Provided by: ser2net_4.6.0-1build2_amd64 
NAME
/etc/ser2net/ser2net.yaml - Serial to network proxy configuration file
DESCRIPTION
ser2net used to be a program for connection network connections to serial ports. It's now
a program for connecting accepter gensio to connecting gensios. See gensio(5) for details
on gensios.
ser2net is configured with YAML, which is flexible and easy to use. Look at yaml
documentation on the internet for how that works.
However, there are two types of YAML files that ser2net can use: version 1 and version 2.
Version 1 YAML files have more capability than version 2 files, but they are non-standard
YAML, a standard YAML parser cannot read them. ser2net will autodetect the version based
upon what it finds.
In version 2, you can have multiple documents in a file and ser2net will read all of them.
YAML separates documents in a file with a single "---" by itself at the beginning of a
line. Though you can only have one set of defaults, defines, connections, etc. in a
document, you can have multiple documents in a file to allow more than one. You might,
for instance, group all the connections with a certain set of defaults into its own
document.
DEFINE SPECIFICATION
YAML has the ability to create aliases that can be used elsewhere in the configuration
file. These can be used for tying things together between parts of the file, or (as an
extension to YAML) for string substitution.
You define an alias in version 1 with the following:
define: &aliasname alias text
This will create an alias with the given name. Then you can use it elsewhere like:
banner: *aliasname
and the banner will be "alias text". Unlike standard YAML, you can also use this inside
strings using
*(aliasname)
so if you have
banner: My banner *(aliasname) is here
The banner will be "My banner alias text is here". See the YAML documentation for how
spaces are handled, but as a note, use quotes if you are not sure, like:
define: &aliasname "alias text"
banner: "My banner *(aliasname) is here"
If you for some reason need "*(" in your text, use "*(*" for that.
For version 2 YAML files, the definition is:
defines:
aliasname: alias text
aliasname2: alias text 2
where you can list as many aliases as you like. In version 2, you always refer to an
alias with "=" instead of "*", like:
banner: "My banner =(aliasname) is here"
and if you for some reason need "=(" in your text, use "=(=" for that.
In version 2, per standard YAML, you can only have one defines section, so they must all
be together.
INCLUDING OTHER FILES
A YAML file may include another file at the main level, with:
include: <filename>
This filename can include globs, and all referenced files are included. These must be
full yaml files, but are included in context at this point, with all the defines,
connection names, etc. This can let you have individual connections in individual files
to ease management.
In version 2, You can only have one include in each document for legal YAML, so if you
need multiple includes you will have to have multiple documents.
USING EXTERNAL FILES
You may want to store passwords and such in external files for better security. For
version 1, putting "*{filename}" in a YAML scalar will put the file's contents into the
scalar at that point. If you need a "*{" in the string for some reason, use "*{*".
For version 2, use "={filename}" instead. And "={=" to include a "={" in a file.
CONNECTION SPECIFICATION
A connection is a structure that describes how to connect an accepting gensio to a
connecting gensio.
An connection specification in version 1 starts with:
connection: &<alias>
<definition>
In version 2, it's specified as:
connections:
<alias>:
<definition>
In version 2, all the connections must occur together in one place.
The <definition> of a connection is the same for version 1 and version 2:
accepter: <accepter>
timeout: <number>
enable: on|off
connector: <connector>
options:
<option name>: <option value>
<option name>: <option value>...
An <accepter> is an accepting gensio specification. When ser2net receives a connection on
the accepter, it attempts to make a connection to the <connector> gensio. The alias is
required, it sets the name that is used for the connection in the admin interface and for
referencing from rotators.
If the connection receive no activity in <timeout> seconds, ser2net will close the
connection. Setting <timeout> to zero disables the timeout. The timeout field is
optional and defaults to zero.
The connection may be enabled or disabled with the enable. The enable field is optional
and defaults to on. This is useful for temporarily disabling port by setting enable to
off and sending a SIGHUP. If there are users connected and you disable a port and send a
SIGHUP, the users will be kicked off.
An option is a configuration setting that doesn't have anything to do with specific
gensios, they are controls for ser2net in general. The option section is optional.
See gensio(5) for a lot of information about the specific gensios available.
To allow a TCP connection to a serial port and ignore modem control, you can do:
connection: &toS0tcp
accepter: tcp,1234
connector: serialdev,/dev/ttyS0,local
Both accepting and connecting gensios stack, so if you want to add telnet with RFC2217
support, you can do:
connection: &toS0telnet
accepter: telnet(rfc2217),tcp,1234
connector: serialdev,/dev/ttyS0,local
If you want to accept a telnet over SCTP connection only on IPv6 localhost and connect to
a telnet connection with SSL over tcp, you can do:
connection: &tomyhost
accepter: telnet,sctp,::1,1234
connector: telnet,ssl,tcp,myhost.domain.org,1234
RFC2217 support only make sense with a serial-capable device as the connector. Also note
that IPv6 is fully supported. Accepters will generally default to being both IPv4 and
IPv6 unless otherwise specified. See gensio(5) for details.
