Configure Console Only Login On Ubuntu 16.04+ Desktop

Occasionally we may want to login to our Ubuntu Desktop as console only mode (for eg: running our Ubuntu desktop as a bare metal hypervisor, only to launch Virtual Machines which will be connected remotely).

This will help to run the desktop with bare minimum memory (120MB RAM on Ubuntu 16.04) and CPU usage.

By default Ubuntu Desktop 16.04+ does not provide (which has Systemd than the legacy init system) this option, and you’ve to configure the same. Once configured you will get a new Grub menu entry on startup, to login as Console Mode.

1. Copy a sample menu entry from (/boot/grub/grub.cfg) to (/etc/grub.d/40_custom)

   Sample:

   menuentry 'Ubuntu' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-simple-0e341ce4-5a12-4a6d-a997-5336d1670353' {

          recordfail

          load_video

          gfxmode $linux_gfx_mode

          insmod gzio

          if [ x$grub_platform = xxen ]; then insmod xzio; insmod lzopio; fi

          insmod part_msdos

          insmod ext2

          set root='hd2,msdos5'

          if [ x$feature_platform_search_hint = xy ]; then

            search --no-floppy --fs-uuid --set=root --hint-bios=hd2,msdos5 --hint-efi=hd2,msdos5 --hint-baremetal=ahci2,msdos5  0e341ce4-5a12-4a6d-a997-5336d1670353

          else

            search --no-floppy --fs-uuid --set=root 0e341ce4-5a12-4a6d-a997-5336d1670353

          fi

           linux /boot/vmlinuz-4.15.0-54-generic root=UUID=0e341ce4-5a12-4a6d-a997-5336d1670353 ro  ipv6.disable=1  scsi_mod.use_blk_mq=1

          initrd /boot/initrd.img-4.15.0-54-generic

   }

    

2. Update the copied entry as per below (highlighted text). The crux is ‘systemd.unit’ property.

   Sample:

   menuentry 'Ubuntu-TextMode' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-simple-0e341ce4-5a12-4a6d-a997-5336d1670353' {

          recordfail

          #load_video

          #gfxmode $linux_gfx_mode

          insmod gzio

          if [ x$grub_platform = xxen ]; then insmod xzio; insmod lzopio; fi

          insmod part_msdos

          insmod ext2

          set root='hd2,msdos5'

          if [ x$feature_platform_search_hint = xy ]; then

            search --no-floppy --fs-uuid --set=root --hint-bios=hd2,msdos5 --hint-efi=hd2,msdos5 --hint-baremetal=ahci2,msdos5  0e341ce4-5a12-4a6d-a997-5336d1670353

          else

            search --no-floppy --fs-uuid --set=root 0e341ce4-5a12-4a6d-a997-5336d1670353

          fi

           linux /vmlinuz root=UUID=0e341ce4-5a12-4a6d-a997-5336d1670353 systemd.unit=multi-user.target ro  ipv6.disable=1  scsi_mod.use_blk_mq=1

          initrd /initrd.img

   }

   
   

3. Update grub using (Sudo update-grub2)

4. Reboot

5. Select the menu entry “Ubuntu-TextMode’

Enable High Performance, Block Multi Queue-IO Scheduler under Ubuntu 16.04 Desktop

Compared to Single Queue-IO Schedulers (eg. cfq, deadline etc), we can gain a high IO performance improvment through MultiQueue IO Schedulers (eg bfq, kyber). These are the new IO Schedulers built in to Linux Kernal 4.12+, but disabled until 5.0. It uses multiple IO Queue (leveraging CPU cores) to provide a high responsive system. These are specificaly designed for Desktop OS. Its architecture has been detailed here and here.

