The format of the conserver.cf file is made up of named blocks of
keyword/value pairs, comments, and optional whitespace for formatting
flexibility. The block types as well as the keywords are pre-defined and
explained in the BLOCKS section. A comment is an unquoted pound-sign
to a newline. See the PARSER section for full details on whitespace
and quoting.
Let me first show you a sample block with a couple of
keyword/value pairs to make the description a bit simpler to understand.
-
console simple { master localhost; type exec; rw *; }
This is actually a fully functional conserver.cf file (if certain
conditions are met...and if you can list those conditions, you can probably
can skip to the BLOCKS section).
Our example is made of up of a console-block named ``simple'' with
three keyword/value pairs. What this does is define a console named
``simple'', makes the master of that console the host ``localhost'', makes
the type an exec-style console, and gives every user read/write permission.
This is the generic format of the file:
-
block-type block-name { keyword value; ... }
To show the addition of comments and whitespace, here is the
example reformatted (but functionally equivalent):
-
# define a console named "simple"
console simple {
# setting all required values...
master localhost;
type exec; # exec-style console
rw *; # allow any username
}
The parser has six characters that it considers special. These
are: ``{'', ``}'', ``;'', ``#'', ``\'', and ``"''. The first three
(hereby called tokens) define the format of the configuration blocks and are
used as word separators, the next is the comment character, and the last two
are quoting characters.
Word separation occurs when the parser encounters an unquoted
token and, in certain cases, whitespace. Whitespace is only used as a word
separator when the parser is looking for a block-type or keyword. When it's
looking for a block-name or value, whitespace is like any other character,
which allows you to embed whitespace in a block-name or value without having
to quote it. Here is an example:
-
default my defs { rw *; include other defs ; }
The block-type is ``default'', the block-name is ``my defs'', and
the value for the keyword ``include'' is ``other defs''. Whitespace around
tokens are ignored so you get ``other defs'' instead of ``other defs '' as
the value.
The only way to use one of the special characters as part of a
block-name or value is to quote it.
Quoting is a simple matter of prefixing a character with a
backslash or surrounding a group of characters with double-quotes. If a
character is prefixed by a backslash, the next character is a literal (so
``\\'' produces a ``\'', ``\"'' produces ``"'', ``\{'' produces a
``{'', etc.). For double-quoted strings, all characters are literal except
for ``\"'', which embeds a double-quote.
Adding a variety of quotes to our example without changing the
meaning of things, we have:
-
"defa"ult my\ defs { rw *; in\clude "other defs" ; }
There is one special line the parser recognizes: a ``#include''
statement. It is of the form:
- #include filename
Any whitespace around filename is ignored, but whitespace
embedded inside is preserved. Everything in filename is taken
literally, so none of the normal parser quoting applies. The #include
must begin in ``column 0'' - no whitespace is allowed between it and the
start of the physical line. There is an include file depth limit of 10 to
prevent infinite recursion.
- access
hostname|ipaddr
-
Define an access block for the host named hostname or using the
address ipaddr. If the value of ``*'' is used, the access block
will be applied to all conserver hosts. Access lists are used in a first
match fashion (top down), so order is important.
- admin
[!]username[,...]|""
-
Define a list of users making up the admin list for the console server. If
username matches a previously defined group name, all members of
the previous group are applied to the admin list (with access reversed if
prefixed with a `!'). If username doesn't match a previously
defined group and username begins with `@', the name (minus the
`@') is checked against the host's group database. All users found in the
group will be granted (or denied, if prefixed with `!') access. If
username doesn't match a previous group and doesn't begin with `@',
the users will be granted (or denied, if prefixed with `!') access. If the
null string (``""'') is used, any users previously
defined for the console servers's admin list are removed.
- allowed
hostname[,...]
-
The list of hostnames are added to the ``allowed'' list, which grants
connections from the hosts but requires username authentication.
- include
accessgroup
-
The access lists defined using the name accessgroup are applied to
the current access block. The included access block must be previously
defined.
- limited
[!]username[,...]|""
-
Define a list of users with limited functionality on the console server.
These users will not be allowed to suspend their connection, shift to
another console, or attach to a local command. If username matches
a previously defined group name, all members of the previous group are
applied to the admin list (with access reversed if prefixed with a `!').