And yes, SCTP is supported and is highly recommended if you can use it. Multi-homing
alone is worth it.
You could create a secure login with telnet RFC2217 support that then connects to an IPMI
sol connection. Notice how splitting the connector line is done with YAML.
connection: &authsol
accepter: telnet(rfc2217),mux,certauth,ssl,sctp,1234
connector: ipmisol,lan -U ipmiusr -P test -p 9001
ipmiserver.domain.org,9600
options:
banner: My banner
These are some examples. For SSL and certauth, I have ignored the authentication
configuration, more on that later. Using authentication is strongly recommended, it's
easy now with gtlssh and if you need to use it from a program, it's easy with gensio.
There is even python support. Adding support for other scripting languages shouldn't be
too hard.
SPECIAL STRING HANDLING
Some string values, like banners, have special formatting for inserting various values.
These are all prepended with '\'. This takes the standard "C" \x characters.
\a - bell
\b - backspace
\f - form feed
\n - newline
\r - carriage return
\t - tab
\v - vertical tab
\\ - \
\? - ?
\' - '
\" - "
\nnn - octal value for nnn
\xXX - hex value for XX
\d - The connector string (/dev/ttyS0, etc.)
\o - The name of the connection.
\p - Network port number
\B - The serial port parameters (eg 9600N81) if applicable
\Y -> year
\y -> day of the year (days since Jan 1)
\M -> month (Jan, Feb, Mar, etc.)
\m -> month (as a number)
\A -> day of the week (Mon, Tue, etc.)
\D -> day of the month
\e -> epoc (seconds since Jan 1, 1970)
\U -> microseconds in the current second
\p -> local port number
\I -> remote IP address (in dot format)
\H -> hour (24-hour time)
\h -> hour (12-hour time)
\i -> minute
\S -> second
\q -> am/pm
\P -> AM/PM
These sequences may be used to make the filename unique per open and identify which
port/device the filename was for. Note that in filenames when using \d or \o, everything
up to and including last / in the device name is removed, because you can't have a / in a
filename. So in a filename /dev/ttyS0 would become just ttyS0.
Note that in banners and other strings going out (not filenames) you must use \r\n to send
a new line; this is raw handling and \n will only go down one line, it will not return to
the beginning of the line.
CONNECTION SPECIFICATION OPTIONS
kickolduser: true|false sets the port so that the previous user will be kicked off if a
new user comes in. Useful if you forget to log off from someplace else a lot.
banner: <banner string> displays the given banner when a client connects. It uses string
handling as described in "SPECIAL STRING HANDLING" above.
signature: <signature string> sends RFC2217 signature on clients request. This may be an
empty string.
openstr: <openstr name string> Send the given string to the device on first open. This
may be an empty string. It uses string handling as described in "SPECIAL STRING HANDLING"
above.
closestr: <closestr name> Send the given string to the device on final close. This may be
an empty string. It uses string handling as described in "SPECIAL STRING HANDLING" above.
closeon: <closeon string> If the given string is seen coming from the connector side of
the connection, close the connection. The comparison here is, for simplicity, simplistic.
Complex expressions with repetitive things may not compare correctly. For instance, if
your closeon strings is "ababc" and your input strings is "abababc", the comparison will
fail because the comparison algorithm will see "ababa" and will fail on the final "a" and
start over at "abc", which won't match. This shouldn't cause a problem most cases, but if
it does, contact the authors and it can be improved.
accepter-retry-time: <time in seconds> If the accepter does not come up at startup, wait
this many seconds and retry it.
connector-retry-time: <time in seconds> On a connect-back port, if the connector does not
come up or goes down. wait this many seconds and retry it.
trace-read: <filename> When the acceptor is opened, open the given file and store all data
read from the physical device (and thus written to the client's network/acceptor port) in
the file. If the file already exists, it is appended. The file is closed when the port
is closed. The filename uses string handling as described in "SPECIAL STRING HANDLING"
above.
trace-write: <filename> Like tr, but traces data written to the connecting gensio.
trace-both: <filename> trace both read and written data to the same file. Note that this
is independent of tr and tw, so you may be tracing read, write, and both to different
files.
trace-hexdump: true|false turns on/off hexdump output to all trace files. Each line in
the trace file will be 8 (or less) bytes in canonical hex+ASCII format. This is useful
for debugging a binary protocol.
trace-timestamp: true|false adds/removes a timestamp to all of the trace files. A
timestamp is prepended to each line if hexdump is active for the trace file. A
timestamped line is also recorded in the trace file when a remote client connects or
disconnects from the port.
