Displaying Physical Volumes
There are three commands you can use to display properties of LVM physical volumes: pvs,pvdisplay, and pvscan.
The pvs command provides physical volume information in a configurable form, displaying one line per physical volume. The pvs command provides a great deal of format control, and is useful for scripting.
The pvdisplay command provides a verbose multi-line output for each physical volume. It displays physical properties (size, extents, volume group, etc.) in a fixed format.
The following example shows the output of the pvdisplay command for a single physical volume.
Scanning for Block Devices
You can scan for block devices that may be used as physical volumes with the lvmdiskscan
command, as shown in the following example.
# lvmdiskscan
lvmdiskscan
[-d|--debug]
[-h|--help]
[-l|--lvmpartition]
[--version]
PS command: process tree, threads, security
To print a process tree:
To get info about threads:
To get security info:
ps -eo euser,ruser,suser,fuser,f,comm,label
ps axZ
ps -eM
Minor page fault
If the page is loaded in memory at the time the fault is generated, but is not marked in the memory management unit as being loaded in memory, then it is called a minor or soft page fault.
The page fault handler in the operating system merely needs to make the entry for that page in the memory management unit point to the page in memory and indicate that the page is loaded in memory; it does not need to read the page into memory. This could happen if the memory is shared by different programs and the page is already brought into memory for other programs. The page could also have been removed from a process’s Working Set, but not yet written to disk or erased, such as in operating systems that use Secondary Page Caching. For example, an application software may remove a page that does not need to be written to disk (if it has remained unchanged since it was last read from disk, for example) and place it on a Free Page List if the working set is deemed too large.
However, the page contents are not overwritten until the page is assigned elsewhere, meaning it is still available if it is referenced by the original process before being allocated. Since these faults do not involve disk latency, they are faster and less expensive than major page faults.
what is the root zone?
The DNS translates domain names that humans can remember into the numbers used by computers to look up its destination (a little like a phone book is used to look-up a phone number). It does this in stages. The first place it ‘looks’ is the top level of the directory service - or “root zone”. So to use www.google.com as an example, your computer ‘asks’ the root zone directory (or top level) where to find information on “.com”. After it gets a response it then asks the “.com” directory service identified by the root where to find information on .google.com (the second level), and finally asking the google.com directory service identified by “.com” what the address for www.google.com is (the third level). After that process – which is almost instantaneous – the full address is provided to your computer. Different entities manage each one of these directory services: google.com by Google, “.com” by VeriSign Corporation (other top level domains are managed by other organizations), and the root zone by ICANN.
