I am using a BeagleBone board running Debian.

When I plug in a USB cellular modem, this creates the following files in the /dev folder: ttyACM0, ttyACM1, ttyACM2, ttyACM3, ttyModem0, ttyModem1, ttyModem2 and ttyModem3.

I can't find enough information on this. How and why does it create all these files?

Are these files specific to the modem, or general files that are part of the kernel?

dmesg output when I plug in the device :

 new high-speed USB device number 4 using musb-hdrc
[  663.611026] usb 1-1.1: New USB device found, idVendor=1e2d, 
[  663.611046] usb 1-1.1: New USB device strings: Mfr=1, Product=2, 
[  663.611053] usb 1-1.1: Product: ELSx
[  663.611059] usb 1-1.1: Manufacturer: Cinterion Wireless Modules
[  663.651549] cdc_acm 1-1.1:1.0: ttyACM0: USB ACM device
[  663.659983] cdc_acm 1-1.1:1.2: ttyACM1: USB ACM device
[  663.668360] cdc_acm 1-1.1:1.4: ttyACM2: USB ACM device
[  663.679311] cdc_acm 1-1.1:1.6: ttyACM3: USB ACM device
[  663.689635] cdc_acm 1-1.1:1.8: ttyACM4: USB ACM device
[  663.708738] cdc_ether 1-1.1:1.10 usb0: register 'cdc_ether' at usb-musb- 
hdrc.1-1.1, CDC Ethernet Device, fa:96:11:12:13:14
[  663.718331] cdc_ether 1-1.1:1.10 usb0: kevent 12 may have been dropped
[  663.734877] cdc_ether 1-1.1:1.12 usb1: register 'cdc_ether' at usb-musb- 
hdrc.1-1.1, CDC Ethernet Device, fa:96:11:12:13:16
[  663.838982] 8021q: 802.1Q VLAN Support v1.8
[  663.863935] cdc_ether 1-1.1:1.10 usb0: kevent 12 may have been dropped
[  663.870702] cdc_ether 1-1.1:1.10 usb0: kevent 12 may have been dropped
[  663.914471] IPv6: ADDRCONF(NETDEV_UP): usb0: link is not ready
  • 2
    It refers to I/O hardware (likely serial outputs) detected on your board. Without any other details, it is impossible to know exactly what they are. Please provide more information so we can provide some answers. You should provide the appropriate part of dmesg to see what these devices are. – Paradox May 16 '19 at 17:06
  • @Paradox I've included the appropriate part of dmesg in the question. Thanks – Engineer999 May 16 '19 at 17:20
  • Could you add what this device is, specifically? – Paradox May 16 '19 at 17:26
  • It's a Zoom 4625 USB cellular modem – Engineer999 May 16 '19 at 17:28
  • From the dmesg, this creates 5 ttyACM* devices and 2 ttyModem*, not 4 and 4 as in the description. As to why this particular modem creates that many, only the manufacturer knows. Possible reasons: A bug; different interfaces to access different parts of the modem (control vs. data); different interfaces for different bands; or even something else. – dirkt May 17 '19 at 7:55

/dev/ttyACMX is a USB communication device (CDC) of sub-type "abstract control model" (ACM).

As far as I can tell, each ttyACMX is an alias to the corresponding ttyModemX, which is a GSM modem.

  • Why are there four devices tho, and not just one? – Engineer999 May 16 '19 at 17:38

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