[trace-read-|trace-write-|trace-both-]hexdump: true|false turns on/off hexdump output for
only one trace file. May be combined with hexdump. Order is important.
[trace-read-|trace-write-|trace-both-]timestamp: true|false adds/removes a timestamp to
only one the trace files May be combined with [-]timestamp. Order is important.
telnet-brk-on-sync: true|false causes a telnet sync operation to send a break. By default
data is flushed until the data mark, but no break is sent.
chardelay: true|false enables the small wait after each character received on the
connecting gensio before sending data on the accepted gensio. Normally ser2net will wait
the time it takes to receive 2 serial port characters, or at least 1000us, before sending.
This allows more efficient use of network resources when receiving large amounts of data,
but gives reasonable interactivity. Default is true.
Note that this feature is designed to balance network efficiency and interactivity. It is
not designed to give guarantees of minimum chunk of data size, as task scheduling and
network stacks can modify these things, too.
chardelay-scale: <number> sets the time, measured in tenths of serial port characters, to
wait after receiving from nothing from the connection before sending to the accepted
gensio. So setting this to 25 will cause ser2net to wait the amount of time it takes to
receive 2.5 serial port characters after receiving the last character before sending the
data on to the TCP port. The default value is 20, max is 1000. This is ignored for non-
serial gensios.
chardelay-min: <number> is the same as chardelay-scale, but in microseconds. The larger
of chardelay-scale and chardelay-min is used. The default value is 1000, max is 100000.
chardelay-max: <number> sets the maximum delay that ser2net will wait, in microseconds,
after receiving a character, before sending the data. The default value is 20000, max is
1000000. This keeps the connection working smoothly at slow speeds.
sendon: <sendon string> If the given string is seen coming from the connector side of the
connection, sends buffered data up to and including the string. Disabled by default. As an
example, this can be set to \r\n with appropriate chardelay settings to send one line at a
time. It uses string handling as described in "SPECIAL STRING HANDLING" above. See the
notes on the closeon string for important information on how the comparison is done.
dev-to-net-bufsize: <number> sets the size of the buffer reading from the connecting
gensio and writing to the accepted gensio.
net-to-dev-bufsize: <number> sets the size of the buffer reading from the accepted gensio
and writing to the connecting gensio.
led-tx: <led-alias> use the previously defined led to indicate serial tx traffic on this
port. For version 2 this should be a YAML alias, like *led2. For version 2 just use the
name, like led2.
led-rx: <led-alias> use the previously defined led to indicate serial rx traffic on this
port. For version 2 this should be a YAML alias, like *led2. For version 2 just use the
name, like led2.
max-connections: <number> set the maximum number of connections that can be made on this
particular TCP port. If you make more than one connection to the same port, each ports
output goes to the device, and the device output goes to all ports simultaneously. See
"MULTIPLE CONNECTIONS" below for details. The default is 1.
remaddr: <addr>[;<addr>[;...]] specifies the allowed remote connections, where the addr
is a standard address, generally in the form <ip address>,<port>. Multiple addresses can
be separated by semicolons, and you can specify remaddr more than once.
If you set the port for an address to zero, ser2net will accept a connection from any port
from the given network host.
no-con-to-acc: true|false If true, do not transfer any data from the connector to the
accepter. Throw any data received from the connecter away.
no-acc-to-con: true|false If true, do not transfer any data from the accepter to the
connecter. Throw any data received from the accepter away.
connback: <connector>[;<connector>[;...]] specifies reverse connections that will be made
when data comes in on the device. When data comes in on the device side (the connection's
main connector) ser2net will connect to each connback specified. No connection is made
until data comes in, and normal connection timeouts apply.
Note that this will use one of the connection's connections all the time. You may need to
increase max-connections if you need more than one or want to accept incoming connections,
too.
Connect back addresses must match the format of the accepter address. So, for instance,
if your accepter is "telnet,tcp,1234" your connect back address must be something like
"telnet,tcp,hostname,1123".
The port will send no data to any connect back unless all the connect backs are connected.
A connect back port can also have connections made to it if you set the number of
connections larger than the number of connect backs specified. However, those connections
will receive no data from the port uness all connect backs have been established.
connback-timeout: <time in seconds> specifies a separate timeout for connect back ports.
