none
consists of a number of commands. Each command accepts a number of arguments and options. The following sections will describe each command in detail.
Borg only supports taking options (-v and --list in the example) to the left or right of all positional arguments (repo::archive and path in the example), but not in between them:
borg extract -v --list repo::archive path # good and preferred
borg extract repo::archive path -v --list # also works
borg extract -v repo::archive path --list # works, but ugly
borg extract repo::archive -v --list path # BADThis is due to a problem in the argparse module: http://bugs.python.org/issue15112
Local filesystem (or locally mounted network filesystem):
/path/to/repo - filesystem path to repo directory, absolute path
path/to/repo - filesystem path to repo directory, relative path
Also, stuff like ~/path/to/repo or ~other/path/to/repo works (this is expanded by your shell).
Note: you may also prepend a file:// to a filesystem path to get URL style.
Remote repositories accessed via ssh user@host:
user@host:/path/to/repo - remote repo, absolute path
ssh://user@host:port/path/to/repo - same, alternative syntax, port can be given
Remote repositories with relative pathes can be given using this syntax:
user@host:path/to/repo - path relative to current directory
user@host:~/path/to/repo - path relative to user's home directory
user@host:~other/path/to/repo - path relative to other's home directory
Note: giving user@host:/./path/to/repo or user@host:/~/path/to/repo or user@host:/~other/path/to/repo is also supported, but not required here.
Remote repositories with relative pathes, alternative syntax with port:
ssh://user@host:port/./path/to/repo - path relative to current directory
ssh://user@host:port/~/path/to/repo - path relative to user's home directory
ssh://user@host:port/~other/path/to/repo - path relative to other's home directory
If you frequently need the same repo URL, it is a good idea to set the BORG_REPO environment variable to set a default for the repo URL:
export BORG_REPO='ssh://user@host:port/path/to/repo'Then just leave away the repo URL if only a repo URL is needed and you want to use the default - it will be read from BORG_REPO then.
Use :: syntax to give the repo URL when syntax requires giving a positional argument for the repo (e.g. borg mount :: /mnt).
Many commands want either a repository (just give the repo URL, see above) or an archive location, which is a repo URL followed by ::archive_name.
Archive names must not contain the / (slash) character. For simplicity, maybe also avoid blanks or other characters that have special meaning on the shell or in a filesystem (borg mount will use the archive name as directory name).
If you have set BORG_REPO (see above) and an archive location is needed, use ::archive_name - the repo URL part is then read from BORG_REPO.
The log level of the builtin logging configuration defaults to WARNING. This is because we want to be mostly silent and only output warnings, errors and critical messages.
Log levels: DEBUG < INFO < WARNING < ERROR < CRITICAL
Use --debug to set DEBUG log level -to get debug, info, warning, error and critical level output.
Use --info (or -v or --verbose) to set INFO log level -to get info, warning, error and critical level output.
Use --warning (default) to set WARNING log level -to get warning, error and critical level output.
Use --error to set ERROR log level -to get error and critical level output.
Use --critical to set CRITICAL log level -to get critical level output.
While you can set misc. log levels, do not expect that every command will give different output on different log levels - it's just a possibility.
Warning
Options --critical and --error are provided for completeness, their usage is not recommended as you might miss important information.
Warning
While some options (like --stats or --list) will emit more informational messages, you have to use INFO (or lower) log level to make them show up in log output. Use -v or a logging configuration.
can exit with the following return codes (rc):
0 = success (logged as INFO)
1 = warning (operation reached its normal end, but there were warnings -
you should check the log, logged as WARNING)
2 = error (like a fatal error, a local or remote exception, the operation
did not reach its normal end, logged as ERROR)
128+N = killed by signal N (e.g. 137 == kill -9)If you use --show-rc, the return code is also logged at the indicated level as the last log entry.
uses some environment variables for automation:
- General:
- BORG_REPO
When set, use the value to give the default repository location. If a command needs an archive parameter, you can abbreviate as ::archive. If a command needs a repository parameter, you can either leave it away or abbreviate as ::, if a positional parameter is required.
