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227 lines
9.7 KiB
ReStructuredText
227 lines
9.7 KiB
ReStructuredText
.. _faq:
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.. include:: global.rst.inc
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Frequently asked questions
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==========================
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Can I backup VM disk images?
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----------------------------
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Yes, the `deduplication`_ technique used by
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|project_name| makes sure only the modified parts of the file are stored.
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Also, we have optional simple sparse file support for extract.
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Can I backup from multiple servers into a single repository?
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------------------------------------------------------------
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Yes, but in order for the deduplication used by |project_name| to work, it
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needs to keep a local cache containing checksums of all file
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chunks already stored in the repository. This cache is stored in
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``~/.cache/borg/``. If |project_name| detects that a repository has been
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modified since the local cache was updated it will need to rebuild
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the cache. This rebuild can be quite time consuming.
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So, yes it's possible. But it will be most efficient if a single
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repository is only modified from one place. Also keep in mind that
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|project_name| will keep an exclusive lock on the repository while creating
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or deleting archives, which may make *simultaneous* backups fail.
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Which file types, attributes, etc. are preserved?
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-------------------------------------------------
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* Directories
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* Regular files
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* Hardlinks (considering all files in the same archive)
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* Symlinks (stored as symlink, the symlink is not followed)
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* Character and block device files
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* FIFOs ("named pipes")
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* Name
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* Contents
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* Time of last modification (nanosecond precision with Python >= 3.3)
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* IDs of owning user and owning group
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* Names of owning user and owning group (if the IDs can be resolved)
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* Unix Mode/Permissions (u/g/o permissions, suid, sgid, sticky)
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* Extended Attributes (xattrs) on Linux, OS X and FreeBSD
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* Access Control Lists (ACL_) on Linux, OS X and FreeBSD
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* BSD flags on OS X and FreeBSD
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Which file types, attributes, etc. are *not* preserved?
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-------------------------------------------------------
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* UNIX domain sockets (because it does not make sense - they are
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meaningless without the running process that created them and the process
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needs to recreate them in any case). So, don't panic if your backup
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misses a UDS!
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* The precise on-disk representation of the holes in a sparse file.
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Archive creation has no special support for sparse files, holes are
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backed up as (deduplicated and compressed) runs of zero bytes.
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Archive extraction has optional support to extract all-zero chunks as
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holes in a sparse file.
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Why is my backup bigger than with attic? Why doesn't |project_name| do compression by default?
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----------------------------------------------------------------------------------------------
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Attic was rather unflexible when it comes to compression, it always
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compressed using zlib level 6 (no way to switch compression off or
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adjust the level or algorithm).
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|project_name| offers a lot of different compression algorithms and
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levels. Which of them is the best for you pretty much depends on your
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use case, your data, your hardware -- so you need to do an informed
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decision about whether you want to use compression, which algorithm
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and which level you want to use. This is why compression defaults to
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none.
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How can I specify the encryption passphrase programmatically?
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-------------------------------------------------------------
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The encryption passphrase can be specified programmatically using the
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`BORG_PASSPHRASE` environment variable. This is convenient when setting up
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automated encrypted backups. Another option is to use
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key file based encryption with a blank passphrase. See
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:ref:`encrypted_repos` for more details.
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.. _password_env:
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.. note:: Be careful how you set the environment; using the ``env``
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command, a ``system()`` call or using inline shell scripts
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might expose the credentials in the process list directly
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and they will be readable to all users on a system. Using
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``export`` in a shell script file should be safe, however, as
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the environment of a process is `accessible only to that
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user
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<https://security.stackexchange.com/questions/14000/environment-variable-accessibility-in-linux/14009#14009>`_.
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When backing up to remote encrypted repos, is encryption done locally?
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----------------------------------------------------------------------
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Yes, file and directory metadata and data is locally encrypted, before
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leaving the local machine. We do not mean the transport layer encryption
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by that, but the data/metadata itself. Transport layer encryption (e.g.
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when ssh is used as a transport) applies additionally.
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When backing up to remote servers, do I have to trust the remote server?
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------------------------------------------------------------------------
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Yes and No.
