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TC: A Tor control protocol (Version 1)
0. Scope
This document describes an implementation-specific protocol that is used
for other programs (such as frontend user-interfaces) to communicate with a
locally running Tor process. It is not part of the Tor onion routing
This protocol replaces version 0 of TC, which is now deprecated. For
reference, TC is described in "control-spec-v0.txt". Implementors are
recommended to avoid using TC directly, but instead to use a library that
can easily be updated to use the newer protocol. (Version 0 is used by Tor
versions 0.1.0.x; the protocol in this document only works with Tor
versions in the 0.1.1.x series and later.)
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
"OPTIONAL" in this document are to be interpreted as described in
RFC 2119.
1. Protocol outline
TC is a bidirectional message-based protocol. It assumes an underlying
stream for communication between a controlling process (the "client"
or "controller") and a Tor process (or "server"). The stream may be
implemented via TCP, TLS-over-TCP, a Unix-domain socket, or so on,
but it must provide reliable in-order delivery. For security, the
stream should not be accessible by untrusted parties.
In TC, the client and server send typed messages to each other over the
underlying stream. The client sends "commands" and the server sends
By default, all messages from the server are in response to messages from
the client. Some client requests, however, will cause the server to send
messages to the client indefinitely far into the future. Such
"asynchronous" replies are marked as such.
Servers respond to messages in the order messages are received.
1.1. Forward-compatibility
This is an evolving protocol; new client and server behavior will be
allowed in future versions. To allow new backward-compatible client
on behalf of the client, we may add new commands and allow existing
commands to take new arguments in future versions. To allow new
backward-compatible server behavior, we note various places below
where servers speaking a future versions of this protocol may insert
new data, and note that clients should/must "tolerate" unexpected
elements in these places. There are two ways that we do this:
* Adding a new field to a message:
For example, we might say "This message has three space-separated
fields; clients MUST tolerate more fields." This means that a
client MUST NOT crash or otherwise fail to parse the message or
other subsequent messages when there are more than three fields, and
that it SHOULD function at least as well when more fields are
provided as it does when it only gets the fields it accepts. The
most obvious way to do this is by ignoring additional fields; the
next-most-obvious way is to report additional fields verbatim to the
user, perhaps as part of an expert UI.
* Adding a new possible value to a list of alternatives:
For example, we might say "This field will be OPEN, CLOSED, or
CONNECTED. Clients MUST tolerate unexpected values." This means
that a client MUST NOT crash or otherwise fail to parse the message
or other subsequent when there are unexpected values, and that the
client SHOULD try to handle the rest of the message as well as it
can. The most obvious way to do this is by pretending that each
list of alternatives has an additional "unrecognized value" element,
and mapping any unrecognized values to that element; the
next-most-obvious way is to create a separate "unrecognized value"
element for each unrecognized value.
Clients SHOULD NOT "tolerate" unrecognized alternatives by
pretending that the message containing them is absent. For example,
a stream closed for an unrecognized reason is nevertheless closed,
and should be reported as such.
2. Message format
2.1. Description format
The message formats listed below use ABNF as described in RFC 2234.
The protocol itself is loosely based on SMTP (see RFC 2821).
We use the following nonterminals from RFC 2822: atom, qcontent
We define the following general-use nonterminals:
String = DQUOTE *qcontent DQUOTE
There are explicitly no limits on line length. All 8-bit characters are
permitted unless explicitly disallowed.
Wherever CRLF is specified to be accepted from the controller, Tor MAY also
accept LF. Tor, however, MUST NOT generate LF instead of CRLF.
Controllers SHOULD always send CRLF.
2.2. Commands from controller to Tor
Command = Keyword OptArguments CRLF / "+" Keyword OptArguments CRLF CmdData
Keyword = 1*ALPHA
OptArguments = [ SP *(SP / VCHAR) ]
A command is either a single line containing a Keyword and arguments, or a
multiline command whose initial keyword begins with +, and whose data
section ends with a single "." on a line of its own. (We use a special
character to distinguish multiline commands so that Tor can correctly parse
multi-line commands that it does not recognize.) Specific commands and
their arguments are described below in section 3.
2.3. Replies from Tor to the controller
Reply = SyncReply / AsyncReply
SyncReply = *(MidReplyLine / DataReplyLine) EndReplyLine
AsyncReply = *(MidReplyLine / DataReplyLine) EndReplyLine
MidReplyLine = StatusCode "-" ReplyLine
DataReplyLine = StatusCode "+" ReplyLine Data
EndReplyLine = StatusCode SP ReplyLine
ReplyLine = [ReplyText] CRLF
ReplyText = XXXX
StatusCode = 3DIGIT
Specific replies are mentioned below in section 3, and described more fully
in section 4.
[Compatibility note: versions of Tor before sometimes
generate AsyncReplies of the form "*(MidReplyLine / DataReplyLine)".
This is incorrect, but controllers that need to work with these
versions of Tor should be prepared to get multi-line AsyncReplies with
the final line (usually "650 OK") omitted.]
2.4. General-use tokens
; CRLF means, "the ASCII Carriage Return character (decimal value 13)
; followed by the ASCII Linefeed character (decimal value 10)."
; How a controller tells Tor about a particular OR. There are four
; possible formats:
; $Fingerprint -- The router whose identity key hashes to the fingerprint.
; This is the preferred way to refer to an OR.
; $Fingerprint~Nickname -- The router whose identity key hashes to the
; given fingerprint, but only if the router has the given nickname.
; $Fingerprint=Nickname -- The router whose identity key hashes to the
; given fingerprint, but only if the router is Named and has the given
; nickname.
; Nickname -- The Named router with the given nickname, or, if no such
; router exists, any router whose nickname matches the one given.
; This is not a safe way to refer to routers, since Named status
; could under some circumstances change over time.
; The tokens that implement the above follow:
ServerSpec = LongName / Nickname
LongName = Fingerprint [ ( "=" / "~" ) Nickname ]
Fingerprint = "$" 40*HEXDIG
NicknameChar = "a"-"z" / "A"-"Z" / "0" - "9"
Nickname = 1*19 NicknameChar
; What follows is an outdated way to refer to ORs.
; Feature VERBOSE_NAMES replaces ServerID with LongName in events and
; GETINFO results. VERBOSE_NAMES can be enabled starting in Tor version
; and it is always-on in and later.
ServerID = Nickname / Fingerprint
; Unique identifiers for streams or circuits. Currently, Tor only
; uses digits, but this may change
StreamID = 1*16 IDChar
CircuitID = 1*16 IDChar
Address = ip4-address / ip6-address / hostname (XXXX Define these)
; A "CmdData" section is a sequence of octets concluded by the terminating
; sequence CRLF "." CRLF. The terminating sequence may not appear in the
; body of the data. Leading periods on lines in the data are escaped with
; an additional leading period as in RFC 2821 section 4.5.2.
CmdData = *DataLine "." CRLF
DataLine = CRLF / "." 1*LineItem CRLF / NonDotItem *LineItem CRLF
LineItem = NonCR / 1*CR NonCRLF
NonDotItem = NonDotCR / 1*CR NonCRLF
; ISOTime, ISOTime2, and ISOTime2Frac are time formats as specified in
; ISO8601.
; example ISOTime: "2012-01-11 12:15:33"
; example ISOTime2: "2012-01-11T12:15:33"
; example ISOTime2Frac: "2012-01-11T12:15:33.51"
IsoDatePart = 4*DIGIT "-" 2*DIGIT "-" 2*DIGIT
IsoTimePart = 2*DIGIT ":" 2*DIGIT ":" 2*DIGIT
ISOTime = IsoDatePart " " IsoTimePart
ISOTime2 = IsoDatePart "T" IsoTimePart
ISOTime2Frac = IsoTime2 [ "." 1*DIGIT ]
3. Commands
All commands are case-insensitive, but most keywords are case-sensitive.
Change the value of one or more configuration variables. The syntax is:
"SETCONF" 1*(SP keyword ["=" value]) CRLF
value = String / QuotedString
Tor behaves as though it had just read each of the key-value pairs
from its configuration file. Keywords with no corresponding values have
their configuration values reset to 0 or NULL (use RESETCONF if you want
to set it back to its default). SETCONF is all-or-nothing: if there
is an error in any of the configuration settings, Tor sets none of them.
Tor responds with a "250 configuration values set" reply on success.
If some of the listed keywords can't be found, Tor replies with a
"552 Unrecognized option" message. Otherwise, Tor responds with a
"513 syntax error in configuration values" reply on syntax error, or a
"553 impossible configuration setting" reply on a semantic error.
When a configuration option takes multiple values, or when multiple
configuration keys form a context-sensitive group (see GETCONF below), then
setting _any_ of the options in a SETCONF command is taken to reset all of
the others. For example, if two ORBindAddress values are configured, and a
SETCONF command arrives containing a single ORBindAddress value, the new
command's value replaces the two old values.
Sometimes it is not possible to change configuration options solely by
issuing a series of SETCONF commands, because the value of one of the
configuration options depends on the value of another which has not yet
been set. Such situations can be overcome by setting multiple configuration
options with a single SETCONF command (e.g. SETCONF ORPort=443
Remove all settings for a given configuration option entirely, assign
its default value (if any), and then assign the String provided.
Typically the String is left empty, to simply set an option back to
its default. The syntax is:
"RESETCONF" 1*(SP keyword ["=" String]) CRLF
Otherwise it behaves like SETCONF above.