Normally it uses the main timeout, this lets you have a different one. Setting it to
zero, like the main timeout, disables the timeout.
authdir: <directory string> specified the authentication directory to use for this
connection.
pamauth: <service name> Enables PAM authentication and sets the PAM service name.
allowed-users: <space separated list of names> The users that are allowed to use this
connections. This has no meaning if authentication is not enabled on the connections. If
this is not set or defaulted, all users are allowed. If this is set to an empty set of
users, then no users are allowed. This may be specified more than once, each one adds
more users.
mdns: true|false Enables/disables mdns support for the connection. If you set this and
mdns is available, ser2net will create a service on mdns for the port.
mdns-interface: <num> Sets the specific network interface to advertise the device.
Defaults to -1, which means all network interfaces.
mdns-nettype: unspec|ipv4|ipv6 Sets which network type to provide for the device
advertisement. Defaults to unspec, which means do ipv4 and ipv6.
mdns-name: <string> Sets the name in the mDNS advertisement. Defaults to the connection
name.
mdns-type: <string> Sets the type in the mDNS advertisement. Defaults to "_iostream._xxx"
where xxx is either tcp, udp # # or sctp base on the gensio type.
mdns-domain: <string> Sets the name in the mDNS advertisement. Defaults to the system
setting. Don't set this unless you really know what you are doing.
mdns-host: <string> Sets the host in the mDNS advertisement. Defaults to the system
setting. Don't set this unless you really know what you are doing.
mdns-txt: <string> Adds a text string to the mDNS advertisement. The string should be in
the form "name=value". You can put anything you want in the strings. Two default strings
are added by ser2net: "provider=ser2net" and "gensiostack=..." where the stack of gensios
is added, like "telnet(rfc2217),tcp)". The idea of gensiostack is you can just tack on
the address to the end an make a connection using str_to_gensio().
mdns-sysattrs: true|false On Linux adds system attributes from sysfs for USB serial ports
to the mDNS txt fields. If the serial port is USB, it adds "devicetype=serialusb" and the
following attributes from sysfs: bInterfaceNumber, interface, idProduct, idVendor, serial,
manufacturer, product. If they are not present in sysfs, they are not added. If the
serial port is not USB, then "devicetype=serial" is added.
Note: Be *very* careful when using a gensiostack with str_to_gensio(). Just blindly
calling str_to_gensio() with it could result in significant security issues, as it can
pass pty, stdio, trace, etc. gensios in it. You must either validate that the stack is a
safe set or just use it for information. You have been warned. Be careful.
ROTATOR
A rotator allows a single network connection to connect to one of a number of connections.
A version 1 rotator specification starts with:
rotator: &<alias>
<definition>
A version 2 rotator specification starts with:
rotators:
<alias>:
<definition>
Just like connections, in version 2 you have to put all the rotators together.
The definition of a rotator is almost the same between version 1 and version 2:
accepter: <accepter>
connections: [
<connection alias>,
<connection alias>....
]
options:
<option name>: <option val>
<option name>: <option val>...
A rotator has four possible options, "authdir", "pamauth", "allowed-users", and "accepter-
retry-time", both same as connections.
For version 1, you should use YAML aliases for the connections. For version 2, just use
the alias names.
Connections to the accepter will go through the set of connections and find the first
unused one and use that. The next connection will start after the last connection used.
Note that disabled connections are still accessible through rotators.
Note that the security of the connection is NOT used, only the security of the rotator.
SER2NET DEFAULTS
To set a default in version 1, do:
default:
name: <default name>
value: <default value>
class: <default class>
In version 2, like other things, the defaults are all in one place in a document, like:
defaults:
<name>:
value: <default value>
class: <default class>
<name2>:
value: <default value>
class: <default class>
The class is optional, if it is not there it sets the base default for all classes that is
used unelss overridden for a specific class. If the class is there, it sets the default
for a specific gensio class. There is also a ser2net class that is for ser2net specific
options.
The class is useful if you want different values for different gensio types. For
instance, if you wanted all serial ports to run at 9600 baud and all IPMI SOL connections
to run at 115200 baud, you could do:
default:
name: speed
value: 9600
class: serialdev
default:
name: speed
value: 115200
class: ipmisol
The value is also optional, if it is not present a string value is set to NULL and an
integer value is set to 0.
The order in the file is important, you must set a default before it is used, and you can
change the value of the default. It will affect all uses following the setting.
To delete a default value for class (so it will use the base default), for version 1 do:
delete_default:
name: <default name>,
class: <default class>
For version 2, do:
delete_defaults:
<default name>: [ <class1>, <class2>, ... ]
<default name2>: [ <class1>, <class2>, ... ]
and it will delete the defaults for the classes in the list after it.