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No, as far as data confidentiality is concerned - if you use encryption,
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all your files/dirs data and metadata are stored in their encrypted form
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into the repository.
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Yes, as an attacker with access to the remote server could delete (or
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otherwise make unavailable) all your backups.
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If a backup stops mid-way, does the already-backed-up data stay there?
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----------------------------------------------------------------------
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Yes, |project_name| supports resuming backups.
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During a backup a special checkpoint archive named ``<archive-name>.checkpoint``
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is saved every checkpoint interval (the default value for this is 5
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minutes) containing all the data backed-up until that point. This means
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that at most <checkpoint interval> worth of data needs to be retransmitted
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if a backup needs to be restarted.
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Once your backup has finished successfully, you can delete all ``*.checkpoint``
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archives.
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If it crashes with a UnicodeError, what can I do?
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-------------------------------------------------
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Check if your encoding is set correctly. For most POSIX-like systems, try::
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export LANG=en_US.UTF-8 # or similar, important is correct charset
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I can't extract non-ascii filenames by giving them on the commandline!?
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-----------------------------------------------------------------------
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This might be due to different ways to represent some characters in unicode
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or due to other non-ascii encoding issues.
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If you run into that, try this:
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- avoid the non-ascii characters on the commandline by e.g. extracting
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the parent directory (or even everything)
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- mount the repo using FUSE and use some file manager
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Can |project_name| add redundancy to the backup data to deal with hardware malfunction?
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---------------------------------------------------------------------------------------
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No, it can't. While that at first sounds like a good idea to defend against
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some defect HDD sectors or SSD flash blocks, dealing with this in a
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reliable way needs a lot of low-level storage layout information and
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control which we do not have (and also can't get, even if we wanted).
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So, if you need that, consider RAID or a filesystem that offers redundant
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storage or just make backups to different locations / different hardware.
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See also `ticket 225 <https://github.com/borgbackup/borg/issues/225>`_.
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Can |project_name| verify data integrity of a backup archive?
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-------------------------------------------------------------
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Yes, if you want to detect accidental data damage (like bit rot), use the
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``check`` operation. It will notice corruption using CRCs and hashes.
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If you want to be able to detect malicious tampering also, use a encrypted
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repo. It will then be able to check using CRCs and HMACs.
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.. _a_status_oddity:
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I am seeing 'A' (added) status for a unchanged file!?
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-----------------------------------------------------
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The files cache is used to determine whether |project_name| already
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"knows" / has backed up a file and if so, to skip the file from
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chunking. It does intentionally *not* contain files that:
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- have >= 10 as "entry age" (|project_name| has not seen this file for a while)
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- have a modification time (mtime) same as the newest mtime in the created
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archive
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So, if you see an 'A' status for unchanged file(s), they are likely the files
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with the most recent mtime in that archive.
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This is expected: it is to avoid data loss with files that are backed up from
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a snapshot and that are immediately changed after the snapshot (but within
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mtime granularity time, so the mtime would not change). Without the code that
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removes these files from the files cache, the change that happened right after
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the snapshot would not be contained in the next backup as |project_name| would
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think the file is unchanged.
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This does not affect deduplication, the file will be chunked, but as the chunks
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will often be the same and already stored in the repo (except in the above
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mentioned rare condition), it will just re-use them as usual and not store new
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data chunks.
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Since only the files cache is used in the display of files status,
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those files are reported as being added when, really, chunks are
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already used.
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Why was Borg forked from Attic?
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-------------------------------
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Borg was created in May 2015 in response to the difficulty of getting new
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code or larger changes incorporated into Attic and establishing a bigger
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developer community / more open development.
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More details can be found in `ticket 217
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<https://github.com/jborg/attic/issues/217>`_ that led to the fork.
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Borg intends to be:
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* simple:
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* as simple as possible, but no simpler
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* do the right thing by default, but offer options
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* open:
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* welcome feature requests
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* accept pull requests of good quality and coding style
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* give feedback on PRs that can't be accepted "as is"
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* discuss openly, don't work in the dark
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* changing:
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* Borg is not compatible with Attic
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* do not break compatibility accidentally, without a good reason
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or without warning. allow compatibility breaking for other cases.
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* if major version number changes, it may have incompatible changes
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