- BORG_PASSPHRASE
When set, use the value to answer the passphrase question for encrypted repositories. It is used when a passphrase is needed to access an encrypted repo as well as when a new passphrase should be initially set when initializing an encrypted repo.
- BORG_PASSCOMMAND
When set, use the standard output of the command (trailing newlines are stripped) to answer the passphrase question for encrypted repositories. It is used when a passphrase is needed to access an encrypted repo as well as when a new passphrase should be initially set when initializing an encrypted repo. If BORG_PASSPHRASE is also set, it takes precedence.
- BORG_DISPLAY_PASSPHRASE
When set, use the value to answer the "display the passphrase for verification" question when defining a new passphrase for encrypted repositories.
- BORG_LOGGING_CONF
When set, use the given filename as INI-style logging configuration.
- BORG_RSH
When set, use this command instead of
ssh. This can be used to specify ssh options, such as a custom identity filessh -i /path/to/private/key. Seeman sshfor other options.- BORG_REMOTE_PATH
When set, use the given path as borg executable on the remote (defaults to "borg" if unset). Using
--remote-path PATHcommandline option overrides the environment variable.- BORG_FILES_CACHE_TTL
When set to a numeric value, this determines the maximum "time to live" for the files cache entries (default: 20). The files cache is used to quickly determine whether a file is unchanged. The FAQ explains this more detailed in:
always_chunking- TMPDIR
where temporary files are stored (might need a lot of temporary space for some operations)
- Some automatic "answerers" (if set, they automatically answer confirmation questions):
- BORG_UNKNOWN_UNENCRYPTED_REPO_ACCESS_IS_OK=no (or =yes)
For "Warning: Attempting to access a previously unknown unencrypted repository"
- BORG_RELOCATED_REPO_ACCESS_IS_OK=no (or =yes)
For "Warning: The repository at location ... was previously located at ..."
- BORG_CHECK_I_KNOW_WHAT_I_AM_DOING=NO (or =YES)
For "Warning: 'check --repair' is an experimental feature that might result in data loss."
- BORG_DELETE_I_KNOW_WHAT_I_AM_DOING=NO (or =YES)
For "You requested to completely DELETE the repository including all archives it contains:"
Note: answers are case sensitive. setting an invalid answer value might either give the default answer or ask you interactively, depending on whether retries are allowed (they by default are allowed). So please test your scripts interactively before making them a non-interactive script.
- Directories:
- BORG_KEYS_DIR
Default to '~/.config/borg/keys'. This directory contains keys for encrypted repositories.
- BORG_SECURITY_DIR
Default to '~/.config/borg/security'. This directory is used by Borg to track various pieces of security-related data.
- BORG_CACHE_DIR
Default to '~/.cache/borg'. This directory contains the local cache and might need a lot of space for dealing with big repositories).
- Building:
- BORG_OPENSSL_PREFIX
Adds given OpenSSL header file directory to the default locations (setup.py).
- BORG_LZ4_PREFIX
Adds given LZ4 header file directory to the default locations (setup.py).
Please note:
- be very careful when using the "yes" sayers, the warnings with prompt exist for your / your data's security/safety
- also be very careful when putting your passphrase into a script, make sure it has appropriate file permissions (e.g. mode 600, root:root).
might use a lot of resources depending on the size of the data set it is dealing with.
If one uses in a client/server way (with a ssh: repository), the resource usage occurs in part on the client and in another part on the server.
If one uses as a single process (with a filesystem repo), all the resource usage occurs in that one process, so just add up client + server to get the approximate resource usage.
- CPU client:
borg create: does chunking, hashing, compression, crypto (high CPU usage) chunks cache sync: quite heavy on CPU, doing lots of hashtable operations. borg extract: crypto, decompression (medium to high CPU usage) borg check: similar to extract, but depends on options given. borg prune / borg delete archive: low to medium CPU usage borg delete repo: done on the server It won't go beyond 100% of 1 core as the code is currently single-threaded. Especially higher zlib and lzma compression levels use significant amounts of CPU cycles. Crypto might be cheap on the CPU (if hardware accelerated) or expensive (if not).