Enabling the same On Ubuntu 16.04 has been mentiond below:

1. Add both mq-deadline, bfq and kyber-iosched, to /etc/modules, to load the modules on startup

2. Append, scsi_mod.use_blk_mq=1 to the GRUB_CMDLINE_LINUX parameter in /etc/default/grub file

3. Create /etc/udev/rules.d/60-scheduler.rules, to assign bfq and kyber to block devices

eg:

# set bfq scheduler for non-rotating disks | SDD
ACTION=="add|change", KERNEL=="sd[a-z]", TEST!="queue/rotational", ATTR{queue/scheduler}="bfq"
ACTION=="add|change", KERNEL=="sd[a-z]", ATTR{queue/rotational}=="0", ATTR{queue/scheduler}="bfq"

# set kyber scheduler for rotating disks | HDD
ACTION=="add|change", KERNEL=="sd[a-z]", ATTR{queue/rotational}=="1", ATTR{queue/scheduler}="kyber"

4. Update grub using “sudo update-grub2” and reboot

5. Now your SSD would be using bfq scheduler, and HDD using kyber scheduler. Enjoy your high responsive system !

References:

https://www.omgubuntu.co.uk/2017/07/linux-kernel-4-12-released-bfq

https://www.thomas-krenn.com/en/wiki/Linux_Multi-Queue_Block_IO_Queueing_Mechanism_(blk-mq)

https://lwn.net/Articles/767987/

https://lwn.net/Articles/784267/

https://wiki.ubuntu.com/Kernel/Reference/IOSchedulers

https://www.stephenrlang.com/2018/01/io-scheduler-tuning/

https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/7.2_release_notes/storage

https://www.hecticgeek.com/2016/09/supercharge-ubuntu-16-04-lts-xanmod-kernel/

https://www.cnx-software.com/2019/08/14/bfq-budget-fair-queuing-i-o-scheduler-improves-linux-systems-responsiveness-video/

https://unix.stackexchange.com/questions/375600/how-to-enable-and-use-the-bfq-scheduler

https://wiki.debian.org/SSDOptimization#Low-Latency_IO-Scheduler

Virtualization to outperform Bare Metal performance? Simulating a RAM Cache, RAID Controller in a Desktop System

In general you could get a near native performance on Qemu-KVM following the instructions, specified in this article. 

Now what if you could get performance levels that can outperform the host system?

In Qemu-KVM, there are options to enable the same, which will provide you performance, more than the Bare Metal system, by the use of aggressive caching.

Note: This inherently has the risk of data loss, in case of a host failure or crash, hence not recommended for production workloads.

This tweaks can be applied to a POC/Development VM, by which you can complete your tasks much faster than before. To overcome data loss/OS corruption, its always recommended that you snapshot your Virtual disks before enabling this mode. So in case of any issues, you could revert back to your previous working image.

Below are the performance level, we’ve achieved with/without the Virtual Disk performance options. We’ve seen 60-70% performance gain on an average, once the system is up and running.

Windows7 VM	Normal (Seconds)	With IO Tweaks (Seconds)
System Reboots	57	13
Opening Visual Studio 2013	8	3
System Shutdown	21	9

 

The tests are comleted on a Windows7 VM with the below configuration:

This would be a great option for development and Virtual machines for POCs, typical usecase under Desktops/Laptops. The settings are related to IO mode on the virtual disks, and which extensively use caching, and most of the writes to disk, will be kept in cache, until there is sufficient data. Once it has, it will write them to disk in one go. This is “Analogous to RAID controller with RAM cache”, and KVM brings this feature to a normal desktop/laptop without any major efforts

 

During the initial startup, performance levels remain at par, however the performance will steadily move up, once you’ve the system up and running and more data has been cached in host overtime.

This level of performance may not be achievable from a Windows Desktop (Running on Bare Metal), as it would periodically synchronize IO with the underlying disks, which will hinder the performance for high data reliability.

You could get additional preformance boost, if you use the “raw” storage format, instead of “qcow2”

To know more, read through the below posts:

QEMU Disk IO performance comparison: Native or threads?

VIRTUALIZATION TUNING AND OPTIMIZATION GUIDE…

Virtual IO CACHING…

How to improve Windows perfomance when running inside KVM…

What is the memory module on a RAID card needed for?