OpenVPN Management Interface Notes
----------------------------------
The OpenVPN Management interface allows OpenVPN to
be administratively controlled from an external program via
a TCP socket.
The interface has been specifically designed for GUI developers
and those who would like to programmatically or remotely control
an OpenVPN daemon.
The management interface is implemented using a client/server TCP
connection, where OpenVPN will listen on a provided IP address
and port for incoming management client connections.
The management protocol is currently cleartext without an explicit
security layer. For this reason, it is recommended that the
management interface either listen on localhost (127.0.0.1)
or on the local VPN address. It's possible to remotely connect
to the management interface over the VPN itself, though some
capabilities will be limited in this mode, such as the ability
to provide private key passwords.
Future versions of the management interface may allow out-of-band
connections (i.e. not over the VPN) and secured with SSL/TLS.
The management interface is enabled in the OpenVPN
configuration file using the following directive:
--management
See the man page for documentation on this and related
directives.
Once OpenVPN has started with the management layer enabled,
you can telnet to the management port (make sure to use
a telnet client which understands "raw" mode).
Once connected to the management port, you can use
the "help" command to list all commands.
COMMAND -- echo
---------------
The echo capability is used to allow GUI-specific
parameters to be either embedded in the OpenVPN config file
or pushed to an OpenVPN client from a server.
Command examples:
echo on -- turn on real-time notification of echo messages
echo all -- print the current echo history list
echo off -- turn off real-time notification of echo messages
echo on all -- atomically enable real-time notification,
plus show any messages in history buffer
For example, suppose you are developing a OpenVPN GUI and
you want to give the OpenVPN server the ability to ask
the GUI to forget any saved passwords.
In the OpenVPN server config file, add:
push "echo forget-passwords"
When the OpenVPN client receives its pulled list of directives
from the server, the "echo forget-passwords" directive will
be in the list, and it will cause the management interface
to save the "forget-passwords" string in its list of echo
parameters.
The management client can use "echo all" to output the full
list of echoed parameters, "echo on" to turn on real-time
notification of echoed parameters via the ">ECHO:" prefix,
or "echo off" to turn off real-time notification.
When the GUI connects to the OpenVPN management socket, it
can issue an "echo all" command, which would produce output
like this:
1101519562,forget-passwords
END
Essentially the echo command allowed us to pass parameters from
the OpenVPN server to the OpenVPN client, and then to the
management client (such as a GUI). The large integer is the
unix date/time when the echo parameter was received.
If the management client had issued the command "echo on",
it would have enabled real-time notifications of echo
parameters. In this case, our "forget-passwords" message
would be output like this:
>ECHO:1101519562,forget-passwords
Like the log command, the echo command can atomically show
history while simultaneously activating real-time updates:
echo on all
The size of the echo buffer is currently hardcoded to 100
messages.
COMMAND -- exit, quit
---------------------
Close the managment session, and resume listening on the
management port for connections from other clients. Currently,
the OpenVPN daemon can at most support a single management client
any one time.
COMMAND -- help
---------------
Print a summary of commands.
COMMAND -- hold
---------------
The hold command can be used to manipulate the hold flag,
or release OpenVPN from a hold state.
If the hold flag is set on initial startup or
restart, OpenVPN will hibernate prior to initializing
the tunnel until the management interface receives
a "hold release" command.
The --management-hold directive of OpenVPN can be used
to start OpenVPN with the hold flag set.
The hold flag setting is persistent and will not
be reset by restarts.
OpenVPN will indicate that it is in a hold state by
sending a real-time notification to the management
client:
>HOLD:Waiting for hold release
Command examples:
hold -- show current hold flag, 0=off, 1=on.
hold on -- turn on hold flag so that future restarts
will hold.
hold off -- turn off hold flag so that future restarts will
not hold.
hold release -- leave hold state and start OpenVPN, but
do not alter the current hold flag setting.
COMMAND -- kill
---------------
In server mode, kill a particlar client instance.
Command examples:
kill Test-Client -- kill the client instance having a
common name of "Test-Client".
kill 1.2.3.4:4000 -- kill the client instance having a
source address and port of 1.2.3.4:4000
Use the "status" command to see which clients are connected.
COMMAND -- log
--------------
Show the OpenVPN log file. Only the most recent n lines
of the log file are cached by the management interface, where
n is controlled by the OpenVPN --management-log-cache directive.
