Static Route in Ubuntu. How To?

1. Login in the system with the system administrator privilege.

2. Open the network configuration file with a editor. I will be using “vi editor” in this case.

example : “vi /etc/network/interfaces“

3. Go to last line and add your routing.

example “up route add -net 192.168.1.0 netmask 255.255.255.0 dev eth0“

4. Save your changes and exit the editor.

5. Restart the network service with “/etc/init.d/networking restart“

6. Verify your routing by sending “route” command.

What is the difference between Xen PV, Xen KVM and HVM?

Xen supported virtualization types

Xen supports running two different types of guests. Xen guests are often called as domUs (unprivileged domains). Both guest types (PV, HVM) can be used at the same time on a single Xen system.

Xen Paravirtualization (PV)

Paravirtualization is an efficient and lightweight virtualization technique introduced by Xen, later adopted also by other virtualization solutions. Paravirtualization doesn't require virtualization extensions from the host CPU. However paravirtualized guests require special kernel that is ported to run natively on Xen, so the guests are aware of the hypervisor and can run efficiently without emulation or virtual emulated hardware. Xen PV guest kernels exist for Linux, NetBSD, FreeBSD, OpenSolaris and Novell Netware operating systems.

PV guests don't have any kind of virtual emulated hardware, but graphical console is still possible using guest pvfb (paravirtual framebuffer). PV guest graphical console can be viewed using VNC client, or Redhat's virt-viewer. There's a separate VNC server in dom0 for each guest's PVFB.

Upstream kernel.org Linux kernels since Linux 2.6.24 include Xen PV guest (domU) support based on the Linux pvops framework, so every upstream Linux kernel can be automatically used as Xen PV guest kernel without any additional patches or modifications.

See XenParavirtOps wiki page for more information about Linux pvops Xen support.

Xen Full virtualization (HVM)

Fully virtualized aka HVM (Hardware Virtual Machine) guests require CPU virtualization extensions from the host CPU (Intel VT, AMD-V). Xen uses modified version of Qemu to emulate full PC hardware, including BIOS, IDE disk controller, VGA graphic adapter, USB controller, network adapter etc for HVM guests. CPU virtualization extensions are used to boost performance of the emulation. Fully virtualized guests don't require special kernel, so for example Windows operating systems can be used as Xen HVM guest. Fully virtualized guests are usually slower than paravirtualized guests, because of the required emulation.

To boost performance fully virtualized HVM guests can use special paravirtual device drivers to bypass the emulation for disk and network IO. Xen Windows HVM guests can use the opensource GPLPV drivers. See XenLinuxPVonHVMdrivers wiki page for more information about Xen PV-on-HVM drivers for Linux HVM guests.

KVM is not Xen at all, it is another technology, where KVM is a Linux native kernel module and not an additional kernel, like Xen. Which makes KVM a better design. the downside here is that KVM is newer than Xen, so it might be lacking some of the features.

How to disable USB port on linux server?

To disable USB port on the machine, you have to edit the file /etc/grub.conf
# vim /etc/grub.conf   (or) # vim /boot/grub/grub.conf



Then add the kernel parameter as follows


kernel /vlinuz ..... rhgb quiet nousb


Now reboot the system and check that  all your usb ports disabled.

how a linux command work internally?

You can use strace command to understanding how a linux command work internally. For example, to check on the ls command


strace is a system call monitor command and provides information about system calls made by an application, including the call arguments and return value.


# strace -c /bin/ls
anaconda-ks.cfg  Desktop  index.hml    install.log.syslog  samba-latest.tar.gz
as               file5    install.log  samba-3.5.9         vmware-tools-distrib
% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
100.00    0.000039           1        27           mmap2
  0.00    0.000000           0        12           read
  0.00    0.000000           0         2           write
  0.00    0.000000           0        13           open
  0.00    0.000000           0        14           close
  0.00    0.000000           0         1           execve
  0.00    0.000000           0         2         1 access
  0.00    0.000000           0         3           brk
  0.00    0.000000           0         2           ioctl
  0.00    0.000000           0         4           munmap
  0.00    0.000000           0         1           uname
  0.00    0.000000           0         5           mprotect
  0.00    0.000000           0         2           rt_sigaction
  0.00    0.000000           0         1           rt_sigprocmask
  0.00    0.000000           0         1           getrlimit
  0.00    0.000000           0        13           fstat64
  0.00    0.000000           0         2           getdents64
  0.00    0.000000           0         1           fcntl64
  0.00    0.000000           0         1           futex
  0.00    0.000000           0         1           set_thread_area
  0.00    0.000000           0         1           set_tid_address
  0.00    0.000000           0         1           set_robust_list
------ ----------- ----------- --------- --------- ----------------
100.00    0.000039                   110         1 total