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?

Yes, you could just copy all the files. Make sure you do that while no backup is running (use borg with-lock ...). So what you get here is this:

  • client machine —borg create—> repo1
  • repo1 —copy—> repo2

There is no special borg command to do the copying, just use cp or rsync if you want to do that.

But think about whether that is really what you want. If something goes wrong in repo1, you will have the same issue in repo2 after the copy.

If you want to have 2 independent backups, it is better to do it like this:

  • client machine —borg create—> repo1
  • client machine —borg create—> repo2

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 Support for file metadata.
  • 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 #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 Note about archive limitations and #1452.

    borg info shows how large (relative to the maximum size) existing archives are.

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.

How can I backup huge file(s) over a unstable connection?

This is not a problem anymore.

For more details, see If a backup stops mid-way, does the already-backed-up data stay there?.

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 If a backup stops mid-way, does the already-backed-up data stay there?.

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 #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 #2252.

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:

  1. Defective hardware: described below.
  2. 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 Important notes.

Finding defective hardware


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 (applies only to Intel processors).

Repairing a damaged repository

With any defective hardware found and replaced, the damage done to the repository needs to be ascertained and fixed.

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 $REPOSITORY:main-$(date +%Y-%m-%d) --exclude /var/log /
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 borg recreate command to rewrite all archives with a different --exclude pattern. See the examples in the borg recreate manpage for more information.


How can I specify the encryption passphrase programmatically?

There are several ways to specify a passphrase without human intervention:


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.


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.

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 ~/.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 Repository encryption 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"

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 auto_start >> /etc/pam.d/login"
sudo sh -c "echo password optional >> /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"


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).


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 concerned - if you use encryption, all your files/dirs data and metadata are stored in their encrypted form into the repository.

Yes, as an attacker with access to the remote server could delete (or otherwise make unavailable) all your backups.

How can I protect against a hacked backup client?

Assume you backup your backup client machine C to the backup server S and C gets hacked. In a simple push setup, the attacker could then use borg on C to delete all backups residing on S.

These are your options to protect against that:

  • Do not allow to permanently delete data from the repo, see Append-only mode.
  • Use a pull-mode setup using ssh -R, see #900.
  • Mount C’s filesystem on another machine and then create a backup of it.
  • Do not give C filesystem-level access to S.

How can I protect against a hacked backup server?

Just in case you got the impression that pull-mode backups are way more safe than push-mode, you also need to consider the case that your backup server S gets hacked. In case S has access to a lot of clients C, that might bring you into even bigger trouble than a hacked backup client in the previous FAQ entry.

These are your options to protect against that:

  • Use the standard push-mode setup (see also previous FAQ entry).
  • Mount (the repo part of) S’s filesystem on C.
  • Do not give S file-system level access to C.
  • Have your backup server at a well protected place (maybe not reachable from the internet), configure it safely, apply security updates, monitor it, ...

How can I protect against theft, sabotage, lightning, fire, ...?

In general: if your only backup medium is nearby the backupped machine and always connected, you can easily get into trouble: they likely share the same fate if something goes really wrong.


  • have multiple backup media
  • have media disconnected from network, power, computer
  • have media at another place
  • have a relatively recent backup on your media

How do I report a security issue with Borg?

Send a private email to the security contact if you think you have discovered a security issue. Please disclose security issues responsibly.

Common issues

Why do I get “connection closed by remote” after a while?

When doing a backup to a remote server (using a ssh: repo URL), it sometimes stops after a while (some minutes, hours, ... - not immediately) with “connection closed by remote” error message. Why?

That’s a good question and we are trying to find a good answer in #636.

Why am I seeing idle borg serve processes on the repo server?

Maybe the ssh connection between client and server broke down and that was not yet noticed on the server. Try these settings:

# /etc/ssh/sshd_config on borg repo server - kill connection to client
# after ClientAliveCountMax * ClientAliveInterval seconds with no response
ClientAliveInterval 20
ClientAliveCountMax 3

If you have multiple borg create ... ; borg create ... commands in a already serialized way in a single script, you need to give them --lock-wait N (with N being a bit more than the time the server needs to terminate broken down connections and release the lock).