Command examples:
log on -- Enable real-time output of log messages.
log all -- Show currently cached log file history.
log on all -- Atomically show all currently cached log file
history then enable real-time notification of
new log file messages.
log off -- Turn off real-time notification of log messages.
log 20 -- Show the most recent 20 lines of log file history.
Real-time notification format:
Real-time log messages begin with the ">LOG:" prefix followed
by the following comma-separated fields:
(a) unix integer date/time,
(b) zero or more message flags in a single string:
I -- informational
F -- fatal error
N -- non-fatal error
W -- warning
D -- debug, and
(c) message text.
COMMAND -- mute
---------------
Change the OpenVPN --mute parameter. The mute parameter is
used to silence repeating messages of the same message
category.
Command examples:
mute 40 -- change the mute parameter to 40
mute -- show the current mute setting
COMMAND -- net
--------------
(Windows Only) Produce output equivalent to the OpenVPN
--show-net directive. The output includes OpenVPN's view
of the system network adapter list and routing table based
on information returned by the Windows IP helper API.
COMMAND -- password and username
--------------------------------
The password command is used to pass passwords to OpenVPN.
If OpenVPN is run with the --management-query-passwords
directive, it will query the management interface for RSA
private key passwords and the --auth-user-pass
username/password.
When OpenVPN needs a password from the management interface,
it will produce a real-time ">PASSWORD:" message.
Example 1:
>PASSWORD:Need 'Private Key' password
OpenVPN is indicating that it needs a password of type
"Private Key".
The management client should respond to this query as follows:
password "Private Key" foo
Example 2:
>PASSWORD:Need 'Auth' username/password
OpenVPN needs a --auth-user-pass password. The management
client should respond:
username "Auth" foo
password "Auth" bar
The username/password itself can be in quotes, and special
characters such as double quote or backslash must be escaped,
for example,
password "Private Key" "foo\"bar"
The escaping rules are the same as for the config file.
See the "Command Parsing" section below for more info.
The PASSWORD real-time message type can also be used to
indicate password or other types of authentication failure:
Example 3: The private key password is incorrect and OpenVPN
is exiting:
>PASSWORD:Verification Failed: 'Private Key'
Example 4: The --auth-user-pass username/password failed,
and OpenVPN is exiting:
>PASSWORD:Verification Failed: 'Auth'
COMMAND -- forget-passwords
---------------------------
The forget-passwords command will cause the daemon to forget passwords
entered during the session.
Command example:
forget-passwords -- forget passwords entered so far.
COMMAND -- signal
-----------------
The signal command will send a signal to the OpenVPN daemon.
The signal can be one of SIGHUP, SIGTERM, SIGUSR1, or SIGUSR2.
Command example:
signal SIGUSR1 -- send a SIGUSR1 signal to daemon
COMMAND -- state
----------------
Show the current OpenVPN state, show state history, or
enable real-time notification of state changes.
These are the OpenVPN states:
CONNECTING -- OpenVPN's initial state.
WAIT -- (Client only) Waiting for initial response
from server.
AUTH -- (Client only) Authenticating with server.
GET_CONFIG -- (Client only) Downloading configuration options
from server.
ASSIGN_IP -- Assigning IP address to virtual network
interface.
ADD_ROUTES -- Adding routes to system.
CONNECTED -- Initialization Sequence Completed.
RECONNECTING -- A restart has occurred.
EXITING -- A graceful exit is in progress.
Command examples:
state -- Print current OpenVPN state.
state on -- Enable real-time notification of state changes.
state off -- Disable real-time notification of state changes.
state all -- Print current state history.
state 3 -- Print the 3 most recent state transitions.
state on all -- Atomically show state history while at the
same time enable real-time state notification
of future state transitions.
The output format consists of 4 comma-separated parameters:
(a) the integer unix date/time,
(b) the state name,
(c) optional descriptive string (used mostly on RECONNECTING
and EXITING to show the reason for the disconnect),
(d) optional TUN/TAP local IP address (shown for ASSIGN_IP
and CONNECTED), and
(e) optional address of remote server (OpenVPN 2.1 or higher).
Real-time state notifications will have a ">STATE:" prefix
prepended to them.
