1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
|
.. include:: global.rst.inc
.. highlight:: none
.. _faq:
Frequently asked questions
==========================
Usage & Limitations
###################
Can I backup from multiple servers into a single repository?
------------------------------------------------------------
Yes, but in order for the deduplication used by Borg to work, it
needs to keep a local cache containing checksums of all file
chunks already stored in the repository. This cache is stored in
``~/.cache/borg/``. If Borg detects that a repository has been
modified since the local cache was updated it will need to rebuild
the cache. This rebuild can be quite time consuming.
So, yes it's possible. But it will be most efficient if a single
repository is only modified from one place. Also keep in mind that
Borg will keep an exclusive lock on the repository while creating
or deleting archives, which may make *simultaneous* backups fail.
Can I copy or synchronize my repo to another location?
------------------------------------------------------
If you want to have redundant backup repositories (preferably at separate
locations), the recommended way to do that is like this:
- ``borg init repo1``
- ``borg init repo2``
- client machine ---borg create---> repo1
- client machine ---borg create---> repo2
This will create distinct repositories (separate repo ID, separate
keys) and nothing bad happening in repo1 will influence repo2.
Some people decide against above recommendation and create identical
copies of a repo (using some copy / sync / clone tool).
While this might be better than having no redundancy at all, you have
to be very careful about how you do that and what you may / must not
do with the result (if you decide against our recommendation).
What you would get with this is:
- client machine ---borg create---> repo
- repo ---copy/sync---> copy-of-repo
There is no special borg command to do the copying, you could just
use any reliable tool that creates an identical copy (cp, rsync, rclone
might be options).
But think about whether that is really what you want. If something goes
wrong in repo, you will have the same issue in copy-of-repo.
Make sure you do the copy/sync while no backup is running, see
:ref:`borg_with-lock` about how to do that.
Also, you must not run borg against multiple instances of the same repo
(like repo and copy-of-repo) as that would create severe issues:
- Data loss: they have the same repository ID, so the borg client will
think they are identical and e.g. use the same local cache for them
(which is an issue if they happen to be not the same).
See :issue:`4272` for an example.
- Encryption security issues if you would update repo and copy-of-repo
independently, due to AES counter reuse.
There is also a similar encryption security issue for the disaster case:
If you lose repo and the borg client-side config/cache and you restore
the repo from an older copy-of-repo, you also run into AES counter reuse.
Which file types, attributes, etc. are *not* preserved?
-------------------------------------------------------
* UNIX domain sockets (because it does not make sense - they are
meaningless without the running process that created them and the process
needs to recreate them in any case). So, don't panic if your backup
misses a UDS!
* The precise on-disk (or rather: not-on-disk) representation of the holes
in a sparse file.
Archive creation has no special support for sparse files, holes are
backed up as (deduplicated and compressed) runs of zero bytes.
Archive extraction has optional support to extract all-zero chunks as
holes in a sparse file.
* Some filesystem specific attributes, like btrfs NOCOW, see :ref:`platforms`.
* For hardlinked symlinks, the hardlinking can not be archived (and thus,
the hardlinking will not be done at extraction time). The symlinks will
be archived and extracted as non-hardlinked symlinks, see :issue:`2379`.
Are there other known limitations?
----------------------------------
- A single archive can only reference a limited volume of file/dir metadata,
usually corresponding to tens or hundreds of millions of files/dirs.
When trying to go beyond that limit, you will get a fatal IntegrityError
exception telling that the (archive) object is too big.
An easy workaround is to create multiple archives with fewer items each.
See also the :ref:`archive_limitation` and :issue:`1452`.
:ref:`borg_info` shows how large (relative to the maximum size) existing
archives are.
- borg extract only supports restoring into an empty destination. After that,
the destination will exactly have the contents of the extracted archive.
If you extract into a non-empty destination, borg will (for example) not
remove files which are in the destination, but not in the archive.
See :issue:`4598` for a workaround and more details.
.. _checkpoints_parts:
If a backup stops mid-way, does the already-backed-up data stay there?
----------------------------------------------------------------------
Yes, Borg supports resuming backups.
During a backup a special checkpoint archive named ``<archive-name>.checkpoint``
is saved every checkpoint interval (the default value for this is 30
minutes) containing all the data backed-up until that point.