The borg cache eats way too much disk space, what can I do?

There is a temporary (but maybe long lived) hack to avoid using lots of disk space for chunks.archive.d (see #235 for details):

# this assumes you are working with the same user as the backup.
cd ~/.cache/borg/$(borg config /path/to/repo id)
rm -rf chunks.archive.d ; touch chunks.archive.d

This deletes all the cached archive chunk indexes and replaces the directory that kept them with a file, so borg won’t be able to store anything “in” there in future.

This has some pros and cons, though:

  • much less disk space needs for ~/.cache/borg.
  • chunk cache resyncs will be slower as it will have to transfer chunk usage metadata for all archives from the repository (which might be slow if your repo connection is slow) and it will also have to build the hashtables from that data. chunk cache resyncs happen e.g. if your repo was written to by another machine (if you share same backup repo between multiple machines) or if your local chunks cache was lost somehow.

The long term plan to improve this is called “borgception”, see #474.

Can I backup my root partition (/) with Borg?

Backing up your entire root partition works just fine, but remember to exclude directories that make no sense to backup, such as /dev, /proc, /sys, /tmp and /run, and to use --one-file-system if you only want to backup the root partition (and not any mounted devices e.g.).

If it crashes with a UnicodeError, what can I do?

Check if your encoding is set correctly. For most POSIX-like systems, try:

export LANG=en_US.UTF-8  # or similar, important is correct charset

I can’t extract non-ascii filenames by giving them on the commandline!?

This might be due to different ways to represent some characters in unicode or due to other non-ascii encoding issues.

If you run into that, try this:

  • avoid the non-ascii characters on the commandline by e.g. extracting the parent directory (or even everything)
  • mount the repo using FUSE and use some file manager

I am seeing ‘A’ (added) status for an unchanged file!?

The files cache is used to determine whether Borg already “knows” / has backed up a file and if so, to skip the file from chunking. It does intentionally not contain files that have a modification time (mtime) same as the newest mtime in the created archive.

So, if you see an ‘A’ status for unchanged file(s), they are likely the files with the most recent mtime in that archive.

This is expected: it is to avoid data loss with files that are backed up from a snapshot and that are immediately changed after the snapshot (but within mtime granularity time, so the mtime would not change). Without the code that removes these files from the files cache, the change that happened right after the snapshot would not be contained in the next backup as Borg would think the file is unchanged.

This does not affect deduplication, the file will be chunked, but as the chunks will often be the same and already stored in the repo (except in the above mentioned rare condition), it will just re-use them as usual and not store new data chunks.

If you want to avoid unnecessary chunking, just create or touch a small or empty file in your backup source file set (so that one has the latest mtime, not your 50GB VM disk image) and, if you do snapshots, do the snapshot after that.

Since only the files cache is used in the display of files status, those files are reported as being added when, really, chunks are already used.

It always chunks all my files, even unchanged ones!

Borg maintains a files cache where it remembers the mtime, size and inode of files. When Borg does a new backup and starts processing a file, it first looks whether the file has changed (compared to the values stored in the files cache). If the values are the same, the file is assumed unchanged and thus its contents won’t get chunked (again).

Borg can’t keep an infinite history of files of course, thus entries in the files cache have a “maximum time to live” which is set via the environment variable BORG_FILES_CACHE_TTL (and defaults to 20). Every time you do a backup (on the same machine, using the same user), the cache entries’ ttl values of files that were not “seen” are incremented by 1 and if they reach BORG_FILES_CACHE_TTL, the entry is removed from the cache.

So, for example, if you do daily backups of 26 different data sets A, B, C, ..., Z on one machine (using the default TTL), the files from A will be already forgotten when you repeat the same backups on the next day and it will be slow because it would chunk all the files each time. If you set BORG_FILES_CACHE_TTL to at least 26 (or maybe even a small multiple of that), it would be much faster.

