To find out which tty's are attached to which processes use the "ps -a" command at the shell prompt (command line). Look at the "tty" column. For the shell process you're in, /dev/tty is the terminal you are now using. Type "tty" at the shell prompt to see what it is (see manual pg.
To enable the serial console for your custom Linux VM image, enable console access in the file /etc/inittab to run a terminal on ttyS0 . For example: S0:12345:respawn:/sbin/agetty -L 115200 console vt102 . You may also need to spawn a getty on ttyS0. This can be done with systemctl start [email protected] .
The /sys
filesystem should contain plenty information for your quest. My system (2.6.32-40-generic #87-Ubuntu) suggests:
/sys/class/tty
Which gives you descriptions of all TTY devices known to the system. A trimmed down example:
# ll /sys/class/tty/ttyUSB*
lrwxrwxrwx 1 root root 0 2012-03-28 20:43 /sys/class/tty/ttyUSB0 -> ../../devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.4/2-1.4:1.0/ttyUSB0/tty/ttyUSB0/
lrwxrwxrwx 1 root root 0 2012-03-28 20:44 /sys/class/tty/ttyUSB1 -> ../../devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.3/2-1.3:1.0/ttyUSB1/tty/ttyUSB1/
Following one of these links:
# ll /sys/class/tty/ttyUSB0/
insgesamt 0
drwxr-xr-x 3 root root 0 2012-03-28 20:43 ./
drwxr-xr-x 3 root root 0 2012-03-28 20:43 ../
-r--r--r-- 1 root root 4096 2012-03-28 20:49 dev
lrwxrwxrwx 1 root root 0 2012-03-28 20:43 device -> ../../../ttyUSB0/
drwxr-xr-x 2 root root 0 2012-03-28 20:49 power/
lrwxrwxrwx 1 root root 0 2012-03-28 20:43 subsystem -> ../../../../../../../../../../class/tty/
-rw-r--r-- 1 root root 4096 2012-03-28 20:43 uevent
Here the dev
file contains this information:
# cat /sys/class/tty/ttyUSB0/dev
188:0
This is the major/minor node. These can be searched in the /dev
directory to get user-friendly names:
# ll -R /dev |grep "188, *0"
crw-rw---- 1 root dialout 188, 0 2012-03-28 20:44 ttyUSB0
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:
# ll /sys/class/tty/*/device/driver
lrwxrwxrwx 1 root root 0 2012-03-28 19:07 /sys/class/tty/ttyS0/device/driver -> ../../../bus/pnp/drivers/serial/
lrwxrwxrwx 1 root root 0 2012-03-28 19:07 /sys/class/tty/ttyS1/device/driver -> ../../../bus/pnp/drivers/serial/
lrwxrwxrwx 1 root root 0 2012-03-28 19:07 /sys/class/tty/ttyS2/device/driver -> ../../../bus/platform/drivers/serial8250/
lrwxrwxrwx 1 root root 0 2012-03-28 19:07 /sys/class/tty/ttyS3/device/driver -> ../../../bus/platform/drivers/serial8250/
lrwxrwxrwx 1 root root 0 2012-03-28 20:43 /sys/class/tty/ttyUSB0/device/driver -> ../../../../../../../../bus/usb-serial/drivers/ftdi_sio/
lrwxrwxrwx 1 root root 0 2012-03-28 21:15 /sys/class/tty/ttyUSB1/device/driver -> ../../../../../../../../bus/usb-serial/drivers/ftdi_sio/
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:
flu0@laptop:~$ ls /dev/serial/
total 0
drwxr-xr-x 2 root root 60 2011-07-20 17:12 by-id/
drwxr-xr-x 2 root root 60 2011-07-20 17:12 by-path/
flu0@laptop:~$ ls /dev/serial/by-id/
total 0
lrwxrwxrwx 1 root root 13 2011-07-20 17:12 usb-Prolific_Technology_Inc._USB-Serial_Controller-if00-port0 -> ../../ttyUSB0
flu0@laptop:~$ ls /dev/serial/by-path/
total 0
lrwxrwxrwx 1 root root 13 2011-07-20 17:12 pci-0000:00:0b.0-usb-0:3:1.0-port0 -> ../../ttyUSB0
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.