This checkpoint archive is a valid archive,
but it is only a partial backup (not all files that you wanted to backup are
contained in it). Having it in the repo until a successful, full backup is
completed is useful because it references all the transmitted chunks up
to the checkpoint. This means that in case of an interruption, you only need to
retransfer the data since the last checkpoint.
If a backup was interrupted, you normally do not need to do anything special,
just invoke ``borg create`` as you always do. If the repository is still locked,
you may need to run ``borg break-lock`` before the next backup. You may use the
same archive name as in previous attempt or a different one (e.g. if you always
include the current datetime), it does not matter.
Borg always does full single-pass backups, so it will start again
from the beginning - but it will be much faster, because some of the data was
already stored into the repo (and is still referenced by the checkpoint
archive), so it does not need to get transmitted and stored again.
Once your backup has finished successfully, you can delete all
``<archive-name>.checkpoint`` archives. If you run ``borg prune``, it will
also care for deleting unneeded checkpoints.
Note: the checkpointing mechanism creates hidden, partial files in an archive,
so that checkpoints even work while a big file is being processed.
They are named ``<filename>.borg_part_<N>`` and all operations usually ignore
these files, but you can make them considered by giving the option
``--consider-part-files``. You usually only need that option if you are
really desperate (e.g. if you have no completed backup of that file and you'ld
rather get a partial file extracted than nothing). You do **not** want to give
that option under any normal circumstances.
Note that checkpoints inside files are created only since version 1.1,
make sure you have an up-to-date version of borgbackup if you want to continue instead of retransferring a huge file.
In some cases, there is only an outdated version shipped with your distribution (e.g. Debian). See :ref:`installation`.
How can I backup huge file(s) over a unstable connection?
---------------------------------------------------------
This is not a problem anymore.
For more details, see :ref:`checkpoints_parts`.
How can I restore huge file(s) over an unstable connection?
-----------------------------------------------------------
If you cannot manage to extract the whole big file in one go, you can extract
all the part files and manually concatenate them together.
For more details, see :ref:`checkpoints_parts`.
Can Borg add redundancy to the backup data to deal with hardware malfunction?
-----------------------------------------------------------------------------
No, it can't. While that at first sounds like a good idea to defend against
some defect HDD sectors or SSD flash blocks, dealing with this in a
reliable way needs a lot of low-level storage layout information and
control which we do not have (and also can't get, even if we wanted).
So, if you need that, consider RAID or a filesystem that offers redundant
storage or just make backups to different locations / different hardware.
See also :issue:`225`.
Can Borg verify data integrity of a backup archive?
---------------------------------------------------
Yes, if you want to detect accidental data damage (like bit rot), use the
``check`` operation. It will notice corruption using CRCs and hashes.
If you want to be able to detect malicious tampering also, use an encrypted
repo. It will then be able to check using CRCs and HMACs.
Can I use Borg on SMR hard drives?
----------------------------------
SMR (shingled magnetic recording) hard drives are very different from
regular hard drives. Applications have to behave in certain ways or
performance will be heavily degraded.
Borg 1.1 ships with default settings suitable for SMR drives,
and has been successfully tested on *Seagate Archive v2* drives
using the ext4 file system.
Some Linux kernel versions between 3.19 and 4.5 had various bugs
handling device-managed SMR drives, leading to IO errors, unresponsive
drives and unreliable operation in general.
For more details, refer to :issue:`2252`.
.. _faq-integrityerror:
I get an IntegrityError or similar - what now?
----------------------------------------------
A single error does not necessarily indicate bad hardware or a Borg
bug. All hardware exhibits a bit error rate (BER). Hard drives are typically
specified as exhibiting fewer than one error every 12 to 120 TB
(one bit error in 10e14 to 10e15 bits). The specification is often called
*unrecoverable read error rate* (URE rate).
Apart from these very rare errors there are two main causes of errors:
(i) Defective hardware: described below.
(ii) Bugs in software (Borg, operating system, libraries):
Ensure software is up to date.
Check whether the issue is caused by any fixed bugs described in :ref:`important_notes`.
.. rubric:: Finding defective hardware
.. note::
Hardware diagnostics are operating system dependent and do not
apply universally. The commands shown apply for popular Unix-like
systems. Refer to your operating system's manual.
Checking hard drives
Find the drive containing the repository and use *findmnt*, *mount* or *lsblk*
to learn the device path (typically */dev/...*) of the drive.
