Josef “Jeff” Sipek

Serial Console in a Zone

In the past, I’ve talked about serial consoles. I have described how to set up a serial console on Solaris/OpenIndiana. I’ve talked about Grub’s composite console in Illumos-based distros. This time, I’m going do describe the one trick necessary to get tip(1) in a zone working.

In my case, I am using SmartOS to run my zones. Sadly, SmartOS doesn’t support device pass-through of this sort, so I have to tweak the zone config after I create the zone with vmadm.

Let’s assume that the serial port I want to pass through is /dev/term/a. Passing it through into a zone is as easy as:

[root@isis ~]# zonecfg -z 7cff99f6-2b01-464d-9f72-d0ef16ce48af
zonecfg:7cff99f6-2b01-464d-9f72-d0ef16ce48af> add device
zonecfg:7cff99f6-2b01-464d-9f72-d0ef16ce48af:device> set match=/dev/term/a
zonecfg:7cff99f6-2b01-464d-9f72-d0ef16ce48af:device> end
zonecfg:7cff99f6-2b01-464d-9f72-d0ef16ce48af> commit

At this point, you’ll probably want to reboot the zone (I don’t remember if it is strictly necessary). Once it is back up, you’ll want to get into the zone and point your software of choice at /dev/term/a. It doesn’t matter that you are in a zone. The same configuration rules apply — in my case, it’s the same change to /etc/remote as I described previously.

Grub Composite Console

In the past, I’ve described how to get a serial console going on Illumos based systems. If you ever used a serial console in Grub (regardless of the OS you ended up booting), you probably know that telling Grub to output to a serial port causes the VGA console to become totally useless — it’s blank.

Well, if you are using Illumos, you are in luck. About 5 months ago, Joyent integrated a “composite console” in Grub. You can read the full description in the bug report/feature request. The short version is: all grub output can be sent to both the VGA console as well as over a serial port.

It is very easy to configure. In your menu.lst, change the terminal to composite. For example, this comes from my test box’s config file (omitting the uninteresting bits):

serial --unit=0 --speed=115200
terminal composite

Note the use of composite instead of serial. That’s all there is to it.

Serial Console

Over the past couple of days, I’ve been testing my changes to the crashdump core in Illumos. (Here’s why.) I do most of my development on my laptop — either directly, or I use it to ssh into a dev box. For Illumos development, I use the ssh approach. Often, I end up using my ancient desktop (pre-HyperThreading era 2GHz Pentium 4) as a test machine. It gets pretty annoying to have a physical keyboard and monitor to deal with when the system crashes. The obvious solution is to use a serial console. Sadly, all the “Solaris serial console howtos” leave a lot to be desired. As a result, I am going to document the steps here. I’m connecting from Solaris to Solaris. If you use Linux on one of the boxes, you will have to do it a little differently.

Test Box

First, let’s change the console speed from the default 9600 to a more reasonable 115200. In /etc/ttydefs change the console line to:

console:115200 hupcl opost onlcr:115200::console

Second, we need to tell the kernel to use the serial port as a console. Here, I’m going to assume that you are using the first serial port (i.e., ttya). So, open up your Grub config (/rpool/boot/grub/menu.lst assuming your root pool is rpool) and find the currently active entry.

You’ll see something like this:

title openindiana-8
findroot (pool_rpool,0,a)
bootfs rpool/ROOT/openindiana-8
splashimage /boot/splashimage.xpm
foreground FF0000
background A8A8A8
kernel$ /platform/i86pc/kernel/$ISADIR/unix -B $ZFS-BOOTFS
module$ /platform/i86pc/$ISADIR/boot_archive

We need to add two options. One to tell the kernel to use the serial port as a console, and one to tell it the serial config (rate, parity, etc.).

You’ll want to change the kernel$ line to:

kernel$ /platform/i86pc/kernel/$ISADIR/unix -B $ZFS-BOOTFS,console=ttya,ttya-mode="115200,8,n,1,-" -k

Note that we appended the options with commas to the existing -B. If you do not already have a -B, just add it and the two new options. The -k will make the kernel drop into the debugger when bad things happen. You can omit it if you just want a serial console without the debugger getting loaded.

There’s one last thing left to do. Let’s tell grub to use the same serial port and not use a splash image. This can be done by adding these lines to the top of your menu.lst:

serial --unit=0 --speed=115200
terminal serial

and removing (commenting out) the splashimage line.

So, what happens if you make all these changes and then beadm creates a new BE? The right thing! beadm will copy over all the kernel options so your new BE will just work.

Dev Box

I use OpenIndiana on my dev box. I could have used minicom, but I find minicom to be a huge pain unless you have a modem you want to talk to. I’m told that screen can talk to serial ports as well. I decided to keep things super-simple and configured tip.

First, one edits /etc/remote. I just changed the definition for hardwire to point to the first serial port (/dev/term/a) and use the right speed (115200):


Then, I can just run a simple command to get the other system:

$ tip hardwire

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