Bug 41211 - Describe how to configure serial access (serial console) via ucr
Describe how to configure serial access (serial console) via ucr
Status: RESOLVED WONTFIX
Product: Z_SDB
Classification: Unclassified
Component: New entries
unspecified
All other
: P5 enhancement
: ---
Assigned To: Christina Scheinig
http://sdb.univention.de/admin/index....
:
Depends on:
Blocks:
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Reported: 2016-05-06 11:14 CEST by Lutz Willek
Modified: 2020-07-02 17:20 CEST (History)
5 users (show)

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What kind of report is it?: Bug Report
What type of bug is this?: 2: Improvement: Would be a product improvement
Who will be affected by this bug?: 1: Will affect a very few installed domains
How will those affected feel about the bug?: 1: Nuisance – not a big deal but noticeable
User Pain: 0.011
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Description Lutz Willek 2016-05-06 11:14:05 CEST
Hello Univention,

This bug report is related to:

Bug 40596 - option to configure serial access (serial console) via ucr
(http://errata.software-univention.de/ucs/4.1/171.html)

The aims of #40596:
* serial access is completely configurable via ucr
* Some basic documentation "how to configure serial console in UCS servers" is available

After errata 171, serial access is completely configurable via ucr: Thanks a lot for applying the patches.

But there is still no documentation or sdb entry about how to configure this task.

Furthermore, the sdb-entry with id #1308 (Boot loader and bootsplash) is misleading now, because configuring a serial console is possible without patching a configuration file now. (Topic: "Advanced options" in sdb #1308)

I'm going to write some basic documentation.
Ff possible, please add this documentation (after review) as a new sdb entry.

Best regards
Lutz Willek
Comment 1 Lutz Willek 2016-05-06 13:52:40 CEST
Product: 	UCS
Component: 	Grub
Version: 	UCS 4.1

sdb.univention.de
Category: 13 
Category-Name: Boot loader and bootsplash
URL: http://sdb.univention.de/category/13/boot-loader-and-bootsplash.html

Suggested entry: How to configure grub serial access (serial console)
Suggested Tags: console, serial, ipmi, grub, GRUB2, boot, Linux

Related sdb entrys:
* #42
* #1308
* #1360

###################



How to configure grub serial access (serial console)
====================================================

For the average user a serial console has no advantage compared to a graphical console offered by a directly attached keyboard and screen.
But there are some scenarios where serial consoles are useful:

* Systems administration of remote computers via remote management (ipmi)
* Console redirection to non-standard settings
* Recording boot console messages
* Handicapped (blind) administrators who can not do anything with a graphical output
* Disable graphical grub output (text output only)

Note "Hardware Servers":
Many USB serial converters don't work reliably, please use the hardwares serial console or "console re-direction" on affected servers. 
Many servers support serial console re-direction over network nowadays, for example over IPMI.

Note "Virtual Servers":
Please add a virtual "serial console device" on affected virtual servers.

Note "UCS Version":
The following does not apply on systems earlier UCS 4.1, erratum #171.
On affected systems, please update first to UCS 4.1 erratum #171 or higher.



Problems/Tasks to solve
-----------------------

* Disable graphical output of grub, enable text output:
To disable the graphical output of grub:

 # ucr set grub/terminal='console'
 # reboot


* Configure serial access (standard serial settings)

The serial connection is being made at 115200/8n1, on first serial port. Default fallback if your hardware does not support 115200 baud, is 9600/8n1.
Default console (/dev/console) is always the first entry given to ucr variable "grub/terminal".

This makes the VGA console the default console, as "console" is given first:

 # ucr set grub/terminal='console serial'
 # reboot

This makes the serial console the default console, as "serial" is given first:

 # ucr set grub/terminal='serial console'
 # reboot


* Configure serial access (standard serial settings)

Serial settings are configurable via ucr variable "grub/serialcommand". This variable accepts many other options, please refer to http://www.gnu.org/software/grub/manual/grub.html#serial for more details. Note that the serial port is not used as a communication channel unless a terminal is configured (see above: "grub/terminal")
Example to configure serial access to the second console:

 # ucr set grub/serialcommand='serial --unit=1 --speed=115200 --word=8 --parity=no --stop=1'



Related: handicapped (blind) administrators
-------------------------------------------

Especially for blind administrators, any graphical output during or after the boot is not only useless but a hindrance.
In addition to disable the graphical output of grub (see above) the following settings may be usefull:

To disable graphical startup animation:
 # ucr set grub/bootsplash=nosplash

To disable the graphical welcome-screen after boot:
 # ucr set welcome-screen/autostart=disabled



Related: Configure a login prompt on the serial console
-------------------------------------------------------

In addition to redirect grub messages, you often want to configure a login prompt (getty) via serial console.
This is already prepared in the /etc/inittab file and only needs to be activated.
To use the standard settings, simply enable the line beginning with '#T0:':

 # sed -i -re '/^#?T0:/s/#//' /etc/inittab
 # reboot


To customize settings, the file /etc/inittab must be edited manually. As an example, in order to use the second serial port:
 
 # Example how to put a getty on a serial line (for a terminal)
 #
 T0:23:respawn:/sbin/getty -L ttyS1 115200 vt102



Related: Configure serial settings in older UCS installations
-------------------------------------------------------------

WARNING: ONLY FOR OLDER INSTALLATIONS

Of course we recommend an version update to to UCS 4.1 erratum #171 or higher.
Should this not be possible, some settings can be adjusted directly, e.g. as follows:


 # Re-direct GRUB input/output to serial console:
 cat >>/etc/univention/templates/files/etc/default/grub <<__GRUB__
 GRUB_TERMINAL=serial
 GRUB_SERIAL_COMMAND="serial --unit=0 --speed=115200 --word=8 --parity=no --stop=1"
 __GRUB__
 ucr commit /etc/default/grub
Comment 2 Lutz Willek 2016-05-06 13:55:24 CEST
please review, and if possible add to a new sdb entry, Thanks.

Best Regards
Lutz Willek
Comment 3 Ingo Steuwer univentionstaff 2020-07-02 17:20:15 CEST
Changes and improvements for SDB entries aren't tracked in Bugzilla anymore, so I close these entries. Please comment on help.univention.com or get in touch with the Univention Support team in case you have any suggestions for the SDB.