You must supply the class, you cannot delete base defaults.
The following default values are specific to ser2net, given with their default values:
telnet-brk-on-sync: false
If a telnet sync is received, send a break on the connected gensio (if applicable).
By default data is flushed until the data mark, but no break is sent.
kickolduser: false
If a new user comes in on a connection that already has a user, kick off the
previous user.
chardelay: true
Enable asmall wait after each character received on the serial port before sending
data on the TCP port. Normally ser2net will wait the time it takes to receive 2
serial port characters, or at least 1000us, before sending on the TCP port. This
allows more efficient use of network resources when receiving large amounts of
data, but gives reasonable interactivity.
chardelay-scale: 20
sets the number of serial port characters, in tenths of a character, to wait after
receiving from the serial port and sending to the TCP port. So setting this to 25
will cause ser2net to wait the amount of time it takes to receive 2.5 serial port
characters before sending the data on to the TCP port. This can range from 1-1000.
chardelay-min: 1000
sets the minimum delay that ser2net will wait, in microseconds. If the calculation
for chardelay-scale results in a value smaller than this number, this number will
be used instead. The default value is 1000. This can range from 1-100000.
net-to-dev-bufsize: 64
sets the size of the buffer reading from the network port and writing to the serial
device.
dev-to-net-bufsize: 64
sets the size of the buffer reading from the serial device and writing to the
network port.
max-connections: 1
set the maximum number of connections that can be made on this particular TCP port.
If you make more than one connection to the same port, each ports output goes to
the device, and the device output goes to all ports simultaneously. See "MULTIPLE
CONNECTIONS" below. for details.
remaddr: [!]<addr>[;[!]<addr>[;...]]
specifies the allowed remote connections, where the addr is a standard address in
the form (see "network port" above). Multiple addresses can be separated by
semicolons, and you can specify remaddr more than once. If you set the port for an
address to zero, ser2net will accept a connection from any port from the given
network host. If a "!" is given at the beginning of the address, the address is a
"connect back" address. If a connect back address is specified, one of the network
connections (see max-connections) is reserved for that address. If data comes in
on the device, ser2net will attempt to connect to the address. This works on TCP
and UDP.
authdir: /usr/share/ser2net/auth
The authentication directory for ser2net. The AUTHENTICATION for more details.
authdir-admin: /etc/ser2net/auth
The authentication directory for ser2net for admin connections. The
"ADMIN_CONNECTIONS" for more details.
pamauth: <NULL>
The PAM service name for ser2net PAM authentication (<NULL> for disabled).
pamauth-admin: <NULL>
The PAM service name for ser2net admin connection PAM authentication (<NULL> for
disabled). See "ADMIN_CONNECTIONS" for more details.
mdns-interface: -1
The default mDNS interface.
mdns-type: <NULL>
The default mDNS type.
mdns-domain: <NULL>
The default mDNS domain.
mdns-host: <NULL>
The default mDNS host.
ADMIN CONNECTIONS
There is an admin accepter that you can define for ser2net, it lets you log in, look at
status, and change some things. See "ADMIN INTERFACE" in ser2net(8) for detail on how to
use it. The format is:
admin: [&<name>]
accepter: <accepter>
options:
<option name>: <option value>
<option name>: <option value>...
The following authentications options available are "authdir-admin", which sets the
authentication directory for the admin port and "pamauth-admin" which sets the PAM service
name and enables PAM authentication. Both are different than "authdir" resp. "pamauth"
for connections, though you can set it to the same value.
In addition, the same mdns option are available for admin ports as are available for
connections. And you can set an optional alias that will also set the mdna name.
Like connections, default mdns options work for "mdns-interface", "mdna-type", "mdns-
domain", and "mdns-host". Unlike connections, the "mdns" boolean does not come from the
default, you must specify it as an admin option to turn on mdns for the admin port. This
is to allow it to be specified separately and maintain backwards compatibility.
LEDS
ser2net can flash LEDs during serial activity. To create an LED in version 1, do:
led: &<alias>
driver: sysfs
options:
<option name>: <option value>
<option name>: <option value>
In version 2, use:
leds:
<alias>:
driver: sysfs
options:
<option name>: <option value>
<option name>: <option value>
<alias>:
driver: sysfs
options:
<option name>: <option value>
<option name>: <option value>
The only supported driver is sysfs. Supported options are:
device: <sysfs device name> gives the name of the LED in /sys/class/led. These generally
have ":" in them, so you will need to put the name in quotes. This is required.
duration: <time in ms> The time in milliseconds to flash the LED. Defaults to 10.
state: <number> The value to set the LED to to enable it. Defaults to 1, but may need to
be a different value.