Request the value of a configuration variable. The syntax is:
"GETCONF" 1*(SP keyword) CRLF
If all of the listed keywords exist in the Tor configuration, Tor replies
with a series of reply lines of the form:
250 keyword=value
If any option is set to a 'default' value semantically different from an
empty string, Tor may reply with a reply line of the form:
250 keyword
Value may be a raw value or a quoted string. Tor will try to use
unquoted values except when the value could be misinterpreted through
not being quoted.
If some of the listed keywords can't be found, Tor replies with a
"552 unknown configuration keyword" message.
If an option appears multiple times in the configuration, all of its
key-value pairs are returned in order.
Some options are context-sensitive, and depend on other options with
different keywords. These cannot be fetched directly. Currently there
is only one such option: clients should use the "HiddenServiceOptions"
virtual keyword to get all HiddenServiceDir, HiddenServicePort,
HiddenServiceVersion, and HiddenserviceAuthorizeClient option settings.
Request the server to inform the client about interesting events. The
syntax is:
EventCode = "CIRC" / "STREAM" / "ORCONN" / "BW" / "DEBUG" /
Any events *not* listed in the SETEVENTS line are turned off; thus, sending
SETEVENTS with an empty body turns off all event reporting.
The server responds with a "250 OK" reply on success, and a "552
Unrecognized event" reply if one of the event codes isn't recognized. (On
error, the list of active event codes isn't changed.)
If the flag string "EXTENDED" is provided, Tor may provide extra
information with events for this connection; see 4.1 for more information.
NOTE: All events on a given connection will be provided in extended format,
or none.
NOTE: "EXTENDED" was first supported in Tor; it is
always-on in Tor and later.
Each event is described in more detail in Section 4.1.
Sent from the client to the server. The syntax is:
The server responds with "250 OK" on success or "515 Bad authentication" if
the authentication cookie is incorrect. Tor closes the connection on an
authentication failure.
The authentication token can be specified as either a quoted ASCII string,
or as an unquoted hexadecimal encoding of that same string (to avoid escaping
For information on how the implementation securely stores authentication
information on disk, see section 5.1.
Before the client has authenticated, no command other than
controller sends any other command, or sends a malformed command, or
sends an unsuccessful AUTHENTICATE command, or sends PROTOCOLINFO or
AUTHCHALLENGE more than once, Tor sends an error reply and closes
the connection.
To prevent some cross-protocol attacks, the AUTHENTICATE command is still
required even if all authentication methods in Tor are disabled. In this
case, the controller should just send "AUTHENTICATE" CRLF.
(Versions of Tor before and did not close the
connection after an authentication failure.)
Sent from the client to the server. The syntax is:
Instructs the server to write out its config options into its torrc. Server
returns "250 OK" if successful, or "551 Unable to write configuration
to disk" if it can't write the file or some other error occurs.
See also the "getinfo config-text" command, if the controller wants
to write the torrc file itself.
Sent from the client to the server. The syntax is:
Signal = "RELOAD" / "SHUTDOWN" / "DUMP" / "DEBUG" / "HALT" /
"HUP" / "INT" / "USR1" / "USR2" / "TERM" / "NEWNYM" /
The meaning of the signals are:
RELOAD -- Reload: reload config items. (like HUP)
SHUTDOWN -- Controlled shutdown: if server is an OP, exit immediately.
If it's an OR, close listeners and exit after
ShutdownWaitLength seconds. (like INT)
DUMP -- Dump stats: log information about open connections and
circuits. (like USR1)
DEBUG -- Debug: switch all open logs to loglevel debug. (like USR2)
HALT -- Immediate shutdown: clean up and exit now. (like TERM)
CLEARDNSCACHE -- Forget the client-side cached IPs for all hostnames.
NEWNYM -- Switch to clean circuits, so new application requests
don't share any circuits with old ones. Also clears
the client-side DNS cache. (Tor MAY rate-limit its
response to this signal.)
The server responds with "250 OK" if the signal is recognized (or simply
closes the socket if it was asked to close immediately), or "552
Unrecognized signal" if the signal is unrecognized.
Sent from the client to the server. The syntax is:
"MAPADDRESS" 1*(Address "=" Address SP) CRLF
The first address in each pair is an "original" address; the second is a
"replacement" address. The client sends this message to the server in
order to tell it that future SOCKS requests for connections to the original
address should be replaced with connections to the specified replacement
address. If the addresses are well-formed, and the server is able to
fulfill the request, the server replies with a 250 message:
250 OldAddress2=NewAddress2
containing the source and destination addresses. If request is
malformed, the server replies with "512 syntax error in command
argument". If the server can't fulfill the request, it replies with
"451 resource exhausted".
The client may decline to provide a body for the original address, and
instead send a special null address ("" for IPv4, "::0" for IPv6, or
"." for hostname), signifying that the server should choose the original
address itself, and return that address in the reply. The server
should ensure that it returns an element of address space that is unlikely
to be in actual use. If there is already an address mapped to the
destination address, the server may reuse that mapping.
If the original address is already mapped to a different address, the old
mapping is removed. If the original address and the destination address
are the same, the server removes any mapping in place for the original
S: 250
{Note: This feature is designed to be used to help Tor-ify applications
that need to use SOCKS4 or hostname-less SOCKS5. There are three
approaches to doing this:
1. Somehow make them use SOCKS4a or SOCKS5-with-hostnames instead.
2. Use tor-resolve (or another interface to Tor's resolve-over-SOCKS
feature) to resolve the hostname remotely. This doesn't work
with special addresses like x.onion or x.y.exit.
3. Use MAPADDRESS to map an IP address to the desired hostname, and then
arrange to fool the application into thinking that the hostname
has resolved to that IP.
This functionality is designed to help implement the 3rd approach.}
Mappings set by the controller last until the Tor process exits:
they never expire. If the controller wants the mapping to last only
a certain time, then it must explicitly un-map the address when that
time has elapsed.
Sent from the client to the server. The syntax is as for GETCONF:
"GETINFO" 1*(SP keyword) CRLF
one or more NL-terminated strings. The server replies with an INFOVALUE
message, or a 551 or 552 error.
Unlike GETCONF, this message is used for data that are not stored in the Tor
configuration file, and that may be longer than a single line. On success,
one ReplyLine is sent for each requested value, followed by a final 250 OK
ReplyLine. If a value fits on a single line, the format is:
If a value must be split over multiple lines, the format is:
Recognized keys and their values include:
"version" -- The version of the server's software, including the name
of the software. (example: "Tor")
"config-file" -- The location of Tor's configuration file ("torrc").
"config-text" -- The contents that Tor would write if you send it
a SAVECONF command, so the controller can write the file to
disk itself. [First implemented in]
["exit-policy/prepend" -- The default exit policy lines that Tor will
*prepend* to the ExitPolicy config option.
-- Never implemented. Useful?]
"exit-policy/default" -- The default exit policy lines that Tor will
*append* to the ExitPolicy config option.
"desc/id/<OR identity>" or "desc/name/<OR nickname>" -- the latest
server descriptor for a given OR.
"md/id/<OR identity>" or "md/name/<OR nickname>" -- the latest
microdescriptor for a given OR. [First implemented in]
"desc-annotations/id/<OR identity>" -- outputs the annotations string
(source, timestamp of arrival, purpose, etc) for the corresponding
descriptor. [First implemented in]
"extra-info/digest/<digest>" -- the extrainfo document whose digest (in
hex) is <digest>. Only available if we're downloading extra-info
"ns/id/<OR identity>" or "ns/name/<OR nickname>" -- the latest router
status info (v2 directory style) for a given OR. Router status
info is as given in
dir-spec.txt, and reflects the current beliefs of this Tor about the
router in question. Like directory clients, controllers MUST
tolerate unrecognized flags and lines. The published date and
descriptor digest are those believed to be best by this Tor,
not necessarily those for a descriptor that Tor currently has.
[First implemented in]
"ns/all" -- Router status info (v2 directory style) for all ORs we
have an opinion about, joined by newlines. [First implemented
"ns/purpose/<purpose>" -- Router status info (v2 directory style)
for all ORs of this purpose. Mostly designed for /ns/purpose/bridge
queries. [First implemented in]
"desc/all-recent" -- the latest server descriptor for every router that
Tor knows about.
"network-status" -- a space-separated list (v1 directory style)
of all known OR identities. This is in the same format as the
router-status line in v1 directories; see dir-spec-v1.txt section
3 for details. (If VERBOSE_NAMES is enabled, the output will
not conform to dir-spec-v1.txt; instead, the result will be a
space-separated list of LongName, each preceded by a "!" if it is
believed to be not running.) This option is deprecated; use
"ns/all" instead.
"address-mappings/control" -- a \r\n-separated list of address
mappings, each in the form of "from-address to-address expiry".
The 'config' key returns those address mappings set in the
configuration; the 'cache' key returns the mappings in the
client-side DNS cache; the 'control' key returns the mappings set
via the control interface; the 'all' target returns the mappings
set through any mechanism.
Expiry is formatted as with ADDRMAP events, except that "expiry" is
always a time in GMT or the string "NEVER"; see section 4.1.7.
First introduced in
"addr-mappings/*" -- as for address-mappings/*, but without the
expiry portion of the value. Use of this value is deprecated
since; use address-mappings instead.
