MANDOS(8) | Mandos Manual | MANDOS(8) |
NAME¶
mandos - Gives encrypted passwords to authenticated Mandos clientsSYNOPSIS¶
mandos
[ --interface NAME |
-i NAME]
[ --address ADDRESS |
-a ADDRESS]
[ --port PORT | -p PORT]
[ --priority PRIORITY]
[ --servicename NAME]
[ --configdir DIRECTORY]
[ --debug]
[ --debuglevel LEVEL]
[ --no-dbus]
[ --no-ipv6]
[ --no-restore]
[ --statedir DIRECTORY]
[ --socket FD]
mandos
{ --help | -h}
mandos
--version
mandos
--check
DESCRIPTION¶
PURPOSE¶
The purpose of this is to enable remote and unattended rebooting of client host computer with an encrypted root file system. See the section called “OVERVIEW” for details.OPTIONS¶
--help, -hShow a help message and exit
--interface NAME, -i NAME
If this is specified, the server will only
announce the service and listen to requests on the specified network
interface. Default is to use all available interfaces. Note: a failure
to bind to the specified interface is not considered critical, and the server
will not exit, but instead continue normally.
--address ADDRESS, -a ADDRESS
If this option is used, the server will only
listen to the specified IPv6 address. If a link-local address is specified, an
interface should be set, since a link-local address is only valid on a single
interface. By default, the server will listen to all available addresses. If
set, this must normally be an IPv6 address; an IPv4 address can only be
specified using IPv4-mapped IPv6 address syntax:
“::FFFF:192.0.2.3”. (Only if IPv6 usage is disabled (see
below) must this be an IPv4 address.)
--port PORT, -p PORT
If this option is used, the server will bind
to that port. By default, the server will listen to an arbitrary port given by
the operating system.
--check
Run the server’s self-tests. This
includes any unit tests, etc.
--debug
If the server is run in debug mode, it will
run in the foreground and print a lot of debugging information. The default is
to not run in debug mode.
--debuglevel LEVEL
Set the debugging log level. LEVEL is a
string, one of “CRITICAL”, “ERROR”,
“WARNING”, “INFO”, or “DEBUG”, in order of
increasing verbosity. The default level is “WARNING”.
--priority PRIORITY
GnuTLS priority string for the TLS handshake.
The default is “SECURE256:!CTYPE-X.509:+CTYPE-OPENPGP”. See
gnutls_priority_init(3) for the syntax. Warning: changing this
may make the TLS handshake fail, making server-client communication
impossible.
--servicename NAME
Zeroconf service name. The default is
“Mandos”. This only needs to be changed if for some reason is
would be necessary to run more than one server on the same host. This
would not normally be useful. If there are name collisions on the same
network, the newer server will automatically rename itself to
“Mandos #2”, and so on; therefore, this option is not needed in
that case.
--configdir DIRECTORY
Directory to search for configuration files.
Default is “/etc/mandos”. See mandos.conf(5) and
mandos-clients.conf(5).
--version
Prints the program version and exit.
--no-dbus
This option controls whether the server will
provide a D-Bus system bus interface. The default is to provide such an
interface.
See also the section called “D-BUS INTERFACE”.
--no-ipv6
This option controls whether the server will
use IPv6 sockets and addresses. The default is to use IPv6. This option should
never normally be turned off, even in IPv4-only environments.
This is because mandos-client(8mandos) will normally use IPv6
link-local addresses, and will not be able to find or connect to the server if
this option is turned off. Only advanced users should consider changing
this option.
--no-restore
This option controls whether the server will
restore its state from the last time it ran. Default is to restore last state.
See also the section called “PERSISTENT STATE”.
--statedir DIRECTORY
Directory to save (and restore) state in.
Default is “/var/lib/mandos”.
--socket FD
If this option is used, the server will not
create a new network socket, but will instead use the supplied file
descriptor. By default, the server will create a new network socket.