COMMAND -- status
-----------------
Show current daemon status information, in the same format as
that produced by the OpenVPN --status directive.
Command examples:
status -- Show status information using the default status
format version.
status 2 -- Show status information using status format version 2.
COMMAND -- username
-------------------
See the "password" section above.
COMMAND -- verb
---------------
Change the OpenVPN --verb parameter. The verb parameter
controls the output verbosity, and may range from 0 (no output)
to 15 (maximum output). See the OpenVPN man page for additional
info on verbosity levels.
Command examples:
verb 4 -- change the verb parameter to 4
mute -- show the current verb setting
COMMAND -- version
------------------
Show the current OpenVPN and Management Interface versions.
COMMAND -- auth-retry
---------------------
Set the --auth-retry setting to control how OpenVPN responds to
username/password authentication errors. See the manual page
for more info.
Command examples:
auth-retry interact -- Don't exit when bad username/passwords are entered.
Query for new input and retry.
COMMAND -- needok (OpenVPN 2.1 or higher)
------------------------------------------
Confirm a ">NEED-OK" real-time notification, normally used by
OpenVPN to block while waiting for a specific user action.
Example:
OpenVPN needs the user to insert a cryptographic token,
so it sends a real-time notification:
>NEED-OK:Need 'token-insertion-request' confirmation MSG:Please insert your cryptographic token
The management client, if it is a GUI, can flash a dialog
box containing the text after the "MSG:" marker to the user.
When the user acknowledges the dialog box,
the management client can issue this command:
needok token-insertion-request ok
or
needok token-insertion-request cancel
COMMAND -- needstr (OpenVPN 2.1 or higher)
-------------------------------------------
Confirm a ">NEED-STR" real-time notification, normally used by
OpenVPN to block while waiting for a specific user input.
Example:
OpenVPN needs the user to specify some input, so it sends a
real-time notification:
>NEED-STR:Need 'name' input MSG:Please specify your name
The management client, if it is a GUI, can flash a dialog
box containing the text after the "MSG:" marker to the user.
When the user acknowledges the dialog box,
the management client can issue this command:
needstr name "John"
COMMAND -- pkcs11-id-count (OpenVPN 2.1 or higher)
---------------------------------------------------
Retrieve available number of certificates.
Example:
pkcs11-id-count
>PKCS11ID-COUNT:5
COMMAND -- pkcs11-id-get (OpenVPN 2.1 or higher)
-------------------------------------------------
Retrieve certificate by index, the ID string should be provided
as PKCS#11 identity, the blob is BASE64 encoded certificate.
Example:
pkcs11-id-get 1
PKCS11ID-ENTRY:'1', ID:'<snip>', BLOB:'<snip>'
COMMAND -- client-auth (OpenVPN 2.1 or higher)
-----------------------------------------------
Authorize a ">CLIENT:CONNECT" or ">CLIENT:REAUTH" request and specify
"client-connect" configuration directives in a subsequent text block.
The OpenVPN server should have been started with the
--management-client-auth directive so that it will ask the management
interface to approve client connections.
client-auth {CID} {KID}
line_1
line_2
...
line_n
END
CID,KID -- client ID and Key ID. See documentation for ">CLIENT:"
notification for more info.
line_1 to line_n -- client-connect configuration text block, as would be
returned by a --client-connect script. The text block may be null, with
"END" immediately following the "client-auth" line (using a null text
block is equivalent to using the client-auth-nt command).
A client-connect configuration text block contains OpenVPN directives
that will be applied to the client instance object representing a newly
connected client.
COMMAND -- client-auth-nt (OpenVPN 2.1 or higher)
--------------------------------------------------
Authorize a ">CLIENT:CONNECT" or ">CLIENT:REAUTH" request without specifying
client-connect configuration text.
The OpenVPN server should have been started with the
--management-client-auth directive so that it will ask the management
interface to approve client connections.
client-auth-nt {CID} {KID}
CID,KID -- client ID and Key ID. See documentation for ">CLIENT:"
notification for more info.
COMMAND -- client-deny (OpenVPN 2.1 or higher)
-----------------------------------------------
Deny a ">CLIENT:CONNECT" or ">CLIENT:REAUTH" request.
client-deny {CID} {KID} "reason-text"
CID,KID -- client ID and Key ID. See documentation for ">CLIENT:"
notification for more info.
reason-text: a human-readable message explaining why the authentication
request was denied. This message will be output to the OpenVPN log
file or syslog.
