By UNIX domain socket?
By normal TCP/UDP socket?
In my xenomai layer, I have use xddp to generate one virtual port(/dev/rtp0), normal Linux process can access by open this port, and read/write the stream. But it seams difficult for Qt to access the port using QFile.
By UNIX domain socket?
By normal TCP/UDP socket?
the answer is: yes, both, why not?
Qt processes are normal processes, and they can do whatever other linux processes can do. You should be able to open a device file like you'd open it in any other process. Also note that no-one's forcing you to use QFile; you can use normal fopen/fread/mmap/ioctl.. whatever you do to interact with your /dev/rtp0, but I don't think there's anything stopping you from handling files as QFile and getting the low-level file descripter as soon as you need it from that class.
I tested the QLocalServer, it works! The Qt process can send data to the xenomai process by the UNIX domain socket.
I found a couple of answers, but they seem to be specifically relating to Windows machines.
So my question is what are the differences between pipes and sockets, and when/how should you choose one over the other?
what are the differences between pipes and sockets, and when/how should you choose one over the other?
Both pipes and sockets handle byte streams, but they do it in different ways...
pipes only exist within a specific host, and they refer to buffering between virtual files, or connecting the output / input of processes within that host. There are no concepts of packets within pipes.
sockets packetize communication using IPv4 or IPv6; that communication can extend beyond localhost. Note that different endpoints of a socket can share the same IP address; however, they must listen on different TCP / UDP ports to do so.
Usage:
Use pipes:
when you want to read / write data as a file within a specific server. If you're using C, you read() and write() to a pipe.
when you want to connect the output of one process to the input of another process... see popen()
Use sockets to send data between different IPv4 / IPv6 endpoints. Very often, this happens between different hosts, but sockets could be used within the same host
BTW, you can use netcat or socat to join a socket to a pipe.
To complete the answer given by Mike, it is important to mention the existence of UNIX domain sockets, which are available on any POSIX compliant operating system. Although very similar to "normal" internet sockets in terms of usage semantics, they are purely local to the machine (of course internet sockets can also work locally), and thus almost behave like a pipe. Almost, because a UNIX pipe is by definition unidirectional:
Pipes and FIFOs (also known as named pipes) provide a unidirectional
interprocess communication channel. A pipe has a read end and a write
end. Data written to the write end of a pipe can be read from the read
end of the pipe. (excerpt from the man page pipe(7))
UNIX domain sockets also have a very unusual feature, as besides data, they also allow sending file descriptors: this way, an unprivileged process can access any file whose descriptor has been sent over the socket. This technique, according to Wikipedia, is used by the ClamAV antivirus scanning daemon.
So, I've taken a handful of programming courses(object-oriented, web) but never had "hands-on" projects where it's outside of coding.
Now I'm trying to figure out what these SSH stuff is about, I can't even figure out which client to use, so picked filezilla for now.
My question is, where can I read more about these terms like ports, and whatnots, in a way so I'm not learning aimlessly.
Thanks!
Basically, SSH is a way to command another computer exactly what to do over the Internet. You can execute any commend the remote system has, and your user has permission for.
The Internet
The Internet runs on a series of protocols collectively named TCP/IP. TCP/IP defines a way to find and address individual computers (IP) and a way to communicate between them (TCP).
You can think of computers on the Internet as a large collection of office buildings all close together. Each office has the exact same number of windows: 65535. Offices (computers) communicate by stringing channels between windows (ports). Each channel has two ends, called sockets. Each socket is associated with a port on the respective computer. We send data back and forth, and then the connection is closed.
Client/Server
There are two types of computers on the Internet: clients, and servers. Clients request information, and servers provide it. Ports 1-1024 are reserved for servers, 1 port per protocol. The full list is here, and as you can see, it is not without contention.
Let's say you visit a website
Your browser, the client program, sees that you typed "stackoverflow.com", and using DNS, discovers that stackoverflow.com is computer number 64.34.119.12. This is it's IP address. It allows your computer to find the network stackoverflow.com is located in, route to it, and establish a connection to the Stack Overflow web server. The web server is a program that accepts client requests from a browser like yours.
They speak in a protocol called HTTP - it allows your browser to request a page determined by a URL. The server sees the request, runs a program to construct a web page (or retrieves an HTML file, image, or any other file), and sends the result back to the browser. Port 80 has been reserved for HTTP. That means, your computer chooses a random port to connect from, and connects to port #80 on the server.
Unix and the shell
The majority of the Web (The Internet, even) runs on an OS called Linux (a Unix variant), instead of something like Windows. Unix systems possess a command-line interface, running a program called a "shell", which is a direct interface to the system. The shell accepts input, one command at a time. You type text in, and it spits out the out put of the command.
Secure Shell
SSH allows you to do this securely. All data traffic is encrypted using a well-studied published "public-key" cryptographic system. (In fact, it was major news when a vulnerability was discovered in a supporting encryption scheme, see these advisories).
SSH is a protocol commonly running on port 22. Anyone with a computer on the Internet (not behind a firewall) can run an SSH server, and allow users to connect to it and execute commands.
