What is NSS and how to use it ?

NSS – Named Saved Systems

An NSS is a copy of an operating system’s kernel or nucleus, which that has been saved in a chunk of CP’s storage.

Using an NSS to IPL an operating system has several advantages over using disks.

First, only one copy of the operating system will exist in memory no matter how many guests have IPLed it. This can lead to tremendous storage savings if you have numerous guests.

Second, because only one copy of the operating system exists, then updating everyone who uses it to a newer version is as simple as replacing that single NSS. To IPL from an NSS, provide the name of the saved system

From a performance perspective, there are benefits to this support:
it substantially reduces the amount of real storage that we need, and provides  better performance for a guest.

If viewed from a Linux perspective, having a large part of the kernel resident in storage would speed up the boot of the operating system significantly.

A guest would boot a NSS called, for example


instead of using a virtual device number such as

 IPL 500

The most common example of a NSS in z/VM is CMS.

And if you issue the command  (from a privileged user)


you will see many other functions (such as HELP, CMS Pipeline and NLS or National Language Support), that are DCSSs and which benefit using this support
Most z/VM installations have a CMS NSS set up.
Example of IPL of the CMS named saved system

z/VM V5.3.0 2007-05-02 16:25
Ready; T=0.01/0.01 09:37:40

Notice that CMS starts exactly the same way that it did when we IPLed the 190 disk.


Setting up a Linux NSS

Perform these steps to create a Linux NSS:

  1. Boot Linux.
  2. Insert savesys=<nssname> into the kernel parameter file used by your boot configuration, where <nssname> is the name you want to assign to the NSS. The name can be 1-8 characters long and must consist of alphabetic or numeric characters. Examples of valid names include: 73248734, NSSCSITE, or NSS1234. Be sure not to assign a name that matches any of the device numbers used at your installation.
  3.  Issue a zipl command to write the modified configuration to the boot device.
  4. you can also create nss via CP  “IPL <devno> PARM savesys=<nssname>”
  5.  Close down Linux.
  6. Issue an IPL command to boot Linux from the device that holds the Linux kernel. During the IPL process, the NSS is created and Linux is actually booted from the NSS.
  7. now you can boot another machine with your new created NSS  IPL <nss_name>




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Posted in z/VM, zlinux

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