OVERVIEW¶
This is part of the Mandos system for allowing computers to have encrypted root file systems and at the same time be capable of remote and/or unattended reboots. The computers run a small client program in the initial RAM disk environment which will communicate with a server over a network. All network communication is encrypted using TLS. The clients are identified by the server using an OpenPGP key; each client has one unique to it. The server sends the clients an encrypted password. The encrypted password is decrypted by the clients using the same OpenPGP key, and the password is then used to unlock the root file system, whereupon the computers can continue booting normally. This program is the server part. It is a normal server program and will run in a normal system environment, not in an initial RAM disk environment.NETWORK PROTOCOL¶
The Mandos server announces itself as a Zeroconf service of type “_mandos._tcp”. The Mandos client connects to the announced address and port, and sends a line of text where the first whitespace-separated field is the protocol version, which currently is “1”. The client and server then start a TLS protocol handshake with a slight quirk: the Mandos server program acts as a TLS “client” while the connecting Mandos client acts as a TLS “server”. The Mandos client must supply an OpenPGP certificate, and the fingerprint of this certificate is used by the Mandos server to look up (in a list read from clients.conf at start time) which binary blob to give the client. No other authentication or authorization is done by the server.Mandos Client | Direction | Mandos Server |
Connect | -> | |
“1\r\n” | -> | |
TLS handshake as TLS “server” | <-> | TLS handshake as TLS “client” |
OpenPGP public key (part of TLS handshake) | -> | |
<- | Binary blob (client will assume OpenPGP data) | |
<- | Close |
CHECKING¶
The server will, by default, continually check that the clients are still up. If a client has not been confirmed as being up for some time, the client is assumed to be compromised and is no longer eligible to receive the encrypted password. (Manual intervention is required to re-enable a client.) The timeout, extended timeout, checker program, and interval between checks can be configured both globally and per client; seeAPPROVAL¶
The server can be configured to require manual approval for a client before it is sent its secret. The delay to wait for such approval and the default action (approve or deny) can be configured both globally and per client; see mandos-clients.conf(5). By default all clients will be approved immediately without delay. This can be used to deny a client its secret if not manually approved within a specified time. It can also be used to make the server delay before giving a client its secret, allowing optional manual denying of this specific client.LOGGING¶
The server will send log message with various severity levels to /dev/log. With the --debug option, it will log even more messages, and also show them on the console.PERSISTENT STATE¶
Client settings, initially read from clients.conf, are persistent across restarts, and run-time changes will override settings in clients.conf. However, if a setting is changed (or a client added, or removed) in clients.conf, this will take precedence.D-BUS INTERFACE¶
The server will by default provide a D-Bus system bus interface. This interface will only be accessible by the root user or a Mandos-specific user, if such a user exists. For documentation of the D-Bus API, see the file DBUS-API.EXIT STATUS¶
The server will exit with a non-zero exit status only when a critical error is encountered.ENVIRONMENT¶
PATHTo start the configured checker (see the
section called “CHECKING”), the server uses /bin/sh, which in turn
uses PATH to search for matching commands if an absolute path is not
given. See sh(1).
FILES¶
Use the --configdir option to change where mandos looks for its configurations files. The default file names are listed here. /etc/mandos/mandos.confServer-global settings. See
mandos.conf(5) for details.
/etc/mandos/clients.conf
List of clients and client-specific settings.
See mandos-clients.conf(5) for details.
/var/run/mandos.pid
The file containing the process id of the
mandos process started last.
/dev/log
/var/lib/mandos
Directory where persistent state will be
saved. Change this with the --statedir option. See also the
--no-restore option.
/dev/log
The Unix domain socket to where local syslog
messages are sent.
/bin/sh
This is used to start the configured checker
command for each client. See mandos-clients.conf(5) for details.
BUGS¶
This server might, on especially fatal errors, emit a Python backtrace. This could be considered a feature. There is no fine-grained control over logging and debug output. Debug mode is conflated with running in the foreground. This server does not check the expire time of clients’ OpenPGP keys.EXAMPLE¶
Normal invocation needs no options:SECURITY¶
SERVER¶
Running this mandos server program should not in itself present any security risk to the host computer running it. The program switches to a non-root user soon after startup.CLIENTS¶
The server only gives out its stored data to clients which does have the OpenPGP key of the stored fingerprint. This is guaranteed by the fact that the client sends its OpenPGP public key in the TLS handshake; this ensures it to be genuine. The server computes the fingerprint of the key itself and looks up the fingerprint in its list of clients. The clients.conf file (see mandos-clients.conf(5)) must be made non-readable by anyone except the user starting the server (usually root). As detailed in the section called “CHECKING”, the status of all client computers will continually be checked and be assumed compromised if they are gone for too long. For more details on client-side security, see mandos-client(8mandos).SEE ALSO¶
Zeroconf is the network protocol standard used
by clients for finding this Mandos server on the local network.
Avahi[2]
Avahi is the library this server calls to
implement Zeroconf service announcements.
GnuTLS[3]
GnuTLS is the library this server uses to
implement TLS for communicating securely with the client, and at the same time
confidently get the client’s public OpenPGP key.
RFC 4291: IP Version 6 Addressing Architecture
Section 2.2: Text Representation of Addresses
Section 2.5.5.2: IPv4-Mapped IPv6 Address
Section 2.5.6, Link-Local IPv6 Unicast Addresses
RFC 4346: The Transport Layer Security (TLS) Protocol Version 1.1
The clients use IPv6 link-local addresses,
which are immediately usable since a link-local addresses is automatically
assigned to a network interfaces when it is brought up.
TLS 1.1 is the protocol implemented by
GnuTLS.
RFC 4880: OpenPGP Message Format
The data sent to clients is binary encrypted
OpenPGP data.
RFC 5081: Using OpenPGP Keys for Transport Layer Security
This is implemented by GnuTLS and used by this
server so that OpenPGP keys can be used.
COPYRIGHT¶
Copyright © 2008-2012 Teddy Hogeborn, Björn PåhlssonNOTES¶
- 1.
- Zeroconf
- 2.
- Avahi
- 3.
- GnuTLS
2012-05-26 | Mandos 1.5.5 |