Note that client-deny denies a specific Key ID (pertaining to a
TLS renegotiation). A client-deny command issued in response to
an initial TLS key negotiation (notified by ">CLIENT:CONNECT") will
terminate the client session after returning "AUTH-FAILED" to the client.
On the other hand, a client-deny command issued in response to
a TLS renegotiation (">CLIENT:REAUTH") will invalidate the renegotiated
key, however the TLS session associated with the currently active
key will continue to live for up to --tran-window seconds before
expiration.
To immediately kill a client session, use "client-kill".
COMMAND -- client-kill (OpenVPN 2.1 or higher)
-----------------------------------------------
Immediately kill a client instance by CID.
client-kill {CID}
CID -- client ID. See documentation for ">CLIENT:" notification for more
info.
COMMAND -- client-pf (OpenVPN 2.1 or higher)
---------------------------------------------
Push a packet filter file to a specific client.
The OpenVPN server should have been started with the
--management-client-pf directive so that it will require that
VPN tunnel packets sent or received by client instances must
conform to that client's packet filter configuration.
client-pf {CID}
line_1
line_2
...
line_n
END
CID -- client ID. See documentation for ">CLIENT:" notification for
more info.
line_1 to line_n -- the packet filter configuration file for this
client.
Packet filter file grammar:
[CLIENTS DROP|ACCEPT]
{+|-}common_name1
{+|-}common_name2
. . .
[SUBNETS DROP|ACCEPT]
{+|-}subnet1
{+|-}subnet2
. . .
[END]
Subnet: IP-ADDRESS | IP-ADDRESS/NUM_NETWORK_BITS | "unknown"
CLIENTS refers to the set of clients (by their common-name) which
this instance is allowed ('+') to connect to, or is excluded ('-')
from connecting to. Note that in the case of client-to-client
connections, such communication must be allowed by the packet filter
configuration files of both clients AND the --client-to-client
directive must have been specified in the OpenVPN server config.
SUBNETS refers to IP addresses or IP address subnets which this
client instance may connect to ('+') or is excluded ('-') from
connecting to, and applies to IPv4 and ARP packets. The special
"unknown" tag refers to packets of unknown type, i.e. a packet that
is not IPv4 or ARP.
DROP or ACCEPT defines default policy when there is no explicit match
for a common-name or subnet. The [END] tag must exist.
Notes:
* The SUBNETS section currently only supports IPv4 addresses and
subnets.
* A given client or subnet rule applies to both incoming and
outgoing packets.
* The CLIENTS list is order-invariant. Because the list is stored
as a hash-table, the order of the list does not affect its function.
* The SUBNETS table is scanned sequentially, and the first item to
match is chosen. Therefore the SUBNETS table is NOT order-invariant.
* No client-to-client communication is allowed unless the
--client-to-client configuration directive is enabled AND
the CLIENTS list of BOTH clients allows the communication.
Example packet filter spec, as transmitted to the management interface:
client-pf 42
[CLIENTS ACCEPT]
-accounting
-enigma
[SUBNETS DROP]
-10.46.79.9
+10.0.0.0/8
[END]
END
The above example sets the packet filter policy for the client
identified by CID=42. This client may connect to all other clients
except those having a common name of "accounting" or "enigma".
The client may only interact with external IP addresses in the
10.0.0.0/8 subnet, however access to 10.46.79.9 is specifically
excluded.
Another example packet filter spec, as transmitted to the
management interface:
client-pf 99
[CLIENTS DENY]
+public
[SUBNETS ACCEPT]
+10.10.0.1
-10.0.0.0/8
-unknown
[END]
END
The above example sets the packet filter policy for the client
identified by CID=99. This client may not connect to any other
clients except those having a common name of "public". It may
interact with any external IP address except those in the
10.0.0.0/8 netblock. However interaction with one address in
the 10.0.0.0/8 netblock is allowed: 10.10.0.1. Also, the client
may not interact with external IP addresses using an "unknown"
protocol (i.e. one that is not IPv4 or ARP).
OUTPUT FORMAT
-------------
(1) Command success/failure indicated by "SUCCESS: [text]" or
"ERROR: [text]".
(2) For commands which print multiple lines of output,
the last line will be "END".