Then, smartmontools can retrieve self-diagnostics of the drive in question::
# smartctl -a /dev/sdSomething
The *Offline_Uncorrectable*, *Current_Pending_Sector* and *Reported_Uncorrect*
attributes indicate data corruption. A high *UDMA_CRC_Error_Count* usually
indicates a bad cable.
I/O errors logged by the system (refer to the system journal or
dmesg) can point to issues as well. I/O errors only affecting the
file system easily go unnoticed, since they are not reported to
applications (e.g. Borg), while these errors can still corrupt data.
Drives can corrupt some sectors in one event, while remaining
reliable otherwise. Conversely, drives can fail completely with no
advance warning. If in doubt, copy all data from the drive in
question to another drive -- just in case it fails completely.
If any of these are suspicious, a self-test is recommended::
# smartctl -t long /dev/sdSomething
Running ``fsck`` if not done already might yield further insights.
Checking memory
Intermittent issues, such as ``borg check`` finding errors
inconsistently between runs, are frequently caused by bad memory.
Run memtest86+ (or an equivalent memory tester) to verify that
the memory subsystem is operating correctly.
Checking processors
Processors rarely cause errors. If they do, they are usually overclocked
or otherwise operated outside their specifications. We do not recommend to
operate hardware outside its specifications for productive use.
Tools to verify correct processor operation include Prime95 (mprime), linpack,
and the `Intel Processor Diagnostic Tool
<https://downloadcenter.intel.com/download/19792/Intel-Processor-Diagnostic-Tool>`_
(applies only to Intel processors).
.. rubric:: Repairing a damaged repository
With any defective hardware found and replaced, the damage done to the repository
needs to be ascertained and fixed.
:ref:`borg_check` provides diagnostics and ``--repair`` options for repositories with
issues. We recommend to first run without ``--repair`` to assess the situation.
If the found issues and proposed repairs seem right, re-run "check" with ``--repair`` enabled.
Why is the time elapsed in the archive stats different from wall clock time?
----------------------------------------------------------------------------
Borg needs to write the time elapsed into the archive metadata before finalizing
the archive, compacting the segments, and committing the repo & cache. This means
when Borg is run with e.g. the ``time`` command, the duration shown in the archive
stats may be shorter than the full time the command runs for.
How do I configure different prune policies for different directories?
----------------------------------------------------------------------
Say you want to prune ``/var/log`` faster than the rest of
``/``. How do we implement that? The answer is to backup to different
archive *names* and then implement different prune policies for
different prefixes. For example, you could have a script that does::
borg create --exclude /var/log $REPOSITORY:main-$(date +%Y-%m-%d) /
borg create $REPOSITORY:logs-$(date +%Y-%m-%d) /var/log
Then you would have two different prune calls with different policies::
borg prune --verbose --list -d 30 --prefix main- "$REPOSITORY"
borg prune --verbose --list -d 7 --prefix logs- "$REPOSITORY"
This will keep 7 days of logs and 30 days of everything else. Borg 1.1
also supports the ``--glob-archives`` parameter.
How do I remove files from an existing backup?
----------------------------------------------
Say you now want to remove old logfiles because you changed your
backup policy as described above. The only way to do this is to use
the :ref:`borg_recreate` command to rewrite all archives with a
different ``--exclude`` pattern. See the examples in the
:ref:`borg_recreate` manpage for more information.
Can I safely change the compression level or algorithm?
--------------------------------------------------------
The compression level and algorithm don't affect deduplication. Chunk ID hashes
are calculated *before* compression. New compression settings
will only be applied to new chunks, not existing chunks. So it's safe
to change them.
Security
########
How can I specify the encryption passphrase programmatically?
-------------------------------------------------------------
There are several ways to specify a passphrase without human intervention:
Setting ``BORG_PASSPHRASE``
The passphrase can be specified using the ``BORG_PASSPHRASE`` enviroment variable.
This is often the simplest option, but can be insecure if the script that sets it
is world-readable.
.. _password_env:
.. note:: Be careful how you set the environment; using the ``env``
command, a ``system()`` call or using inline shell scripts
(e.g. ``BORG_PASSPHRASE=hunter2 borg ...``)
might expose the credentials in the process list directly
and they will be readable to all users on a system. Using
``export`` in a shell script file should be safe, however, as
the environment of a process is `accessible only to that
user
<https://security.stackexchange.com/questions/14000/environment-variable-accessibility-in-linux/14009#14009>`_.