If username doesn't match a previously defined group and
username begins with `@', the name (minus the `@') is checked
against the host's group database. All users found in the group will be
granted (or denied, if prefixed with `!') access. If username
doesn't match a previous group and doesn't begin with `@', the users will
be granted (or denied, if prefixed with `!') access. If the null string
(``""'') is used, any users previously defined for the
console server's limited list are removed.
- rejected
hostname[,...]
-
The list of hostnames are added to the ``rejected'' list, which rejects
connections from the hosts.
- trusted
hostname[,...]
-
The list of hostnames are added to the ``trusted'' list, which grants
connections from the hosts without username authentication.
- break
n
-
Define a break sequence where (1 <= n <= 9) or (a <=
n <= z). Break sequences are accessed via the ``^Ecln''
client escape sequence.
- confirm
yes|true|on|no|false|off
-
Set whether or not to ask the client for confirmation before sending the
break sequence. The default is ``no''.
- delay
n
-
Set the time delay for the \d sequence to n milliseconds. The
default time delay is 250ms.
- string
breakseq
-
Assign the string breakseq to the specified slot n. A break
sequence is a simple character string with the exception of `\' and
`^':
- \a
- alert
- \b
- backspace
- \d
- delay specified by the delay option.
- \f
- form-feed
- \n
- newline
- \r
- carriage-return
- \t
- tab
- \v
- vertical-tab
- \z
- serial break
- \\
- backslash
- \^
- circumflex
- \ooo
- octal representation of a character (where ooo is one to three
octal digits)
- \c
- character c
- ^?
- delete
- ^c
- control character (c is ``and''ed with 0x1f)
- config
hostname|ipaddr
-
Define a configuration block for the host named hostname or using the
address ipaddr. If the value of ``*'' is used, the configuration
block will be applied to all conserver hosts.
- autocomplete
yes|true|on|no|false|off
-
Turn the console name autocompletion feature on or off. If autocompletion is
on, a client can use any unique leading portion of a console name when
connecting to a console. Autocompletion is on by default.
- defaultaccess
rejected|trusted|allowed
-
Set the default access permission for all hosts not matched by an access
list (see the -a command-line flag).
- daemonmode
yes|true|on|no|false|off
-
Set whether or not to become a daemon when run (see the -d
command-line flag).
- initdelay
number
-
Set the number of seconds between console initializations. All consoles with
the same host value will be throttled as a group (those without a
host value are their own group). In other words, each console
within a group will only be initialized after number seconds passes
from the previous initialization of a console in that group. Different
throttle groups are initialized simultaneously. One warning: since
consoles are split up and managed by seperate conserver processes, it's
possible for more than one conserver process to have a throttle group
based on a particular host value. If this happens, each conserver
process will throttle their groups independently of the other conserver
processes, which results in a more rapid initialization (per host
value) than one might otherwise expect. If number is zero, all
consoles are initialized without delay.
- logfile
filename
-
Set the logfile to write to when in daemon mode (see the -L
command-line flag).
- passwdfile
filename
-
Set the password file location used for authentication (see the -P
command-line flag).
- primaryport
number|name
-
Set the port used by the master conserver process (see the -p
command-line flag).
- redirect
yes|true|on|no|false|off
-
Turn redirection on or off (see the -R command-line flag).
- reinitcheck
number
-
Set the number of minutes used between reinitialization checks (see the
-O command-line flag).
- secondaryport
number|name
-
Set the base port number used by child processes (see the -b
command-line flag).
- setproctitle
yes|true|on|no|false|off
-
Set whether or not the process title shows master/group functionality as
well as the port number the process is listening on and how many consoles
it is managing. The operating system must support the
setproctitle() call.
- sslcredentials
filename
-
Set the SSL credentials file location (see the -c
command-line flag).
- sslcacertificatefile
filename
-
Load the valid CA certificates for the SSL connection from
the PEM encoded file. This option overrides the global CA list.
- sslreqclientcert
yes|true|on|no|false|off
-
Set whether or not a certificate is required by the client to connect. The
default is ``no''.
- sslrequired
yes|true|on|no|false|off
-
Set whether or not encryption is required when talking to clients (see the
-E command-line flag).
- unifiedlog
filename
-
Set the location of the unified log to filename. See the -U
command-line flag for details.
- console
name
-
Define a console identified as name. The keywords are the same as the
default block with the following addition.