You reference the LED by alias in the connection options section, see that for details.
Make sure you have "modprobe ledtrig-transient" done or the triggers will not work, they
require the transient trigger.
You also probably need root access to access LED settings.
FILENAME, BANNER, AND STRING FORMATTING
NOTE: yaml has it's own quoting mechanism, see below for more details.
Filenames, banners, open/close strings, closeon strings, and sendon strings may contain
normal "C" escape sequences and a large number of other escape sequences, too:
\a - bell
\b - backspace
\f - form feed
\n - newline
\r - carriage return
\t - tab
\v - vertical tab
\\ - \
\? - ?
\' - '
\" - "
\nnn - octal value for nnn
\xXX - hex value for XX
\d - The connecting gensio string (serialdev,/dev/ttyS0, etc.)
\o - The device as specified on the config line (before DEVICE substitution)
\N - The port name
\p - The accepter string
\B - The serial port parameters (eg 9600N81)
\Y -> year
\y -> day of the year (days since Jan 1)
\M -> month (Jan, Feb, Mar, etc.)
\m -> month (as a number)
\A -> day of the week (Mon, Tue, etc.)
\D -> day of the month
\e -> epoc (seconds since Jan 1, 1970)
\U -> microseconds in the current second
\p -> local port number
\I -> remote address of the accepter gensio
\H -> hour (24-hour time)
\h -> hour (12-hour time)
\i -> minute
\S -> second
\q -> am/pm
\P -> AM/PM
In addition, for backwards compatibility because filenames and banners used to have
different formatting, \s is the serial port parameters if in a banner and seconds if in a
filename. Use of this is discouraged as it may change in the future.
These sequences may be used to make the filename unique per open and identify which
port/device the filename was for. Note that in filenames when using \d or \o, everything
up to and including last / in the device name is removed, because you can't have a / in a
filename. So in a filename /dev/ttyS0 would become just ttyS0.
HANDLING QUOTING AND STRING FORMATTING
yaml will process "\" escape sequences in double quotes, so use of double quotes is note
recommended for the above. If you put the values in single quotes, yaml will not process
them and instead pass them through where they can be processed by ser2net.
SPACES, QUOTING AND PUTTING SPACES IN STRINGS
YAML and the accepter/connector processing interact when dealing with quoting. By
default, YAML ignores the number of spaces between elements separated by spaces. Lines
that are indented after an element are considered a continuation of the element, so
something like:
connector: serialdev,/dev/ttyUSB0,
9600n81
local nobreak
rtscts
is the same as
connector: serialdev,/dev/ttyUSB0, 9600n81 local nobreak rtscts
YAML has it's own standard quoting mechanisms, so if you do:
connector: "serialdev,/dev/ttyUSB0,9600n81 local"
the two spaces before "local" will be preserved when passed to the connector processing
(though in this case it won't matter because the connector processing will ignore the
extra spaces).
If you need a significant space, say in a filename passed to a key, You cannot do:
accepter: ssl(CA=/etc/ser2net/my CA/),tcp,3000
because the accepter processing will split the arguments at the space and won't recognize
what "CA/" is. You also cannot do:
accepter: ssl(CA="/etc/ser2net/my CA/"),tcp,3000
because YAML will remove the quotes, this is functionally equivalent to the previous
example. And
accepter: ssl(CA="/etc/ser2net/my\ CA/"),tcp,3000
also will not work, inside of double quotes YAML will convert "\ " to a space. You have a
couple of options. You can do:
accepter: ssl(CA=/etc/ser2net/my\ CA/),tcp,3000
or
accepter: ssl(CA='/etc/ser2net/my\ CA/'),tcp,3000
because outside of quotes YAML will not process the "\ " and it will not process it in
single quotes. Or if you have a lot of spaces or colons, too, you can do:
accepter: ssl(CA="\"/etc/ser2net/my CA/\""),tcp,3000
because inside the outside quotes YAML will convert the '\"' into a '"' and pass it on to
the accepter processing which will interpret the quotes as you would expect.
UDP
UDP handling is a bit different than you might imagine, because it's hard for ser2net to
know where to send the data to. To handle this, UDP ports still have the concept of a
"connection". If a UDP port is not connected, then if it receives a packet the remote
address for that packet is set to the remote end of the "connection". It will do all the
normal new connection operations. ser2net will accept new connections up to "max-
connections" then ignore packets from other addresses until a disconnect occurs.
Unfortunately, there is no easy way to know when to disconnect. You have two basic
options:
• Set a timeout, if the remote end isn't heard from before the timeout, then the port
is disconnected and something else can connect. This means anything that is using
the port must periodically send a packet (empty is fine) to ser2net to keep the
connection alive.
