How to find all serial devices (ttyS, ttyUSB, ..) on Linux without opening them?

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 0drwxr-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 devlrwxrwxrwx 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/dev188:0

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/driverlrwxrwxrwx 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 0drwxr-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 0lrwxrwxrwx 1 root root 13 2011-07-20 17:12 usb-Prolific_Technology_Inc._USB-Serial_Controller-if00-port0 -> ../../ttyUSB0flu0@laptop:~$ ls /dev/serial/by-path/total 0lrwxrwxrwx 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/driverlrwxrwxrwx 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/driverlrwxrwxrwx 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;   }