- aliases
name[,...]|""
-
Define a list of console aliases. If the null string
(``""'') is used, any aliases previously defined for the
console are removed.
- default name
-
Define a block of defaults identified as name. If name is
``*'', the automatically applied default block is defined (basically all
consoles have an implicit ``include "*";'' at the beginning of
their definition).
- baud
300|600|1800|2400|4800|9600|19200|38400|57600|115200|..|4000000
-
Assign the baud rate to the console. Only consoles of type ``device'' will
use this value.
- break
n
-
Assign the break sequence n as the default for the console, which is
used by the ``^Ecl0'' client escape sequence.
- breaklist
n[,...]|""
- Associate a list of break sequences referenced by n with the
console. If ``*'' is used (the default), all defined break sequences will
be available. If the null string (``""'') is used, no
sequences will be available.
- device
filename
-
Assign the serial device filename as the path to the console. Only
consoles of type ``device'' will use this value.
- devicesubst
c=t[n]f[,...]|""
-
Perform character substitutions on the device value. A series of
replacements can be defined by specifying a comma-separated list of
c=t[n]f sequences where c is any
printable character, t specifies the replacement value, n is
a field length (optional), and f is the format string. t can
be one of the characters below, catagorized as a string replacement or a
numeric replacement, which dictates the use of the n and f
fields.
- String
Replacement
- c
- console name
- h
- host value
- r
- replstring value
Numeric Replacement
- b
- baud value
- p
- config port value
- P
- calculated port value
- For string replacements, if the replacement isn't at least n
characters, it will be padded with space characters on the left. f
must be `s'. For numeric replacements, the value will be formatted to at
least n characters, padded with 0s if n begins with a 0, and
space characters otherwise. f must be either `d', `x', `X', `a', or
`A', specifying a decimal, lowercase hexadecimal (0-9a-f), uppercase
hexadecimal (0-9A-F), lowercase alphanumeric (0-9a-z), or uppercase
alphanumeric (0-9A-Z) conversion. If the null string
(``""'') is used, no replacements will be done.
- exec
command|""
-
Assign the string command as the command to access the console.
Conserver will run the command by invoking ``/bin/sh -ce
"command"''. If the null string (``""'')
is used or no exec keyword is specified, conserver will use the
command ``/bin/sh -i''. Only consoles of type ``exec'' will use this
value.
- execrunas
[user][:group]|""
-
By default, the command invoked by exec is run with the same
privileges as the server. If the server is running with root privileges,
this option resets the user and/or group of the invoked process to
user and group respectively. user may be a username
or numeric uid and group may be a group name or numeric gid. Either
one is optional. If the server is not running with root privileges, these
values are not used. If the null string (``""'') is
specified, the default of running with the same privileges as the server
is restored.
- execsubst
c=t[n]f[,...]|""
-
Perform character substitutions on the exec value. See the
devicesubst option for an explanation of the format string. If the
null string (``""'') is used, no replacements will be
done.
- host
hostname
-
Assign hostname as the host to connect to for accessing the console.
You must also set the port option for consoles of type ``host''.
Normally, only consoles of type ``host'' and ``ipmi'' will use this value,
however if the devicesubst, execsubst, or initsubst
keywords are used in any console type, this value is used.
- idlestring
string|""
-
Assign the string that is sent to the console once the console is
idle for an idletimeout amount of time. If the null string
(``""'') is used, the string is unset and the default is
used. The string is interpreted just as a break string is
interpreted (see the break configuration items for details) where
all delays specified (via ``\d'') use the default delay time. The default
string is ``\n''.
- idletimeout
number[s|m|h]
-
Set the idle timeout of the console to number seconds. If an `s',
`m', or `h' is used after number, the specified time is interpreted
as seconds, minutes, or hours. Set the timeout to zero to disable the idle
timeout (the default).
- ipmiciphersuite
number
-
Set the IPMI cipher suite. Syntactically valid values are -1 (the default)
and greater. Check the FreeIPMI documentation for usable values.
- ipmikg
string|""
- Set the BMC authentication key K_g to string. A K_g value is a
simple character string with the exception of `\':
- \\
- backslash
- \ooo
- octal representation of a character (where ooo is one to three
octal digits)
- \c
- character c
- The resulting value must be no more than 20 characters. The null string
(``""'') is the default.
