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 simultaneously.

tcpsvd optionally checks for special instructions depending on the IP address or hostname of the client that initiated the connection, see ipsvd-instruct(5).

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 address.

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 tcp-environ(5)

-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.

-l name 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.

-u user[:group]

drop permissions. Switch user ID to user's UID, and group ID to user's primary GID after creating and binding to the socket. If user is followed by a colon and a group name, the group ID is switched to the GID of group instead. 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 closed.

-C n[:msg]

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 connections.

-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 variables.

-v

verbose. Print verbose messsages to standard output.

-vv

more verbose. Print more verbose messages to standard output.

ipsvd(7), udpsvd(8), ipsvd-instruct(5), ipsvd-cdb(8), sslio(8)

http://smarden.org/ipsvd/

Gerrit Pape <pape@smarden.org>