How to expand disk size of CentOS 7 for VSphere virtual machines

Here I list major steps to extend hard disk (add sda3 partition) from 40GB to 100GB at my CentOS 7 VM. I refer to some internet links to make it work but there also has a bit notice you need to note at some tricks part.

  1. Show current disk partition info and size :

df -h

Filesystem Size Used Avail Use% Mounted on
/dev/mapper/centos-root 38G 34G 3.8G 90% /
devtmpfs 2.0G 0 2.0G 0% /dev
tmpfs 2.0G 80K 2.0G 1% /dev/shm
tmpfs 2.0G 8.9M 2.0G 1% /run
tmpfs 2.0G 0 2.0G 0% /sys/fs/cgroup
/dev/sda1 497M 246M 252M 50% /boot


sda 8:0 0 40G 0 disk 
├─sda1 8:1 0 500M 0 part /boot
└─sda2 8:2 0 39.5G 0 part 
 ├─centos-swap 253:0 0 2G 0 lvm [SWAP]
 └─centos-root 253:1 0 37.5G 0 lvm /
sr0 11:0 1 1024M 0 rom

sudo fdisk -l

Disk /dev/sda: 42.9 GB, 42949672960 bytes, 83886080 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x0001af8a

Device Boot Start End Blocks Id System
/dev/sda1 * 2048 1026047 512000 83 Linux
/dev/sda2 1026048 83886079 41430016 8e Linux LVM

Disk /dev/mapper/centos-swap: 2164 MB, 2164260864 bytes, 4227072 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk /dev/mapper/centos-root: 40.3 GB, 40256929792 bytes, 78626816 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes


 Static hostname: wayne-v-ctos7
 Icon name: computer-vm
 Chassis: vm
 Machine ID: da93c1884d894932aef5bd13121e7478
 Boot ID: 772e152a486c45e58feb119b02a4c5f7
 Operating System: CentOS Linux 7 (Core)
 CPE OS Name: cpe:/o:centos:centos:7
 Kernel: Linux 3.10.0-229.20.1.el7.x86_64
 Architecture: x86_64

shutdown -h now

2. Then shut down VM , back up (export) your VM, and delete all the snpshots of the VM, and then use vSphere Client 5.5 to extend the disk size from 40GB to 100GB. If you do not remove the snapshots, you can not extend disk size!

3. Then start the VM and create a new partition to use the new disk blocks:

sudo fdisk -l
sudo fdisk /dev/sda

Target in fdisk is to Create new primary partition 3(sda3), set type as linux lvm (8e).
n - to create new primary partition 3 use left disk blocks
3 .......
t - to change 3 partition to the 8e type
w - to save and quit

You need to understand why I use 8e here for LVM and these each option doing. use “m” for help inside the fdisk.
4. After reboot the VM, now I have the sda3 but not be used yet. I need to use it to extend the Volume Group:

df -h
sudo fdisk -l
sudo vgdisplay
sudo vgextend centos /dev/sda3
df -h
sudo vgdisplay
sudo lvextend -L+59999M /dev/centos/root 
sudo resize2fs /dev/centos/root  **** for centOS 5,6
sudo xfs_growfs /dev/centos/root  **** for CentOS 7
df -h

Filesystem Size Used Avail Use% Mounted on
/dev/mapper/centos-root 97G 35G 62G 36% /
devtmpfs 2.9G 0 2.9G 0% /dev
tmpfs 2.9G 92K 2.9G 1% /dev/shm
tmpfs 2.9G 8.8M 2.9G 1% /run
tmpfs 2.9G 0 2.9G 0% /sys/fs/cgroup
/dev/sda1 497M 246M 252M 50% /boot


*** About this  command :

sudo lvextend -L+59999M /dev/centos/root

– here I left 60GB but I only use 59.999GB as I need to left a bit space to let system can run it, do not use all space.
and how this /dev/centos/root is got?  centos is the “VG Name”  in the vgdisplay command,  and root is volume, if you see ”df -h“, you should see in this way
/dev/mapper/centos-root  (VolumeGroup-Volume)
So do not make any error at here.

About the each steps means and details, you can refer to these two links:







How you extract the diff from two text files in linux

Q: You have the two files file1.txt and file2.txt. Now what you want to get is the lines in file1, but not in file2, how to do this by command in linux?

A: If your files are sorted already in linux, then there is a command already has this ability to do:


 comm - compare two sorted files line by line

 comm [OPTION]... FILE1 FILE2


-1 suppress lines unique to FILE1

-2 suppress lines unique to FILE2

-3 suppress lines that appear in both files

So this command will solve your issue:

comm -2 -3 file1.txt file2.txt > fileResult.txt


But if your file is not sorted, how?

There is another way to solve this too, suppose all your lines are less than 400 chars.

diff -a --width=400 --suppress-common-lines -y file1.txt file2.txt > fileResult.txt


By this diff command, the result you get is not clear in fact, as it compensates each line with “…..(spaces)….<“, so you still need to find and search this kind of extras and remove them.

If you get a better way in diff way, please let me know. Thanks here.

About MySQL index max length


To fast the search speed such as sort, index is very important tool must to use(INDEX, PRIMARY KEY and  UNIQUE). By default (5.6 version) the InnoDB support the 767 bytes length (<256 UTF8 chars) for a index. But if your text is a bit longer  and you need to index them, what you should do?