- ipmiworkaround
[!]option[,...]|""
-
You can turn off a workaround by prefixing it with a ``!'' character.
So, to turn off the integrity workaround, you would use
!integrity. The following are valid options and their
mapping to FreeIPMI settings:
- If no ipmiworkaround is specified, the ``default''
workaround will be used. The null string (``""'') unsets
all workarounds, including ``default''. See the FreeIPMI
documentation for details on what workarounds affect.
- ipmiprivlevel
user|operator|admin
-
Set the privilege level for the username used during IPMI authentication.
The default privilege level is ``admin''.
- include
default
-
The default block defined using the name default is applied to the
current console or default block. The included default block must be
previously defined.
- initcmd
command|""
-
Invoke command as soon as the console is brought up, redirecting the
console to stdin, stdout, and stderr of command. The command
is passed as an argument to ``/bin/sh -ce''. If the null string
(``""'') is used, the command is unset and nothing is
invoked.
- initrunas
[user][:group]|""
-
By default, the command invoked by initcmd is run with the same
privileges as the server. If the server is running with root privileges,
this option resets the user and/or group of the invoked process to
user and group respectively. user may be a username
or numeric uid and group may be a group name or numeric gid. Either
one is optional. If the server is not running with root privileges, these
values are not used. If the null string (``""'') is
specified, the default of running with the same privileges as the server
is restored.
- initspinmax
n|""
-
Set the maximum number of ``spins'' allowed for the console to n,
where 0 <= n <= 254. A console is determined to be
``spinning'' if an attempt to initialize the console occurs in under
initspintimer seconds from its previous initialization and this
quick initialization occurs initspinmax times in a row. If, at any
point, the time between initializations is greater than
initspintimer, the counter for reaching initspinmax resets
to zero. When a console is determined to be ``spinning'' it is forced
down. If the null string (``""'') is specified, the
default of 5 is used.
- initspintimer
t|""
-
Set the number of seconds a console must be ``up'' to not be considered
``spinning'' to t, where 0 <= t <= 254. See
initspinmax for a full description of console ``spinning.'' If the
null string (``""'') is specified, the default of
1 is used.
- initsubst
c=t[n]f[,...]|""
-
Perform character substitutions on the initcmd value. See the
devicesubst option for an explanation of the format string. If the
null string (``""'') is used, no replacements will be
done.
- logfile
filename|""
-
Assign the logfile specified by filename to the console. Any
occurrence of ``&'' in filename will be replaced with the name
of the console. If the null string (``""'') is used, the
logfile name is unset and no logging will occur.
- logfilemax
number[k|m]
-
Enable automatic rotation of logfile once its size exceeds
number bytes. Specifying k or m interpret
number as kilobytes and megabytes. number must be at least
2048 bytes. A value of zero will turn off automatic rotation of
logfile. The logfile filename will be renamed
filename-YYYYMMDD-HHMMSS, where the extension is the current GMT
year, month, day, hour, minute, and second (to prevent issues with clock
rollbacks). File sizes are checked every 5 minutes with an additional
initial pseudo-random delay of up to one minute (to help prevent all
processes checking all consoles simultaneously). 2.5% (minimum 100 bytes,
maximum 4000 bytes) of the old logfile is read from the end of the file.
All data past the first newline is moved (not copied) to the new logfile
so that a replay of the console works and starts on a line boundary.
- master
hostname|ipaddr
-
Define which conserver host manages the console. The host may be specified
by hostname or using the address ipaddr.
- motd
message|""
-
Set the "message of the day" for the console to message,
which gets displayed when a client attaches to the console. If the null
string (``""'') is used, the MOTD is unset and no message
will occur.
- options
[!]option[,...]|""
-
You can negate the option by prefixing it with a ``!'' character. So,
to turn off the hupcl flag, you would use !hupcl. The
following are valid options:
- ixon
- Enable XON/XOFF flow control on output. Only consoles of
type ``device'' or ``exec'' will use this value. Default is
ixon.
- ixany
- Enable any character to restart output. Only consoles of type ``device''
or ``exec'' will use this value. Default is !ixany.
- ixoff
- Enable XON/XOFF flow control on input. Only consoles of
type ``device'' or ``exec'' will use this value. Default is ixoff
for consoles of type ``device'' and !ixoff for consoles of type
``exec''.