• Use the kickolduser option on the port, any new connection that comes in will
replace the previous connection.
Note that UDP ports handle multiple connections just like TCP ports, so you can have
multiple UDP listeners.
You also have a third option. If you set a remote address (remaddr) with a non-zero port
and a connect back port (see discussion on remote addresses above), ser2net will take one
of the connections and assign it to that port permanently. This is called a fixed remote
address. All the traffic from the device will go to that port. Every fixed remote
address on a UDP port has to have a corresponding connection, so if you have 3 fixed
remote addresses, you must have at least 3 connections.
MULTIPLE CONNECTIONS
As mentioned earlier, you can set max-connections=<n> on a port to allow more than one
connection at a time to the same serial port. These connections will share all the
settings. You cannot have two separate TCP ports connect to the same port at the same
time.
This has some significant interactions with other features:
flow control is not exactly a feature, but more an interaction between the different
connections. If a TCP port stops receiving data from ser2net, all TCP ports connected
will be flow-controlled. This means a single TCP connection can stop all the others.
closeon will close all connections when the closeon sequence is seen.
openstr is only sent when the port is unconnected and the first connections is made.
closestr is only sent when the last port disconnects and there are no more connections to
the port.
Any monitor ("monitor start" from a control connections) will catch input from all network
connections.
kickolduser will kick off an existing connection if a connection comes in on a port that
already has a maximum number of connections. The connection kicked off is arbitrarily
chosen and the algorithm is subject to change.
tracing will trace data from all network connections.
rfc2217 (remote telnet serial control) will change the connection settings on the device
and will be accepted from any network connection.
reconfig on SIGHUP See ser2net(8) "SIGHUP" section for details.
ROTATOR will only choose a port if there are no connections at all on the port. Note that
the use of a rotator with a port with max-connections > 1 will result in undefined
behavior.
timeout will be per TCP port and will only disconnect that TCP port on a timeout.
telnet_brk_on_sync will send a break for any TCP port that does a sync.
showport in the admin interface will show all possible connections, so if you say max-
connections=3 you will get three entries.
showshortport in the admin interface will only show the first live connection, or if no
connection is present it will show whatever the first one was the last time a connection
was present.
AUTHENTICATION AND ENCRYPTION
TCP WRAPPERS
ser2net uses the tcp wrappers interface to implement host-based security. See
hosts_access(5) for a description of the file setup. Two daemons are used by ser2net,
"ser2net" is for the data ports and "ser2net-control" is for the control ports.
ENCRYPTION
ser2net supports SSL encryption using the ssl gensio. To enable encryption, use an
accepter like:
telnet,ssl,tcp,1234
Then you can use gensiot to connect:
gensiot telnet,ssl,<server>,1234
or you can install telnet-ssl and do
telnet -z ssl,secure <server> 1234
The SSL connection is made using the provided keys. In this example ser2net uses the
default keys (as set in the default, see those below). You can also set them using
(key=<keyfile>,cert=<certfile>) after ssl above, or modify the defaults.
If you do not have genuine certificates from a certificate authority, the connection will
fail due to certificate failure. Getting certificates this way is very inconvenient, so
there is another way. You can do:
gtlssh-keygen --keydir /etc/ser2net --commonname "`hostname`-ser2net" serverkey
ser2net
to generate the default keys in /etc/ser2net (or wherever). The certificate/key will be
named /etc/ser2net/ser2net.crt|key.
NOTE: If you compile ser2net yourself, by default autoconf sets the system configuration
directory (normally /etc) as /usr/etc. This is a major annoyance with autoconf. So if
you don't change it, you would need /usr/etc above where it says /etc. However, generally
the right way to do this is to add "--sysconfdir=/etc" to the configure command line when
you configure ser2net. If a distro has compiled ser2net for you, that should have done
that by default, so no worries in that case.
Then copy ser2net.crt over to the user system and provide it to connection commands, like:
gensiot telnet,ssl(CA=ser2net.crt),<server>,1234
or
telnet -z ssl,secure,cacert=ser2net.crt 1234
Then you will have an encrypted connection. Just make sure your certificates are valid.
Note that the "-ser2net" at the end of the key is important because it make the subject
name of the certificate more unique. You can really put anything you want for what you
provide to keygen, as long as you rename it properly. That will be the subject name of
the certificate.
AUTHENTICATION WITH SSL
ser2net provides a way to authenticate with SSL. It's not the greatest, but it does work.
