This is all about Linux tips that will be constantly updated.

Howto let Virtualbox boot from ISO

Create a new machine, then under Settings > Storage, there are 2 controllers (IDE and SATA), pick IDE one and click the Drive Icon there and could “Add a CD/DVD device”, then navigate to the iso file and save those settings.

Set the boot option to begin with CD/DVD, so your machine can take off.

Howto get USB back after dd

You can type dd if=/iso_file of=/dev/sdx bs=4M && sync to burn an image into USB stick, hereby howto reverse it:

  1. Zero its first 512 bytes:

    # dd count=1 bs=512 if=/dev/zero of=/dev/sdx && sync

  2. Then install dosfstools and FAT32 and run:

    # cfdisk /dev/sdx

    # mkfs.vfat -F32 /dev/sdx1

    # dosfslabel /dev/sdx1 The_Label_U_Like

Howto ssh ubuntu in VirtualBox

If you have a Linux machine running in Virtualbox, no matter your host is Linux or not, you can login to the guest by ssh without password.

  1. Shutdown the Virtualbox guest
  2. On the Virtualbox go to File -> Preferences -> Network -> Host-only Networks add one
  3. Configure the guest, Settings -> Network -> Adapter 2, Enable Network Adapter, pick Host-only Adapter for Attached to
  4. Edit the /etc/network/interfaces file and add following block:

autho eth1

iface eth1 inet static

address 192.168.56.110

netmask 255.255.255.0

  1. Then restart the networking using command /etc/init.d/networking restart
  2. Install openssh-server apt-get install openssh-server and set password for root sudo passwd root

  3. Now restart the Virtualbox guest

  4. Edit host’s /etc/hosts, sudo vim /etc/hosts and add a line 192.168.56.110 guest

The next stage is about ssh login with no need of password by using RSA key

  1. On the host machine, generate RSA key by ssh-keygen -t rsa
  2. Copy that public key onto guest machine per scp ~/.ssh/id_rsa.pub You_User_Name@guest: ## Don’t forget the “:” in the end
  3. Then login ssh Your_User_Name@guest
  4. cat id_rsa.pub >> ~/.ssh/authorized_keys
  5. Exit the ssh session and take a try of the new world!!

systemD and boot time

sudo systemd-analyze blame will show you which service takes the longest time, if it’s about journal then you can remove all files within /var/log/journal/ and limit the usage by editing SystemMaxUse=40M of sudo vim /etc/systemd/journald.conf.