- CPU server:
It usually doesn't need much CPU, it just deals with the key/value store (repository) and uses the repository index for that.
borg check: the repository check computes the checksums of all chunks (medium CPU usage) borg delete repo: low CPU usage
- CPU (only for client/server operation):
When using borg in a client/server way with a ssh:-type repo, the ssh processes used for the transport layer will need some CPU on the client and on the server due to the crypto they are doing - esp. if you are pumping big amounts of data.
- Memory (RAM) client:
The chunks index and the files index are read into memory for performance reasons. Might need big amounts of memory (see below). Compression, esp. lzma compression with high levels might need substantial amounts of memory.
- Memory (RAM) server:
The server process will load the repository index into memory. Might need considerable amounts of memory, but less than on the client (see below).
- Chunks index (client only):
Proportional to the amount of data chunks in your repo. Lots of chunks in your repo imply a big chunks index. It is possible to tweak the chunker params (see create options).
- Files index (client only):
Proportional to the amount of files in your last backups. Can be switched off (see create options), but next backup might be much slower if you do. The speed benefit of using the files cache is proportional to file size.
- Repository index (server only):
Proportional to the amount of data chunks in your repo. Lots of chunks in your repo imply a big repository index. It is possible to tweak the chunker params (see create options) to influence the amount of chunks being created.
- Temporary files (client):
Reading data and metadata from a FUSE mounted repository will consume up to the size of all deduplicated, small chunks in the repository. Big chunks won't be locally cached.
- Temporary files (server):
None.
- Cache files (client only):
Contains the chunks index and files index (plus a collection of single-archive chunk indexes which might need huge amounts of disk space, depending on archive count and size - see FAQ about how to reduce).
- Network (only for client/server operation):
If your repository is remote, all deduplicated (and optionally compressed/ encrypted) data of course has to go over the connection (ssh: repo url). If you use a locally mounted network filesystem, additionally some copy operations used for transaction support also go over the connection. If you backup multiple sources to one target repository, additional traffic happens for cache resynchronization.
In case you are interested in more details (like formulas), please see internals.
To display quantities, takes care of respecting the usual conventions of scale. Disk sizes are displayed in decimal, using powers of ten (so kB means 1000 bytes). For memory usage, binary prefixes are used, and are indicated using the IEC binary prefixes, using powers of two (so KiB means 1024 bytes).
We format date and time conforming to ISO-8601, that is: YYYY-MM-DD and HH:MM:SS (24h clock).
For more information about that, see: https://xkcd.com/1179/
Unless otherwise noted, we display local date and time. Internally, we store and process date and time as UTC.
# Local repository (default is to use encryption in repokey mode)
$ borg init /path/to/repo
# Local repository (no encryption)
$ borg init --encryption=none /path/to/repo
# Remote repository (accesses a remote borg via ssh)
$ borg init user@hostname:backup
# Remote repository (store the key your home dir)
$ borg init --encryption=keyfile user@hostname:backupImportant notes about encryption:
It is not recommended to disable encryption. Repository encryption protects you e.g. against the case that an attacker has access to your backup repository.
But be careful with the key / the passphrase:
If you want "passphrase-only" security, use the repokey mode. The key will be stored inside the repository (in its "config" file). In above mentioned attack scenario, the attacker will have the key (but not the passphrase).
If you want "passphrase and having-the-key" security, use the keyfile mode. The key will be stored in your home directory (in .config/borg/keys). In the attack scenario, the attacker who has just access to your repo won't have the key (and also not the passphrase).
Make a backup copy of the key file (keyfile mode) or repo config file (repokey mode) and keep it at a safe place, so you still have the key in case it gets corrupted or lost. Also keep the passphrase at a safe place. The backup that is encrypted with that key won't help you with that, of course.
Make sure you use a good passphrase. Not too short, not too simple. The real encryption / decryption key is encrypted with / locked by your passphrase. If an attacker gets your key, he can't unlock and use it without knowing the passphrase.
Be careful with special or non-ascii characters in your passphrase:
- processes the passphrase as unicode (and encodes it as utf-8), so it does not have problems dealing with even the strangest characters.