"address" -- the best guess at our external IP address. If we
have no guess, return a 551 error. (Added in
"fingerprint" -- the contents of the fingerprint file that Tor
writes as a relay, or a 551 if we're not a relay currently.
(Added in
A series of lines as for a circuit status event. Each line is of
the form described in section 4.1.1, omitting the initial
"650 CIRC ". Note that clients must be ready to accept additional
arguments as described in section 4.1.
A series of lines as for a stream status event. Each is of the form:
StreamID SP StreamStatus SP CircID SP Target CRLF
A series of lines as for an OR connection status event. In Tor with feature VERBOSE_NAMES enabled and in Tor and later by default, each line is of the form:
LongName SP ORStatus CRLF
In Tor versions through with feature
VERBOSE_NAMES turned off and before version, each line
is of the form:
ServerID SP ORStatus CRLF
A series of lines listing the currently chosen entry guards, if any.
In Tor with feature VERBOSE_NAMES enabled and in Tor and later by default, each line is of the form:
LongName SP Status [SP ISOTime] CRLF
In Tor versions through with feature
VERBOSE_NAMES turned off and before version, each line
is of the form:
ServerID2 SP Status [SP ISOTime] CRLF
ServerID2 = Nickname / 40*HEXDIG
The definition of Status is the same for both:
Status = "up" / "never-connected" / "down" /
"unusable" / "unlisted"
[From to, entry-guards was called
"helper-nodes". Tor still supports calling "helper-nodes", but it
is deprecated and should not be used.]
[Older versions of Tor (before 0.1.2.x-final) generated 'down' instead
of unlisted/unusable. Current Tors never generate 'down'.]
[XXXX ServerID2 differs from ServerID in not prefixing fingerprints
with a $. This is an implementation error. It would be nice to add
the $ back in if we can do so without breaking compatibility.]
"traffic/read" -- Total bytes read (downloaded).
"traffic/written" -- Total bytes written (uploaded).
Information about accounting status. If accounting is enabled,
"enabled" is 1; otherwise it is 0. The "hibernating" field is "hard"
if we are accepting no data; "soft" if we're accepting no new
connections, and "awake" if we're not hibernating at all. The "bytes"
and "bytes-left" fields contain (read-bytes SP write-bytes), for the
start and the rest of the interval respectively. The 'interval-start'
and 'interval-end' fields are the borders of the current interval; the
'interval-wake' field is the time within the current interval (if any)
where we plan[ned] to start being active. The times are GMT.
A series of lines listing the available configuration options. Each is
of the form:
OptionName SP OptionType [ SP Documentation ] CRLF
OptionName = Keyword
OptionType = "Integer" / "TimeInterval" / "TimeMsecInterval" /
"DataSize" / "Float" / "Boolean" / "Time" / "CommaList" /
"Dependant" / "Virtual" / "String" / "LineList"
Documentation = Text
A series of lines listing the available GETINFO options. Each is of
one of these forms:
OptionName SP Documentation CRLF
OptionPrefix SP Documentation CRLF
OptionPrefix = OptionName "/*"
A space-separated list of all the events supported by this version of
A space-separated list of all the events supported by this version of
Maps IP addresses to 2-letter country codes. For example,
"GETINFO ip-to-country/" should give "US".
XXX todo.
"process/pid" -- Process id belonging to the main tor process.
"process/uid" -- User id running the tor process, -1 if unknown (this is
unimplemented on Windows, returning -1).
"process/user" -- Username under which the tor process is running,
providing an empty string if none exists (this is unimplemented on
Windows, returning an empty string).
"process/descriptor-limit" -- Upper bound on the file descriptor limit, -1
if unknown.
"dir/status-vote/current/consensus" [added in Tor]
A series of lines listing directory contents, provided according to the
specification for the URLs listed in Section 4.4 of dir-spec.txt. Note
that Tor MUST NOT provide private information, such as descriptors for
routers not marked as general-purpose. When asked for 'authority'
information for which this Tor is not authoritative, Tor replies with
an empty string.
These provide the current internal Tor values for various Tor
states. See Section 4.1.10 for explanations. (Only a few of the
status events are available as getinfo's currently. Let us know if
you want more exposed.)
0 or 1, depending on whether we've found our ORPort reachable.
0 or 1, depending on whether we've found our DirPort reachable.
"OR=" ("0"/"1") SP "DIR=" ("0"/"1")
Combines status/reachability-succeeded/*; controllers MUST ignore
unrecognized elements in this entry.
Returns the most recent bootstrap phase status event
sent. Specifically, it returns a string starting with either
"NOTICE BOOTSTRAP ..." or "WARN BOOTSTRAP ...". Controllers should
use this getinfo when they connect or attach to Tor to learn its
current bootstrap state.
List of currently recommended versions.
Status of the current version. One of: new, old, unrecommended,
recommended, new in series, obsolete, unknown.
A summary of which countries we've seen clients from recently,
formatted the same as the CLIENTS_SEEN status event described in
Section 4.1.14. This GETINFO option is currently available only
for bridge relays.
A space-separated list of the addresses at which Tor is listening for
connections of each specified type. [New in Tor]
C: GETINFO version desc/name/moria1
S: 250+desc/name/moria=
S: [Descriptor for moria]
S: .
S: 250-version=Tor
S: 250 OK
Sent from the client to the server. The format is:
[SP ServerSpec *("," ServerSpec)]
[SP "purpose=" Purpose] CRLF
This request takes one of two forms: either the CircuitID is zero, in
which case it is a request for the server to build a new circuit,
or the CircuitID is nonzero, in which case it is a request for the
server to extend an existing circuit with that ID according to the
specified path.
If the CircuitID is 0, the controller has the option of providing
a path for Tor to use to build the circuit. If it does not provide
a path, Tor will select one automatically from high capacity nodes
according to path-spec.txt.
If CircuitID is 0 and "purpose=" is specified, then the circuit's
purpose is set. Two choices are recognized: "general" and
"controller". If not specified, circuits are created as "general".
If the request is successful, the server sends a reply containing a
message body consisting of the CircuitID of the (maybe newly created)
circuit. The syntax is "250" SP "EXTENDED" SP CircuitID CRLF.
Sent from the client to the server. The format is:
This changes the circuit's purpose. See EXTENDCIRCUIT above for details.
Sent from the client to the server. The format is:
This changes the descriptor's purpose. See +POSTDESCRIPTOR below
for details.
NOTE: This command was disabled and made obsolete as of Tor It doesn't exist anymore, and is listed here only for
historical interest.
Sent from the client to the server. The syntax is:
This message informs the server that the specified stream should be
associated with the specified circuit. Each stream may be associated with
at most one circuit, and multiple streams may share the same circuit.
Streams can only be attached to completed circuits (that is, circuits that
have sent a circuit status 'BUILT' event or are listed as built in a
GETINFO circuit-status request).
If the circuit ID is 0, responsibility for attaching the given stream is
returned to Tor.
If HOP=HopNum is specified, Tor will choose the HopNumth hop in the
circuit as the exit node, rather than the last node in the circuit.
Hops are 1-indexed; generally, it is not permitted to attach to hop 1.
Tor responds with "250 OK" if it can attach the stream, 552 if the circuit
or stream didn't exist, or 551 if the stream couldn't be attached for
another reason.
{Implementation note: Tor will close unattached streams by itself,
roughly two minutes after they are born. Let the developers know if
that turns out to be a problem.}
{Implementation note: By default, Tor automatically attaches streams to
circuits itself, unless the configuration variable
"__LeaveStreamsUnattached" is set to "1". Attempting to attach streams
via TC when "__LeaveStreamsUnattached" is false may cause a race between
Tor and the controller, as both attempt to attach streams to circuits.}
{Implementation note: You can try to attachstream to a stream that
has already sent a connect or resolve request but hasn't succeeded
yet, in which case Tor will detach the stream from its current circuit
before proceeding with the new attach request.}
Sent from the client to the server. The syntax is:
"+POSTDESCRIPTOR" [SP "purpose=" Purpose] [SP "cache=" Cache]
CRLF Descriptor CRLF "." CRLF
This message informs the server about a new descriptor. If Purpose is
specified, it must be either "general", "controller", or "bridge",
else we return a 552 error. The default is "general".
If Cache is specified, it must be either "no" or "yes", else we
return a 552 error. If Cache is not specified, Tor will decide for
itself whether it wants to cache the descriptor, and controllers
must not rely on its choice.
The descriptor, when parsed, must contain a number of well-specified
fields, including fields for its nickname and identity.
If there is an error in parsing the descriptor, the server must send a
"554 Invalid descriptor" reply. If the descriptor is well-formed but
the server chooses not to add it, it must reply with a 251 message
whose body explains why the server was not added. If the descriptor
is added, Tor replies with "250 OK".
Sent from the client to the server. The syntax is:
Tells the server to change the exit address on the specified stream. If
Port is specified, changes the destination port as well. No remapping
is performed on the new provided address.
To be sure that the modified address will be used, this event must be sent
after a new stream event is received, and before attaching this stream to
a circuit.
Tor replies with "250 OK" on success.
Sent from the client to the server. The syntax is:
Tells the server to close the specified stream. The reason should be one
of the Tor RELAY_END reasons given in tor-spec.txt, as a decimal. Flags is
not used currently; Tor servers SHOULD ignore unrecognized flags. Tor may
hold the stream open for a while to flush any data that is pending.
Tor replies with "250 OK" on success, or a 512 if there aren't enough
arguments, or a 552 if it doesn't recognize the StreamID or reason.