- crtscts
- Enable RTS/CTS (hardware) flow control. Only consoles of
type ``device'' will use this value. Default is !crtscts.
- cstopb
- Set two stop bits, rather than one. Only consoles of type ``device'' will
use this value. Default is !cstopb.
- hupcl
- Lower modem control lines after last process closes the device (hang up).
Only consoles of type ``device'' will use this value. Default is
!hupcl.
- ondemand
- Initialize the console when a client requests a connection to the console.
When no clients are connected, bring the console down. The conserver
option -i will set this flag for all consoles. Default is
!ondemand.
- striphigh
- Strip the high bit off all data coming from this console and all clients
connected to this console before processing occurs. The conserver option
-7 will set this flag for all consoles. Default is
!striphigh.
- reinitoncc
- Automatically reinitialize (``bring up'') a downed console when a client
connects. Without this option, a client will be attached to the downed
console and will need to manually reinitialize the console with an escape
sequence. The conserver option -o will set this flag for all
consoles. Default is !reinitoncc.
- autoreinit
- Allow this console to be automatically reinitialized if it unexpectedly
goes down. If the console doesn't come back up, it is retried every
minute. A console of type ``exec'' that exits with a zero exit status is
automatically reinitialized regardless of this setting. The conserver
option -F will unset this flag for all consoles. Default is
autoreinit.
- unloved
- Enable the sending of this console's output (prefixed with its name) to
the daemon's stdout (or the logfile if in daemon mode) when no clients are
connected to the console. The conserver option -u will set this
flag for all consoles. Default is !unloved.
- login
- Allow users to log into this console. If logins are not allowed, conserver
will send a generic message to the client saying so and terminate the
connection. You can override the generic message by setting the
motd message. Default is login.
- parity
even|mark|none|odd|space
-
Set the parity option for the console. Only consoles of type ``device'' will
use this value.
- password
password|""
-
Use password during IPMI authentication. If the null string
(``""'') is used (the default), no password will be
used.
- port
number|name
-
Set the port used to access the console. The port may be specified as a
number or a name. A name will cause a
getservbyname(3) call to look up the port number. The port,
portbase, and portinc values are all used to calculate the
final port number to connect to. The formula used is finalport =
portbase + portinc * port. By using proper values in
the formula, you can reference ports on a terminal server by their
physical numbering of 0..n or 1..n (depending on if you like
zero-based or one-based numbering). Warning: you can generate a -1 value
with this formula, which will become a very high numbered positive value
(since things are stored unsigned). You must also set the host
option as well. Normally, only consoles of type ``host'' will use this
value, however if the devicesubst, execsubst, or
initsubst keywords are used in any console type, this value is
used.
- portbase
number
-
Set the base value for the port calculation formula. number must be 0
or greater. The default is zero. See port for the details of the
formula.
- portinc
number
-
Set the increment value for the port calculation formula. number must
be 0 or greater. The default is one. See port for the details of
the formula.
- protocol
telnet|raw
-
Set the protocol used to send and receive data from the console. If
raw is used, all data is sent ``as is'', unprotected by any
protocol specification. If telnet is used (which is the default),
data is encapsulated in the telnet protocol. The striphigh console
option still applies when data is read by the server, and if enabled, can
impact the encapsulation process.
- replstring
string
-
A generic replacement string that can be used by the devicesubst,
execsubst, and initsubst keywords.
- ro
[!]username[,...]|""
-
Define a list of users making up the read-only access list for the console.
If username matches a previously defined group name, all members of
the previous group are applied to the read-only access list (with access
reversed if prefixed with a `!'). If username doesn't match a
previously defined group and username begins with `@', the name
(minus the `@') is checked against the host's group database. All users
found in the group will be granted (or denied, if prefixed with `!')
read-only access. If username doesn't match a previous group and
doesn't begin with `@', the users will be granted (or denied, if prefixed
with `!') read-only access. If the null string (``""'')
is used, any users previously defined for the console's read-only list are
removed.
- rw
[!]username[,...]|""
-
Define a list of users making up the read-write access list for the console.
If username matches a previously defined group name, all members of
the previous group are applied to the read-write access list (with access
reversed if prefixed with a `!'). If username doesn't match a
previously defined group and username begins with `@', the name
(minus the `@') is checked against the host's group database. All users
found in the group will be granted (or denied, if prefixed with `!')
read-write access. If username doesn't match a previous group and
doesn't begin with `@', the users will be granted (or denied, if prefixed
with `!') read-write access. If the null string (``""'')
is used, any users previously defined for the console's read-write list
are removed.