The majority of systems administrators and software developers using Unix on the server use SSH to configure, control, and upload programs to that server (located in some data center somewhere).
More
There are many many more details to all of this. Any term or acronym above can be typed into Wikipedia for pretty comprehensive information. There are plenty of books on Unix, Networking, and Web programming.
SSH is originally a secured replacement for telnet. The need for SSH arose from the fact that telnet does not support encryption and therefore everything (commands, output and password) was plainly visible on the network for all to see.
Because in the beginning SSH encryption (based on key exchange) was supposed to be strong (and it was indeed a marked improvement), and was open source, it took off rapidly and several extensions to the protocol were added, especially in the domain of remote file manageent and transfer.
In addition, SSH is used in tunelling and port forwarding configurations.
In the domain of file copy there are several options.
SCP: cp (copy). Inspired by rcp, an early file transfer extension to ssh.
SFTP: SSH File Transfer Protocol, a newer SSH extension to support File copy and browsing (but not really like FTP with 2 ports). It is more feature rich than both scp and ftp. Think of it as a remote file system protocol (however, however somewhat slower than scp).
FTPS: FTP over TLS/SSL. Needs 2 ports like ftp, one for command and one for data. Both connections can be encrypted.
Secure FTP. Real FTP tunelled over SSH.
The site to which you will need to connect probably offers SFTP. You just need to declare the remote server connection configuration in Filezilla site manager. You will need to provide the server ip address or name, the SSH server port, usually 22 but there are other possibilities (you should have been provided with this info) and select sftp as server type). When the connection is established, accept the public key and that should be it.
You can then drop your devs on the remote server.
OS choice
You shall first make a kind of choice between 2 worlds (MS or Linux).
Provided that the Linux community is somehow significantly less reluctant to share explanations. Also you will loose less time by choosing one or the other one, avoiding to wonder the same questions twice, with different answers depending on which OS you chose.
I experienced both, starting to search for solutions in the MS world, that I knew. Big mistake, loss of time. Then I changed, too late, to the Linux world. So I would advice to go straight to the linux OS for learning. Really many distributions for this. I would advice Debian (opened, user friendly, simple, safe, huge community) but you'll get as many proposals as there are admin.
OS understanding
http://www.linuxfromscratch.org/lfs/
http://www.ibm.com/developerworks/library/l-bash.html
http://tldp.org/LDP/abs/html/
Specific Questions about SSH
It depends a lot on the system you will choose but you could easily build a small client and a small server, then configure both and use ssh. Your 2 servers could even be hosted on the same machine, locally if you wish. Then you will learn how to set up the ssh-client side (often called ssh_config) and the ssh server side (often named sshd_config, with "d" standing for daemon).
Here you can find explanations about ssh for both worlds :
http://support.suso.com/supki/SSH_Tutorial_for_Linux
Some keywords for your google searches
List_of_TCP_and_UDP_port_numbers
ssh-keygen : encrypted keys (private/public),
ssh-add ssh agent
Gentoo keychain
and later but soon if you administrate your server on your own
The two main ones :
1) iptables
You may start with this and then go further with that one
2) fail2ban
this is a complement tool for which you'll find easily plenty of docs
...
Have fun :-)
EDIT: you can easily experience a Linux machine hosted in a windows OS, using virtualization (virtualbox, vm-ware..). It's a safe start and offer a good payback for this time investment. It would allow you to host as many machines (for example one linux server and one linux client) as you wish, in the limits of your HD room.
I assume you need to learn shell scripting. I recommend this book.
Filezilla is a FTP client. Try Putty - free SSH Client. And of course you need Linux server.
If you want to learn about SSH in depth then may I advise you this book SSH: The Secure Shell The Definitive Guide
See here for more info: http://www.snailbook.com/
I've read the book and learned really a lot. It teaches you all about setting up servers, clients, key agents and various (practical) applications.
How can I do inter-process communication between two remote process on unix C/C++? Currently, popen works for two process on same host? Product need to be capability to call remote process and send /receive the data.
As you mentioned popen you may not realize this already allows you to use ssh to remotely execute a process and treat exactly the same as a locally spawned one.
popen ("ssh user#remotehost /usr/bin/cal", "r")
And a pre-emptive link for further questions on ssh:
https://serverfault.com/questions/117007/ssh-key-questions
why would you nut just open the wild card % in the IP so that they could access the host.. remorely..
192.168.1.% something like that...:D
How many sockets can be created from a port?
It's operating system dependent.
For Windows, look here for the MaxConnections entry.
For Linux, look here as the comment on question says.
This is an operating system limit.
Basically each socket will require a file descriptor (in Linux/Unix terms; it's probably equivalent in Windows). The OS will have a per-process file descriptor limit (say 250-1000) and that'll be the upper limit.
That'll be governed by the number of client-side ports available to your process (that i, when you open a connection to a remote host/port combination, you will also require a port at your end).
The total of client side (or ephemeral) ports will be made available to all the processes on your machine. So it depends on what else is currently running.
The number of ports and the configuration is OS dependent. Just Google for 'max number of ports' plus your OS.