The syntax is:
Flag = "IfUnused"
Tells the server to close the specified circuit. If "IfUnused" is
provided, do not close the circuit unless it is unused.
Other flags may be defined in the future; Tor SHOULD ignore unrecognized
Tor replies with "250 OK" on success, or a 512 if there aren't enough
arguments, or a 552 if it doesn't recognize the CircuitID.
3.18. QUIT
Tells the server to hang up on this controller connection. This command
can be used before authenticating.
Adding additional features to the control protocol sometimes will break
backwards compatibility. Initially such features are added into Tor and
disabled by default. USEFEATURE can enable these additional features.
The syntax is:
FeatureName = 1*(ALPHA / DIGIT / "_" / "-")
Feature names are case-insensitive.
Once enabled, a feature stays enabled for the duration of the connection
to the controller. A new connection to the controller must be opened to
disable an enabled feature.
Features are a forward-compatibility mechanism; each feature will eventually
become a standard part of the control protocol. Once a feature becomes part
of the protocol, it is always-on. Each feature documents the version it was
introduced as a feature and the version in which it became part of the
Tor will ignore a request to use any feature that is always-on. Tor will give
a 552 error in response to an unrecognized feature.
Same as passing 'EXTENDED' to SETEVENTS; this is the preferred way to
request the extended event syntax.
This feature was first introduced in It is always-on
and part of the protocol in Tor and later.
Replaces ServerID with LongName in events and GETINFO results. LongName
provides a Fingerprint for all routers, an indication of Named status,
and a Nickname if one is known. LongName is strictly more informative
than ServerID, which only provides either a Fingerprint or a Nickname.
This feature was first introduced in It is always-on and
part of the protocol in Tor and later.
The syntax is
"RESOLVE" *Option *Address CRLF
Option = "mode=reverse"
Address = a hostname or IPv4 address
This command launches a remote hostname lookup request for every specified
request (or reverse lookup if "mode=reverse" is specified). Note that the
request is done in the background: to see the answers, your controller will
need to listen for ADDRMAP events; see 4.1.7 below.
[Added in Tor]
The syntax is:
The server reply format is:
InfoLine = AuthLine / VersionLine / OtherLine
AuthLine = "250-AUTH" SP "METHODS=" AuthMethod *("," AuthMethod)
*(SP "COOKIEFILE=" AuthCookieFile) CRLF
VersionLine = "250-VERSION" SP "Tor=" TorVersion OptArguments CRLF
AuthMethod =
"NULL" / ; No authentication is required
"HASHEDPASSWORD" / ; A controller must supply the original password
"COOKIE" / ; A controller must supply the contents of a cookie
"SAFECOOKIE" ; A controller must prove knowledge of a cookie
AuthCookieFile = QuotedString
TorVersion = QuotedString
OtherLine = "250-" Keyword OptArguments CRLF
Tor MAY give its InfoLines in any order; controllers MUST ignore InfoLines
with keywords they do not recognize. Controllers MUST ignore extraneous
data on any InfoLine.
PIVERSION is there in case we drastically change the syntax one day. For
now it should always be "1". Controllers MAY provide a list of the
protocolinfo versions they support; Tor MAY select a version that the
controller does not support.
AuthMethod is used to specify one or more control authentication
methods that Tor currently accepts.
AuthCookieFile specifies the absolute path and filename of the
authentication cookie that Tor is expecting and is provided iff the
METHODS field contains the method "COOKIE" and/or "SAFECOOKIE".
Controllers MUST handle escape sequences inside this string.
All authentication cookies are 32 bytes long. Controllers MUST NOT
use the contents of a non-32-byte-long file as an authentication
If the METHODS field contains the method "SAFECOOKIE", every
AuthCookieFile must contain the same authentication cookie.
The COOKIE authentication method exposes the user running a
controller to an unintended information disclosure attack whenever
the controller has greater filesystem read access than the process
that it has connected to. (Note that a controller may connect to a
process other than Tor.) It is almost never safe to use, even if
the controller's user has explicitly specified which filename to
read an authentication cookie from. For this reason, the COOKIE
authentication method has been deprecated and will be removed from
a future version of Tor.
The VERSION line contains the Tor version.
[Unlike other commands besides AUTHENTICATE, PROTOCOLINFO may be used (but
only once!) before AUTHENTICATE.]
[PROTOCOLINFO was not supported before Tor]
The syntax is:
This command allows a controller to upload the text of a config file
to Tor over the control port. This config file is then loaded as if
it had been read from disk.
[LOADCONF was added in Tor]
The syntax is:
This command instructs Tor to shut down (as if it had received
SIGINT or a "SIGNAL INT" controller command) when this control
connection is closed. This command affects each control connection
that sends it independently; if multiple control connections send
the TAKEOWNERSHIP command to a Tor instance, Tor will shut down when
any of those connections closes.
This command is intended to be used with the
__OwningControllerProcess configuration option. A controller that
starts a Tor process which the user cannot easily control or stop
should 'own' that Tor process:
* When starting Tor, the controller should specify its PID in an
__OwningControllerProcess on Tor's command line. This will
cause Tor to poll for the existence of a process with that PID,
and exit if it does not find such a process. (This is not a
completely reliable way to detect whether the 'owning
controller' is still running, but it should work well enough in
most cases.)
* Once the controller has connected to Tor's control port, it
should send the TAKEOWNERSHIP command along its control
connection. At this point, *both* the TAKEOWNERSHIP command and
the __OwningControllerProcess option are in effect: Tor will
exit when the control connection ends *and* Tor will exit if it
detects that there is no process with the PID specified in the
__OwningControllerProcess option.
* After the controller has sent the TAKEOWNERSHIP command, it
should send "RESETCONF __OwningControllerProcess" along its
control connection. This will cause Tor to stop polling for the
existence of a process with its owning controller's PID; Tor
will still exit when the control connection ends.
[TAKEOWNERSHIP was added in Tor]
The syntax is:
SP ClientNonce
ClientNonce = 2*HEXDIG / QuotedString
If the server accepts the command, the server reply format is:
ServerHash = 64*64HEXDIG
ServerNonce = 64*64HEXDIG
The ClientNonce, ServerHash, and ServerNonce values are
encoded/decoded in the same way as the argument passed to the
AUTHENTICATE command. ServerNonce MUST be 32 bytes long.
ServerHash is computed as:
HMAC-SHA256("Tor safe cookie authentication server-to-controller hash",
CookieString | ClientNonce | ServerNonce)
(with the HMAC key as its first argument)
After a controller sends a successful AUTHCHALLENGE command, the
next command sent on the connection must be an AUTHENTICATE command,
and the only authentication string which that AUTHENTICATE command
will accept is:
HMAC-SHA256("Tor safe cookie authentication controller-to-server hash",
CookieString | ClientNonce | ServerNonce)
[Unlike other commands besides AUTHENTICATE, AUTHCHALLENGE may be
used (but only once!) before AUTHENTICATE.]
[AUTHCHALLENGE was added in Tor FIXME.]
4. Replies
Reply codes follow the same 3-character format as used by SMTP, with the
first character defining a status, the second character defining a
subsystem, and the third designating fine-grained information.
The TC protocol currently uses the following first characters:
2yz Positive Completion Reply
The command was successful; a new request can be started.
4yz Temporary Negative Completion reply
The command was unsuccessful but might be reattempted later.
5yz Permanent Negative Completion Reply
The command was unsuccessful; the client should not try exactly
that sequence of commands again.
6yz Asynchronous Reply
Sent out-of-order in response to an earlier SETEVENTS command.
The following second characters are used:
x0z Syntax
Sent in response to ill-formed or nonsensical commands.
x1z Protocol
Refers to operations of the Tor Control protocol.
x5z Tor
Refers to actual operations of Tor system.
The following codes are defined:
250 OK
251 Operation was unnecessary
[Tor has declined to perform the operation, but no harm was done.]
451 Resource exhausted
500 Syntax error: protocol
510 Unrecognized command
511 Unimplemented command
512 Syntax error in command argument
513 Unrecognized command argument
514 Authentication required
515 Bad authentication
550 Unspecified Tor error
551 Internal error
[Something went wrong inside Tor, so that the client's
request couldn't be fulfilled.]
552 Unrecognized entity
[A configuration key, a stream ID, circuit ID, event,
mentioned in the command did not actually exist.]
553 Invalid configuration value
[The client tried to set a configuration option to an
incorrect, ill-formed, or impossible value.]
554 Invalid descriptor
555 Unmanaged entity
650 Asynchronous event notification
Unless specified to have specific contents, the human-readable messages
in error replies should not be relied upon to match those in this document.
