ipsvd-instruct(5)                                            ipsvd-instruct(5)



NAME
       ipsvd-instruct - format of the ipsvd(8) instructions directory

DESCRIPTION
       The internet protocol service daemons, ipsvd(7), can be told to read
       and follow instructions from a directory on incoming connections to the
       socket they listen on.

       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.

MATCHING
       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:

       1.     a.b.c.d

       2.     a.b.c

       3.     a.b

       4.     a

       If the client's hostname has been successfully looked up in DNS:

       5.     moa.bit.smarden.org

       6.     bit.smarden.org

       7.     smarden.org

       8.     org

       And finally the catchall file ``0'' (zero):

       9.     0

       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:

       1.     If neither the user's read permission, nor the user's execute
              permission is set for the file, the connection is closed
              immediately.

       2.     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.

       3.     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).

INSTRUCTIONS
       If 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.

       +VAR=VALUE
              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.

       Cnum[:msg]
              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.

       =hostname[:forward]
              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
              lookups.

       If ipsvd(7) cannot interpret a line, it prints a warning, discards the
       line, and continues with the next instruction if any.

       After processing 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.

EXAMPLE INSTRUCTIONS
       +MEMORY=20000
              This instruction causes the environment variable ``MEMORY'' with
              the value ``20000'' to be available to the program prog that
              handles the connection.

       +DEBUG=
              This instruction adds the variable ``DEBUG'' with an empty value
              to the environment.

       +LOGNAME
              This instructions makes sure that the environment variable
              ``LOGNAME'' is unset when running prog.

       C16    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.

       =floyd.dyn.smarden.org:127.0.0.1
              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.

SEE ALSO
       ipsvd(7), ipsvd-cdb(8), tcpsvd(8), sslsvd(8), udpsvd(8), sslio(8)

       http://smarden.org/ipsvd/

AUTHOR
       Gerrit Pape <pape@smarden.org>



                                                             ipsvd-instruct(5)
