SOCKETPIPE(1) SOCKETPIPE(1)
NAME
socketpipe - zero overhead remote process plumbing
SYNOPSIS
socketpipe [-b] [-i { input generation command [args ... ] } ] -l {
login command [args ... ] } -r { remote command [args ... ] } [-o {
output processing command [args ... ] } ]
DESCRIPTION
Socketpipe connects over a TCP/IP socket the remote command specified
to the local input generation command and/or the local output process-
ing command. At least one of the two local commands must be specified.
The input and output of the remote command are appropriately redirected
so that the remote command's input will come from the local input gen-
eration command and the remote command's output will be sent to the
local output processing command. The remote command is executed on the
machine accessed through the login command. The socketpipe executable
should be available through the execution path in the remote machine.
The braces used for delimiting the commands and their arguments should
be space-separated and can be nested. This feature allows you to setup
complex and efficient topologies of distributed communicating pro-
cesses.
Although the initial socketpipe communication setup is performed
through client-server intermediaries such as ssh(1) or rsh(1), the com-
munication channel that socketpipe establishes is a direct socket con-
nection between the local and the remote commands. Without the use of
socketpipe, when piping remote data through ssh(1) or rsh(1), each data
block is read at the local end by the respective client, is sent to the
remote daemon and written out again to the remote process. The use of
socketpipe removes the inefficiency of the multiple data copies and
context switches and can in some cases provide dramatic throughput
improvements. On the other hand, the confidentiality and integrity of
the data passing through socketpipe's data channel is not protected;
socketpipe should therefore be used only within a confined LAN environ-
ment. (The authentication process uses the protocol of the underlying
login program and is no more or less vulnerable than using the program
in isolation; ssh(1) remains secure, rsh(1) continues to be insecure.)
OPTIONS
-l { login command [args ... ] }
Specify the remote login command (see previous section). Use
arguments to this command to specify the host and authentication
options (e.g. username). The remote login command should accept
as further arguments a command and its arguments and execute it
on the remote host. The remote login command is used to execute
a server instance of socketpipe on the remote host. Typical
examples of remote login commands are ssh(1) and rsh(1).
-r { remote command [args ... ] }
Specify the remote processing command (see previous section).
The remote processing command is executed on the remote machine
with its input, output, or both redirected for processing to
local commands.
-i { input generation command [args ... ] }
Specify the remote input generation command (see previous sec-
tion). The output of the input generation command is redirected
as input to the remote command.
-o { output processing command [args ... ] }
Specify the output processing command (see previous section).
The output of the remote command is redirected as input to the
output processing command.
-b Execute the remote login command in batch mode. This option
should be used when no interaction is needed for authentication
purposes with the remote login command. This is for example the
case when user authentication is performed by means of private
keys (ssh(1)) or (horror) the .rhosts(5) file (rsh(1)). The
option circumvents two problems in OpenSSH_3.5p1 (and possibly
also other remote login commands): the setting of our (shared)
output to non-blocking I/O and attempts to read from the stan-
dard input. The first problem may manifest itself through an
error message of the output processing command such as "stdout:
Resource temporarily unavailable". The second problem will not
allow you to put socketpipe instances in the background, stop-
ping them with a tty input signal (SIGTTIN). The -b option will
close the remote login command's standard output and redirect
its standard input from /dev/null solving those problems. On
the other hand this flag will disable I/O to/from the remote
login command and may therefore interfere with any interaction
required for the authentication process.
EXAMPLE
socketpipe -b -i { tar cf - / } -l { ssh remotehost } -r { dd
of=/dev/st0 bs=32k }
Backup the local host on a tape drive located on remotehost.
socketpipe -b -l { ssh remotehost } -r { dd if=/dev/st0 bs=32k } -o {
tar xpf - /home/luser }
Restore a directory using the tape drive on the remote host.
socketpipe -b -i { tar cf - / } -l { ssh remotehost } -r { bzip2 -c }
-o { dd of=/dev/st0 bs=32k }
Backup the local disk on a local tape, compressing the data on the
(presumably a lot more powerful) remotehost.
SEE ALSO
tcpcat(1), zsh(1)
AUTHOR
Diomidis Spinellis -- <http://www.spinellis.gr>
BUGS
The sockets used to connect the local and remote commands may read or
write only parts of the data specified in a read(2) or write(2) opera-
tion. Although this is standard behavior, and is for example correctly
handled by the stdio(3) library, some commands may not expect it and
may exhibit strange bugs. Most examples in Stevens's "Advanced Pro-
gramming in the UNIX Environment" (Addison-Wesley 1992) would fail
reading from sockets; on the other hand Section 6.6 of Stevens's "UNIX
Network Programming" (Prentice Hall 1990) provides code that deals with
this problem.
1 September 2003 SOCKETPIPE(1)