ipsvd-instruct - format of the ipsvd(8) instructions directory
internet protocol service daemons, ipsvd(7), can be told to read and follow
instructions from a directory on incoming connections to the socket they
For mostly static instructions or for performance reasons, it
is possible to compile the instructions from a directory into a constant
database (cdb) with ipsvd-cdb(8) for faster lookup, and to tell ipsvd(7)
to read the instructions from there.
On each incoming connection,
the ipsvd(7) matches the client’s IP address against files in the instructions
directory. For example, the IP address a.b.c.d which reverse resolves to moa.bit.smarden.org
is matched against the following files in the instructions directory, in
this order, first match wins:
- a.b.c.d .
- a.b.c .
- a.b .
If the client’s hostname has
been successfully looked up in DNS:
- moa.bit.smarden.org .
- bit.smarden.org .
And finally the catchall file ‘‘0’’ (zero):
After successfully matching
a client’s IP address or hostname against the instructions directory, ipsvd(7)
examines the file that matched the IP address or hostname, and acts accordingly:
- If neither the user’s read permission, nor the user’s execute permission
is set for the file, the connection is closed immediately. .
- If the file has
the user’s execute permission set, ipsvd(7) reads the contents of the file
and runs /bin/sh -c ’<contents>’ instead of the default program prog given at
the command line for this connection. .
- If the file has the user’s read permission
set, ipsvd(7) reads the contents of the file and interprets each line as
an instruction for this connection (see below).
If the client’s IP address
or hostname doesn’t match any file in the instructions directory, the default
action is taken (the program prog is run to handle the connection).
ipsvd(7) is given instructions for an incoming connection, it reads the
corresponding file and interprets each line as follows. The file may be
empty, meaning that there is no special instruction.
Empty lines and lines
starting with ‘‘#’’ are ignored.
- environment. If the line starts with
a plus (‘‘+’’), and the string following the plus contains a ‘‘=’’, ipsvd(7) puts
the string following the plus into the environment before starting prog
to handle the connection. If the string following the plus doesn’t contain
a ‘‘=’’, ipsvd(7) makes sure that the environment variable with the name string
is not set.
- concurrency. If the line starts with a ‘‘C’’, and is followed
by a number, the per host concurrency limit for the IP address that initiated
the connection is set to this number. If num is zero, per host concurrency
limit is disabled. If num is followed by ‘‘:msg’’, the message msg is written
to this client if possible, if the per host concurrency limit is reached.
msg may contain backslash-escaped characters as follows: ‘‘\\’’ is converted
to a single backslash, ‘‘\n’’ is converted to a new line character, and ‘‘\r’’ is
converted to a carriage return.
On multiple concurrency instructions the
last processed concurrency instruction is considered. Not all ipsvd(7)’s
support per host concurrency.
- check hostname. If the
line starts with a ‘‘=’’, and is followed by a hostname, ipsvd(7) looks up
the IP addresses for hostname in DNS and checks if the client’s IP address
matches one of these IP addresses. If so, ipsvd(7) stops processing the
instructions here and runs prog. If hostname is followed a colon and forward,
ipsvd(7) now examines the file forward and acts accordingly, instead of
running prog. All check hostname instructions in forward are ignored. If
forward does not exist, the connection is closed.
hostname may be ‘‘0’’ (zero),
matching any IP address.
Note: Using check hostname instructions can cause
significant delay while responding to connection attempts, caused by DNS
If ipsvd(7) cannot interpret a line, it prints a warning, discards
the line, and continues with the next instruction if any.
all instructions, ipsvd(7) runs prog. If the file contains at least one
check hostname instruction, and none was successful, it closes the connection
instead of running prog.
ipsvd-cdb(8), tcpsvd(8), sslsvd(8), udpsvd(8), sslio(8)
- This instruction
causes the environment variable ‘‘MEMORY’’ with the value ‘‘20000’’ to be available
to the program prog that handles the connection.
- This instruction
adds the variable ‘‘DEBUG’’ with an empty value to the environment.
- This instructions makes sure that the environment variable ‘‘LOGNAME’’ is unset
when running prog.
- Set the per host concurrency to 16. A connection will
be closed silently if there are already 16 active connections from this
client’s IP address.
- Check IP address of the dynamic
hostname floyd.dyn.smarden.org. If one of the IP addresses floyd.dyn.smarden.org
currently resolves to matches the client’s IP address, handle the connection
through the file 127.0.0.1 in the instructions directory.
Gerrit Pape <email@example.com>
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