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
75 version >= 1.5.3.1. It also requires par2 if you want fsck to be
76 able to generate the information needed to recover from some types
79 - It currently only works on Linux, MacOS X >= 10.4,
80 NetBSD, Solaris, or Windows (with Cygwin). Patches to support
81 other platforms are welcome.
83 - Any items in "Things that are stupid" below.
93 - Check out the bup source code using git:
95 git clone git://github.com/bup/bup
97 - Install the required python libraries (including the development
100 On very recent Debian/Ubuntu versions, this may be sufficient (run
103 apt-get build-dep bup
105 Otherwise try this (substitute python2.5-dev or python2.6-dev if
106 you have an older system):
108 apt-get install python2.7-dev python-fuse
109 apt-get install python-pyxattr python-pylibacl
110 apt-get install linux-libc-dev
111 apt-get install acl attr
112 apt-get install python-tornado # optional
114 On CentOS (for CentOS 6, at least), this should be sufficient (run
117 yum groupinstall "Development Tools"
118 yum install python python-devel
119 yum install fuse-python pyxattr pylibacl
120 yum install perl-Time-HiRes
122 In addition to the default CentOS repositories, you may need to add
123 RPMForge (for fuse-python) and EPEL (for pyxattr and pylibacl).
125 On Cygwin, install python, make, rsync, and gcc4.
127 If you would like to use the optional bup web server on systems
128 without a tornado package, you may want to try this:
132 - Build the python module and symlinks:
140 The tests should pass. If they don't pass for you, stop here and
141 send an email to bup-list@googlegroups.com. Though if there are
142 symbolic links along the current working directory path, the tests
143 may fail. Running something like this before "make test" should
144 sidestep the problem:
148 - You can install bup via "make install", and override the default
149 destination with DESTDIR and PREFIX.
151 Files are normally installed to "$DESTDIR/$PREFIX" where DESTDIR is
152 empty by default, and PREFIX is set to /usr. So if you wanted to
153 install bup to /opt/bup, you might do something like this:
155 make install DESTDIR=/opt/bup PREFIX=''
157 - The Python executable that bup will use is chosen by ./configure,
158 which will search for a reasonable version unless PYTHON is set in
159 the environment, in which case, bup will use that path. You can
160 see which Python executable was chosen by looking at the
161 configure output, or examining cmd/python-cmd.sh, and you can
162 change the selection by re-running ./configure.
167 Binary packages of bup are known to be built for the following OSes:
170 http://packages.debian.org/search?searchon=names&keywords=bup
172 http://packages.ubuntu.com/search?searchon=names&keywords=bup
173 - pkgsrc (NetBSD, Dragonfly, and others)
174 http://pkgsrc.se/sysutils/bup
175 http://cvsweb.netbsd.org/bsdweb.cgi/pkgsrc/sysutils/bup/
177 https://www.archlinux.org/packages/?sort=&q=bup
183 - Get help for any bup command:
192 - Initialize the default BUP_DIR (~/.bup):
196 - Make a local backup (-v or -vv will increase the verbosity):
199 bup save -n local-etc /etc
201 - Restore a local backup to ./dest:
203 bup restore -C ./dest local-etc/latest/etc
206 - Look at how much disk space your backup took:
210 - Make another backup (which should be mostly identical to the last one;
211 notice that you don't have to *specify* that this backup is incremental,
212 it just saves space automatically):
215 bup save -n local-etc /etc
217 - Look how little extra space your second backup used (on top of the first):
221 - Get a list of your previous backups:
225 - Restore your first backup again:
227 bup restore -C ./dest-2 local-etc/2013-11-23-11195/etc
229 - Make a backup to a remote server which must already have the 'bup' command
230 somewhere in its PATH (see /etc/profile, etc/environment, ~/.profile, or
231 ~/.bashrc), and be accessible via ssh.
232 Make sure to replace SERVERNAME with the actual hostname of your server:
234 bup init -r SERVERNAME:path/to/remote-bup-dir
236 bup save -r SERVERNAME:path/to/remote-bup-dir -n local-etc /etc
238 - Restore a backup from a remote server. (FAIL: unfortunately,
239 unlike "bup join", "bup restore" does not yet support remote
240 restores. See both "bup join" and "Things that are stupid" below.)
