Linux Serial Port
Serial Console Linux distribution availability. For the serial console to function properly, the guest operating system must be configured to read and write console messages to the serial port. Most Endorsed Azure Linux distributions have the serial console configured by default. This limitation can be overcome by special multi-port serial port boards, which are designed to share multiple serial ports over a single IRQ line. Multi-port serial cards supported by Linux include the AST FourPort, the Accent Async board, the Usenet Serial II board, the Bocaboard BB-1004, BB-1008, and BB-2016 boards, and the HUB-6 serial board. Serial Ports under Linux. Traditional hardware serial ports under Linux are named as ttyS. where. can be 1,2,3. Etc for eg ttyS1,ttyS2,ttyS23. Etc.They are similar to COM1,COM2 etc under a windows box. While USB to Serial Converter based serial ports are usually named as ttyUSB. where. can be 1,2,3. Etc for eg ttyUSB0,ttyUSB1 etc. On Linux, I want to send a command string (i.e. Some data) to a serial port (containing control characters), and listen to the response (which also usually might contain control characters).
What is the proper way to get a list of all available serial ports/devices on a Linux system?
In other words, when I iterate over all devices in /dev/, how do I tell which ones are serial ports in the classic way, that is, those usually supporting baud rates and RTS/CTS flow control?
The solution would be coded in C.
I ask because I am using a third-party library that does this clearly wrong: It appears to only iterate over /dev/ttyS*. The problem is that there are, for instance, serial ports over USB (provided by USB-RS232 adapters), and those are listed under /dev/ttyUSB*. And reading the Serial-HOWTO at Linux.org, I get the idea that there'll be other name spaces as well, as time comes.
So I need to find the official way to detect serial devices. The problem is that none appears to be documented, or I can't find it.
I imagine one way would be to open all files from /dev/tty* and call a specific ioctl() on them that is only available on serial devices. Would that be a good solution, though?
Update
hrickards suggested to look at the source for 'setserial'.Its code does exactly what I had in mind:
First, it opens a device with:
Then it invokes:
If that call returns no error, then it's a serial device, apparently.
I found similar code in Serial Programming/termios, which suggested to also add the O_NOCTTY option.
There is one problem with this approach, though:
When I tested this code on BSD Unix (that is, Mac OS X), it worked as well. However, serial devices that are provided through Bluetooth cause the system (driver) to try to connect to the Bluetooth device, which takes a while before it'll return with a timeout error. This is caused by just opening the device. And I can imagine that similar things can happen on Linux as well - ideally, I should not need to open the device to figure out its type. I wonder if there's also a way to invoke ioctl functions without an open, or open a device in a way that it does not cause connections to be made?
What should I do?
11 Answers
The /sys filesystem should contain plenty information for your quest. My system (2.6.32-40-generic #87-Ubuntu) suggests:
Which gives you descriptions of all TTY devices known to the system. A trimmed down example:
Following one of these links:
Here the dev file contains this information:
This is the major/minor node. These can be searched in the /dev directory to get user-friendly names:
The /sys/class/tty dir contains all TTY devices but you might want to exclude those pesky virtual terminals and pseudo terminals. I suggest you examine only those which have a device/driver entry:
In recent kernels (not sure since when) you can list the contents of /dev/serial to get a list of the serial ports on your system. They are actually symlinks pointing to the correct /dev/ node:
This is a USB-Serial adapter, as you can see. Note that when there are no serial ports on the system, the /dev/serial/ directory does not exists. Hope this helps :).
I'm doing something like the following code. It works for USB-devices and also the stupid serial8250-devuices that we all have 30 of - but only a couple of them realy works.
Basically I use concept from previous answers. First enumerate all tty-devices in /sys/class/tty/. Devices that does not contain a /device subdir is filtered away. /sys/class/tty/console is such a device. Then the devices actually containing a devices in then accepted as valid serial-port depending on the target of the driver-symlink fx.
and for ttyS0
All drivers driven by serial8250 must be probes using the previously mentioned ioctl.
Linux Serial Port Information
Only port reporting a valid device-type is valid.
The complete source for enumerating the serialports looks like this. Additions are welcome.
I think I found the answer in my kernel source documentation:/usr/src/linux-2.6.37-rc3/Documentation/filesystems/proc.txt
Here is a link to this file:http://git.kernel.org/?p=linux/kernel/git/next/linux-next.git;a=blob_plain;f=Documentation/filesystems/proc.txt;hb=e8883f8057c0f7c9950fa9f20568f37bfa62f34a
setserial with the -g option appears to do what you want and the C source is available at http://www.koders.com/c/fid39344DABD14604E70DF1B8FEA7D920A94AF78BF8.aspx.
hrickardshrickardsI have no serial device here to test it, but if you have python and dbus you can try it yourself.
If it fails you can search inside hwmanager_i.GetAllDevicesWithProperties() to see if the capability name 'serial' that I just guessed has a different name.
HTH
Linux Serial Port Configuration
I do not have a USB serial device, but there must be a way to find the real ports using the HAL libraries directly:
The posted python-dbus code nor this sh script lists the bluetooth /dev/rfcomm* devices, so it is not the best solution.
Note that on other unix platforms, the serial ports are not named ttyS? and even in linux, some serial cards allow you to name the devices. Assuming a pattern in the serial devices names is wrong.
Linux Serial Port In Use
Using /proc/tty/drivers only indicates which tty drivers are loaded. If you're looking for a list of the serial ports check out /dev/serial, it will have two subdirectories: by-id and by-path.
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I wasn't too much of a fan of the op and ed either.
EX:
Thanks to this post: https://superuser.com/questions/131044/how-do-i-know-which-dev-ttys-is-my-serial-port
My approach via group dialout to get every tty with user 'dialout'ls -l /dev/tty* grep 'dialout'to only get its folderls -l /dev/tty* grep 'dialout' rev cut -d ' ' -f1 rev
easy listen to the tty output e.g. when arduino serial out:head --lines 1 < /dev/ttyUSB0
listen to every tty out for one line only:for i in $(ls -l /dev/tty* grep 'dialout' rev cut -d ' ' -f1 rev); do head --lines 1 < $i; done
I really like the approach via looking for drivers:ll /sys/class/tty/*/device/driver
You can pick the tty-Name now:ls /sys/class/tty/*/device/driver grep 'driver' cut -d '/' -f 5
The serial communication manager library has many API and features targeted for the task you want. If the device is a USB-UART its VID/PID can be used. If the device is BT-SPP than platform specific APIs can be used. Take a look at this project for serial port programming: https://github.com/RishiGupta12/serial-communication-manager