- BUT: that does not necessarily apply to your OS / VM / keyboard configuration.
So better use a long passphrase made from simple ascii chars than one that includes non-ascii stuff or characters that are hard/impossible to enter on a different keyboard layout.
You can change your passphrase for existing repos at any time, it won't affect the encryption/decryption key or other secrets.
# Backup ~/Documents into an archive named "my-documents"
$ borg create /path/to/repo::my-documents ~/Documents
# same, but verbosely list all files as we process them
$ borg create -v --list /path/to/repo::my-documents ~/Documents
# Backup ~/Documents and ~/src but exclude pyc files
$ borg create /path/to/repo::my-files \
~/Documents \
~/src \
--exclude '*.pyc'
# Backup home directories excluding image thumbnails (i.e. only
# /home/*/.thumbnails is excluded, not /home/*/*/.thumbnails)
$ borg create /path/to/repo::my-files /home \
--exclude 're:^/home/[^/]+/\.thumbnails/'
# Do the same using a shell-style pattern
$ borg create /path/to/repo::my-files /home \
--exclude 'sh:/home/*/.thumbnails'
# Backup the root filesystem into an archive named "root-YYYY-MM-DD"
# use zlib compression (good, but slow) - default is no compression
$ borg create -C zlib,6 --one-file-system /path/to/repo::root-{now:%Y-%m-%d} /
# Make a big effort in fine granular deduplication (big chunk management
# overhead, needs a lot of RAM and disk space, see formula in internals
# docs - same parameters as borg < 1.0 or attic):
$ borg create --chunker-params 10,23,16,4095 /path/to/repo::small /smallstuff
# Backup a raw device (must not be active/in use/mounted at that time)
$ dd if=/dev/sdx bs=10M | borg create /path/to/repo::my-sdx -
# No compression (default)
$ borg create /path/to/repo::arch ~
# Super fast, low compression
$ borg create --compression lz4 /path/to/repo::arch ~
# Less fast, higher compression (N = 0..9)
$ borg create --compression zlib,N /path/to/repo::arch ~
# Even slower, even higher compression (N = 0..9)
$ borg create --compression lzma,N /path/to/repo::arch ~
# Use short hostname, user name and current time in archive name
$ borg create /path/to/repo::{hostname}-{user}-{now} ~
# Similar, use the same datetime format as borg 1.1 will have as default
$ borg create /path/to/repo::{hostname}-{user}-{now:%Y-%m-%dT%H:%M:%S} ~
# As above, but add nanoseconds
$ borg create /path/to/repo::{hostname}-{user}-{now:%Y-%m-%dT%H:%M:%S.%f} ~
# Backing up relative paths by moving into the correct directory first
$ cd /home/user/Documents
# The root directory of the archive will be "projectA"
$ borg create /path/to/repo::daily-projectA-{now:%Y-%m-%d} projectA- the --exclude patterns are not like tar. In tar --exclude .bundler/gems will exclude foo/.bundler/gems. In borg it will not, you need to use --exclude '*/.bundler/gems' to get the same effect. See
borg help patternsfor more information.
# Extract entire archive
$ borg extract /path/to/repo::my-files
# Extract entire archive and list files while processing
$ borg extract -v --list /path/to/repo::my-files
# Extract the "src" directory
$ borg extract /path/to/repo::my-files home/USERNAME/src
# Extract the "src" directory but exclude object files
$ borg extract /path/to/repo::my-files home/USERNAME/src --exclude '*.o'
# Restore a raw device (must not be active/in use/mounted at that time)
$ borg extract --stdout /path/to/repo::my-sdx | dd of=/dev/sdx bs=10M- Note: currently, extract always writes into the current working directory ("."),
so make sure you
cdto the right place before callingborg extract.
$ borg create /path/to/repo::archivename ~
$ borg list /path/to/repo
archivename Mon, 2016-02-15 19:50:19
$ borg rename /path/to/repo::archivename newname
$ borg list /path/to/repo
newname Mon, 2016-02-15 19:50:19$ borg list /path/to/repo
Monday Mon, 2016-02-15 19:15:11
repo Mon, 2016-02-15 19:26:54
root-2016-02-15 Mon, 2016-02-15 19:36:29
newname Mon, 2016-02-15 19:50:19
...
