tahoe-lafs/docs/configuration.rst

Configuring a Tahoe-LAFS node

1. Overall Node Configuration
2. Client Configuration
3. Storage Server Configuration
4. Frontend Configuration
5. Running A Helper
6. Running An Introducer
7. Other Files in BASEDIR
8. Other files
9. Backwards Compatibility Files
10. Example

A Tahoe-LAFS node is configured by writing to files in its base directory. These files are read by the node when it starts, so each time you change them, you need to restart the node.

The node also writes state to its base directory, so it will create files on its own.

This document contains a complete list of the config files that are examined by the client node, as well as the state files that you'll observe in its base directory.

The main file is named "tahoe.cfg", and is an ".INI"-style configuration file (parsed by the Python stdlib 'ConfigParser' module: "[name]" section markers, lines with "key.subkey: value", rfc822-style continuations). There are also other files containing information that does not easily fit into this format. The "tahoe create-node" or "tahoe create-client" command will create an initial tahoe.cfg file for you. After creation, the node will never modify the tahoe.cfg file: all persistent state is put in other files.

The item descriptions below use the following types:

boolean

one of (True, yes, on, 1, False, off, no, 0), case-insensitive

strports string

a Twisted listening-port specification string, like "tcp:80" or "tcp:3456:interface=127.0.0.1". For a full description of the format, see the Twisted strports documentation.

FURL string

a Foolscap endpoint identifier, like pb://soklj4y7eok5c3xkmjeqpw@192.168.69.247:44801/eqpwqtzm

Overall Node Configuration

This section controls the network behavior of the node overall: which ports and IP addresses are used, when connections are timed out, etc. This configuration is independent of the services that the node is offering: the same controls are used for client and introducer nodes.

If your node is behind a firewall or NAT device and you want other clients to connect to it, you'll need to open a port in the firewall or NAT, and specify that port number in the tub.port option. If behind a NAT, you may need to set the tub.location option described below.

[node]

nickname = (UTF-8 string, optional)

This value will be displayed in management tools as this node's "nickname". If not provided, the nickname will be set to "<unspecified>". This string shall be a UTF-8 encoded Unicode string.

web.port = (strports string, optional)

This controls where the node's webserver should listen, providing filesystem access and node status as defined in webapi.rst. This file contains a Twisted "strports" specification such as "3456" or "tcp:3456:interface=127.0.0.1". The "tahoe create-node" or "tahoe create-client" commands set the web.port to "tcp:3456:interface=127.0.0.1" by default; this is overridable by the --webport option. You can make it use SSL by writing "ssl:3456:privateKey=mykey.pem:certKey=cert.pem" instead.

If this is not provided, the node will not run a web server.

web.static = (string, optional)

This controls where the /static portion of the URL space is served. The value is a directory name (~username is allowed, and non-absolute names are interpreted relative to the node's basedir), which can contain HTML and other files. This can be used to serve a Javascript-based frontend to the Tahoe-LAFS node, or other services.

The default value is "public_html", which will serve BASEDIR/public_html . With the default settings, http://127.0.0.1:3456/static/foo.html will serve the contents of BASEDIR/public_html/foo.html .

tub.port = (integer, optional)

This controls which port the node uses to accept Foolscap connections from other nodes. If not provided, the node will ask the kernel for any available port. The port will be written to a separate file (named client.port or introducer.port), so that subsequent runs will re-use the same port.

tub.location = (string, optional)

In addition to running as a client, each Tahoe-LAFS node also runs as a server, listening for connections from other Tahoe-LAFS clients. The node announces its location by publishing a "FURL" (a string with some connection hints) to the Introducer. The string it publishes can be found in BASEDIR/private/storage.furl . The tub.location configuration controls what location is published in this announcement.

If you don't provide tub.location, the node will try to figure out a useful one by itself, by using tools like "ifconfig" to determine the set of IP addresses on which it can be reached from nodes both near and far. It will also include the TCP port number on which it is listening (either the one specified by tub.port, or whichever port was assigned by the kernel when tub.port is left unspecified).