Another possible reason is that files don’t always have the same path, for example if you mount a filesystem without stable mount points for each backup or if you are running the backup from a filesystem snapshot whose name is not stable. If the directory where you mount a filesystem is different every time, Borg assume they are different files.

Is there a way to limit bandwidth with Borg?

To limit upload (i.e. borg create) bandwidth, use the --remote-ratelimit option.

There is no built-in way to limit download (i.e. borg extract) bandwidth, but limiting download bandwidth can be accomplished with pipeviewer:

Create a wrapper script: /usr/local/bin/pv-wrapper

    ## -q, --quiet              do not output any transfer information at all
    ## -L, --rate-limit RATE    limit transfer to RATE bytes per second
pv -q -L $RATE  | "$@"

Add BORG_RSH environment variable to use pipeviewer wrapper script with ssh.

export BORG_RSH='/usr/local/bin/pv-wrapper ssh'

Now Borg will be bandwidth limited. Nice thing about pv is that you can change rate-limit on the fly:

pv -R $(pidof pv) -L 102400

I am having troubles with some network/FUSE/special filesystem, why?

Borg is doing nothing special in the filesystem, it only uses very common and compatible operations (even the locking is just “mkdir”).

So, if you are encountering issues like slowness, corruption or malfunction when using a specific filesystem, please try if you can reproduce the issues with a local (non-network) and proven filesystem (like ext4 on Linux).

If you can’t reproduce the issue then, you maybe have found an issue within the filesystem code you used (not with Borg). For this case, it is recommended that you talk to the developers / support of the network fs and maybe open an issue in their issue tracker. Do not file an issue in the Borg issue tracker.

If you can reproduce the issue with the proven filesystem, please file an issue in the Borg issue tracker about that.

Why does running ‘borg check –repair’ warn about data loss?

Repair usually works for recovering data in a corrupted archive. However, it’s impossible to predict all modes of corruption. In some very rare instances, such as malfunctioning storage hardware, additional repo corruption may occur. If you can’t afford to lose the repo, it’s strongly recommended that you perform repair on a copy of the repo.

In other words, the warning is there to emphasize that Borg:
  • Will perform automated routines that modify your backup repository
  • Might not actually fix the problem you are experiencing
  • Might, in very rare cases, further corrupt your repository

In the case of malfunctioning hardware, such as a drive or USB hub corrupting data when read or written, it’s best to diagnose and fix the cause of the initial corruption before attempting to repair the repo. If the corruption is caused by a one time event such as a power outage, running borg check –repair will fix most problems.

Why isn’t there more progress / ETA information displayed?

Some borg runs take quite a bit, so it would be nice to see a progress display, maybe even including a ETA (expected time of “arrival” [here rather “completion”]).

For some functionality, this can be done: if the total amount of work is more or less known, we can display progress. So check if there is a --progress option.

But sometimes, the total amount is unknown (e.g. for borg create we just do a single pass over the filesystem, so we do not know the total file count or data volume before reaching the end). Adding another pass just to determine that would take additional time and could be incorrect, if the filesystem is changing.

Even if the fs does not change and we knew count and size of all files, we still could not compute the borg create ETA as we do not know the amount of changed chunks, how the bandwidth of source and destination or system performance might fluctuate.

You see, trying to display ETA would be futile. The borg developers prefer to rather not implement progress / ETA display than doing futile attempts.

See also:

Why am I getting ‘Operation not permitted’ errors when backing up on sshfs?

By default, sshfs is not entirely POSIX-compliant when renaming files due to a technicality in the SFTP protocol. Fortunately, it also provides a workaround to make it behave correctly:

sshfs -o workaround=rename user@host:dir /mnt/dir


Requirements for the borg single-file binary, esp. (g)libc?

We try to build the binary on old, but still supported systems - to keep the minimum requirement for the (g)libc low. The (g)libc can’t be bundled into the binary as it needs to fit your kernel and OS, but Python and all other required libraries will be bundled into the binary.