$ borg list /path/to/repo::root-2016-02-15
drwxr-xr-x root root 0 Mon, 2016-02-15 17:44:27 .
drwxrwxr-x root root 0 Mon, 2016-02-15 19:04:49 bin
-rwxr-xr-x root root 1029624 Thu, 2014-11-13 00:08:51 bin/bash
lrwxrwxrwx root root 0 Fri, 2015-03-27 20:24:26 bin/bzcmp -> bzdiff
-rwxr-xr-x root root 2140 Fri, 2015-03-27 20:24:22 bin/bzdiff
...
$ borg list /path/to/repo::archiveA --list-format="{mode} {user:6} {group:6} {size:8d} {isomtime} {path}{extra}{NEWLINE}"
drwxrwxr-x user user 0 Sun, 2015-02-01 11:00:00 .
drwxrwxr-x user user 0 Sun, 2015-02-01 11:00:00 code
drwxrwxr-x user user 0 Sun, 2015-02-01 11:00:00 code/myproject
-rw-rw-r-- user user 1416192 Sun, 2015-02-01 11:00:00 code/myproject/file.ext
...
# see what is changed between archives, based on file modification time, size and file path
$ borg list /path/to/repo::archiveA --list-format="{mtime:%s}{TAB}{size}{TAB}{path}{LF}" |sort -n > /tmp/list.archiveA
$ borg list /path/to/repo::archiveB --list-format="{mtime:%s}{TAB}{size}{TAB}{path}{LF}" |sort -n > /tmp/list.archiveB
$ diff -y /tmp/list.archiveA /tmp/list.archiveB
1422781200 0 . 1422781200 0 .
1422781200 0 code 1422781200 0 code
1422781200 0 code/myproject 1422781200 0 code/myproject
1422781200 1416192 code/myproject/file.ext | 1454664653 1416192 code/myproject/file.ext
...# delete a single backup archive:
$ borg delete /path/to/repo::Monday
# delete the whole repository and the related local cache:
$ borg delete /path/to/repo
You requested to completely DELETE the repository *including* all archives it contains:
repo Mon, 2016-02-15 19:26:54
root-2016-02-15 Mon, 2016-02-15 19:36:29
newname Mon, 2016-02-15 19:50:19
Type 'YES' if you understand this and want to continue: YESBe careful, prune is a potentially dangerous command, it will remove backup archives.
The default of prune is to apply to all archives in the repository unless you restrict its operation to a subset of the archives using --prefix. When using --prefix, be careful to choose a good prefix - e.g. do not use a prefix "foo" if you do not also want to match "foobar".
It is strongly recommended to always run prune -v --list --dry-run ... first so you will see what it would do without it actually doing anything.
There is also a visualized prune example in docs/misc/prune-example.txt.
# Keep 7 end of day and 4 additional end of week archives.
# Do a dry-run without actually deleting anything.
$ borg prune -v --list --dry-run --keep-daily=7 --keep-weekly=4 /path/to/repo
# Same as above but only apply to archive names starting with the hostname
# of the machine followed by a "-" character:
$ borg prune -v --list --keep-daily=7 --keep-weekly=4 --prefix='{hostname}-' /path/to/repo
# Keep 7 end of day, 4 additional end of week archives,
# and an end of month archive for every month:
$ borg prune -v --list --keep-daily=7 --keep-weekly=4 --keep-monthly=-1 /path/to/repo
# Keep all backups in the last 10 days, 4 additional end of week archives,
# and an end of month archive for every month:
$ borg prune -v --list --keep-within=10d --keep-weekly=4 --keep-monthly=-1 /path/to/repo$ borg info /path/to/repo::root-2016-02-15
Name: root-2016-02-15
Fingerprint: 57c827621f21b000a8d363c1e163cc55983822b3afff3a96df595077a660be50
Hostname: myhostname
Username: root
Time (start): Mon, 2016-02-15 19:36:29
Time (end): Mon, 2016-02-15 19:39:26
Command line: /usr/local/bin/borg create -v --list -C zlib,6 /path/to/repo::root-2016-02-15 / --one-file-system
Number of files: 38100
Original size Compressed size Deduplicated size
This archive: 1.33 GB 613.25 MB 571.64 MB
All archives: 1.63 GB 853.66 MB 584.12 MB
Unique chunks Total chunks
Chunk index: 36858 48844$ borg mount /path/to/repo::root-2016-02-15 /tmp/mymountpoint
$ ls /tmp/mymountpoint
bin boot etc home lib lib64 lost+found media mnt opt root sbin srv tmp usr var
$ borg umount /tmp/mymountpoint# Create a key file protected repository
$ borg init --encryption=keyfile -v /path/to/repo
Initializing repository at "/path/to/repo"
Enter new passphrase:
Enter same passphrase again:
Remember your passphrase. Your data will be inaccessible without it.
