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 Solaris, or Windows (with Cygwin). Patches to support
80 other platforms are welcome.
86 - Check out the bup source code using git:
88 git clone git://github.com/apenwarr/bup
90 - Install the needed python libraries (including the development
91 libraries). On Debian or Ubuntu, this is usually:
92 apt-get install python2.6-dev python-fuse
94 Substitute python2.5-dev or python2.4-dev if you have an older system.
96 Or on newer Debian/Ubuntu versions, you can try this:
100 - Build the python module and symlinks:
108 (The tests should pass. If they don't pass for you, stop here and send
111 - Try making a local backup as a tar file:
113 tar -cvf - /etc | bup split -n local-etc -vv
115 - Try restoring your backup tarball:
117 bup join local-etc | tar -tf -
119 - Look at how much disk space your backup took:
123 - Make another backup (which should be mostly identical to the last one;
124 notice that you don't have to *specify* that this backup is incremental,
125 it just saves space automatically):
127 tar -cvf - /etc | bup split -n local-etc -vv
129 - Look how little extra space your second backup used on top of the first:
133 - Restore your old backup again (the ~1 is git notation for "one older than
136 bup join local-etc~1 | tar -tf -
138 - Get a list of your previous backups:
140 GIT_DIR=~/.bup git log local-etc
142 - Make a backup on a remote server (which must already have the 'bup' command
143 somewhere in the server's PATH (see /etc/profile, etc/environment,
144 ~/.profile, or ~/.bashrc), and be accessible via ssh.
145 Make sure to replace SERVERNAME with the actual hostname of your server):
147 tar -cvf - /etc | bup split -r SERVERNAME: -n local-etc -vv
149 - Try restoring the remote backup tarball:
151 bup join -r SERVERNAME: local-etc | tar -tf -
153 - Try using the new (slightly experimental) 'bup index' and 'bup save'
154 style backups, which bypass 'tar' but have some missing features (see
155 "Things that are stupid" below):
158 bup save -n local-etc /etc
160 - Do it again and see how fast an incremental backup can be:
163 bup save -n local-etc /etc
165 (You can also use the "-r SERVERNAME:" option to 'bup save', just like
166 with 'bup split' and 'bup join'. The index itself is always local,
167 so you don't need -r there.)
169 That's all there is to it!
175 - FreeBSD's default 'make' command doesn't like bup's Makefile. In order to
176 compile the code, run tests and install bup, you need to install GNU Make
177 from the port named 'gmake' and use its executable instead in the commands
178 seen above. (i.e. 'gmake test' runs bup's test suite)
180 - Python's development headers are automatically installed with the 'python'
181 port so there's no need to install them separately.
183 - To use the 'bup fuse' command, you need to install the fuse kernel module
184 from the 'fusefs-kmod' port in the 'sysutils' section and the libraries from
185 the port named 'py-fusefs' in the 'devel' section.
187 - The 'par2' command can be found in the port named 'par2cmdline'.
189 - In order to compile the documentation, you need pandoc which can be found in
190 the port named 'hs-pandoc' in the 'textproc' section.
198 bup stores its data in a git-formatted repository. Unfortunately, git
199 itself doesn't actually behave very well for bup's use case (huge numbers of
200 files, files with huge sizes, retaining file permissions/ownership are
201 important), so we mostly don't use git's *code* except for a few helper
202 programs. For example, bup has its own git packfile writer written in
205 Basically, 'bup split' reads the data on stdin (or from files specified on
206 the command line), breaks it into chunks using a rolling checksum (similar to
207 rsync), and saves those chunks into a new git packfile. There is one git
210 When deciding whether to write a particular chunk into the new packfile, bup
211 first checks all the other packfiles that exist to see if they already have that
212 chunk. If they do, the chunk is skipped.
214 git packs come in two parts: the pack itself (*.pack) and the index (*.idx).
215 The index is pretty small, and contains a list of all the objects in the
216 pack. Thus, when generating a remote backup, we don't have to have a copy
217 of the packfiles from the remote server: the local end just downloads a copy
218 of the server's *index* files, and compares objects against those when
219 generating the new pack, which it sends directly to the server.
221 The "-n" option to 'bup split' and 'bup save' is the name of the backup you
222 want to create, but it's actually implemented as a git branch. So you can
223 do cute things like checkout a particular branch using git, and receive a
224 bunch of chunk files corresponding to the file you split.
