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Mason Green
Mason Green

Linux Connect To Local Serial Port ##HOT##


The main reason why you need any program like minicom to communicate over a serial port is that the port needs to be set up prior to initiating a connection. If it weren't set up appropriately, the cat and echo commands would not do for you what you might have expected. Notice that once you run a program like minicom, the port is left with the settings that minicom used. You can query the communication settings using the stty program like this:




linux connect to local serial port



If you have done it right; after booting the computer and before running any other program like minicom, the communication settings will be at their default settings. These are probably different than what you will need to make your connection. In this situation, sending the commands cat or echo to the port will either produce garbage or not work at all.


This script is based on another answer, but sends everything over the serial port (except Ctrl+Q), not just single commands followed by Enter. This enables you to use Ctrl+C or Ctrl+Z on the remote host, and to use interactive "GUI" programs like aptitude or alsamixer. It can be quit by pressing Ctrl+Q.


It depends on what you want to do. Do you want to run a shell or applicaiton interactively from the terminal, connect out to another computer over the serial line, automate communication with a device over a serial port?


If you want bidirectional communication then I presume you want something interactive with a human on the terminal. You can configure the system to allow logins from a terminal over a serial port by seting up a getty(1) session on the serial port - getty is the tool for setting up a terminal and allowing logins onto it. Put an entry in your inittab(5) file to run it on the appropriate serial port on a respawn basis.


If you want to connect to a device and initiate automated two way conversations then you could see if expect will get you what you want. Use stty(1) to configure the port to the right parity, baud rate and other relevant settings.


If you want to communicate interactively with another computer over the serial port then you will need terminal emulation software. This does quite a lot - it sets up the port, interprets ANSI or other terminal command sequences (ANSI was far from being the only standard supported by serial terminals). Many terminal emulators also support file transfer protocols such as kermit or zmodem.


Enables X11 forwarding. This can also be specified on a per-host basis in a configuration file. X11 forwarding should be enabled with caution. Users with the ability to bypass file permissions on the remote host (for the user's X authorization database) can access the local X11 display through the forwarded connection. An attacker may then be able to perform activities such as keystroke monitoring. For this reason, X11 forwarding is subjected to X11 SECURITY extension restrictions by default. Please refer to the ssh -Y option and the ForwardX11Trusted directive in ssh_config(5) for more information.


One of the indispensable elements when working on embedded Linux projects is accessing your device via the serial console interface. For this, the computer on which you are developing an embedded system must have a serial port. However, very few computers today have a serial port, and that's why we use USB to serial converters instead.


When you need access to a computer or network console, you can refer to serial console applications. Usually, you require access over SSH to do so. However, from a software and hardware point of view, in some cases, it is also possible to access the console using only serial ports.


You can set the device name by pressing the A key, and the serial port speed by pressing the E key. Then when you exit with Exit, you can use the corresponding serial port.


You can connect to the serial console of your EC2 instance by using the Amazon EC2 console or via SSH. After connecting to the serial console, you can use it for troubleshooting boot, network configuration, and other issues. For more information about troubleshooting, see Troubleshoot your Linux instance using the EC2 Serial Console.


To connect to the serial console using the browser-based client, your browser must support WebSocket. If your browser does not support WebSocket, connect to the serial console using your own key and an SSH client.


The instance must be in the running state. If the instance is in the pending, stopping, stopped, shutting-down, or terminated state, you can't connect to the serial console. For more information about the instance states, see Instance lifecycle.


You can connect to your EC2 instance's serial console by using the browser-based client. You do this by selecting the instance in the Amazon EC2 console and choosing to connect to the serial console. The browser-based client handles the permissions and provides a successful connection.


You can use your own SSH key and connect to your instance from the SSH client of your choice while using the serial console API. This enables you to benefit from the serial console capability to push a public key to the instance.


If a serial console session has already been started for this instance, the command fails because you can only have one session open at a time. It takes 30 seconds to tear down a session after you've disconnected from the serial console in order to allow a new session.


