备忘录

Saturday, 16 February 2019

How to make a disk dump using dd command?

To virtualize a physical PC in VirtualBox (see here), I need a copy of its disk image. The PC is quite old 386 (32bit) and its spec is quite low. So, I choose the less resource demanding Linux distro, Tiny Core (CorePlus version) to boot it up. To hold the big image file, I have a USB external drive in NTFS format. Here is what I did:

1. boot the PC with CorePlus

2. install ntfs-3g extension

3. connect the USB drive to the PC

4. find the device ID of the USB drive (in my case, sdd) with: fdisk -l

5. sudo -s

6. mount /mnt/sdd1

7. cd /mnt/sdd1/

8. dd if=/dev/sda of=sda_image.dd

Sunday, 19 August 2018

How to install RTL8811AU WiFi adapter?

Ubuntu
---------------------------------------------------------------------------------------------------------------------------
# Download Ubuntu desktop 18.04 ISO from here

# write the ISO image to a USB stick using w32 disk imager

# install minimal installation on a laptop using the USB stick

# boot the laptop by holding shift key after BIOS loading screen to get into GRUB)
select option:
Advanced options for Ubuntu
Ubuntu, with Linux 4.15.0-29-generic (recovery mode)
root (Drop to root shell prompt)
:~# mount -o rw,remount /
:~# vi /etc/gdm3/custom.conf
uncomment following line
#WaylandEnable=false in /etc/gdm3/custom.comf
^D

# resume the reboot

sudo apt-get update
sudo apt install dkms
sudo apt install git

# following instruction here to build the driver from source
git clone https://github.com/gnab/rtl8812au.git
sudo cp -r rtl8812au /usr/src/rtl8812au-4.2.2
sudo dkms add -m rtl8812au -v 4.2.2
sudo dkms build -m rtl8812au -v 4.2.2
sudo dkms install -m rtl8812au -v 4.2.2
reboot

Update on 11/02/2019
---------------------------------------------------------------------------------------------------------------------------
I have tried following from here on lubuntu and Mint, Both work well:

sudo apt install git dkms build-essential
git clone https://github.com/abperiasamy/rtl8812AU_8821AU_linux.git
cd rtl8812AU_8821AU_linux
sudo make -f Makefile.dkms install

Note: you may need install the headers first
apt-get install linux-headers-$(uname -r)

Update on 13/02/2019
---------------------------------------------------------------------------------------------------------------------------

Another try on my old Dimension8400 with Debian9, and it seems working as well. Occasionally, the connection is dropped.

BTW, the out-of-box Debian9 has problem with my wifi and it dropped the connection immediately after authenticated with error: DEAUTH_LEAVING

The fix is simple as described here

Sunday, 20 November 2016

如何转换MP3的ID3标签？

mp3文件ID3标签包括歌曲的名字、歌手名字等等。如果这些在播放器里显示为乱码，可按下述步骤修改：

在CentOS6.8系统下：

安装工具包：yum install python-mutagen

显示mp3文件标签：mid3v2 a.mp3

核实mp3文件标签是否为GB18030 编码：mid3iconv -p -e GB18030 -d a.mp3 （若显示为汉字则是）

将当前目录下全部mp3文件标签转换为Unicode编码：find . -name "*mp3" -print0 | xargs -0 mid3iconv -e GB18030 -d

参见：http://ask.xmodulo.com/convert-mp3-id3-tag-encodings-linux.html

Monday, 14 March 2016

How to work with Apache Ignite?

First of all, don't try to build from the source unless you know how to. I have tried following the instruction (BUILDING FROM SOURCE), it simply does not work!

Here is the way working for me:

1. Create a MAVEN project with following files

<1> pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>my.ignite</groupId>
<artifactId>ignite-test</artifactId>
<version>1.0</version>
<packaging>jar</packaging>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<maven.compiler.source>1.7</maven.compiler.source>
<maven.compiler.target>1.7</maven.compiler.target>
</properties>
<dependencies>
<dependency>
<groupId>org.apache.ignite</groupId>
<artifactId>ignite-core</artifactId>
<version>1.5.0.final</version>
</dependency>
<dependency>
<groupId>org.apache.ignite</groupId>
<artifactId>ignite-spring</artifactId>
<version>1.5.0.final</version>
</dependency>
<dependency>
<groupId>org.apache.ignite</groupId>
<artifactId>ignite-indexing</artifactId>
<version>1.5.0.final</version>
</dependency>
<dependency>
<groupId>org.apache.ignite</groupId>
<artifactId>ignite-log4j</artifactId>
<version>1.5.0.final</version>
</dependency>
</dependencies>
<build>
<resources>
<resource>
<directory>src/main/java</directory>
<excludes>
<exclude>**/*.java</exclude>
</excludes>
</resource>
<resource>
<directory>config</directory>
</resource>
</resources>
<plugins>
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>exec-maven-plugin</artifactId>
<version>1.4.0</version>
<executions>
<execution>
<goals>
<goal>exec</goal>
</goals>
</execution>
</executions>
<configuration>
<executable>java</executable>
<arguments>
<argument>-Xms1G</argument>
<argument>-Xmx1G</argument>
<argument>-classpath</argument>
<classpath />
<argument>my.ignite.Test</argument>
</arguments>
<workingDirectory>${project.build.outputDirectory}</workingDirectory>
</configuration>
</plugin>
</plugins>
</build>
</project>

