bup join local-etc~1 | tar -tf -
189 - Get a list of your previous backups:
191 GIT_DIR=~/.bup git log local-etc
193 - Make a backup on a remote server (which must already have the 'bup' command
194 somewhere in the server's PATH (see /etc/profile, etc/environment,
195 ~/.profile, or ~/.bashrc), and be accessible via ssh.
196 Make sure to replace SERVERNAME with the actual hostname of your server):
198 tar -cvf - /etc | bup split -r SERVERNAME: -n local-etc -vv
200 - Try restoring the remote backup tarball:
202 bup join -r SERVERNAME: local-etc | tar -tf -
204 - Try using the new (slightly experimental) 'bup index' and 'bup save'
205 style backups, which bypass 'tar' but have some missing features (see
206 "Things that are stupid" below):
209 bup save -n local-etc /etc
211 - Do it again and see how fast an incremental backup can be:
214 bup save -n local-etc /etc
216 (You can also use the "-r SERVERNAME:" option to 'bup save', just like
217 with 'bup split' and 'bup join'. The index itself is always local,
218 so you don't need -r there.)
220 That's all there is to it!
226 - FreeBSD's default 'make' command doesn't like bup's Makefile. In order to
227 compile the code, run tests and install bup, you need to install GNU Make
228 from the port named 'gmake' and use its executable instead in the commands
229 seen above. (i.e. 'gmake test' runs bup's test suite)
231 - Python's development headers are automatically installed with the 'python'
232 port so there's no need to install them separately.
234 - To use the 'bup fuse' command, you need to install the fuse kernel module
235 from the 'fusefs-kmod' port in the 'sysutils' section and the libraries from
236 the port named 'py-fusefs' in the 'devel' section.
238 - The 'par2' command can be found in the port named 'par2cmdline'.
240 - In order to compile the documentation, you need pandoc which can be found in
241 the port named 'hs-pandoc' in the 'textproc' section.
244 Notes on NetBSD/pkgsrc
245 ----------------------
247 - See pkgsrc/sysutils/bup, which should be the most recent stable
248 release and includes man pages. It also has a reasonable set of
249 dependencies (git, par2, py-fuse-bindings).
251 - The "fuse-python" package referred to is hard to locate, and is a
252 separate tarball for the python language binding distributed by the
253 fuse project on sourceforge. It is available as
254 pkgsrc/filesystems/py-fuse-bindings and on NetBSD 5, "bup fuse"
257 - "bup fuse" presents every directory/file as inode 0. The directory
258 traversal code ("fts") in NetBSD's libc will interpret this as a
259 cycle and error out, so "ls -R" and "find" will not work.
261 - There is no support for ACLs. If/when some entrprising person
262 fixes this, adjust t/compare-trees.
268 - There is no support for ACLs. If/when some entrprising person
269 fixes this, adjust t/compare-trees.
271 - In t/test.sh, two tests have been disabled. These tests check to
272 see that repeated saves produce identical trees and that an
273 intervening index doesn't change the SHA1. Apparently Cygwin has
274 some unusual behaviors with respect to access times (that probably
275 warrant further investigation). Possibly related:
276 http://cygwin.com/ml/cygwin/2007-06/msg00436.html
282 - There is no support for ACLs. If/when some entrprising person
283 fixes this, adjust t/compare-trees.
291 bup stores its data in a git-formatted repository. Unfortunately, git
292 itself doesn't actually behave very well for bup's use case (huge numbers of
293 files, files with huge sizes, retaining file permissions/ownership are
294 important), so we mostly don't use git's *code* except for a few helper
295 programs. For example, bup has its own git packfile writer written in
298 Basically, 'bup split' reads the data on stdin (or from files specified on
299 the command line), breaks it into chunks using a rolling checksum (similar to
300 rsync), and saves those chunks into a new git packfile. There is one git
303 When deciding whether to write a particular chunk into the new packfile, bup
304 first checks all the other packfiles that exist to see if they already have that
305 chunk. If they do, the chunk is skipped.
307 git packs come in two parts: the pack itself (*.pack) and the index (*.idx).
308 The index is pretty small, and contains a list of all the objects in the
309 pack. Thus, when generating a remote backup, we don't have to have a copy
310 of the packfiles from the remote server: the local end just downloads a copy
311 of the server's *index* files, and compares objects against those when
312 generating the new pack, which it sends directly to the server.
314 The "-n" option to 'bup split' and 'bup save' is the name of the backup you
315 want to create, but it's actually implemented as a git branch. So you can
316 do cute things like checkout a particular branch using git, and receive a
317 bunch of chunk files corresponding to the file you split.
319 If you use '-b' or '-t' or '-c' instead of '-n', bup split will output a
320 list of blobs, a tree containing that list of blobs, or a commit containing
321 that tree, respectively, to stdout. You can use this to construct your own
322 scripts that do something with those values.
326 'bup index' walks through your filesystem and updates a file (whose name is,
327 by default, ~/.bup/bupindex) to contain the name, attributes, and an
328 optional git SHA1 (blob id) of each file and directory.
