NAME¶
udpsvd - UDP/IP service daemon
SYNOPSIS¶
udpsvd [-hpvv] [-u
user] [-l name] [-i dir|-x
cdb] [-t
sec]
host port prog
DESCRIPTION¶
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
redirected to standard error, 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.
ATTENTION:¶
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.
OPTIONS¶
- 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.
port may be a name from /etc/services or a number.
- 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. Set uid and gid to the user's uid
and gid, as found in /etc/passwd, before running prog. If
user is followed by a colon and a group, set the gid to
group's gid, as found in /etc/group, instead of
user's gid. If group consists of a colon-separated list of
group names, set the group ids of all listed groups. If user is
prefixed with a colon, the user and all group arguments are
interpreted as uid and gids respectively, and not looked up in the
password or group file. 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.
SEE ALSO¶
ipsvd(7),
tcpsvd(8),
sslsvd(8),
ipsvd-instruct(5),
ipsvd-cdb(8)
http://smarden.org/ipsvd/
AUTHOR¶
Gerrit Pape <pape@smarden.org>