4.1. Asynchronous events
These replies can be sent after a corresponding SETEVENTS command has been
received. They will not be interleaved with other Reply elements, but they
can appear between a command and its corresponding reply. For example,
this sequence is possible:
S: 250 OK
S: 650 CIRC 1000 EXTENDED moria1,moria2
S: 250-SOCKSPORT=9050
S: 250 ORPORT=0
But this sequence is disallowed:
S: 250 OK
S: 250-SOCKSPORT=9050
S: 650 CIRC 1000 EXTENDED moria1,moria2
S: 250 ORPORT=0
Clients MUST tolerate more arguments in an asynchronous reply than
expected, and MUST tolerate more lines in an asynchronous reply than
expected. For instance, a client that expects a CIRC message like:
650 CIRC 1000 EXTENDED moria1,moria2
must tolerate:
650-CIRC 1000 EXTENDED moria1,moria2 0xBEEF
650 ANONYMITY=high
If clients receives extended events (selected by USEFEATUERE
EXTENDED_EVENTS in Tor, and always-on in
Tor 0.2.2.x and later), then each event line as specified below may be
followed by additional arguments and additional lines. Additional
lines will be of the form:
"650" ("-"/" ") KEYWORD ["=" ARGUMENTS] CRLF
Additional arguments will be of the form
SP KEYWORD ["=" ( QuotedString / * NonSpDquote ) ]
Clients MUST tolerate events with arguments and keywords they do not
recognize, and SHOULD process those events as if any unrecognized
arguments and keywords were not present.
Clients SHOULD NOT depend on the order of keywords=value arguments,
and SHOULD NOT depend on there being no new keyword=value arguments
appearing between existing keyword=value arguments, though as of this
writing (Jun 2011) some do. Thus, extensions to this protocol should
add new keywords only after the existing keywords, until all
controllers have been fixed. At some point this "SHOULD NOT" might
become a "MUST NOT".
4.1.1. Circuit status changed
The syntax is:
"650" SP "CIRC" SP CircuitID SP CircStatus [SP Path]
[SP "BUILD_FLAGS=" BuildFlags] [SP "PURPOSE=" Purpose]
[SP "HS_STATE=" HSState] [SP "REND_QUERY=" HSAddress]
[SP "TIME_CREATED=" TimeCreated]
CircStatus =
"LAUNCHED" / ; circuit ID assigned to new circuit
"BUILT" / ; all hops finished, can now accept streams
"EXTENDED" / ; one more hop has been completed
"FAILED" / ; circuit closed (was not built)
"CLOSED" ; circuit closed (was built)
Path = LongName *("," LongName)
; In Tor versions through with feature
; VERBOSE_NAMES turned off and before version, Path
; is as follows:
; Path = ServerID *("," ServerID)
BuildFlags = BuildFlag *("," BuildFlag)
HSAddress = 16*Base32Character
Base32Character = ALPHA / "2" / "3" / "4" / "5" / "6" / "7"
TimeCreated = ISOTime2Frac
Seconds = 1*DIGIT
Microseconds = 1*DIGIT
The path is provided only when the circuit has been extended at least one
The "BUILD_FLAGS" field is provided only in versions
and later. Clients MUST accept build flags not listed above.
Build flags are defined as follows:
ONEHOP_TUNNEL (one-hop circuit, used for tunneled directory conns)
IS_INTERNAL (internal circuit, not to be used for exiting streams)
NEED_CAPACITY (this circuit must use only high-capacity nodes)
NEED_UPTIME (this circuit must use only high-uptime nodes)
The "PURPOSE" field is provided only in versions and
later, and only if extended events are enabled (see 3.19). Clients
MUST accept purposes not listed above. Purposes are defined as
GENERAL (circuit for AP and/or directory request streams)
HS_CLIENT_INTRO (HS client-side introduction-point circuit)
HS_CLIENT_REND (HS client-side rendezvous circuit; carries AP streams)
HS_SERVICE_INTRO (HS service-side introduction-point circuit)
HS_SERVICE_REND (HS service-side rendezvous circuit)
TESTING (reachability-testing circuit; carries no traffic)
CONTROLLER (circuit built by a controller)
The "HS_STATE" field is provided only for hidden-service circuits,
and only in versions and later. Clients MUST accept
hidden-service circuit states not listed above. Hidden-service
circuit states are defined as follows:
HSCI_* (client-side introduction-point circuit states)
HSCI_CONNECTING (connecting to intro point)
HSCI_INTRO_SENT (sent INTRODUCE1; waiting for reply from IP)
HSCI_DONE (received reply from IP relay; closing)
HSCR_* (client-side rendezvous-point circuit states)
HSCR_CONNECTING (connecting to or waiting for reply from RP)
HSCR_ESTABLISHED_IDLE (established RP; waiting for introduction)
HSCR_ESTABLISHED_WAITING (introduction sent to HS; waiting for rend)
HSCR_JOINED (connected to HS)
HSSI_* (service-side introduction-point circuit states)
HSSI_CONNECTING (connecting to intro point)
HSSI_ESTABLISHED (established intro point)
HSSR_* (service-side rendezvous-point circuit states)
HSSR_CONNECTING (connecting to client's rend point)
HSSR_JOINED (connected to client's RP circuit)
The "REND_QUERY" field is provided only for hidden-service-related
circuits, and only in versions and later. Clients
MUST accept hidden service addresses in formats other than that
specified above.
The "TIME_CREATED" field is provided only in versions and
later. TIME_CREATED is the time at which the circuit was created or
The "REASON" field is provided only for FAILED and CLOSED events, and only
if extended events are enabled (see 3.19). Clients MUST accept reasons
not listed above. Reasons are as given in tor-spec.txt, except for:
NOPATH (Not enough nodes to make circuit)
The "REMOTE_REASON" field is provided only when we receive a DESTROY or
TRUNCATE cell, and only if extended events are enabled. It contains the
actual reason given by the remote OR for closing the circuit. Clients MUST
accept reasons not listed above. Reasons are as listed in tor-spec.txt.
4.1.2. Stream status changed
The syntax is:
"650" SP "STREAM" SP StreamID SP StreamStatus SP CircID SP Target
[SP "REASON=" Reason [ SP "REMOTE_REASON=" Reason ]]
[SP "SOURCE=" Source] [ SP "SOURCE_ADDR=" Address ":" Port ]
[SP "PURPOSE=" Purpose]
StreamStatus =
"NEW" / ; New request to connect
"NEWRESOLVE" / ; New request to resolve an address
"REMAP" / ; Address re-mapped to another
"SENTCONNECT" / ; Sent a connect cell along a circuit
"SENTRESOLVE" / ; Sent a resolve cell along a circuit
"SUCCEEDED" / ; Received a reply; stream established
"FAILED" / ; Stream failed and not retriable
"CLOSED" / ; Stream closed
"DETACHED" ; Detached from circuit; still retriable
Target = Address ":" Port
The circuit ID designates which circuit this stream is attached to. If
the stream is unattached, the circuit ID "0" is given.
The "REASON" field is provided only for FAILED, CLOSED, and DETACHED
events, and only if extended events are enabled (see 3.19). Clients MUST
accept reasons not listed above. Reasons are as given in tor-spec.txt,
except for:
END (We received a RELAY_END cell from the other side of this
PRIVATE_ADDR (The client tried to connect to a private address like or over Tor.)
[XXXX document more. -NM]
The "REMOTE_REASON" field is provided only when we receive a RELAY_END
cell, and only if extended events are enabled. It contains the actual
reason given by the remote OR for closing the stream. Clients MUST accept
reasons not listed above. Reasons are as listed in tor-spec.txt.
"REMAP" events include a Source if extended events are enabled:
Source = "CACHE" / "EXIT"
Clients MUST accept sources not listed above. "CACHE" is given if
the Tor client decided to remap the address because of a cached
answer, and "EXIT" is given if the remote node we queried gave us
the new address as a response.
The "SOURCE_ADDR" field is included with NEW and NEWRESOLVE events if
extended events are enabled. It indicates the address and port
that requested the connection, and can be (e.g.) used to look up the
requesting program.
The "PURPOSE" field is provided only for NEW and NEWRESOLVE events, and
only if extended events are enabled (see 3.19). Clients MUST accept
purposes not listed above.
4.1.3. OR Connection status changed
The syntax is:
"650" SP "ORCONN" SP (LongName / Target) SP ORStatus [ SP "REASON="
Reason ] [ SP "NCIRCS=" NumCircuits ] CRLF
; In Tor versions through with feature
; VERBOSE_NAMES turned off and before version, OR
; Connection is as follows:
"650" SP "ORCONN" SP (ServerID / Target) SP ORStatus [ SP "REASON="
Reason ] [ SP "NCIRCS=" NumCircuits ] CRLF
NEW is for incoming connections, and LAUNCHED is for outgoing
connections. CONNECTED means the TLS handshake has finished (in
either direction). FAILED means a connection is being closed that
hasn't finished its handshake, and CLOSED is for connections that
have handshaked.
A LongName or ServerID is specified unless it's a NEW connection, in
which case we don't know what server it is yet, so we use Address:Port.
If extended events are enabled (see 3.19), optional reason and
circuit counting information is provided for CLOSED and FAILED
NumCircuits counts both established and pending circuits.
4.1.4. Bandwidth used in the last second
The syntax is:
"650" SP "BW" SP BytesRead SP BytesWritten *(SP Type "=" Num) CRLF
BytesRead = 1*DIGIT
BytesWritten = 1*DIGIT
Type = "DIR" / "OR" / "EXIT" / "APP" / ...
Num = 1*DIGIT
BytesRead and BytesWritten are the totals. [In a future Tor version,
we may also include a breakdown of the connection types that used
bandwidth this second (not implemented yet).]