You might want to override this value if your node lives behind a firewall that is doing inbound port forwarding, or if you are using other proxies such that the local IP address or port number is not the same one that remote clients should use to connect. You might also want to control this when using a Tor proxy to avoid revealing your actual IP address through the Introducer announcement.

The value is a comma-separated string of host:port location hints, like this:

123.45.67.89:8098,tahoe.example.com:8098,127.0.0.1:8098

A few examples:

• Emulate default behavior, assuming your host has IP address 123.45.67.89 and the kernel-allocated port number was 8098:

  tub.port = 8098
  tub.location = 123.45.67.89:8098,127.0.0.1:8098

• Use a DNS name so you can change the IP address more easily:

  tub.port = 8098
  tub.location = tahoe.example.com:8098

• Run a node behind a firewall (which has an external IP address) that has been configured to forward port 7912 to our internal node's port 8098:

  tub.port = 8098
  tub.location = external-firewall.example.com:7912

• Run a node behind a Tor proxy (perhaps via torsocks), in client-only mode (i.e. we can make outbound connections, but other nodes will not be able to connect to us). The literal 'unreachable.example.org' will not resolve, but will serve as a reminder to human observers that this node cannot be reached. "Don't call us.. we'll call you":

  tub.port = 8098
  tub.location = unreachable.example.org:0

• Run a node behind a Tor proxy, and make the server available as a Tor "hidden service". (This assumes that other clients are running their node with torsocks, such that they are prepared to connect to a .onion address.) The hidden service must first be configured in Tor, by giving it a local port number and then obtaining a .onion name, using something in the torrc file like:

  HiddenServiceDir /var/lib/tor/hidden_services/tahoe
  HiddenServicePort 29212 127.0.0.1:8098

  once Tor is restarted, the .onion hostname will be in /var/lib/tor/hidden_services/tahoe/hostname. Then set up your tahoe.cfg like:

  tub.port = 8098
  tub.location = ualhejtq2p7ohfbb.onion:29212

Most users will not need to set tub.location.

log_gatherer.furl = (FURL, optional)

If provided, this contains a single FURL string that is used to contact a "log gatherer", which will be granted access to the logport. This can be used to gather operational logs in a single place. Note that in previous releases of Tahoe-LAFS, if an old-style BASEDIR/log_gatherer.furl file existed it would also be used in addition to this value, allowing multiple log gatherers to be used at once. As of Tahoe-LAFS v1.9.0, an old-style file is ignored and a warning will be emitted if one is detected. This means that as of Tahoe-LAFS v1.9.0 you can have at most one log gatherer per node. See ticket #1423 about lifting this restriction and letting you have multiple log gatherers.

timeout.keepalive = (integer in seconds, optional)

timeout.disconnect = (integer in seconds, optional)

If timeout.keepalive is provided, it is treated as an integral number of seconds, and sets the Foolscap "keepalive timer" to that value. For each connection to another node, if nothing has been heard for a while, we will attempt to provoke the other end into saying something. The duration of silence that passes before sending the PING will be between KT and 2*KT. This is mainly intended to keep NAT boxes from expiring idle TCP sessions, but also gives TCP's long-duration keepalive/disconnect timers some traffic to work with. The default value is 240 (i.e. 4 minutes).

If timeout.disconnect is provided, this is treated as an integral number of seconds, and sets the Foolscap "disconnect timer" to that value. For each connection to another node, if nothing has been heard for a while, we will drop the connection. The duration of silence that passes before dropping the connection will be between DT-2*KT and 2*DT+2*KT (please see ticket #521 for more details). If we are sending a large amount of data to the other end (which takes more than DT-2*KT to deliver), we might incorrectly drop the connection. The default behavior (when this value is not provided) is to disable the disconnect timer.

