Provided by: mandos_1.8.16-1ubuntu4_all 
NAME
mandos - Gives encrypted passwords to authenticated Mandos clients
SYNOPSIS
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]
[--foreground]
[--no-zeroconf]
mandos {--help | -h}
mandos --version
mandos --check
DESCRIPTION
mandos is a server daemon which handles incoming requests for passwords for a pre-defined list of client
host computers. For an introduction, see intro(8mandos). The Mandos server uses Zeroconf to announce
itself on the local network, and uses TLS to communicate securely with and to authenticate the clients.
The Mandos server uses IPv6 to allow Mandos clients to use IPv6 link-local addresses, since the clients
will probably not have any other addresses configured (see the section called “OVERVIEW”). Any
authenticated client is then given the stored pre-encrypted password for that specific client.
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, -h
Show 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
“SECURE128:!CTYPE-X.509:+CTYPE-RAWPK:!RSA:!VERS-ALL:+VERS-TLS1.3:%PROFILE_ULTRA” when using raw
public keys in TLS, and “SECURE256:!CTYPE-X.509:+CTYPE-OPENPGP:!RSA:+SIGN-DSA-SHA256” when using
OpenPGP keys in TLS,. See gnutls_priority_init(3) for the syntax. Warning: changing this may make
the TLS handshake fail, making server-client communication impossible. Changing this option may also
make the network traffic decryptable by an attacker.
--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.
--foreground
This option will make the server run in the foreground and not write a PID file. The default is to
not run in the foreground, except in debug mode, which implies this option.
--no-zeroconf
This option controls whether the server will announce its existence using Zeroconf. Default is to use
Zeroconf. If Zeroconf is not used, a port number or a socket is required.
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 a TLS 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 a separate 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 a TLS public key, and the key ID of
this public key 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.
Table 1. Mandos Protocol (Version 1)
┌─────────────────────────┬───────────┬──────────────────────────┐
│ Mandos Client │ Direction │ Mandos Server │
├─────────────────────────┼───────────┼──────────────────────────┤
│ Connect │ -> │ │
├─────────────────────────┼───────────┼──────────────────────────┤
│ “1\r\n” │ -> │ │
├─────────────────────────┼───────────┼──────────────────────────┤
│ TLS handshake as TLS │ <-> │ TLS handshake as TLS │
│ “server” │ │ “client” │
├─────────────────────────┼───────────┼──────────────────────────┤
│ 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; see mandos-clients.conf(5).
APPROVAL
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
PATH
To 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.conf
Server-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.
/run/mandos.pid
The file containing the process id of the mandos process started last. Note: If the /run directory
does not exist, /var/run/mandos.pid will be used instead.
/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.
Please report bugs to the Mandos development mailing list: <mandos-dev@recompile.se> (subscription
required). Note that this list is public. The developers can be reached privately at
<mandos@recompile.se> (OpenPGP key fingerprint 153A 37F1 0BBA 0435 987F 2C4A 7223 2973 CA34 C2C4 for
encrypted mail).
EXAMPLE
Normal invocation needs no options:
mandos
Run the server in debug mode, read configuration files from the ~/mandos directory, and use the Zeroconf
service name “Test” to not collide with any other official Mandos server on this host:
mandos --debug --configdir ~/mandos --servicename Test
Run the server normally, but only listen to one interface and only on the link-local address on that
interface:
mandos --interface eth7 --address fe80::aede:48ff:fe71:f6f2
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 correct key ID of the stored key
ID. This is guaranteed by the fact that the client sends its public key in the TLS handshake; this
ensures it to be genuine. The server computes the key ID of the key itself and looks up the key ID 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
intro(8mandos), mandos-clients.conf(5), mandos.conf(5), mandos-client(8mandos), sh(1)
Zeroconf[1]
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 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
The clients use IPv6 link-local addresses, which are immediately usable since a link-local
address is automatically assigned to a network interfaces when it is brought up.
RFC 5246: The Transport Layer Security (TLS) Protocol Version 1.2
TLS 1.2 is the protocol implemented by GnuTLS.
RFC 4880: OpenPGP Message Format
The data sent to clients is binary encrypted OpenPGP data.
RFC 7250: Using Raw Public Keys in Transport Layer Security (TLS) and Datagram Transport Layer Security
(DTLS)
This is implemented by GnuTLS version 3.6.6 and is, if present, used by this server so that raw
public keys can be used.
RFC 6091: Using OpenPGP Keys for Transport Layer Security (TLS) Authentication
This is implemented by GnuTLS before version 3.6.0 and is, if present, used by this server so that
OpenPGP keys can be used.
COPYRIGHT
Copyright © 2008-2019 Teddy Hogeborn, Björn Påhlsson
This manual page is part of Mandos.
Mandos is free software: you can redistribute it and/or modify it under the terms of the GNU General
Public License as published by the Free Software Foundation, either version 3 of the License, or (at your
option) any later version.
Mandos is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the
implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
License for more details.
You should have received a copy of the GNU General Public License along with Mandos. If not, see
http://www.gnu.org/licenses/.
NOTES
1. Zeroconf
http://www.zeroconf.org/
2. Avahi
https://www.avahi.org/
3. GnuTLS
https://gnutls.org/
Mandos 1.8.16 2022-04-24 MANDOS(8)