242 - Defend your backups from death rays (OK fine, more likely from the
243 occasional bad disk block). This writes parity information
244 (currently via par2) for all of the existing data so that bup may
245 be able to recover from some amount of repository corruption:
249 - Use split/join instead of index/save/restore. Try making a local
252 tar -cvf - /etc | bup split -n local-etc -vv
254 - Try restoring the tarball:
256 bup join local-etc | tar -tf -
258 - Look at how much disk space your backup took:
262 - Make another tar backup:
264 tar -cvf - /etc | bup split -n local-etc -vv
266 - Look at how little extra space your second backup used on top of
271 - Restore the first tar backup again (the ~1 is git notation for "one
272 older than the most recent"):
274 bup join local-etc~1 | tar -tf -
276 - Get a list of your previous split-based backups:
278 GIT_DIR=~/.bup git log local-etc
280 - Make a backup on a remote server:
282 tar -cvf - /etc | bup split -r SERVERNAME: -n local-etc -vv
284 - Try restoring the remote backup tarball:
286 bup join -r SERVERNAME: local-etc | tar -tf -
288 That's all there is to it!
294 - FreeBSD's default 'make' command doesn't like bup's Makefile. In order to
295 compile the code, run tests and install bup, you need to install GNU Make
296 from the port named 'gmake' and use its executable instead in the commands
297 seen above. (i.e. 'gmake test' runs bup's test suite)
299 - Python's development headers are automatically installed with the 'python'
300 port so there's no need to install them separately.
302 - To use the 'bup fuse' command, you need to install the fuse kernel module
303 from the 'fusefs-kmod' port in the 'sysutils' section and the libraries from
304 the port named 'py-fusefs' in the 'devel' section.
306 - The 'par2' command can be found in the port named 'par2cmdline'.
308 - In order to compile the documentation, you need pandoc which can be found in
309 the port named 'hs-pandoc' in the 'textproc' section.
312 Notes on NetBSD/pkgsrc
313 ----------------------
315 - See pkgsrc/sysutils/bup, which should be the most recent stable
316 release and includes man pages. It also has a reasonable set of
317 dependencies (git, par2, py-fuse-bindings).
319 - The "fuse-python" package referred to is hard to locate, and is a
320 separate tarball for the python language binding distributed by the
321 fuse project on sourceforge. It is available as
322 pkgsrc/filesystems/py-fuse-bindings and on NetBSD 5, "bup fuse"
325 - "bup fuse" presents every directory/file as inode 0. The directory
326 traversal code ("fts") in NetBSD's libc will interpret this as a
327 cycle and error out, so "ls -R" and "find" will not work.
329 - There is no support for ACLs. If/when some entrprising person
330 fixes this, adjust t/compare-trees.
336 - There is no support for ACLs. If/when some enterprising person
337 fixes this, adjust t/compare-trees.
339 - In t/test.sh, two tests have been disabled. These tests check to
340 see that repeated saves produce identical trees and that an
341 intervening index doesn't change the SHA1. Apparently Cygwin has
342 some unusual behaviors with respect to access times (that probably
343 warrant further investigation). Possibly related:
344 http://cygwin.com/ml/cygwin/2007-06/msg00436.html
350 - There is no support for ACLs. If/when some enterprising person
351 fixes this, adjust t/compare-trees.
360 bup stores its data in a git-formatted repository. Unfortunately, git
361 itself doesn't actually behave very well for bup's use case (huge numbers of
362 files, files with huge sizes, retaining file permissions/ownership are
363 important), so we mostly don't use git's *code* except for a few helper
364 programs. For example, bup has its own git packfile writer written in
367 Basically, 'bup split' reads the data on stdin (or from files specified on
368 the command line), breaks it into chunks using a rolling checksum (similar to
369 rsync), and saves those chunks into a new git packfile. There is at least one
370 git packfile per backup.
372 When deciding whether to write a particular chunk into the new packfile, bup
373 first checks all the other packfiles that exist to see if they already have that
374 chunk. If they do, the chunk is skipped.
376 git packs come in two parts: the pack itself (*.pack) and the index (*.idx).
377 The index is pretty small, and contains a list of all the objects in the
378 pack. Thus, when generating a remote backup, we don't have to have a copy
379 of the packfiles from the remote server: the local end just downloads a copy
380 of the server's *index* files, and compares objects against those when
381 generating the new pack, which it sends directly to the server.
383 The "-n" option to 'bup split' and 'bup save' is the name of the backup you
384 want to create, but it's actually implemented as a git branch. So you can
385 do cute things like checkout a particular branch using git, and receive a
386 bunch of chunk files corresponding to the file you split.
388 If you use '-b' or '-t' or '-c' instead of '-n', bup split will output a
389 list of blobs, a tree containing that list of blobs, or a commit containing
390 that tree, respectively, to stdout. You can use this to construct your own
391 scripts that do something with those values.
396 'bup index' walks through your filesystem and updates a file (whose name is,
397 by default, ~/.bup/bupindex) to contain the name, attributes, and an
398 optional git SHA1 (blob id) of each file and directory.
400 'bup save' basically just runs the equivalent of 'bup split' a whole bunch
401 of times, once per file in the index, and assembles a git tree
402 that contains all the resulting objects. Among other things, that makes
403 'git diff' much more useful (compared to splitting a tarball, which is
404 essentially a big binary blob). However, since bup splits large files into
405 smaller chunks, the resulting tree structure doesn't *exactly* correspond to
406 what git itself would have stored. Also, the tree format used by 'bup save'
407 will probably change in the future to support storing file ownership, more
408 complex file permissions, and so on.