(3) Real-time messages will be in the form ">[source]:[text]",
where source is "CLIENT", "ECHO", "FATAL", "HOLD", "INFO", "LOG",
"NEED-OK", "PASSWORD", or "STATE".
REAL-TIME MESSAGE FORMAT
------------------------
The OpenVPN management interface produces two kinds of
output: (a) output from a command, or (b) asynchronous,
real-time output which can be generated at any time.
Real-time messages start with a '>' character in the first
column and are immediately followed by a type keyword
indicating the type of real-time message. The following
types are currently defined:
CLIENT -- Notification of client connections and disconnections
on an OpenVPN server. Enabled when OpenVPN is started
with the --management-client-auth option. CLIENT
notifications may be multi-line. See "The CLIENT
notification" section below for detailed info.
ECHO -- Echo messages as controlled by the "echo" command.
FATAL -- A fatal error which is output to the log file just
prior to OpenVPN exiting.
HOLD -- Used to indicate that OpenVPN is in a holding state
and will not start until it receives a
"hold release" command.
INFO -- Informational messages such as the welcome message.
LOG -- Log message output as controlled by the "log" command.
NEED-OK -- OpenVPN needs the end user to do something, such as
insert a cryptographic token. The "needok" command can
be used to tell OpenVPN to continue.
NEED-STR -- OpenVPN needs information from end, such as
a certificate to use. The "needstr" command can
be used to tell OpenVPN to continue.
PASSWORD -- Used to tell the management client that OpenVPN
needs a password, also to indicate password
verification failure.
STATE -- Shows the current OpenVPN state, as controlled
by the "state" command.
The CLIENT notification
-----------------------
The ">CLIENT:" notification is enabled by the --management-client-auth
OpenVPN configuration directive that gives the management interface client
the responsibility to authenticate OpenVPN clients after their client
certificate has been verified. CLIENT notifications may be multi-line, and
the sequentiality of a given CLIENT notification, its associated environmental
variables, and the terminating ">CLIENT:ENV,END" line are guaranteed to be
atomic.
CLIENT notification types:
(1) Notify new client connection ("CONNECT") or existing client TLS session
renegotiation ("REAUTH"). Information about the client is provided
by a list of environmental variables which are documented in the OpenVPN
man page. The environmental variables passed are equivalent to those
that would be passed to an --auth-user-pass-verify script.
>CLIENT:CONNECT|REAUTH,{CID},{KID}
>CLIENT:ENV,name1=val1
>CLIENT:ENV,name2=val2
>CLIENT:ENV,...
>CLIENT:ENV,END
(2) Notify existing client disconnection. The environmental variables passed
are equivalent to those that would be passed to a --client-disconnect
script.
>CLIENT:DISCONNECT,{CID}
>CLIENT:ENV,name1=val1
>CLIENT:ENV,name2=val2
>CLIENT:ENV,...
>CLIENT:ENV,END
(3) Notify that a particular virtual address or subnet
is now associated with a specific client.
>CLIENT:ADDRESS,{CID},{ADDR},{PRI}
Variables:
CID -- Client ID, numerical ID for each connecting client, sequence = 0,1,2,...
KID -- Key ID, numerical ID for the key associated with a given client TLS session,
sequence = 0,1,2,...
PRI -- Primary (1) or Secondary (0) VPN address/subnet. All clients have at least
one primary IP address. Secondary address/subnets are associated with
client-specific "iroute" directives.
ADDR -- IPv4 address/subnet in the form 1.2.3.4 or 1.2.3.0/255.255.255.0
In the unlikely scenario of an extremely long-running OpenVPN server,
CID and KID should be assumed to recycle to 0 after (2^32)-1, however this
recycling behavior is guaranteed to be collision-free.
Command Parsing
---------------
The management interface uses the same command line lexical analyzer
as is used by the OpenVPN config file parser.
Whitespace is a parameter separator.
Double quotation or single quotation characters ("", '') can be used
to enclose parameters containing whitespace.
Backslash-based shell escaping is performed, using the following
mappings, when not in single quotations:
\\ Maps to a single backslash character (\).
\" Pass a literal doublequote character ("), don't
interpret it as enclosing a parameter.
\[SPACE] Pass a literal space or tab character, don't
interpret it as a parameter delimiter.