4.1.5. Log messages
The syntax is:
"650" SP Severity SP ReplyText CRLF
"650+" Severity CRLF Data 650 SP "OK" CRLF
Severity = "DEBUG" / "INFO" / "NOTICE" / "WARN"/ "ERR"
4.1.6. New descriptors available
"650" SP "NEWDESC" 1*(SP LongName) CRLF
; In Tor versions through with feature
; VERBOSE_NAMES turned off and before version, it
; is as follows:
"650" SP "NEWDESC" 1*(SP ServerID) CRLF
4.1.7. New Address mapping
"650" SP "ADDRMAP" SP Address SP NewAddress SP Expiry
[SP Error] SP GMTExpiry CRLF
NewAddress = Address / "<error>"
Error = "error=" ErrorCode
ErrorCode = XXXX
Error and GMTExpiry are only provided if extended events are enabled.
Expiry is expressed as the local time (rather than GMT). This is a bug,
left in for backward compatibility; new code should look at GMTExpiry
These events are generated when a new address mapping is entered in the
cache, or when the answer for a RESOLVE command is found.
4.1.8. Descriptors uploaded to us in our role as authoritative dirserver
"650" "+" "AUTHDIR_NEWDESCS" CRLF Action CRLF Message CRLF
Descriptor CRLF "." CRLF "650" SP "OK" CRLF
Message = Text
4.1.9. Our descriptor changed
[First added in]
4.1.10. Status events
based on occurrences in the Tor process pertaining to the general state of
the program. Generally, they correspond to log messages of severity Notice
or higher. They differ from log messages in that their format is a
specified interface.
"650" SP StatusType SP StatusSeverity SP StatusAction
[SP StatusArguments] CRLF
StatusSeverity = "NOTICE" / "WARN" / "ERR"
StatusAction = 1*ALPHA
StatusArguments = StatusArgument *(SP StatusArgument)
StatusArgument = StatusKeyword '=' StatusValue
StatusKeyword = 1*(ALNUM / "_")
StatusValue = 1*(ALNUM / '_') / QuotedString
StatusAction is a string, and StatusArguments is a series of
keyword=value pairs on the same line. Values may be space-terminated
strings, or quoted strings.
These events are always produced with EXTENDED_EVENTS and
VERBOSE_NAMES; see the explanations in the USEFEATURE section
for details.
Controllers MUST tolerate unrecognized actions, MUST tolerate
unrecognized arguments, MUST tolerate missing arguments, and MUST
tolerate arguments that arrive in any order.
Each event description below is accompanied by a recommendation for
controllers. These recommendations are suggestions only; no controller
is required to implement them.
Compatibility note: versions of Tor before incorrectly
generated "STATUS_SERVER" as "STATUS_SEVER". To be compatible with those
versions, tools should accept both.
Actions for STATUS_GENERAL events can be as follows:
Tor spent enough time without CPU cycles that it has closed all
its circuits and will establish them anew. This typically
happens when a laptop goes to sleep and then wakes up again. It
also happens when the system is swapping so heavily that Tor is
starving. The "time" argument specifies the number of seconds Tor
thinks it was unconscious for (or alternatively, the number of
seconds it went back in time).
This status event is sent as NOTICE severity normally, but WARN
severity if Tor is acting as a server currently.
{Recommendation for controller: ignore it, since we don't really
know what the user should do anyway. Hm.}
"RECOMMENDED=\"version, version, ...\""
Tor has found that directory servers don't recommend its version of
the Tor software. RECOMMENDED is a comma-and-space-separated string
of Tor versions that are recommended. REASON is NEW if this version
of Tor is newer than any recommended version, OBSOLETE if
this version of Tor is older than any recommended version, and
UNRECOMMENDED if some recommended versions of Tor are newer and
some are older than this version. (The "OBSOLETE" reason was called
"OLD" from Tor up to and including
{Controllers may want to suggest that the user upgrade OLD or
UNRECOMMENDED versions. NEW versions may be known-insecure, or may
simply be development versions.}
Tor has reached its ulimit -n or whatever the native limit is on file
descriptors or sockets. CURRENT is the number of sockets Tor
currently has open. The user should really do something about
this. The "current" argument shows the number of connections currently
{Controllers may recommend that the user increase the limit, or
increase it for them. Recommendations should be phrased in an
OS-appropriate way and automated when possible.}
Tor has encountered a situation that its developers never expected,
and the developers would like to learn that it happened. Perhaps
the controller can explain this to the user and encourage her to
file a bug report?
{Controllers should log bugs, but shouldn't annoy the user in case a
bug appears frequently.}
SKEW="+" / "-" SECONDS
"OR:" IP ":" Port /
If "SKEW" is present, it's an estimate of how far we are from the
time declared in the source. (In other words, if we're an hour in
the past, the value is -3600.) "MIN_SKEW" is present, it's a lower
bound. If the source is a DIRSERV, we got the current time from a
connection to a dirserver. If the source is a NETWORKSTATUS, we
decided we're skewed because we got a v2 networkstatus from far in
the future. If the source is OR, the skew comes from a NETINFO
cell from a connection to another relay. If the source is
CONSENSUS, we decided we're skewed because we got a networkstatus
consensus from the future.
{Tor should send this message to controllers when it thinks the
skew is so high that it will interfere with proper Tor operation.
Controllers shouldn't blindly adjust the clock, since the more
accurate source of skew info (DIRSERV) is currently
"METHOD=" libevent method
"VERSION=" libevent version
Tor knows about bugs in using the configured event method in this
version of libevent. "BROKEN" libevents won't work at all;
"BUGGY" libevents might work okay; "SLOW" libevents will work
fine, but not quickly. If "RECOVERED" is YES, Tor managed to
switch to a more reliable (but probably slower!) libevent method.
{Controllers may want to warn the user if this event occurs, though
generally it's the fault of whoever built the Tor binary and there's
not much the user can do besides upgrade libevent or upgrade the
Tor believes that none of the known directory servers are
reachable -- this is most likely because the local network is
down or otherwise not working, and might help to explain for the
user why Tor appears to be broken.
{Controllers may want to warn the user if this event occurs; further
action is generally not possible.}
Tor has received and validated a new consensus networkstatus.
(This event can be delayed a little while after the consensus
is received, if Tor needs to fetch certificates.)
Actions for STATUS_CLIENT events can be as follows:
"TAG=" Keyword
"SUMMARY=" String
["WARNING=" String
"REASON=" Keyword
"COUNT=" num
Tor has made some progress at establishing a connection to the
Tor network, fetching directory information, or making its first
circuit; or it has encountered a problem while bootstrapping. This
status event is especially useful for users with slow connections
or with connectivity problems.
"Progress" gives a number between 0 and 100 for how far through
the bootstrapping process we are. "Summary" is a string that can
be displayed to the user to describe the *next* task that Tor
will tackle, i.e., the task it is working on after sending the
status event. "Tag" is a string that controllers can use to
recognize bootstrap phases, if they want to do something smarter
than just blindly displaying the summary string; see Section 5
for the current tags that Tor issues.
The StatusSeverity describes whether this is a normal bootstrap
phase (severity notice) or an indication of a bootstrapping
problem (severity warn).
For bootstrap problems, we include the same progress, tag, and
summary values as we would for a normal bootstrap event, but we
also include "warning", "reason", "count", and "recommendation"
key/value combos. The "count" number tells how many bootstrap
problems there have been so far at this phase. The "reason"
string lists one of the reasons allowed in the ORCONN event. The
"warning" argument string with any hints Tor has to offer about
why it's having troubles bootstrapping.
The "reason" values are long-term-stable controller-facing tags to
identify particular issues in a bootstrapping step. The warning
strings, on the other hand, are human-readable. Controllers
SHOULD NOT rely on the format of any warning string. Currently
the possible values for "recommendation" are either "ignore" or
"warn" -- if ignore, the controller can accumulate the string in
a pile of problems to show the user if the user asks; if warn,
the controller should alert the user that Tor is pretty sure
there's a bootstrapping problem.
Currently Tor uses recommendation=ignore for the first
nine bootstrap problem reports for a given phase, and then
uses recommendation=warn for subsequent problems at that
phase. Hopefully this is a good balance between tolerating
occasional errors and reporting serious problems quickly.
Tor now knows enough network-status documents and enough server
descriptors that it's going to start trying to build circuits now.
{Controllers may want to use this event to decide when to indicate
progress to their users, but should not interrupt the user's browsing
to tell them so.}
We discarded expired statuses and router descriptors to fall
below the desired threshold of directory information. We won't
try to build any circuits until ENOUGH_DIR_INFO occurs again.
{Controllers may want to use this event to decide when to indicate
progress to their users, but should not interrupt the user's browsing
to tell them so.}
Tor is able to establish circuits for client use. This event will
only be sent if we just built a circuit that changed our mind --
that is, prior to this event we didn't know whether we could
establish circuits.
{Suggested use: controllers can notify their users that Tor is
ready for use as a client once they see this status event. [Perhaps
controllers should also have a timeout if too much time passes and
this event hasn't arrived, to give tips on how to troubleshoot.
On the other hand, hopefully Tor will send further status events
if it can identify the problem.]}
We are no longer confident that we can build circuits. The "reason"
keyword provides an explanation: which other status event type caused
our lack of confidence.
{Controllers may want to use this event to decide when to indicate
progress to their users, but should not interrupt the user's browsing
to do so.}
[Note: only REASON=CLOCK_JUMPED is implemented currently.]
"PORT=" port
A stream was initiated to a port that's commonly used for
vulnerable-plaintext protocols. If the Result is "reject", we
refused the connection; whereas if it's "warn", we allowed it.