Key in "/root/.config/borg/keys/mnt_backup" created.
Keep this key safe. Your data will be inaccessible without it.
Synchronizing chunks cache...
Archives: 0, w/ cached Idx: 0, w/ outdated Idx: 0, w/o cached Idx: 0.
Done.
# Change key file passphrase
$ borg change-passphrase -v /path/to/repo
Enter passphrase for key /root/.config/borg/keys/mnt_backup:
Enter new passphrase:
Enter same passphrase again:
Remember your passphrase. Your data will be inaccessible without it.
Key updatedborg serve has special support for ssh forced commands (see authorized_keys example below): it will detect that you use such a forced command and extract the value of the --restrict-to-path option(s). It will then parse the original command that came from the client, makes sure that it is also borg serve and enforce path restriction(s) as given by the forced command. That way, other options given by the client (like --info or --umask) are preserved (and are not fixed by the forced command).
# Allow an SSH keypair to only run borg, and only have access to /path/to/repo.
# Use key options to disable unneeded and potentially dangerous SSH functionality.
# This will help to secure an automated remote backup system.
$ cat ~/.ssh/authorized_keys
command="borg serve --restrict-to-path /path/to/repo",no-pty,no-agent-forwarding,no-port-forwarding,no-X11-forwarding,no-user-rc ssh-rsa AAAAB3[...]# Upgrade the borg repository to the most recent version.
$ borg upgrade -v /path/to/repo
making a hardlink copy in /path/to/repo.upgrade-2016-02-15-20:51:55
opening attic repository with borg and converting
no key file found for repository
converting repo index /path/to/repo/index.0
converting 1 segments...
converting borg 0.xx to borg current
no key file found for repositoryattic offered a "passphrase" encryption mode, but this was removed in borg 1.0 and replaced by the "repokey" mode (which stores the passphrase-protected encryption key into the repository config).
Thus, to upgrade a "passphrase" attic repo to a "repokey" borg repo, 2 steps are needed, in this order:
- borg upgrade repo
- borg migrate-to-repokey repo
There are some more commands (all starting with "debug-") which are all not intended for normal use and potentially very dangerous if used incorrectly.
For example, borg debug-put-obj and borg debug-delete-obj will only do what their name suggests: put objects into repo / delete objects from repo.
Please note:
- they will not update the chunks cache (chunks index) about the object
- they will not update the manifest (so no automatic chunks index resync is triggered)
- they will not check whether the object is in use (e.g. before delete-obj)
- they will not update any metadata which may point to the object
They exist to improve debugging capabilities without direct system access, e.g. in case you ever run into some severe malfunction. Use them only if you know what you are doing or if a trusted developer tells you what to do.
Here are misc. notes about topics that are maybe not covered in enough detail in the usage section.
borg create -v --list outputs a verbose list of all files, directories and other file system items it considered (no matter whether they had content changes or not). For each item, it prefixes a single-letter flag that indicates type and/or status of the item.
If you are interested only in a subset of that output, you can give e.g. --filter=AME and it will only show regular files with A, M or E status (see below).
A uppercase character represents the status of a regular file relative to the "files" cache (not relative to the repo -- this is an issue if the files cache is not used). Metadata is stored in any case and for 'A' and 'M' also new data chunks are stored. For 'U' all data chunks refer to already existing chunks.
