Manual Reference Pages - UDPSVD (8)
udpsvd - UDP/IP service daemon
udpsvd [-hpvv] [-u
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
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
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
UDP is a connectionless protocol.
Most programs that handle user datagrams, such as
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 doesnt 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
that fork to establish a separate connection to the client when receiving
In general its adequate to set up special instructions for programs that
support being run by tcpwrapper.
host either is a hostname, or a dotted-decimal IP address, or 0.
host is 0,
udpsvd accepts datagrams to any local IP address.
udpsvd accepts datagrams to
port may be a name from /etc/services or a number.
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
-x cdb ||
read instructions for handling new connections from the constant database
cdb. The constant database normally is created from an instructions directory by
-t sec ||
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 wasnt accessed within the last
udpsvd does not discard or remove a file if the users write permission is not set,
for those files the timeout is disabled.
Default is 0, which means that the timeout is disabled.
-l name ||
Do not look up the local hostname in DNS, but use
name as hostname.
udpsvd looks up the local hostname once at startup.
-u [:]user[:group] |
Set uid and gid to the
users uid and gid, as found in
/etc/passwd, before running
user is followed by a colon and a
group, set the gid to
groups gid, as found in
/etc/group, instead of
group consists of a colon-separated list of group names,
set the group ids of all listed groups.
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.
Look up the clients hostname in DNS.
After looking up the clients hostname in DNS, look up the IP addresses in
DNS for that hostname, and forget the hostname if none of the addresses
match the clients IP address.
You should set this option if you use hostname based instructions.
The -p option implies the -h option.
Print verbose messages to standard output.
Print more verbose messages to standard output.
Gerrit Pape <email@example.com>
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