330 'bup save' basically just runs the equivalent of 'bup split' a whole bunch
331 of times, once per file in the index, and assembles a git tree
332 that contains all the resulting objects. Among other things, that makes
333 'git diff' much more useful (compared to splitting a tarball, which is
334 essentially a big binary blob). However, since bup splits large files into
335 smaller chunks, the resulting tree structure doesn't *exactly* correspond to
336 what git itself would have stored. Also, the tree format used by 'bup save'
337 will probably change in the future to support storing file ownership, more
338 complex file permissions, and so on.
340 If a file has previously been written by 'bup save', then its git blob/tree
341 id is stored in the index. This lets 'bup save' avoid reading that file to
342 produce future incremental backups, which means it can go *very* fast unless
343 a lot of files have changed.
346 Things that are stupid for now but which we'll fix later
347 --------------------------------------------------------
349 Help with any of these problems, or others, is very welcome. Join the
350 mailing list (see below) if you'd like to help.
352 - 'bup save' and 'bup restore' have immature metadata support.
354 On the plus side, they actually do have support now, but it's new,
355 and not remotely as well tested as tar/rsync/whatever's. If you'd
356 like to help test, please do (see t/compare-trees for one
359 In addition, at the moment, if any strip or graft-style options
360 are specified to 'bup save', then no metadata will be written for
361 the root directory. That's obviously less than ideal.
363 - bup is overly optimistic about mmap. Right now bup just assumes
364 that it can mmap as large a block as it likes, and that mmap will
365 never fail. Yeah, right... If nothing else, this has failed on
366 32-bit architectures (and 31-bit is even worse -- looking at you,
369 To fix this, we might just implement a FakeMmap[1] class that uses
370 normal file IO and handles all of the mmap methods[2] that bup
371 actually calls. Then we'd swap in one of those whenever mmap
374 This would also require implementing some of the methods needed to
375 support "[]" array access, probably at a minimum __getitem__,
376 __setitem__, and __setslice__ [3].
378 [1] http://comments.gmane.org/gmane.comp.sysutils.backup.bup/613
379 [2] http://docs.python.org/2/library/mmap.html
380 [3] http://docs.python.org/2/reference/datamodel.html#emulating-container-types
382 - 'bup index' is slower than it should be.
384 It's still rather fast: it can iterate through all the filenames on my
385 600,000 file filesystem in a few seconds. But it still needs to rewrite
386 the entire index file just to add a single filename, which is pretty
387 nasty; it should just leave the new files in a second "extra index" file
390 - bup could use inotify for *really* efficient incremental backups.
392 You could even have your system doing "continuous" backups: whenever a
393 file changes, we immediately send an image of it to the server. We could
394 give the continuous-backup process a really low CPU and I/O priority so
395 you wouldn't even know it was running.
397 - bup currently has no features that prune away *old* backups.
399 Because of the way the packfile system works, backups become "entangled"
400 in weird ways and it's not actually possible to delete one pack
401 (corresponding approximately to one backup) without risking screwing up
404 git itself has lots of ways of optimizing this sort of thing, but its
405 methods aren't really applicable here; bup packfiles are just too huge.
406 We'll have to do it in a totally different way. There are lots of
407 options. For now: make sure you've got lots of disk space :)
409 - bup has never been tested on anything but Linux, MacOS, and Windows+Cygwin.
411 There's nothing that makes it *inherently* non-portable, though, so
412 that's mostly a matter of someone putting in some effort. (For a
413 "native" Windows port, the most annoying thing is the absence of ssh in
414 a default Windows installation.)
416 - bup needs better documentation.
418 According to a recent article about bup in Linux Weekly News
419 (https://lwn.net/Articles/380983/), "it's a bit short on examples and
420 a user guide would be nice." Documentation is the sort of thing that
421 will never be great unless someone from outside contributes it (since
422 the developers can never remember which parts are hard to understand).
424 - bup is "relatively speedy" and has "pretty good" compression.
426 ...according to the same LWN article. Clearly neither of those is good
427 enough. We should have awe-inspiring speed and crazy-good compression.
428 Must work on that. Writing more parts in C might help with the speed.
432 Actually, that's not stupid, but you might consider it a limitation.
433 There are a bunch of Linux GUI backup programs; someday I expect someone
434 will adapt one of them to use bup.
440 bup has an extensive set of man pages. Try using 'bup help' to get
441 started, or use 'bup help SUBCOMMAND' for any bup subcommand (like split,
442 join, index, save, etc.) to get details on that command.
444 For further technical details, please see ./DESIGN.
450 bup is a work in progress and there are many ways it can still be improved.
451 If you'd like to contribute patches, ideas, or bug reports, please join the
454 You can find the mailing list archives here:
456 http://groups.google.com/group/bup-list
458 and you can subscribe by sending a message to:
460 bup-list+subscribe@googlegroups.com
462 Please see <a href="HACKING">./HACKING</a> for
463 additional information, i.e. how to submit patches (hint - no pull
464 requests), how we handle branches, etc.