tcpsvd - TCP/IP service daemon
tcpsvd [-hpEvv] [-c n] [-C n:msg] [-b n] [-u user] [-l name] [-i dir|-x
cdb] [ -t sec] host port prog
tcpsvd creates a TCP/IP socket, binds it to the address host:port, and
listens on the socket for incoming connections.
On each incoming connection, tcpsvd conditionally runs a program, with
standard input reading from the socket, and standard output writing to
the socket, to handle this connection. tcpsvd keeps listening on the
socket for new connections, and can handle multiple connections
tcpsvd optionally checks for special instructions depending on the IP
address or hostname of the client that initiated the connection, see
host host either is a hostname, or a dotted-decimal IP address, or 0.
If host is 0, tcpsvd accepts connections to any local IP
port tcpsvd accepts connections to host:port. port may be a name
from /etc/services or a number.
prog prog consists of one or more arguments. For each connection,
tcpsvd normally runs prog, with file descriptor 0 reading from
the network, and file descriptor 1 writing to the network. By
default it also sets up TCP-related environment variables, see
-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; tcpsvd 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. This option must be set if tcpsvd listens
on port 53 to avoid loops.
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.
-c n concurrency. Handle up to n connections simultaneously.
Default is 30. If there are n connections active, tcpsvd defers
acceptance of a new connection until an active connection is
per host concurrency. Allow only up to n connections from the
same IP address simultaneously. If there are n active
connections from one IP address, new incoming connections from
this IP address are closed immediately. If n is followed by
:msg, the message msg is written to the client if possible,
before closing the connection. By default msg is empty. See
ipsvd-instruct(5) for supported escape sequences in msg.
For each accepted connection, the current per host concurrency
is available through the environment variable TCPCONCURRENCY. n
and msg can be overwritten by ipsvd(7) instructions, see ipsvd-
instruct(5). By default tcpsvd doesn’t keep track of
-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 about
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.
-b n backlog. Allow a backlog of approximately n TCP SYNs. On some
systems n is silently limited. Default is 20.
-E no special environment. Do not set up TCP-related environment
-v verbose. Print verbose messsages to standard output.
-vv more verbose. Print more verbose messages to standard output.
ipsvd(7), sslsvd(8), udpsvd(8), ipsvd-instruct(5), ipsvd-cdb(8),
Gerrit Pape <email@example.com>