Using ``BORG_PASSCOMMAND`` with a properly permissioned file
Another option is to create a file with a password in it in your home
directory and use permissions to keep anyone else from reading it. For
example, first create a key::
head -c 1024 /dev/urandom | base64 > ~/.borg-passphrase
chmod 400 ~/.borg-passphrase
Then in an automated script one can put::
export BORG_PASSCOMMAND="cat $HOME/.borg-passphrase"
and Borg will automatically use that passphrase.
Using keyfile-based encryption with a blank passphrase
It is possible to encrypt your repository in ``keyfile`` mode instead of the default
``repokey`` mode and use a blank passphrase for the key file (simply press Enter twice
when ``borg init`` asks for the password). See :ref:`encrypted_repos`
for more details.
Using ``BORG_PASSCOMMAND`` with macOS Keychain
macOS has a native manager for secrets (such as passphrases) which is safer
than just using a file as it is encrypted at rest and unlocked manually
(fortunately, the login keyring automatically unlocks when you login). With
the built-in ``security`` command, you can access it from the command line,
making it useful for ``BORG_PASSCOMMAND``.
First generate a passphrase and use ``security`` to save it to your login
(default) keychain::
security add-generic-password -D secret -U -a $USER -s borg-passphrase -w $(head -c 1024 /dev/urandom | base64)
In your backup script retrieve it in the ``BORG_PASSCOMMAND``::
export BORG_PASSCOMMAND="security find-generic-password -a $USER -s borg-passphrase -w"
Using ``BORG_PASSCOMMAND`` with GNOME Keyring
GNOME also has a keyring daemon that can be used to store a Borg passphrase.
First ensure ``libsecret-tools``, ``gnome-keyring`` and ``libpam-gnome-keyring``
are installed. If ``libpam-gnome-keyring`` wasn't already installed, ensure it
runs on login::
sudo sh -c "echo session optional pam_gnome_keyring.so auto_start >> /etc/pam.d/login"
sudo sh -c "echo password optional pam_gnome_keyring.so >> /etc/pam.d/passwd"
# you may need to relogin afterwards to activate the login keyring
Then add a secret to the login keyring::
head -c 1024 /dev/urandom | base64 | secret-tool store borg-repository repo-name --label="Borg Passphrase"
If a dialog box pops up prompting you to pick a password for a new keychain, use your
login password. If there is a checkbox for automatically unlocking on login, check it
to allow backups without any user intervention whatsoever.
Once the secret is saved, retrieve it in a backup script using ``BORG_PASSCOMMAND``::
export BORG_PASSCOMMAND="secret-tool lookup borg-repository repo-name"
.. note:: For this to automatically unlock the keychain it must be run
in the ``dbus`` session of an unlocked terminal; for example, running a backup
script as a ``cron`` job might not work unless you also ``export DISPLAY=:0``
so ``secret-tool`` can pick up your open session. `It gets even more complicated`__
when you are running the tool as a different user (e.g. running a backup as root
with the password stored in the user keyring).
__ https://github.com/borgbackup/borg/pull/2837#discussion_r127641330
Using ``BORG_PASSCOMMAND`` with KWallet
KDE also has a keychain feature in the form of KWallet. The command-line tool
``kwalletcli`` can be used to store and retrieve secrets. Ensure ``kwalletcli``
is installed, generate a passphrase, and store it in your "wallet"::
head -c 1024 /dev/urandom | base64 | kwalletcli -Pe borg-passphrase -f Passwords
Once the secret is saved, retrieve it in a backup script using ``BORG_PASSCOMMAND``::
export BORG_PASSCOMMAND="kwalletcli -e borg-passphrase -f Passwords"
When backing up to remote encrypted repos, is encryption done locally?
----------------------------------------------------------------------
Yes, file and directory metadata and data is locally encrypted, before
leaving the local machine. We do not mean the transport layer encryption
by that, but the data/metadata itself. Transport layer encryption (e.g.
when ssh is used as a transport) applies additionally.
When backing up to remote servers, do I have to trust the remote server?
------------------------------------------------------------------------
Yes and No.
No, as far as data confidentiality is c
|