226 If you use '-b' or '-t' or '-c' instead of '-n', bup split will output a
227 list of blobs, a tree containing that list of blobs, or a commit containing
228 that tree, respectively, to stdout. You can use this to construct your own
229 scripts that do something with those values.
233 'bup index' walks through your filesystem and updates a file (whose name is,
234 by default, ~/.bup/bupindex) to contain the name, attributes, and an
235 optional git SHA1 (blob id) of each file and directory.
237 'bup save' basically just runs the equivalent of 'bup split' a whole bunch
238 of times, once per file in the index, and assembles a git tree
239 that contains all the resulting objects. Among other things, that makes
240 'git diff' much more useful (compared to splitting a tarball, which is
241 essentially a big binary blob). However, since bup splits large files into
242 smaller chunks, the resulting tree structure doesn't *exactly* correspond to
243 what git itself would have stored. Also, the tree format used by 'bup save'
244 will probably change in the future to support storing file ownership, more
245 complex file permissions, and so on.
247 If a file has previously been written by 'bup save', then its git blob/tree
248 id is stored in the index. This lets 'bup save' avoid reading that file to
249 produce future incremental backups, which means it can go *very* fast unless
250 a lot of files have changed.
253 Things that are stupid for now but which we'll fix later
254 --------------------------------------------------------
256 Help with any of these problems, or others, is very welcome. Join the
257 mailing list (see below) if you'd like to help.
259 - 'bup save' and 'bup restore' don't know about file metadata.
261 That means we aren't saving file attributes, mtimes, ownership, hard
262 links, MacOS resource forks, etc. Clearly this needs to be improved.
264 - 'bup index' is slower than it should be.
266 It's still rather fast: it can iterate through all the filenames on my
267 600,000 file filesystem in a few seconds. But it still needs to rewrite
268 the entire index file just to add a single filename, which is pretty
269 nasty; it should just leave the new files in a second "extra index" file
272 - bup could use inotify for *really* efficient incremental backups.
274 You could even have your system doing "continuous" backups: whenever a
275 file changes, we immediately send an image of it to the server. We could
276 give the continuous-backup process a really low CPU and I/O priority so
277 you wouldn't even know it was running.
279 - bup currently has no features that prune away *old* backups.
281 Because of the way the packfile system works, backups become "entangled"
282 in weird ways and it's not actually possible to delete one pack
283 (corresponding approximately to one backup) without risking screwing up
286 git itself has lots of ways of optimizing this sort of thing, but its
287 methods aren't really applicable here; bup packfiles are just too huge.
288 We'll have to do it in a totally different way. There are lots of
289 options. For now: make sure you've got lots of disk space :)
291 - bup has never been tested on anything but Linux, MacOS, and Windows+Cygwin.
293 There's nothing that makes it *inherently* non-portable, though, so
294 that's mostly a matter of someone putting in some effort. (For a
295 "native" Windows port, the most annoying thing is the absence of ssh in
296 a default Windows installation.)
298 - bup needs better documentation.
300 According to a recent article about git in Linux Weekly News
301 (https://lwn.net/Articles/380983/), "it's a bit short on examples and
302 a user guide would be nice." Documentation is the sort of thing that
303 will never be great unless someone from outside contributes it (since
304 the developers can never remember which parts are hard to understand).
306 - bup is "relatively speedy" and has "pretty good" compression.
308 ...according to the same LWN article. Clearly neither of those is good
309 enough. We should have awe-inspiring speed and crazy-good compression.
310 Must work on that. Writing more parts in C might help with the speed.
314 Actually, that's not stupid, but you might consider it a limitation.
315 There are a bunch of Linux GUI backup programs; someday I expect someone
316 will adapt one of them to use bup.
322 bup has an extensive set of man pages. Try using 'bup help' to get
323 started, or use 'bup help SUBCOMMAND' for any bup subcommand (like split,
324 join, index, save, etc.) to get details on that command.
330 bup is a work in progress and there are many ways it can still be improved.
331 If you'd like to contribute patches, ideas, or bug reports, please join the
334 You can find the mailing list archives here:
336 http://groups.google.com/group/bup-list
338 and you can subscribe by sending a message to:
340 bup-list+subscribe@googlegroups.com