410 If a file has previously been written by 'bup save', then its git blob/tree
411 id is stored in the index. This lets 'bup save' avoid reading that file to
412 produce future incremental backups, which means it can go *very* fast unless
413 a lot of files have changed.
416 Things that are stupid for now but which we'll fix later
417 ========================================================
419 Help with any of these problems, or others, is very welcome. Join the
420 mailing list (see below) if you'd like to help.
422 - 'bup restore' can't pull directly from a remote server.
424 So in one sense "save -r" is a dead-end right now. Obviously you
425 can use "ssh SERVER bup restore -C ./dest..." to create a tree you
426 can transfer elsewhere via rsync/tar/whatever, but that's *lame*.
428 Until we fix it, you may be able to mount the remote BUP_DIR via
429 sshfs and then restore "normally", though that hasn't been
432 - 'bup save' and 'bup restore' have immature metadata support.
434 On the plus side, they actually do have support now, but it's new,
435 and not remotely as well tested as tar/rsync/whatever's. However,
436 you have to start somewhere, and as of 0.25, we think it's ready
437 for more general use. Please let us know if you have any trouble.
439 Also, if any strip or graft-style options are specified to 'bup
440 save', then no metadata will be written for the root directory.
441 That's obviously less than ideal.
443 - bup is overly optimistic about mmap. Right now bup just assumes
444 that it can mmap as large a block as it likes, and that mmap will
445 never fail. Yeah, right... If nothing else, this has failed on
446 32-bit architectures (and 31-bit is even worse -- looking at you,
449 To fix this, we might just implement a FakeMmap[1] class that uses
450 normal file IO and handles all of the mmap methods[2] that bup
451 actually calls. Then we'd swap in one of those whenever mmap
454 This would also require implementing some of the methods needed to
455 support "[]" array access, probably at a minimum __getitem__,
456 __setitem__, and __setslice__ [3].
458 [1] http://comments.gmane.org/gmane.comp.sysutils.backup.bup/613
459 [2] http://docs.python.org/2/library/mmap.html
460 [3] http://docs.python.org/2/reference/datamodel.html#emulating-container-types
462 - 'bup index' is slower than it should be.
464 It's still rather fast: it can iterate through all the filenames on my
465 600,000 file filesystem in a few seconds. But it still needs to rewrite
466 the entire index file just to add a single filename, which is pretty
467 nasty; it should just leave the new files in a second "extra index" file
470 - bup could use inotify for *really* efficient incremental backups.
472 You could even have your system doing "continuous" backups: whenever a
473 file changes, we immediately send an image of it to the server. We could
474 give the continuous-backup process a really low CPU and I/O priority so
475 you wouldn't even know it was running.
477 - bup currently has no way to prune *old* backups.
479 Because of the way the packfile system works, backups become "entangled"
480 in weird ways and it's not actually possible to delete one pack
481 (corresponding approximately to one backup) without risking screwing up
484 git itself has lots of ways of optimizing this sort of thing, but its
485 methods aren't really applicable here; bup packfiles are just too huge.
486 We'll have to do it in a totally different way. There are lots of
487 options. For now: make sure you've got lots of disk space :)
489 Until we fix this, one possible workaround is to just start a new
490 BUP_DIR occasionally, i.e. bup-2013-10, bup-2013-11...
492 - bup has never been tested on anything but Linux, MacOS, and Windows+Cygwin.
494 There's nothing that makes it *inherently* non-portable, though, so
495 that's mostly a matter of someone putting in some effort. (For a
496 "native" Windows port, the most annoying thing is the absence of ssh in
497 a default Windows installation.)
499 - bup needs better documentation.
501 According to a recent article about bup in Linux Weekly News
502 (https://lwn.net/Articles/380983/), "it's a bit short on examples and
503 a user guide would be nice." Documentation is the sort of thing that
504 will never be great unless someone from outside contributes it (since
505 the developers can never remember which parts are hard to understand).
507 - bup is "relatively speedy" and has "pretty good" compression.
509 ...according to the same LWN article. Clearly neither of those is good
510 enough. We should have awe-inspiring speed and crazy-good compression.
511 Must work on that. Writing more parts in C might help with the speed.
515 Actually, that's not stupid, but you might consider it a limitation.
516 There are a bunch of Linux GUI backup programs; someday I expect someone
517 will adapt one of them to use bup.
523 bup has an extensive set of man pages. Try using 'bup help' to get
524 started, or use 'bup help SUBCOMMAND' for any bup subcommand (like split,
525 join, index, save, etc.) to get details on that command.
527 For further technical details, please see ./DESIGN.
533 bup is a work in progress and there are many ways it can still be improved.
534 If you'd like to contribute patches, ideas, or bug reports, please join the
537 You can find the mailing list archives here:
539 http://groups.google.com/group/bup-list
541 and you can subscribe by sending a message to:
543 bup-list+subscribe@googlegroups.com
545 Please see <a href="HACKING">./HACKING</a> for
546 additional information, i.e. how to submit patches (hint - no pull
547 requests), how we handle branches, etc.