G. Pape
ipsvd
udpsvd - UDP/IP service daemon
udpsvd [-hpvv] [-u user] [-l name]
[-i dir|-x cdb] [-t sec] host port prog
udpsvd creates an UDP/IP
socket, binds it to the address host:port, and listens on the socket for
incoming datagrams.
If a datagram is available on the socket, udpsvd conditionally
starts a program, with standard input reading from the socket, and standard
output writing to the socket, to handle this, and possibly more, datagrams.
udpsvd does not start the program if another program that it has started
before still is running. If the program exits, udpsvd again listens to the
socket until a new datagram is available. If there are still datagrams available
on the socket, the program is restarted immediately.
udpsvd optionally checks
for special intructions depending on the IP address or hostname of the
client sending the datagram which not yet was handled by a running program,
see ipsvd-instruct(5) for details.
UDP is a connectionless protocol.
Most programs that handle user datagrams, such as talkd(8), keep running
after receiving a datagram, and process subsequent datagrams sent to the
socket until a timeout is reached. udpsvd only checks special instructions
for a datagram that causes a startup of the program; not if a program handling
datagrams already is running. It doesn't make much sense to restrict access
through special instructions when using such a program.
On the other hand,
it makes perfectly sense with programs like tftpd(8), that fork to establish
a separate connection to the client when receiving the datagram. In general
it's adequate to set up special instructions for programs that support being
run by tcpwrapper.
- host
- host either is a hostname, or a dotted-decimal
IP address, or 0. If host is 0, udpsvd accepts datagrams to any local IP
address.
- port
- udpsvd accepts datagrams to host:port.
- prog
- prog consists of
one or more arguments. udpsvd normally runs prog to handle a datagram, and
possibly more, that is sent to the socket, if there is no program that
was started before by udpsvd still running and handling datagrams.
- -i dir
- read instructions for handling new connections from the instructions directory
dir. See ipsvd-instruct(5) for details.
- -x cdb
- read instructions for handling
new connections from the constant database cdb. The constant database normally
is created from an instructions directory by running ipsvd-cdb(8).
- -t sec
- timeout. This option only takes effect if the -i option is given. While checking
the instructions directory, check the time of last access of the file that
matches the clients address or hostname if any, discard and remove the
file if it wasn't accessed within the last sec seconds; udpsvd does not
discard or remove a file if the user's write permission is not set, for
those files the timeout is disabled. Default is 0, which means that the
timeout is disabled.
- -l name
- local hostname. Do not look up the local hostname
in DNS, but use name as hostname. By default udpsvd looks up the local hostname
once at startup.
- -u user[:group]
- drop permissions. Switch user ID to user's
UID, and group ID to user's primary GID after creating and binding to the
socket. If user is followed by a colon and a group name, the group ID is
switched to the GID of group instead. All supplementary groups are removed.
- -h
- Look up the client's hostname in DNS.
- -p
- paranoid. After looking up the client's
hostname in DNS, look up the IP addresses in DNS for that hostname, and
forget the hostname if none of the addresses match the client's IP address.
You should set this option if you use hostname based instructions. The -p
option implies the -h option.
- -v
- verbose. Print verbose messages to standard
output.
- -vv
- more verbose. Print more verbose messages to standard output.
ipsvd(7), tcpsvd(8), ipsvd-instruct(5), ipsvd-cdb(8)
http://smarden.org/ipsvd/
Gerrit Pape <pape@smarden.org>
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