See ticket #521 for a discussion of how to pick these timeout values. Using 30 minutes means we'll disconnect after 22 to 68 minutes of inactivity. Receiving data will reset this timeout, however if we have more than 22min of data in the outbound queue (such as 800kB in two pipelined segments of 10 shares each) and the far end has no need to contact us, our ping might be delayed, so we may disconnect them by accident.

ssh.port = (strports string, optional)

ssh.authorized_keys_file = (filename, optional)

This enables an SSH-based interactive Python shell, which can be used to inspect the internal state of the node, for debugging. To cause the node to accept SSH connections on port 8022 from the same keys as the rest of your account, use:

[tub]
ssh.port = 8022
ssh.authorized_keys_file = ~/.ssh/authorized_keys

tempdir = (string, optional)

This specifies a temporary directory for the web-API server to use, for holding large files while they are being uploaded. If a web-API client attempts to upload a 10GB file, this tempdir will need to have at least 10GB available for the upload to complete.

The default value is the tmp directory in the node's base directory (i.e. BASEDIR/tmp), but it can be placed elsewhere. This directory is used for files that usually (on a Unix system) go into /tmp. The string will be interpreted relative to the node's base directory.

Client Configuration

[client]

introducer.furl = (FURL string, mandatory)

This FURL tells the client how to connect to the introducer. Each Tahoe-LAFS grid is defined by an introducer. The introducer's FURL is created by the introducer node and written into its base directory when it starts, whereupon it should be published to everyone who wishes to attach a client to that grid

helper.furl = (FURL string, optional)

If provided, the node will attempt to connect to and use the given helper for uploads. See helper.rst for details.

key_generator.furl = (FURL string, optional)

If provided, the node will attempt to connect to and use the given key-generator service, using RSA keys from the external process rather than generating its own.

stats_gatherer.furl = (FURL string, optional)

If provided, the node will connect to the given stats gatherer and provide it with operational statistics.

shares.needed = (int, optional) aka "k", default 3

shares.total = (int, optional) aka "N", N >= k, default 10

shares.happy = (int, optional) 1 <= happy <= N, default 7

These three values set the default encoding parameters. Each time a new file is uploaded, erasure-coding is used to break the ciphertext into separate pieces. There will be N (i.e. shares.total) pieces created, and the file will be recoverable if any k (i.e. shares.needed) pieces are retrieved. The default values are 3-of-10 (i.e. shares.needed = 3, shares.total = 10). Setting k to 1 is equivalent to simple replication (uploading N copies of the file).

These values control the tradeoff between storage overhead, performance, and reliability. To a first approximation, a 1MB file will use (1MB * N/k) of backend storage space (the actual value will be a bit more, because of other forms of overhead). Up to N-k shares can be lost before the file becomes unrecoverable, so assuming there are at least N servers, up to N-k servers can be offline without losing the file. So large N/k ratios are more reliable, and small N/k ratios use less disk space. Clearly, k must never be greater than N.

Large values of N will slow down upload operations slightly, since more servers must be involved, and will slightly increase storage overhead due to the hash trees that are created. Large values of k will cause downloads to be marginally slower, because more servers must be involved. N cannot be larger than 256, because of the 8-bit erasure-coding algorithm that Tahoe-LAFS uses.

shares.happy allows you control over the distribution of your immutable file. For a successful upload, shares are guaranteed to be initially placed on at least shares.happy distinct servers, the correct functioning of any k of which is sufficient to guarantee the availability of the uploaded file. This value should not be larger than the number of servers on your grid.

A value of shares.happy <= k is allowed, but does not provide any redundancy if some servers fail or lose shares.

(Mutable files use a different share placement algorithm that does not currently consider this parameter.)

Frontend Configuration

The Tahoe client process can run a variety of frontend file-access protocols. You will use these to create and retrieve files from the virtual filesystem. Configuration details for each are documented in the following protocol-specific guides:

HTTP

Tahoe runs a webserver by default on port 3456. This interface provides a human-oriented "WUI", with pages to create, modify, and browse directories and files, as well as a number of pages to check on the status of your Tahoe node. It also provides a machine-oriented "WAPI", with a REST-ful HTTP interface that can be used by other programs (including the CLI tools). Please see frontends/webapi.rst for full details, and the web.port and web.static config variables above. The frontends/download-status.rst document also describes a few WUI status pages.

CLI

The main "bin/tahoe" executable includes subcommands for manipulating the filesystem, uploading/downloading files, and creating/running Tahoe nodes. See frontends/CLI.rst for details.