You must enable clientauth on ssl:
telnet,ssl(clientauth),tcp,1234
or set it in the default. Then you must create a certificate with the username as the
common name. You can do this with:
gtlssh-keygen --keydir outdir --commonname username keygen keyname
which will generate keyname.crt and keyname.key in outdir. Then put keyname.crt in
ser2net's <authdir>/username/allowed_certs. By default <authdir> is
/usr/share/ser2net/auth, but you can change that with the authdir default in the ser2net
config file or by setting authdir on individual connections (in case you want different
ones for different ports). You then must rehash the allowed_certs directory:
gtlssh-keygen rehash <authdir>/username/allowed_certs
Then restart/reload ser2net and use one of these very long lines to telnet into it:
gensiot telnet,ssl(CA=ser2net.crt,cert=username.crt,key=username.key),<server>,1234
telnet -z ssl,secure,cacert=ser2net.crt,cert=username.crt,key=username.key server
1234
AUTHENTICATION WITH CERTAUTH (GTLSSH)
All of the above is a big pain. Fortunately there is an easier way. gtlssh is a ssh-like
program, but runs over TLS and it implements a ssh-like authentication protocol using the
certauth gensio.
ser2net supports this authentication system running on top of the ssl and certauth
gensios. Those gensios provide the framework for handling authentication, ser2net itself
controls it.
This uses the same authdir and allowed keys directory as before, and still requires a
server certificate, but the self-signed one generated with gtlssh-keygen works fine
without doing anything special. Add certauth to the port line:
telnet,mux,certauth,ssl,tcp,1234
and *make sure* clientauth is disabled for ssl (or ssl will still attempt to authenticate
the client). Disabled is the default but in case you changed, the default...
The mux entry is because gtlssh uses the mux gensio to allow multiple channels on the same
session. It wasn't there with older (pre 1.2) version of gtlssh, but is required for
newer one. gtlssh also has a --nomux option, just in case.
The gtlssh program does its own certificate handling. Look at the gtlssh man page for
detail on that. Take the certificate for gtlssh and put it in the
authdir/username/allowed_certs directory and reshash it as before. gtlssh will *not* use
the common name provided in the certificate, instead it users a username provided by
gtlssh. Then connect with gtlssh:
gtlssh --nosctp --telnet username@server 1234
The --nosctp thing keep gtlssh from trying sctp, which will fail because we put tcp in the
port line. You could use sctp there and get all its advantages for free! Then --nosctp
would no longer be required to avoid the nagging.
The username is optional if it's the same as your current user. If you have not connected
to that server/port before, gtlssh will ask you to verify it, much like ssh does. If
certificates, IP address, etc. change, gtlssh will tell you about it.
If you do not want to use a certificate (certificates are certainly preferred, but may not
always be workable) you can use a password login, too. You must set enable-password in the
certauth gensio options for passwords to work. When you connect with gtlssh, if
certificate validate fails, you will be prompted for the password. Password authentication
can be performed in two different ways. Both are mutually exclusive, depending on
whether pamauth is set or not:
• To authenticate using the PAM library set the PAM service name via pamauth option.
• Put a password in authdir/username/password. If it matches the first line in the
password file and pamauth is not set, then authentication will succeed.
AUTHENTICATION AND ROTATORS
Rotators are a special case. BE CAREFUL. A rotator has its own authentication. If you
set up authentication on a port that is part of a rotator, that port's authentication is
not used. Only the rotator's authentication is used.
ENCRYPTION, AUTHENTICATION, AND DEFAULT CERTIFICATES
ser2net expects default certificates and public keys in /etc/ser2net, and these are set as
gensio defaults. This means that any outgoing connection from ser2net, whether in a
connector or in a connback, will use these keys. If they aren't there or have expired or
something you will get confusing errors about not being able to open the certificates.
To solve this, you can disable the certificates by adding "cert=" to the gensio
specification for ssl and certauth on outgoing connections. This will disable the
certificates for the specific gensio, and is probably what you want. If you are making
connections and authenticating to the remote server, the default certificate and private
key are probably not what you want, either.
SIGNALS
SIGHUP
If ser2net receives a SIGHUP, it will reread it configuration file and make the
appropriate changes. If an inuse port is changed or deleted, the actual change will
not occur until the port is disconnected.
ERRORS
Almost all error output goes to syslog, not standard output.
FILES
/etc/ser2net/ser2net.yaml, /etc/ser2net/ser2net.key, /etc/ser2net/ser2net.crt,
/usr/share/ser2net
SEE ALSO
ser2net(8) telnet(1), hosts_access(5), gensio(5), gtlssh(1), gtlssh-keygen(1)
KNOWN PROBLEMS
If they were known, they would be fixed :).
AUTHOR
Corey Minyard <minyard@acm.org>