If your system fulfills the minimum (g)libc requirement (see the README that is released with the binary), there should be no problem. If you are slightly below the required version, maybe just try. Due to the dynamic loading (or not loading) of some shared libraries, it might still work depending on what libraries are actually loaded and used.

In the borg git repository, there is scripts/ that can determine (based on the symbols’ versions they want to link to) whether a set of given (Linux) binaries works with a given glibc version.

Why was Borg forked from Attic?

Borg was created in May 2015 in response to the difficulty of getting new code or larger changes incorporated into Attic and establishing a bigger developer community / more open development.

More details can be found in ticket 217 that led to the fork.

Borg intends to be:

  • simple:
    • as simple as possible, but no simpler
    • do the right thing by default, but offer options
  • open:
    • welcome feature requests
    • accept pull requests of good quality and coding style
    • give feedback on PRs that can’t be accepted “as is”
    • discuss openly, don’t work in the dark
  • changing:
    • Borg is not compatible with Attic
    • do not break compatibility accidentally, without a good reason or without warning. allow compatibility breaking for other cases.
    • if major version number changes, it may have incompatible changes

Migrating from Attic

What are the differences between Attic and Borg?

Borg is a fork of Attic and maintained by “The Borg collective”.

Here’s a (incomplete) list of some major changes:

  • lots of attic issues fixed (see issue #5), including critical data corruption bugs and security issues.
  • more open, faster paced development (see issue #1)
  • less chunk management overhead (less memory and disk usage for chunks index)
  • faster remote cache resync (useful when backing up multiple machines into same repo)
  • compression: no, lz4, zlib or lzma compression, adjustable compression levels
  • repokey replaces problematic passphrase mode (you can’t change the passphrase nor the pbkdf2 iteration count in “passphrase” mode)
  • simple sparse file support, great for virtual machine disk files
  • can read special files (e.g. block devices) or from stdin, write to stdout
  • mkdir-based locking is more compatible than attic’s posix locking
  • uses fadvise to not spoil / blow up the fs cache
  • better error messages / exception handling
  • better logging, screen output, progress indication
  • tested on misc. Linux systems, 32 and 64bit, FreeBSD, OpenBSD, NetBSD, macOS

Please read the Changelog (or docs/changes.rst in the source distribution) for more information.

Borg is not compatible with original Attic (but there is a one-way conversion).

How do I migrate from Attic to Borg?

Use borg upgrade. This is a one-way process that cannot be reversed.

There are some caveats:

  • The upgrade can only be performed on local repositories. It cannot be performed on remote repositories.
  • If the repository is in “keyfile” encryption mode, the keyfile must exist locally or it must be manually moved after performing the upgrade:
    1. Get the repository ID with borg config /path/to/repo id.
    2. Locate the attic key file at ~/.attic/keys/. The correct key for the repository starts with the line ATTIC_KEY <repository id>.
    3. Copy the attic key file to ~/.config/borg/keys/
    4. Change the first line from ATTIC_KEY ... to BORG_KEY ....
    5. Verify that the repository is now accessible (e.g. borg list <repository>).
  • Attic and Borg use different “chunker params”. This means that data added by Borg won’t deduplicate with the existing data stored by Attic. The effect is lessened if the files cache is used with Borg.
  • Repositories in “passphrase” mode must be migrated to “repokey” mode using Upgrading a passphrase encrypted attic repo. Borg does not support the “passphrase” mode any other way.

Why is my backup bigger than with attic?

Attic was rather unflexible when it comes to compression, it always compressed using zlib level 6 (no way to switch compression off or adjust the level or algorithm).

The default in Borg is lz4, which is fast enough to not use significant CPU time in most cases, but can only achieve modest compression. It still compresses easily compressed data fairly well.

zlib compression with all levels (1-9) as well as LZMA (1-6) are available as well, for cases where they are worth it.

Which choice is the best option depends on a number of factors, like bandwidth to the repository, how well the data compresses, available CPU power and so on.