FTP, SFTP

Tahoe can also run both FTP and SFTP servers, and map a username/password pair to a top-level Tahoe directory. See frontends/FTP-and-SFTP.rst for instructions on configuring these services, and the [ftpd] and [sftpd] sections of tahoe.cfg.

Drop-Upload

As of Tahoe-LAFS v1.9.0, a node running on Linux can be configured to automatically upload files that are created or changed in a specified local directory. See frontends/drop_upload.rst for details.

Storage Server Configuration

[storage]

enabled = (boolean, optional)

If this is True, the node will run a storage server, offering space to other clients. If it is False, the node will not run a storage server, meaning that no shares will be stored on this node. Use False for clients who do not wish to provide storage service. The default value is True.

readonly = (boolean, optional)

If True, the node will run a storage server but will not accept any shares, making it effectively read-only. Use this for storage servers that are being decommissioned: the storage/ directory could be mounted read-only, while shares are moved to other servers. Note that this currently only affects immutable shares. Mutable shares (used for directories) will be written and modified anyway. See ticket #390 for the current status of this bug. The default value is False.

reserved_space = (str, optional)

If provided, this value defines how much disk space is reserved: the storage server will not accept any share that causes the amount of free disk space to drop below this value. (The free space is measured by a call to statvfs(2) on Unix, or GetDiskFreeSpaceEx on Windows, and is the space available to the user account under which the storage server runs.)

This string contains a number, with an optional case-insensitive scale suffix like "K" or "M" or "G", and an optional "B" or "iB" suffix. So "100MB", "100M", "100000000B", "100000000", and "100000kb" all mean the same thing. Likewise, "1MiB", "1024KiB", and "1048576B" all mean the same thing.

"tahoe create-node" generates a tahoe.cfg with "reserved_space=1G", but you may wish to raise, lower, or remove the reservation to suit your needs.

expire.enabled =

expire.mode =

expire.override_lease_duration =

expire.cutoff_date =

expire.immutable =

expire.mutable =

These settings control garbage collection, in which the server will delete shares that no longer have an up-to-date lease on them. Please see garbage-collection.rst for full details.

Running A Helper

A "helper" is a regular client node that also offers the "upload helper" service.

[helper]

enabled = (boolean, optional)

If True, the node will run a helper (see helper.rst for details). The helper's contact FURL will be placed in private/helper.furl, from which it can be copied to any clients that wish to use it. Clearly nodes should not both run a helper and attempt to use one: do not create helper.furl and also define [helper]enabled in the same node. The default is False.

Running An Introducer

The introducer node uses a different .tac file (named "introducer.tac"), and pays attention to the [node] section, but not the others.

The Introducer node maintains some different state than regular client nodes.

BASEDIR/introducer.furl

This is generated the first time the introducer node is started, and used again on subsequent runs, to give the introduction service a persistent long-term identity. This file should be published and copied into new client nodes before they are started for the first time.

Other Files in BASEDIR

Some configuration is not kept in tahoe.cfg, for the following reasons:

• it is generated by the node at startup, e.g. encryption keys. The node never writes to tahoe.cfg.
• it is generated by user action, e.g. the "tahoe create-alias" command.

In addition, non-configuration persistent state is kept in the node's base directory, next to the configuration knobs.

This section describes these other files.

private/node.pem

This contains an SSL private-key certificate. The node generates this the first time it is started, and re-uses it on subsequent runs. This certificate allows the node to have a cryptographically-strong identifier (the Foolscap "TubID"), and to establish secure connections to other nodes.

storage/

Nodes that host StorageServers will create this directory to hold shares of files on behalf of other clients. There will be a directory underneath it for each StorageIndex for which this node is holding shares. There is also an "incoming" directory where partially-completed shares are held while they are being received.

tahoe-client.tac

This file defines the client, by constructing the actual Client instance each time the node is started. It is used by the "twistd" daemonization program (in the -y mode), which is run internally by the "tahoe start" command. This file is created by the "tahoe create-node" or "tahoe create-client" commands.