- tasklist
c[,...]|""
- Associate a list of tasks referenced by c with the console. If
``*'' is used (the default), all defined tasks will be available. If the
null string (``""'') is used, no tasks will be
available.
- timestamp
[number[m|h|d|l]][a][b]|""
-
Specifies the time between timestamps applied to the console log file and
whether to log read/write connection actions. The timestamps look like
``[-- MARK -- Mon Jan 25 14:46:56 1999]''. The `m', `h', and
`d' tags specify ``minutes'' (the default), ``hours'', and
``days''. The `l' tag specifies ``lines'' and will cause timestamps
of the form ``[Mon Jan 25 14:46:56 PST 1999]'' to be placed every
number lines (a newline character signifies a new line). So, ``5h''
specifies every five hours and ``2l'' specifies every two lines. An
`a' can be specified to add logs of ``attached'', ``detached'', and
``bumped'' actions, including the user's name and the host from which the
client connection was made. A `b' can be specified to add logging
of break sequences sent to the console.
- type
device|ipmi|exec|host|noop|uds
-
Set the type of console. A type of ``device'' should be used for
local serial ports (also set the device value). A type of
``ipmi'' should be used for IPMI serial over LAN consoles (also set
the host value and possibly the username, password,
and ipmi* values). A type of ``exec'' should be used for
command invocations (perhaps also set the exec value). A type of
``host'' should be used for terminal servers and other TCP
socket-based interaction (also set the host and port
values). A type of ``noop'' should be used as a placeholder - it
does nothing, ignores any logfile value and forces the
!nologin option (so you might want to set the motd value). A
type of ``uds'' should be used for Unix domain sockets (also set
the uds option).
- uds
filename
-
Assign the Unix domain socket filename as the path to the console.
Only consoles of type ``uds'' will use this value.
- udssubst
c=t[n]f[,...]|""
-
Perform character substitutions on the uds value. See the
devicesubst option for an explanation of the format string. If the
null string (``""'') is used, no replacements will be
done.
- username
username|""
-
Use username during IPMI authentication. If the null string
(``""'') is used (the default), the ``null'' user will be
used.
- group
name
-
Define a user group identified as name.
- users
[!]username[,...]|""
-
Define a list of users making up the group name. If username
matches a previously defined group name, all members of the previous group
are applied to the current group (with access reversed if prefixed with a
`!'). If username doesn't match a previously defined group and
username begins with `@', the name (minus the `@') is checked
against the host's group database. All users found in the group will be
recorded with (or without, if prefixed with `!') access. If
username doesn't match a previous group and doesn't begin with `@',
the users will be recorded with (or without, if prefixed with `!') access.
If the null string (``""'') is used, any users previously
defined for this group are removed.
- task c
-
Define a task where c is a lowercase alphanumeric (0-9a-z). Tasks are
invoked via the ``^Ec!c'' client escape sequence.
- cmd
command|""
-
Invoke command on the server when instructed by the client. All file
descriptors are closed, except for stderr (which is inherited from the
server). The command is passed as an argument to ``/bin/sh -ce''
and is a ``fire and forget'' methodology (you need to check logs for any
issues). If the null string (``""'') is used, the entire
task definition is ignored.
- confirm
yes|true|on|no|false|off
-
Set whether or not to ask the client for confirmation before invoking the
task. The default is ``no''.
- description
string
-
Set a description for the task. When a client lists tasks, string
will be printed instead of the command defined above. If the null string
(``""'') is used, the command defined above will be
printed.
- runas
[user][:group]|""
-
By default, the command invoked by cmd is run with the same
privileges as the server. If the server is running with root privileges,
this option resets the user and/or group of the invoked process to
user and group respectively. user may be a username
or numeric uid and group may be a group name or numeric gid. Either
one is optional. If the server is not running with root privileges, these
values are not used. If the null string (``""'') is
specified, the default of running with the same privileges as the server
is restored.
- subst
c=t[n]f[,...]|""
-
Perform character substitutions on the cmd value. See the
devicesubst option for an explanation of the format string. If the
null string (``""'') is used, no replacements will be
done.
Bryan Stansell, conserver.com