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OS X:Terminal Break for Serial Console on OS X

15th May 2009 By 7 Comments

In a previous post Serial Console on OS X I wrote about how to connect a USB-Serial converter to console into Cisco router and use the ‘screen’ command.

To perform a password recovery on a Cisco router you need to issue a “terminal break” character to interrupt the boot process. The Cisco page on terminal break shows a lot of break sequences.

The break sequence for “screen” is to use Ctrl-A and then Ctrl-B. The Ctrl-A shifts the focus back to the screen process (away from the serial console) and the Ctrl-B issues the break sequence.

You may need to break more than once. This is done by Ctrl-A, Ctrl-B, Ctrl-B, Ctrl-B.

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About Greg Ferro

Greg Ferro is a Network Engineer/Architect, mostly focussed on Data Centre, Security Infrastructure, and recently Virtualization. He has over 20 years in IT, in wide range of employers working as a freelance consultant including Finance, Service Providers and Online Companies. He is CCIE#6920 and has a few ideas about the world, but not enough to really count.

He is a host on the Packet Pushers Podcast, blogger at EtherealMind.com and on Twitter @etherealmind and Google Plus

  • Dmitri

    …and if it works for you – you’re lucky, because not very many USB to Serial adapters pass “break”.

  • http://cisco.markom.info/ Marko Milivojevic

    I believe that the problem with break on OSX is with Prolific driver. You may wish to try open source one. I had no luck with it (didn’t handle large buffers when pasting) and I’m stuck with Prolific driver.

  • http://www.garysmith.org.uk Gary Smith

    I think it does depend on the chipset of the convertor – I’ve got a PL2303 based unit here and I’ve been struggling to find a way to issue a break with it. I don’t believe it’s possible to do, although there’s been many rumours about the functionality being added in to a later release of the driver.

    Cheers,

    Gary Smith

  • Chris Welsh

    IT WORKED FOR ME – I’m using iTerm though, rather than the built in Apple Terminal program.

    Thanks Greg.

    • Joe Finley

      Ok, here’s what I did.

      download – Installed ITERM
      download – install the opensource PROLIFIC drivers
      ——Not sure if this made any difference——
      Open Network Interfaces – Selected USB-Serial D2″, created a new profile “SERIAL”
      Clicked Advanced.. “Modem – Vendor Null Modem” Model “9600″ (OK)
      Clicked on the USB-Seral D1 to “Default”
      ———————————————-

      Open iTerm, typed “ls -la /dev/tty.*”

      crw-rw-rw- 1 root wheel 11, 4 Jul 6 13:22 /dev/tty.Bluetooth-Modem
      crw-rw-rw- 1 root wheel 11, 0 Jul 6 13:21 /dev/tty.Bluetooth-PDA-Sync
      crw-rw-rw- 1 root wheel 11, 12 Jul 6 13:35 /dev/tty.PL2303-00301124
      crw-rw-rw- 1 root wheel 11, 2 Jul 6 13:21 /dev/tty.jfinleysiphone-Wireless
      crw-rw-rw- 1 root wheel 11, 10 Jul 6 13:27 /dev/tty.usbserial

      Then I typed screen “/dev/tty.PL2303-00301124 9600″
      Assuming the opensource is “PL2303-00301124″
      Powercycled the router & hit control-a & control-b many times

      Finally received the ROM-MON!

  • Volker

    An alternative is to set the lowest possible speed for the port, e.g. 110 baud. Pressing SPACE or ENTER should get you into ROMMON. Switch back to 9600 baud after a minute to see the command line. This should work with all adapters especially if they don’t support the Break signal.

    Volker

  • Darrell Burnett

    If you have virtualization software installed (Fusion, Parallels, etc) you can run Putty from a Windows XP VM for example. Pass the USB to serial adapter to Windows and run Putty. In the Putty console window there is an option to pass the break function (Special Command -> break), this works well. IO Gear is the USB to serial adapter I use, and I never had a problem passing the break function over IO Gear cables.