{Controllers should warn their users when this occurs, unless they
happen to know that the application using Tor is in fact doing so
correctly (e.g., because it is part of a distributed bundle). They
might also want some sort of interface to let the user configure
their RejectPlaintextPorts and WarnPlaintextPorts config options.}
"ADDRESS=" IP:port
A connection was made to Tor's SOCKS port using one of the SOCKS
approaches that doesn't support hostnames -- only raw IP addresses.
If the client application got this address from gethostbyname(),
it may be leaking target addresses via DNS.
{Controllers should warn their users when this occurs, unless they
happen to know that the application using Tor is in fact doing so
correctly (e.g., because it is part of a distributed bundle).}
A connection was made to Tor's SOCKS port that tried to use it
for something other than the SOCKS protocol. Perhaps the user is
using Tor as an HTTP proxy? The DATA is the first few characters
sent to Tor on the SOCKS port.
{Controllers may want to warn their users when this occurs: it
indicates a misconfigured application.}
Some application gave us a funny-looking hostname. Perhaps
it is broken? In any case it won't work with Tor and the user
should know.
{Controllers may want to warn their users when this occurs: it
usually indicates a misconfigured application.}
Actions for STATUS_SERVER can be as follows:
Our best idea for our externally visible IP has changed to 'IP'.
If 'HOSTNAME' is present, we got the new IP by resolving 'NAME'. If the
method is 'CONFIGURED', the IP was given verbatim as a configuration
option. If the method is 'RESOLVED', we resolved the Address
configuration option to get the IP. If the method is 'GETHOSTNAME',
we resolved our hostname to get the IP. If the method is 'INTERFACE',
we got the address of one of our network interfaces to get the IP. If
the method is 'DIRSERV', a directory server told us a guess for what
our IP might be.
{Controllers may want to record this info and display it to the user.}
We're going to start testing the reachability of our external OR port
or directory port.
{This event could affect the controller's idea of server status, but
the controller should not interrupt the user to tell them so.}
We successfully verified the reachability of our external OR port or
directory port (depending on which of ORADDRESS or DIRADDRESS is
{This event could affect the controller's idea of server status, but
the controller should not interrupt the user to tell them so.}
We successfully uploaded our server descriptor to at least one
of the directory authorities, with no complaints.
{Originally, the goal of this event was to declare "every authority
has accepted the descriptor, so there will be no complaints
about it." But since some authorities might be offline, it's
harder to get certainty than we had thought. As such, this event
is equivalent to ACCEPTED_SERVER_DESCRIPTOR below. Controllers
should just look at ACCEPTED_SERVER_DESCRIPTOR and should ignore
this event for now.}
We just got a new networkstatus consensus, and whether we're in
it or not in it has changed. Specifically, status is "listed"
if we're listed in it but previous to this point we didn't know
we were listed in a consensus; and status is "unlisted" if we
thought we should have been listed in it (e.g. we were listed in
the last one), but we're not.
{Moving from listed to unlisted is not necessarily cause for
alarm. The relay might have failed a few reachability tests,
or the Internet might have had some routing problems. So this
feature is mainly to let relay operators know when their relay
has successfully been listed in the consensus.}
[Not implemented yet. We should do this in 0.2.2.x. -RD]
"ERR=" message
One of our nameservers has changed status.
{This event could affect the controller's idea of server status, but
the controller should not interrupt the user to tell them so.}
All of our nameservers have gone down.
{This is a problem; if it happens often without the nameservers
coming up again, the user needs to configure more or better
Our DNS provider is providing an address when it should be saying
"NOTFOUND"; Tor will treat the address as a synonym for "NOTFOUND".
{This is an annoyance; controllers may want to tell admins that their
DNS provider is not to be trusted.}
Our DNS provider is giving a hijacked address instead of well-known
websites; Tor will not try to be an exit node.
{Controllers could warn the admin if the relay is running as an
exit node: the admin needs to configure a good DNS server.
Alternatively, this happens a lot in some restrictive environments
(hotels, universities, coffeeshops) when the user hasn't registered.}
A directory authority rejected our descriptor. Possible reasons
include malformed descriptors, incorrect keys, highly skewed clocks,
and so on.
{Controllers should warn the admin, and try to cope if they can.}
A single directory authority accepted our descriptor.
// actually notice
{This event could affect the controller's idea of server status, but
the controller should not interrupt the user to tell them so.}
We failed to connect to our external OR port or directory port
{This event could affect the controller's idea of server status. The
controller should warn the admin and suggest reasonable steps to take.}
4.1.11. Our set of guard nodes has changed
"650" SP "GUARD" SP Type SP Name SP Status ... CRLF
Type = "ENTRY"
Name = The (possibly verbose) nickname of the guard affected.
Status = "NEW" | "UP" | "DOWN" | "BAD" | "GOOD" | "DROPPED"
[explain states. XXX]
4.1.12. Network status has changed
"650" "+" "NS" CRLF 1*NetworkStatus "." CRLF "650" SP "OK" CRLF
The event is used whenever our local view of a relay status changes.
This happens when we get a new v3 consensus (in which case the entries
we see are a duplicate of what we see in the NEWCONSENSUS event,
below), but it also happens when we decide to mark a relay as up or
down in our local status, for example based on connection attempts.
[First added in]
4.1.13. Bandwidth used on an application stream
The syntax is:
"650" SP "STREAM_BW" SP StreamID SP BytesWritten SP BytesRead CRLF
BytesWritten = 1*DIGIT
BytesRead = 1*DIGIT
BytesWritten and BytesRead are the number of bytes written and read
by the application since the last STREAM_BW event on this stream.
Note that from Tor's perspective, *reading* a byte on a stream means
that the application *wrote* the byte. That's why the order of "written"
vs "read" is opposite for stream_bw events compared to bw events.
These events are generated about once per second per stream; no events
are generated for streams that have not written or read. These events
apply only to streams entering Tor (such as on a SOCKSPort, TransPort,
or so on). They are not generated for exiting streams.
4.1.14. Per-country client stats
The syntax is:
"650" SP "CLIENTS_SEEN" SP TimeStarted SP CountrySummary CRLF
We just generated a new summary of which countries we've seen clients
from recently. The controller could display this for the user, e.g.
in their "relay" configuration window, to give them a sense that they
are actually being useful.
Currently only bridge relays will receive this event, but once we figure
out how to sufficiently aggregate and sanitize the client counts on
main relays, we might start sending these events in other cases too.
TimeStarted is a quoted string indicating when the reported summary
counts from (in GMT).
The CountrySummary keyword has as its argument a comma-separated,
possibly empty set of "countrycode=count" pairs. For example (without
650-CLIENTS_SEEN TimeStarted="2008-12-25 23:50:43"
4.1.15. New consensus networkstatus has arrived
The syntax is:
"650" "+" "NEWCONSENSUS" CRLF 1*NetworkStatus "." CRLF "650" SP
A new consensus networkstatus has arrived. We include NS-style lines for
every relay in the consensus. NEWCONSENSUS is a separate event from the
NS event, because the list here represents every usable relay: so any
relay *not* mentioned in this list is implicitly no longer recommended.
[First added in]
4.1.16. New circuit buildtime has been set
The syntax is:
"TIMEOUT_MS=" Timeout SP "XM=" Xm SP "ALPHA=" Alpha SP
"CLOSE_MS=" CloseTimeout SP "CLOSE_RATE=" CloseRate
Total = Integer count of timeouts stored
Timeout = Integer timeout in milliseconds
Xm = Estimated integer Pareto parameter Xm in milliseconds
Alpha = Estimated floating point Paredo paremter alpha
Quantile = Floating point CDF quantile cutoff point for this timeout
TimeoutRate = Floating point ratio of circuits that timeout
CloseTimeout = How long to keep measurement circs in milliseconds
CloseRate = Floating point ratio of measurement circuits that are closed
A new circuit build timeout time has been set. If Type is "COMPUTED",
Tor has computed the value based on historical data. If Type is "RESET",
initialization or drastic network changes have caused Tor to reset
the timeout back to the default, to relearn again. If Type is
"SUSPENDED", Tor has detected a loss of network connectivity and has
temporarily changed the timeout value to the default until the network
recovers. If type is "DISCARD", Tor has decided to discard timeout
values that likely happened while the network was down. If type is
"RESUME", Tor has decided to resume timeout calculation.
The Total value is the count of circuit build times Tor used in
computing this value. It is capped internally at the maximum number
of build times Tor stores (NCIRCUITS_TO_OBSERVE).
The Timeout itself is provided in milliseconds. Internally, Tor rounds
this value to the nearest second before using it.
[First added in]
4.1.17. Signal received
The syntax is:
"650" SP "SIGNAL" SP Signal CRLF
A signal has been received and actions taken by Tor. The meaning of each
signal, and the mapping to Unix signals, is as defined in section 3.7.
Future versions of Tor MAY generate signals other than those listed here;
controllers MUST be able to accept them.
If Tor chose to ignore a signal (such as NEWNYM), this event will not be
sent. Note that some options (like ReloadTorrcOnSIGHUP) may affect the
semantics of the signals here.
Note that the HALT (SIGTERM) and SHUTDOWN (SIGINT) signals do not currently
generate any event.
[First added in]
4.1.18. Configuration changed
The syntax is:
StartReplyLine *(MidReplyLine) EndReplyLine
StartReplyLine = "650-CONF_CHANGED" CRLF
MidReplyLine = "650-" KEYWORD ["=" VALUE] CRLF
EndReplyLine = "650 OK"
Tor configuration options have changed (such as via a SETCONF or RELOAD
signal). KEYWORD and VALUE specify the configuration option that was changed.