- 'A' = regular file, added (see also
a_status_oddityin the FAQ) - 'M' = regular file, modified
- 'U' = regular file, unchanged
- 'E' = regular file, an error happened while accessing/reading this file
A lowercase character means a file type other than a regular file, borg usually just stores their metadata:
- 'd' = directory
- 'b' = block device
- 'c' = char device
- 'h' = regular file, hardlink (to already seen inodes)
- 's' = symlink
- 'f' = fifo
Other flags used include:
- 'i' = backup data was read from standard input (stdin)
- '-' = dry run, item was not backed up
- '?' = missing status code (if you see this, please file a bug report!)
The chunker params influence how input files are cut into pieces (chunks) which are then considered for deduplication. They also have a big impact on resource usage (RAM and disk space) as the amount of resources needed is (also) determined by the total amount of chunks in the repository (see Indexes / Caches memory usage for details).
--chunker-params=10,23,16,4095 results in a fine-grained deduplication and creates a big amount of chunks and thus uses a lot of resources to manage them. This is good for relatively small data volumes and if the machine has a good amount of free RAM and disk space.
--chunker-params=19,23,21,4095 (default) results in a coarse-grained deduplication and creates a much smaller amount of chunks and thus uses less resources. This is good for relatively big data volumes and if the machine has a relatively low amount of free RAM and disk space.
If you already have made some archives in a repository and you then change chunker params, this of course impacts deduplication as the chunks will be cut differently.
In the worst case (all files are big and were touched in between backups), this will store all content into the repository again.
Usually, it is not that bad though:
- usually most files are not touched, so it will just re-use the old chunks it already has in the repo
- files smaller than the (both old and new) minimum chunksize result in only one chunk anyway, so the resulting chunks are same and deduplication will apply
If you switch chunker params to save resources for an existing repo that already has some backup archives, you will see an increasing effect over time, when more and more files have been touched and stored again using the bigger chunksize and all references to the smaller older chunks have been removed (by deleting / pruning archives).
If you want to see an immediate big effect on resource usage, you better start a new repository when changing chunker params.
For more details, see chunker_details.
You can use these borg create options to not store the respective timestamp into the archive, in case you do not really need it.
Besides saving a little space for the not archived timestamp, it might also affect metadata stream deduplication: if only this timestamp changes between backups and is stored into the metadata stream, the metadata stream chunks won't deduplicate just because of that.
If you use --umask, make sure that all repository-modifying borg commands (create, delete, prune) that access the repository in question use the same --umask value.
If multiple machines access the same repository, this should hold true for all of them.
The --read-special option is special - you do not want to use it for normal full-filesystem backups, but rather after carefully picking some targets for it.
The option --read-special triggers special treatment for block and char device files as well as FIFOs. Instead of storing them as such a device (or FIFO), they will get opened, their content will be read and in the backup archive they will show up like a regular file.
Symlinks will also get special treatment if (and only if) they point to such a special file: instead of storing them as a symlink, the target special file will get processed as described above.
One intended use case of this is backing up the contents of one or multiple block devices, like e.g. LVM snapshots or inactive LVs or disk partitions.
You need to be careful about what you include when using --read-special, e.g. if you include /dev/zero, your backup will never terminate.
Restoring such files' content is currently only supported one at a time via --stdout option (and you have to redirect stdout to where ever it shall go, maybe directly into an existing device file of your choice or indirectly via dd).
To some extent, mounting a backup archive with the backups of special files via borg mount and then loop-mounting the image files from inside the mount point will work. If you plan to access a lot of data in there, it likely will scale and perform better if you do not work via the FUSE mount.
Imagine you have made some snapshots of logical volumes (LVs) you want to backup.
Note
For some scenarios, this is a good method to get "crash-like" consistency (I call it crash-like because it is the same as you would get if you just hit the reset button or your machine would abrubtly and completely crash). This is better than no consistency at all and a good method for some use cases, but likely not good enough if you have databases running.
