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
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.
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
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.
tcpsvd(8), sslsvd(8), ipsvd-instruct(5), ipsvd-cdb(8)
- 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.
- udpsvd accepts datagrams
to host:port. port may be a name from /etc/services or a number.
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
- -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.
- Look up the
client’s hostname in DNS.
- 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.
- verbose. Print verbose messages to standard output.
verbose. Print more verbose messages to standard output.
Gerrit Pape <firstname.lastname@example.org>
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