Undefined configuration options contain only the KEYWORD.
4.1.19. Circuit status changed slightly
The syntax is:
"650" SP "CIRC_MINOR" SP CircuitID SP CircEvent [SP Path]
[SP "BUILD_FLAGS=" BuildFlags] [SP "PURPOSE=" Purpose]
[SP "HS_STATE=" HSState] [SP "REND_QUERY=" HSAddress]
[SP "TIME_CREATED=" TimeCreated]
CircEvent =
"PURPOSE_CHANGED" / ; circuit purpose or HS-related state changed
"CANNIBALIZED" ; circuit cannibalized
Clients MUST accept circuit events not listed above.
The "OLD_PURPOSE" field is provided for both PURPOSE_CHANGED and
CANNIBALIZED events. The "OLD_HS_STATE" field is provided whenever
the "OLD_PURPOSE" field is provided and is a hidden-service-related
Other fields are as specified in section 4.1.1 above.
[First added in]
5. Implementation notes
5.1. Authentication
If the control port is open and no authentication operation is enabled, Tor
trusts any local user that connects to the control port. This is generally
a poor idea.
If the 'CookieAuthentication' option is true, Tor writes a "magic
cookie" file named "control_auth_cookie" into its data directory (or
to another file specified in the 'CookieAuthFile' option). To
authenticate, the controller must demonstrate that it can read the
contents of the cookie file:
* Current versions of Tor support cookie authentication
using the "COOKIE" authentication method: the controller sends the
contents of the cookie file, encoded in hexadecimal. This
authentication method exposes the user running a controller to an
unintended information disclosure attack whenever the controller
has greater filesystem read access than the process that it has
connected to. (Note that a controller may connect to a process
other than Tor.) It is almost never safe to use, even if the
controller's user has explicitly specified which filename to read
an authentication cookie from. For this reason, the COOKIE
authentication method has been deprecated and will be removed from
Tor before some future version of Tor.
* 0.2.2.x versions of Tor starting with, and all versions of
Tor after, support cookie authentication using the
"SAFECOOKIE" authentication method, which discloses much less
information about the contents of the cookie file.
If the 'HashedControlPassword' option is set, it must contain the salted
hash of a secret password. The salted hash is computed according to the
S2K algorithm in RFC 2440 (OpenPGP), and prefixed with the s2k specifier.
This is then encoded in hexadecimal, prefixed by the indicator sequence
"16:". Thus, for example, the password 'foo' could encode to:
salt hashed value
You can generate the salt of a password by calling
'tor --hash-password <password>'
or by using the example code in the Python and Java controller libraries.
To authenticate under this scheme, the controller sends Tor the original
secret that was used to generate the password, either as a quoted string
or encoded in hexadecimal.
5.2. Don't let the buffer get too big.
If you ask for lots of events, and 16MB of them queue up on the buffer,
the Tor process will close the socket.
5.3. Backward compatibility with v0 control protocol.
The 'version 0' control protocol was replaced in Tor 0.1.1.x. Support
was removed in Tor 0.2.0.x. Every non-obsolete version of Tor now
supports the version 1 control protocol.
For backward compatibility with the "version 0" control protocol,
Tor used to check whether the third octet of the first command is zero.
(If it was, Tor assumed that version 0 is in use.)
This compatibility was removed in Tor and
5.4. Tor config options for use by controllers
Tor provides a few special configuration options for use by controllers.
These options can be set and examined by the SETCONF and GETCONF commands,
but are not saved to disk by SAVECONF.
Generally, these options make Tor unusable by disabling a portion of Tor's
normal operations. Unless a controller provides replacement functionality
to fill this gap, Tor will not correctly handle user requests.
If true, Tor will try to launch all directory operations through
anonymous connections. (Ordinarily, Tor only tries to anonymize
requests related to hidden services.) This option will slow down
directory access, and may stop Tor from working entirely if it does not
yet have enough directory information to build circuits.
(Boolean. Default: "0".)
If true, Tor will not launch preemptive "general-purpose" circuits for
streams to attach to. (It will still launch circuits for testing and
for hidden services.)
(Boolean. Default: "0".)
If true, Tor will not automatically attach new streams to circuits;
instead, the controller must attach them with ATTACHSTREAM. If the
controller does not attach the streams, their data will never be routed.
(Boolean. Default: "0".)
As HashedControlPassword, but is not saved to the torrc file by
SAVECONF. Added in Tor
If this option is true (the default), we reload the torrc from disk
every time we get a SIGHUP (from the controller or via a signal).
Otherwise, we don't. This option exists so that controllers can keep
their options from getting overwritten when a user sends Tor a HUP for
some other reason (for example, to rotate the logs).
(Boolean. Default: "1")
If this option is set to a process ID, Tor will periodically check
whether a process with the specified PID exists, and exit if one
does not. Added in Tor This option's intended use
is documented in section 3.23 with the related TAKEOWNERSHIP
Note that this option can only specify a single process ID, unlike
the TAKEOWNERSHIP command which can be sent along multiple control
(String. Default: unset.)
5.5. Phases from the Bootstrap status event.
This section describes the various bootstrap phases currently reported
by Tor. Controllers should not assume that the percentages and tags
listed here will continue to match up, or even that the tags will stay
in the same order. Some phases might also be skipped (not reported)
if the associated bootstrap step is already complete, or if the phase
no longer is necessary. Only "starting" and "done" are guaranteed to
exist in all future versions.
Current Tor versions enter these phases in order, monotonically.
Future Tors MAY revisit earlier stages.
Phase 0:
tag=starting summary="Starting"
Tor starts out in this phase.
Phase 5:
tag=conn_dir summary="Connecting to directory mirror"
Tor sends this event as soon as Tor has chosen a directory mirror --
e.g. one of the authorities if bootstrapping for the first time or
after a long downtime, or one of the relays listed in its cached
directory information otherwise.
Tor will stay at this phase until it has successfully established
a TCP connection with some directory mirror. Problems in this phase
generally happen because Tor doesn't have a network connection, or
because the local firewall is dropping SYN packets.
Phase 10:
tag=handshake_dir summary="Finishing handshake with directory mirror"
This event occurs when Tor establishes a TCP connection with a relay used
as a directory mirror (or its https proxy if it's using one). Tor remains
in this phase until the TLS handshake with the relay is finished.
Problems in this phase generally happen because Tor's firewall is
doing more sophisticated MITM attacks on it, or doing packet-level
keyword recognition of Tor's handshake.
Phase 15:
tag=onehop_create summary="Establishing one-hop circuit for dir info"
Once TLS is finished with a relay, Tor will send a CREATE_FAST cell
to establish a one-hop circuit for retrieving directory information.
It will remain in this phase until it receives the CREATED_FAST cell
back, indicating that the circuit is ready.
Phase 20:
tag=requesting_status summary="Asking for networkstatus consensus"
Once we've finished our one-hop circuit, we will start a new stream
for fetching the networkstatus consensus. We'll stay in this phase
until we get the 'connected' relay cell back, indicating that we've
established a directory connection.
Phase 25:
tag=loading_status summary="Loading networkstatus consensus"
Once we've established a directory connection, we will start fetching
the networkstatus consensus document. This could take a while; this
phase is a good opportunity for using the "progress" keyword to indicate
partial progress.
This phase could stall if the directory mirror we picked doesn't
have a copy of the networkstatus consensus so we have to ask another,
or it does give us a copy but we don't find it valid.
Phase 40:
tag=loading_keys summary="Loading authority key certs"
Sometimes when we've finished loading the networkstatus consensus,
we find that we don't have all the authority key certificates for the
keys that signed the consensus. At that point we put the consensus we
fetched on hold and fetch the keys so we can verify the signatures.
Phase 45
tag=requesting_descriptors summary="Asking for relay descriptors"
Once we have a valid networkstatus consensus and we've checked all
its signatures, we start asking for relay descriptors. We stay in this
phase until we have received a 'connected' relay cell in response to
a request for descriptors.
Phase 50:
tag=loading_descriptors summary="Loading relay descriptors"
We will ask for relay descriptors from several different locations,
so this step will probably make up the bulk of the bootstrapping,
especially for users with slow connections. We stay in this phase until
we have descriptors for at least 1/4 of the usable relays listed in
the networkstatus consensus. This phase is also a good opportunity to
use the "progress" keyword to indicate partial steps.
Phase 80:
tag=conn_or summary="Connecting to entry guard"
Once we have a valid consensus and enough relay descriptors, we choose
some entry guards and start trying to build some circuits. This step
is similar to the "conn_dir" phase above; the only difference is
the context.
If a Tor starts with enough recent cached directory information,
its first bootstrap status event will be for the conn_or phase.
Phase 85:
tag=handshake_or summary="Finishing handshake with entry guard"
This phase is similar to the "handshake_dir" phase, but it gets reached
if we finish a TCP connection to a Tor relay and we have already reached
the "conn_or" phase. We'll stay in this phase until we complete a TLS
handshake with a Tor relay.
Phase 90:
tag=circuit_create summary="Establishing circuits"
Once we've finished our TLS handshake with an entry guard, we will
set about trying to make some 3-hop circuits in case we need them soon.
Phase 100:
tag=done summary="Done"
A full 3-hop exit circuit has been established. Tor is ready to handle
application connections now.
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