$ ls -al /sys/class/tty/ttyUSB0//device/driver
lrwxrwxrwx 1 root root 0 sep 6 21:28 /sys/class/tty/ttyUSB0//device/driver -> ../../../bus/platform/drivers/usbserial
and for ttyS0
$ ls -al /sys/class/tty/ttyS0//device/driver
lrwxrwxrwx 1 root root 0 sep 6 21:28 /sys/class/tty/ttyS0//device/driver -> ../../../bus/platform/drivers/serial8250
All drivers driven by serial8250 must be probes using the previously mentioned ioctl.
if (ioctl(fd, TIOCGSERIAL, &serinfo)==0) {
// If device type is no PORT_UNKNOWN we accept the port
if (serinfo.type != PORT_UNKNOWN)
the_port_is_valid
Only port reporting a valid device-type is valid.
The complete source for enumerating the serialports looks like this. Additions are welcome.
#include <stdlib.h>
#include <dirent.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <string.h>
#include <fcntl.h>
#include <termios.h>
#include <sys/ioctl.h>
#include <linux/serial.h>
#include <iostream>
#include <list>
using namespace std;
static string get_driver(const string& tty) {
struct stat st;
string devicedir = tty;
// Append '/device' to the tty-path
devicedir += "/device";
// Stat the devicedir and handle it if it is a symlink
if (lstat(devicedir.c_str(), &st)==0 && S_ISLNK(st.st_mode)) {
char buffer[1024];
memset(buffer, 0, sizeof(buffer));
// Append '/driver' and return basename of the target
devicedir += "/driver";
if (readlink(devicedir.c_str(), buffer, sizeof(buffer)) > 0)
return basename(buffer);
}
return "";
}
static void register_comport( list<string>& comList, list<string>& comList8250, const string& dir) {
// Get the driver the device is using
string driver = get_driver(dir);
// Skip devices without a driver
if (driver.size() > 0) {
string devfile = string("/dev/") + basename(dir.c_str());
// Put serial8250-devices in a seperate list
if (driver == "serial8250") {
comList8250.push_back(devfile);
} else
comList.push_back(devfile);
}
}
static void probe_serial8250_comports(list<string>& comList, list<string> comList8250) {
struct serial_struct serinfo;
list<string>::iterator it = comList8250.begin();
// Iterate over all serial8250-devices
while (it != comList8250.end()) {
// Try to open the device
int fd = open((*it).c_str(), O_RDWR | O_NONBLOCK | O_NOCTTY);
if (fd >= 0) {
// Get serial_info
if (ioctl(fd, TIOCGSERIAL, &serinfo)==0) {
// If device type is no PORT_UNKNOWN we accept the port
if (serinfo.type != PORT_UNKNOWN)
comList.push_back(*it);
}
close(fd);
}
it ++;
}
}
list<string> getComList() {
int n;
struct dirent **namelist;
list<string> comList;
list<string> comList8250;
const char* sysdir = "/sys/class/tty/";
// Scan through /sys/class/tty - it contains all tty-devices in the system
n = scandir(sysdir, &namelist, NULL, NULL);
if (n < 0)
perror("scandir");
else {
while (n--) {
if (strcmp(namelist[n]->d_name,"..") && strcmp(namelist[n]->d_name,".")) {
// Construct full absolute file path
string devicedir = sysdir;
devicedir += namelist[n]->d_name;
// Register the device
register_comport(comList, comList8250, devicedir);
}
free(namelist[n]);
}
free(namelist);
}
// Only non-serial8250 has been added to comList without any further testing
// serial8250-devices must be probe to check for validity
probe_serial8250_comports(comList, comList8250);
// Return the lsit of detected comports
return comList;
}
int main() {
list<string> l = getComList();
list<string>::iterator it = l.begin();
while (it != l.end()) {
cout << *it << endl;
it++;
}
return 0;
}
I found
dmesg | grep tty
doing the job.
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