The format of the public DNS name of the serial console service in the AWS GovCloud (US) Regions is serial-console.ec2-instance-connect.GovCloud-region.amazonaws.com. In the following example, the serial console service is in the us-gov-east-1 Region.


When you connect for the first time to the serial console, you are prompted to verify the fingerprint. You can compare the serial console fingerprint with the fingerprint that's displayed for verification. If these fingerprints don't match, someone might be attempting a "man-in-the-middle" attack. If they match, you can confidently connect to the serial console.


I'm running Ubuntu 10.04 as a virtual machine on my Mac using virtualbox. My idea was to set up a virtual serial connection and write from the host to the guest. Hopefully something as simple as cat "Hello World" > /tmp/fake_serial in a host terminal, and for that to be read by the program in the link above.


So to get this working I just added another Ubuntu VM on VirtualBox, and connected the two together via a virtual serial port. My main, original VM, which I use for a lot of developing will be referred to as VM1. The new VM, with a small hardrive that will only be used for sending messages to VM1 will be called VM2. These are both Ubuntu 10.04 VMs.


You should see Hello appear in the terminal open in VM1. When you're done running screen press ctrl-a k to kill it, otherwise if you try to do other stuff with the serial port you may get an error message saying that the port is busy.


When I had to do some serial port testing from my real to virtual machine I ended up doing a "loop back" type testing. I took two USB-Serial converters and a RS232 F-F adaptor and connected my machine to itself. Then in VirtualBox under Settings->USB you can route one of the two USB-Serial converters to be "owned" by your VirtualBox.


You can tell VirtualBox to connect the virtual serial port to a software pipe on the host. ... On a Mac, Linux or Solaris host, a local domain socket is used ... On Linux there are various tools which can connect to a local domain socket or create one in server mode. The most flexible tool is socat and is available as part of many distributions.


You can use a pty ("pseudo-teletype", where a serial port is a "real teletype") for this. From one end, open /dev/ptyp5, and then attach your program to /dev/ttyp5; ttyp5 will act just like a serial port, but will send/receive everything it does via /dev/ptyp5.


When the module is loaded, it creates 4 pairs of serial ports. The devices are /dev/tnt0 to /dev/tnt7 where tnt0 is connected to tnt1, tnt2 is connected to tnt3, etc.You may need to fix the file permissions to be able to use the devices.


You may want to look at Tibbo VSPDL for creating a linux virtual serial port using a Kernel driver -- it seems pretty new, and is available for download right now (beta version). Not sure about the license at this point, or whether they want to make it available commercially only in the future.


In Open Source, Remserial (GPL) may also do what you want, using Unix PTY's. It transmits the serial data in "raw form" to a network socket; STTY-like setup of terminal parameters must be done when creating the port, changing them later like described in RFC 2217 does not seem to be supported. You should be able to run two remserial instances to create a virtual nullmodem like com0com, except that you'll need to set up port speed etc in advance.


Socat (also GPL) is like an extended variant of Remserial with many many more options, including a "PTY" method for redirecting the PTY to something else, which can be another instance of Socat. For Unit tets, socat is likely nicer than remserial because you can directly cat files into the PTY. See the PTY example on the manpage. A patch exists under "contrib" to provide RFC2217 support for negotiating serial line settings.


RFC 2217 covers a com port to TCP/IP standard that allows a client on one system to emulate a serial port to the local programs, while transparently sending and receiving data and control signals to a server on another system which actually has the serial port. Here's a high-level overview.


What you would do is find or implement a client com port driver that would implement the client side of the system on your PC - appearing to be a real serial port but in reality shuttling everything to a server. You might be able to get this driver for free from Digi, Lantronix, etc in support of their real standalone serial port servers.


Alternately, the serial port driver source for Linux is readily available. Take that, gut the hardware control pieces, and have that one driver run two /dev/ttySx ports, as a simple loopback. Then connect your real program to the ttyS2 and your simulator to the other ttySx. 350c69d7ab


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