1. The autocons.py script checks /proc/cmdline for console=ttyS, and then does nothing if a serial console has been directly specified. It should similarly do nothing if no SPCR table is available to detect the serial port and speed, or if the table is available or says unavailable.
2. DCD is ‘data carrier detect’. I suspect on most, but at least I can confirm on Lenovo servers that the BMC asserts/deasserts DCD signal on the UART if a user connects/disconnects to the remote serial. I was originally going to just put it out there, but when I saw I could make the screen redraw on connection loss/re-establish, thought I’d see if that would pan out. In an ideal world, we could instruct the kernel to do this. I have had a discussion with the kernel developer that added just that, but only for earlyprintk. He was thinking such an option may be nice, but impractical by default (since SPCR is frequently there even if a user doesn’t know what a serial port is). So currently we can do our best with userspace to at least reduce assumptions that things ‘hang’, but not get panic/sysrq without console= From: Song BJ Yang <yang...@cn.ibm.com> Sent: Tuesday, March 19, 2019 5:25 AM To: xcat-user@lists.sourceforge.net Cc: xcat-user@lists.sourceforge.net Subject: [External] Re: [xcat-user] Automatic console support interesting feature. I would like to take a look at your scripts. several questions: 1. is this automatic console behavior only availabe when `console=` not specified in the kernel options? 2. what is "DCD"? ------------------------------------------------------------------------------ YANG Song (杨嵩) IBM China System Technology Laboratory Tel: 86-10-82452903 Email: yang...@cn.ibm.com<mailto:yang...@cn.ibm.com> Address: Building 28, ZhongGuanCun Software Park, No.8, Dong Bei Wang West Road, Haidian District Beijing 100193, PRC 北京市海淀区东北旺西路8号中关村软件园28号楼 邮编: 100193 ----- Original message ----- From: Jarrod Johnson <jjohns...@lenovo.com<mailto:jjohns...@lenovo.com>> To: "xCAT Users Mailing list (xcat-user@lists.sourceforge.net<mailto:xcat-user@lists.sourceforge.net>)" <xcat-user@lists.sourceforge.net<mailto:xcat-user@lists.sourceforge.net>> Cc: Subject: [xcat-user] Automatic console support Date: Tue, Mar 19, 2019 3:37 AM One major contributor to new-user confusion has been the oddity of the console behavior. Generally I see: -When I run rcons, I don’t see anything (because it’s on the video port only) -When I attach a video cable, I don’t see anything (because it’s on the rcons session). To mitigate this, I’ve started doing some automatic console behavior changes. Starting with Lenovo’s next release of genesis the first step is being made. If genesis boots without console=ttyS, it will then try to automatically put ‘a’ console on the appropriate serial port and speed. For the typical install, this means the discovery boot will have rcons output where it formerly did not. As always, genesis still makes sure that the video console also has access. Limitations of this will be that the rcons at best still won’t show kernel panic output and won’t take sysrq input, console=ttyS will remain required. I didn’t want to open a pull request since, for example, it uses python and I think the upstream genesis doesn’t have python yet. It works by using ACPI to see what, if any, serial console should be used and at what speed. It then does the appropriate calls to set the baud rate. From that point forward, it uses DCD to determine whether the console is in use, producing the rather useful behavior of redrawing the screen on ‘ipmitool sol activate’ or similar. If there is interest, here are the two files in our xCAT tree that do this: https://github.com/xcat2/xcat-core/blob/lenovobuild2.14/xCAT-genesis-scripts/usr/lib/dracut/hooks/cmdline/09-autoconsole.sh https://github.com/xcat2/xcat-core/blob/lenovobuild2.14/xCAT-genesis-scripts/usr/bin/autocons.py I do plan for OS deployment to try for similar ‘best effort’, depending on what I can do in the respective OS, ensuring that if possible the OS install is available through both consoles or at least some explanatory message in the ‘not console’ access channel. console=ttyS is still the desired result, but at least things may be less confusing getting started for some. _______________________________________________ xCAT-user mailing list xCAT-user@lists.sourceforge.net<mailto:xCAT-user@lists.sourceforge.net> https://lists.sourceforge.net/lists/listinfo/xcat-user
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