Then you create a backup archive of all these snapshots. The backup process will see a "frozen" state of the logical volumes, while the processes working in the original volumes continue changing the data stored there.
You also add the output of lvdisplay to your backup, so you can see the LV sizes in case you ever need to recreate and restore them.
After the backup has completed, you remove the snapshots again. :
$ # create snapshots here
$ lvdisplay > lvdisplay.txt
$ borg create --read-special /path/to/repo::arch lvdisplay.txt /dev/vg0/*-snapshot
$ # remove snapshots hereNow, let's see how to restore some LVs from such a backup. :
$ borg extract /path/to/repo::arch lvdisplay.txt
$ # create empty LVs with correct sizes here (look into lvdisplay.txt).
$ # we assume that you created an empty root and home LV and overwrite it now:
$ borg extract --stdout /path/to/repo::arch dev/vg0/root-snapshot > /dev/vg0/root
$ borg extract --stdout /path/to/repo::arch dev/vg0/home-snapshot > /dev/vg0/homeA repository can be made "append-only", which means that Borg will never overwrite or delete committed data. This is useful for scenarios where multiple machines back up to a central backup server using borg serve, since a hacked machine cannot delete backups permanently.
To activate append-only mode, edit the repository config file and add a line append_only=1 to the [repository] section (or edit the line if it exists).
In append-only mode Borg will create a transaction log in the transactions file, where each line is a transaction and a UTC timestamp.
In addition, borg serve can act as if a repository is in append-only mode with its option --append-only. This can be very useful for fine-tuning access control in .ssh/authorized_keys :
command="borg serve --append-only ..." ssh-rsa <key used for not-always-trustable backup clients>
command="borg serve ..." ssh-rsa <key used for backup management>Please note that if you run borg init via a borg serve --append-only server, the repository config will be created with a append_only=1 entry. This behaviour is subject to change in a later borg version. So, be aware of it for now, but do not rely on it.
Suppose an attacker remotely deleted all backups, but your repository was in append-only mode. A transaction log in this situation might look like this: :
transaction 1, UTC time 2016-03-31T15:53:27.383532
transaction 5, UTC time 2016-03-31T15:53:52.588922
transaction 11, UTC time 2016-03-31T15:54:23.887256
transaction 12, UTC time 2016-03-31T15:55:54.022540
transaction 13, UTC time 2016-03-31T15:55:55.472564From your security logs you conclude the attacker gained access at 15:54:00 and all the backups where deleted or replaced by compromised backups. From the log you know that transactions 11 and later are compromised. Note that the transaction ID is the name of the last file in the transaction. For example, transaction 11 spans files 6 to 11.
In a real attack you'll likely want to keep the compromised repository intact to analyze what the attacker tried to achieve. It's also a good idea to make this copy just in case something goes wrong during the recovery. Since recovery is done by deleting some files, a hard link copy (cp -al) is sufficient.
The first step to reset the repository to transaction 5, the last uncompromised transaction, is to remove the hints.N and index.N files in the repository (these two files are always expendable). In this example N is 13.
Then remove or move all segment files from the segment directories in data/ starting with file 6:
rm data/**/{6..13}That's all to it.
As data is only appended, and nothing removed, commands like prune or delete won't free disk space, they merely tag data as deleted in a new transaction.
Be aware that as soon as you write to the repo in non-append-only mode (e.g. prune, delete or create archives from an admin machine), it will remove the deleted objects permanently (including the ones that were already marked as deleted, but not removed, in append-only mode).
Note that you can go back-and-forth between normal and append-only operation by editing the configuration file, it's not a "one way trip".
Append-only mode is not respected by tools other than Borg. rm still works on the repository. Make sure that backup client machines only get to access the repository via borg serve.
Ensure that no remote access is possible if the repository is temporarily set to normal mode for e.g. regular pruning.
Further protections can be implemented, but are outside of Borgs scope. For example, file system snapshots or wrapping borg serve to set special permissions or ACLs on new data files.
When running using an automated script, ssh might still ask for a password, even if there is an SSH key for the target server. Use this to make scripts more robust:
export BORG_RSH='ssh -oBatchMode=yes'