tahoe-introducer.tac

This file is used to construct an introducer, and is created by the "tahoe create-introducer" command.

tahoe-key-generator.tac

This file is used to construct a key generator, and is created by the "tahoe create-key-gernerator" command.

tahoe-stats-gatherer.tac

This file is used to construct a statistics gatherer, and is created by the "tahoe create-stats-gatherer" command.

private/control.furl

This file contains a FURL that provides access to a control port on the client node, from which files can be uploaded and downloaded. This file is created with permissions that prevent anyone else from reading it (on operating systems that support such a concept), to insure that only the owner of the client node can use this feature. This port is intended for debugging and testing use.

private/logport.furl

This file contains a FURL that provides access to a 'log port' on the client node, from which operational logs can be retrieved. Do not grant logport access to strangers, because occasionally secret information may be placed in the logs.

private/helper.furl

If the node is running a helper (for use by other clients), its contact FURL will be placed here. See helper.rst for more details.

private/root_dir.cap (optional)

The command-line tools will read a directory cap out of this file and use it, if you don't specify a '--dir-cap' option or if you specify '--dir-cap=root'.

private/convergence (automatically generated)

An added secret for encrypting immutable files. Everyone who has this same string in their private/convergence file encrypts their immutable files in the same way when uploading them. This causes identical files to "converge" -- to share the same storage space since they have identical ciphertext -- which conserves space and optimizes upload time, but it also exposes file contents to the possibility of a brute-force attack by people who know that string. In this attack, if the attacker can guess most of the contents of a file, then they can use brute-force to learn the remaining contents.

So the set of people who know your private/convergence string is the set of people who converge their storage space with you when you and they upload identical immutable files, and it is also the set of people who could mount such an attack.

The content of the private/convergence file is a base-32 encoded string. If the file doesn't exist, then when the Tahoe-LAFS client starts up it will generate a random 256-bit string and write the base-32 encoding of this string into the file. If you want to converge your immutable files with as many people as possible, put the empty string (so that private/convergence is a zero-length file).

Other files

logs/

Each Tahoe-LAFS node creates a directory to hold the log messages produced as the node runs. These logfiles are created and rotated by the "twistd" daemonization program, so logs/twistd.log will contain the most recent messages, logs/twistd.log.1 will contain the previous ones, logs/twistd.log.2 will be older still, and so on. twistd rotates logfiles after they grow beyond 1MB in size. If the space consumed by logfiles becomes troublesome, they should be pruned: a cron job to delete all files that were created more than a month ago in this logs/ directory should be sufficient.

my_nodeid

this is written by all nodes after startup, and contains a base32-encoded (i.e. human-readable) NodeID that identifies this specific node. This NodeID is the same string that gets displayed on the web page (in the "which peers am I connected to" list), and the shortened form (the first few characters) is recorded in various log messages.

Example

The following is a sample tahoe.cfg file, containing values for some of the keys described in the previous section. Note that this is not a recommended configuration (most of these are not the default values), merely a legal one.

[node]
nickname = Bob's Tahoe-LAFS Node
tub.port = 34912
tub.location = 123.45.67.89:8098,44.55.66.77:8098
web.port = 3456
log_gatherer.furl = pb://soklj4y7eok5c3xkmjeqpw@192.168.69.247:44801/eqpwqtzm
timeout.keepalive = 240
timeout.disconnect = 1800
ssh.port = 8022
ssh.authorized_keys_file = ~/.ssh/authorized_keys


[client]
introducer.furl = pb://ok45ssoklj4y7eok5c3xkmj@tahoe.example:44801/ii3uumo
helper.furl = pb://ggti5ssoklj4y7eok5c3xkmj@helper.tahoe.example:7054/kk8lhr


[storage]
enabled = True
readonly = True
sizelimit = 10000000000


[helper]
enabled = True

Old Configuration Files

Tahoe-LAFS releases before v1.3.0 had no tahoe.cfg file, and used distinct files for each item. This is no longer supported and if you have configuration in the old format you must manually convert it to the new format for Tahoe-LAFS to detect it. See historical/configuration.rst.