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# Bitcoin Core file system
**Contents**
- [Data directory location](#data-directory-location)
- [Data directory layout](#data-directory-layout)
- [Multi-wallet environment](#multi-wallet-environment)
- [GUI settings](#gui-settings)
- [Legacy subdirectories and files](#legacy-subdirectories-and-files)
- [Notes](#notes)
## Data directory location
The data directory is the default location where the Bitcoin Core files are stored.
1. The default data directory paths for supported platforms are:
Platform | Data directory path
---------|--------------------
Linux | `$HOME/.bitcoin/`
macOS | `$HOME/Library/Application Support/Bitcoin/`
Windows | `%APPDATA%\Bitcoin\` <sup>[\[1\]](#note1)</sup>
2. The non-default data directory path can be specified by `-datadir` option.
3. All content of the data directory, except for `bitcoin.conf` file, is chain-specific. This means the actual data directory paths for non-mainnet cases differ:
Chain option | Data directory path
--------------------|--------------------
no option (mainnet) | *path_to_datadir*`/`
`-testnet` | *path_to_datadir*`/testnet3/`
`-regtest` | *path_to_datadir*`/regtest/`
## Data directory layout
Subdirectory | File(s) | Description
-------------------|-----------------------|------------
`blocks/` | | Blocks directory; can be specified by `-blocksdir` option (except for `blocks/index/`)
`blocks/index/` | LevelDB database | Block index; `-blocksdir` option does not affect this path
`blocks/` | `blkNNNNN.dat`<sup>[\[2\]](#note2)</sup> | Actual Bitcoin blocks (in network format, dumped in raw on disk, 128 MiB per file)
`blocks/` | `revNNNNN.dat`<sup>[\[2\]](#note2)</sup> | Block undo data (custom format)
`chainstate/` | LevelDB database | Blockchain state (a compact representation of all currently unspent transaction outputs and some metadata about the transactions they are from)
`indexes/txindex/` | LevelDB database | Transaction index; *optional*, used if `-txindex=1`
`indexes/blockfilter/basic/db/` | LevelDB database | Blockfilter index LevelDB database for the basic filtertype; *optional*, used if `-blockfilterindex=basic`
`indexes/blockfilter/basic/` | `fltrNNNNN.dat`<sup>[\[2\]](#note2)</sup> | Blockfilter index filters for the basic filtertype; *optional*, used if `-blockfilterindex=basic`
`wallets/` | | [Contains wallets](#multi-wallet-environment); can be specified by `-walletdir` option; if `wallets/` subdirectory does not exist, a wallet resides in the data directory
`./` | `banlist.dat` | Stores the IPs/subnets of banned nodes
`./` | `bitcoin.conf` | User-defined [configuration settings](bitcoin-conf.md) for `bitcoind` or `bitcoin-qt`. File is not written to by the software and must be created manually. Path can be specified by `-conf` option
`./` | `bitcoind.pid` | Stores the process ID (PID) of `bitcoind` or `bitcoin-qt` while running; created at start and deleted on shutdown; can be specified by `-pid` option
`./` | `debug.log` | Contains debug information and general logging generated by `bitcoind` or `bitcoin-qt`; can be specified by `-debuglogfile` option
`./` | `fee_estimates.dat` | Stores statistics used to estimate minimum transaction fees and priorities required for confirmation
`./` | `guisettings.ini.bak` | Backup of former [GUI settings](#gui-settings) after `-resetguisettings` option is used
`./` | `mempool.dat` | Dump of the mempool's transactions
`./` | `onion_private_key` | Cached Tor onion service private key for `-listenonion` option
`./` | `peers.dat` | Peer IP address database (custom format)
`./` | `settings.json` | Read-write settings set through GUI or RPC interfaces, augmenting manual settings from [bitcoin.conf](bitcoin-conf.md). File is created automatically if read-write settings storage is not disabled with `-nosettings` option. Path can be specified with `-settings` option
`./` | `.cookie` | Session RPC authentication cookie; if used, created at start and deleted on shutdown; can be specified by `-rpccookiefile` option
`./` | `.lock` | Data directory lock file
## Multi-wallet environment
Wallets are Berkeley DB (BDB) databases:
Subdirectory | File(s) | Description
-------------|-------------------|------------
`database/` | BDB logging files | Part of BDB environment; created at start and deleted on shutdown; a user *must keep it as safe* as personal wallet `wallet.dat`
`./` | `db.log` | BDB error file
`./` | `wallet.dat` | Personal wallet (BDB) with keys and transactions
`./` | `.walletlock` | Wallet lock file
1. Each user-defined wallet named "wallet_name" resides in `wallets/wallet_name/` subdirectory.
2. The default (unnamed) wallet resides in `wallets/` subdirectory; if the latter does not exist, the wallet resides in the data directory.
3. A wallet database path can be specified by `-wallet` option.
4. `wallet.dat` files must not be shared across different node instances, as that can result in key-reuse and double-spends due the lack of synchronization between instances.
5. Any copy or backup of the wallet should be done through a `backupwallet` call in order to update and lock the wallet, preventing any file corruption caused by updates during the copy.
## GUI settings
`bitcoin-qt` uses [`QSettings`](https://doc.qt.io/qt-5/qsettings.html) class; this implies platform-specific [locations where application settings are stored](https://doc.qt.io/qt-5/qsettings.html#locations-where-application-settings-are-stored).
## Legacy subdirectories and files
These subdirectories and files are no longer used by the Bitcoin Core:
Path | Description | Repository notes
---------------|-------------|-----------------
`blktree/` | Blockchain index; replaced by `blocks/index/` in [0.8.0](https://github.com/bitcoin/bitcoin/blob/master/doc/release-notes/release-notes-0.8.0.md#improvements) | [PR #2231](https://github.com/bitcoin/bitcoin/pull/2231), [`8fdc94cc`](https://github.com/bitcoin/bitcoin/commit/8fdc94cc8f0341e96b1edb3a5b56811c0b20bd15)
`coins/` | Unspent transaction output database; replaced by `chainstate/` in 0.8.0 | [PR #2231](https://github.com/bitcoin/bitcoin/pull/2231), [`8fdc94cc`](https://github.com/bitcoin/bitcoin/commit/8fdc94cc8f0341e96b1edb3a5b56811c0b20bd15)
`blkindex.dat` | Blockchain index BDB database; replaced by {`chainstate/`, `blocks/index/`, `blocks/revNNNNN.dat`<sup>[\[2\]](#note2)</sup>} in 0.8.0 | [PR #1677](https://github.com/bitcoin/bitcoin/pull/1677)
`blk000?.dat` | Block data (custom format, 2 GiB per file); replaced by `blocks/blkNNNNN.dat`<sup>[\[2\]](#note2)</sup> in 0.8.0 | [PR #1677](https://github.com/bitcoin/bitcoin/pull/1677)
`addr.dat` | Peer IP address BDB database; replaced by `peers.dat` in [0.7.0](https://github.com/bitcoin/bitcoin/blob/master/doc/release-notes/release-notes-0.7.0.md) | [PR #1198](https://github.com/bitcoin/bitcoin/pull/1198), [`928d3a01`](https://github.com/bitcoin/bitcoin/commit/928d3a011cc66c7f907c4d053f674ea77dc611cc)
## Notes
<a name="note1">1</a>. The `/` (slash, U+002F) is used as the platform-independent path component separator in this paper.
<a name="note2">2</a>. `NNNNN` matches `[0-9]{5}` regex.
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