udpsvd - UDP/IP service daemon
udpsvd [-hpvv] [-u user] [-l name] [-i dir|-x cdb] [-t sec] host port
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
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. 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.
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.
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.
ipsvd(7), tcpsvd(8), sslsvd(8), ipsvd-instruct(5), ipsvd-cdb(8)
Gerrit Pape <firstname.lastname@example.org>