You have to understand that two file format concepts of Antelope(default) and Barracuda(start from version 5.6 mySQL). Refer to the MySQL manual :

  • Antelope is the original InnoDB file format, which previously did not have a name. It supports COMPACT and REDUNDANT row formats for InnoDB tables and is the default file format in MySQL 5.6 to ensure maximum compatibility with earlier MySQL versions that do not support the Barracuda file format.

So you see that new file format can support up to 3027 bytes for index, which will improve the search speed a lot for long text. Here is the steps to change to make the large index works:

You can change the config in the my.cnf (/etc/mysql/my.cnf)


or you can dynamic change at the console:

SET GLOBAL innodb_file_format=Barracuda;
SET GLOBAL innodb_file_per_table=ON;     (default is on already)
SET GLOBAL innodb_large_prefix=1
All of those settings are captured as a table is created. (You could change existing tables using ALTER.)

About the
ROW_FORMAT=DYNAMIC;      ( or COMPRESSED  to save space but cost CPU)
ROW_FORMAT=DYNAMIC can be append to the end of CREATE or used in the ALTER TABLE.  MySQL WorkBench also support you this at alter table at “options” tab.

How to make the Linux guest screen display properly in Hyper-V


I have worked on the Linux guest on Hyper-V recently, to set a proper screen display is more troublesome than in VirtualBox. (Running Linux on Hyper-V is not a good idea as obviously running slowly, even MS support integration in most Linux kernel to run them. ).

Here is the notes for the CentOS and Ubuntu:

For CentOS and Red Hat


grubby --update-kernel=ALL --args="video=hyperv_fb:1024x768"


For Ubuntu

Install linux-image-extras (hyperv-drivers):

sudo apt-get install linux-image-extra-virtual

Open the Terminal and type:

sudo gedit /etc/default/grub

Find the line starting with GRUB_CMDLINE_LINUX_DEFAULT, and add


or your preferred resolution in between the quotes (The maximum possible resolution is 1920×1080) like this:

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash video=hyperv_fb:1920x1080"

Save and Exit.


sudo update-grub

Restart Hyper-V (restarting Ubuntu (Linux) might be enough.


Improve the Mybatis performance


Some tips on improve the Mybatis performance.

  1. Set fetchSize to a considerable amount.
  2. Only retrieve needed columns from DB and map them to the Java object.
  3.  Try to reduce the nested selects in one user interaction, try to use more nested joins  in the SQL level in one time DB call.
  4.  Use cache integration to improve re-read speed.  Such as Memcached or  Ehcache
  5. SQL  and DB self optimization, such as index for sort and order



How to run Memcached on Mybatis


1. Install Memcache

To start, install memcached via apt-get. such as in the Ubuntu 12.04

sudo apt-get install memcached

It auto starts the memcached

ps -ax | grep memcac
21199 ?        Sl     0:00 /usr/bin/memcached -m 64 -p 11211 -u memcache -l

Refer to official Mybatis link:
Add the jar to your maven

 and then add the memcached to your mapper if you want which MyBatis mapper to use it.
<mapper namespace="org.acme.FooMapper">
  <cache type="org.mybatis.caches.memcached.MemcachedCache" />
Create a file and put to your class path, eg resources folder.
# any string identifier
# space separated list of ${host}:${port}
org.mybatis.caches.memcached.expiration = 600
org.mybatis.caches.memcached.asyncget = true
# the expiration time (in seconds)
org.mybatis.caches.memcached.timeout = 600
org.mybatis.caches.memcached.timeoutunit = java.util.concurrent.TimeUnit.SECONDS
# if true, objects will be GZIP compressed before putting them to Memcached
org.mybatis.caches.memcached.compression = false

In fact if you add multiple cache server at org.mybatis.caches.memcached.servers, it will has fail over ability among them. auto continue using live one if one die.

This intergration in fact based on the Spymemcached, is an asynchronous supported, single-threaded Memcached client. When you call any caching-related method on spymemcached’s MemcachedClient, it will be handled asynchronously. The client call method handles writing the details of the operation that should be performed into a queue and returning the control back to the client making the call. The actual interaction with the Memcached server, meanwhile, is handled by a separate thread that runs in the background.

My testing prove that it can improve the loading DB data at least 50% reading time if data has been in memcached. So this also proves that Mybatis self cache is not enough  big because it is not designed for cache only.


puppet- on windows common issues – 2

By W.ZH Sept 2013

About Web Platform Installer

WebPI is a very powerful tool to install many MS product, normal way you have know already. here I am going to talk about the command line way.

you need this as in puppet install the MS product, at most time, you do not want the GUI comes out and need user interactive for the EULA or others.

You need a silent install and control to agent windows system.

Here is the link to learn WPI:

under your PC,

C:\Program Files\Microsoft\Web Platform Installer

and then you can use WPI exe to do many things:

WebPICMD.exe /List /ListOption:Avaliable
WebPICMD.exe /Install /Products:OfficeToolsForVS2012RTW

You can use follow package to auto install the WPI on agent system:
  package { ‘Microsoft Web Platform Installer 4.6’:
ensure => installed,
source => “C:\\TEMP\\WebPlatformInstaller_amd64_en-US.msi”,

With WPI ready, many MS product you can use either online or offline model to install them on silent model.

Here I just give you one small example for install the Web Deploy 2.1.

exec { ‘Web Deployment Tool 2.1’ :
command => “\”C:\\Program Files\\Microsoft\\Web Platform Installer\\WebPICMD.exe\” /install /Products:WDeploy_2_1  /AcceptEULA”,
provider => windows,
timeout => 500,
WDeploy_2_1 is hte name you get by API list feature.