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
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
tcpsvd optionally checks for special instructions
depending on the IP address or hostname of the client that initiated the
connection, see ipsvd-instruct(5).
ipsvd(7), sslsvd(8), udpsvd(8), ipsvd-instruct(5), ipsvd-cdb(8),
- 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,
- -i dir
- read instructions for handling new connections
from the instructions directory dir. See ipsvd-instruct(5) for details.
- 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
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
- 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
- -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
Gerrit Pape <email@example.com>
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