|tcpsvd(8)||System Manager's Manual||tcpsvd(8)|
NAME¶tcpsvd - TCP/IP service daemon
SYNOPSIS¶tcpsvd [-hpEvv] [-c n] [-C n:msg] [-b n] [-u user] [-l name] [-i dir|-x cdb] [ -t sec] host port prog
DESCRIPTION¶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 either is a hostname, or a dotted-decimal IP address, or 0. If host is 0, tcpsvd accepts connections to any local IP address.
- tcpsvd accepts connections to host:port. port may be a name from /etc/services or a number.
- 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. 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 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.
- 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 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.
- no special environment. Do not set up TCP-related environment variables.
- verbose. Print verbose messsages to standard output.
- more verbose. Print more verbose messages to standard output.