<2> src\main\java\my\ignite\Test.java

package my.ignite;

import org.apache.ignite.IgniteException;
import org.apache.ignite.Ignition;

public class Test {

public static void main(String[] args) throws IgniteException {
Ignition.start("ignite.xml");
}
}

<3> config\ignite.xml

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:util="http://www.springframework.org/schema/util"

xsi:schemaLocation="

http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd

http://www.springframework.org/schema/util

http://www.springframework.org/schema/util/spring-util.xsd">

</bean>

<list>

<util:constant static-field="org.apache.ignite.events.EventType.EVT_TASK_STARTED"/>

<util:constant static-field="org.apache.ignite.events.EventType.EVT_TASK_FINISHED"/>

<util:constant static-field="org.apache.ignite.events.EventType.EVT_TASK_FAILED"/>

<util:constant static-field="org.apache.ignite.events.EventType.EVT_TASK_TIMEDOUT"/>

<util:constant static-field="org.apache.ignite.events.EventType.EVT_TASK_SESSION_ATTR_SET"/>

<util:constant static-field="org.apache.ignite.events.EventType.EVT_TASK_REDUCED"/>

<util:constant static-field="org.apache.ignite.events.EventType.EVT_CACHE_OBJECT_PUT"/>

<util:constant static-field="org.apache.ignite.events.EventType.EVT_CACHE_OBJECT_READ"/>

<util:constant static-field="org.apache.ignite.events.EventType.EVT_CACHE_OBJECT_REMOVED"/>

</list>

</property>

<!--

Ignite provides several options for automatic discovery that can be used

instead os static IP based discovery. For information on all options refer

to our documentation: http://apacheignite.readme.io/docs/cluster-config

-->

<list>

</list>

</property>

</bean>

</property>

</bean>

</property>

</bean>

</beans>

<4> config\java.util.logging.properties

handlers=java.util.logging.ConsoleHandler, org.apache.ignite.logger.java.JavaLoggerFileHandler

.level=INFO

java.util.logging.ConsoleHandler.formatter=org.apache.ignite.logger.java.JavaLoggerFormatter

java.util.logging.ConsoleHandler.level=INFO

org.apache.ignite.logger.java.JavaLoggerFileHandler.formatter=org.apache.ignite.logger.java.JavaLoggerFormatter

org.apache.ignite.logger.java.JavaLoggerFileHandler.pattern=ignite-%{id8}.%g.log

org.apache.ignite.logger.java.JavaLoggerFileHandler.level=INFO

org.apache.ignite.logger.java.JavaLoggerFileHandler.limit=10485760

org.apache.ignite.logger.java.JavaLoggerFileHandler.count=10

2. mvn compile

[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building ignite-test 1.0
[INFO] ------------------------------------------------------------------------
[INFO]
[INFO] --- maven-resources-plugin:2.5:resources (default-resources) @ ignite-test ---
[debug] execute contextualize
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] Copying 0 resource
[INFO] Copying 2 resources
[INFO]
[INFO] --- maven-compiler-plugin:2.3.2:compile (default-compile) @ ignite-test ---
[INFO] Nothing to compile - all classes are up to date
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 0.641s
[INFO] Finished at: Mon Mar 14 20:31:27 GMT 2016
[INFO] Final Memory: 4M/15M
[INFO] ------------------------------------------------------------------------

3. mvn exec:exec

[INFO] Scanning for projects...

[INFO]

[INFO] ------------------------------------------------------------------------

[INFO] Building ignite-test 1.0

[INFO] ------------------------------------------------------------------------

[INFO]

[INFO] --- exec-maven-plugin:1.4.0:exec (default-cli) @ ignite-test ---

[20:31:34] __________ ________________

[20:31:34] / _/ ___/ |/ / _/_ __/ __/

[20:31:34] _/ // (7 7 // / / / / _/

[20:31:34] /___/\___/_/|_/___/ /_/ /___/

[20:31:34]

[20:31:34] ver. 1.5.0-final#20151229-sha1:f1f8cda2

[20:31:34] 2015 Copyright(C) Apache Software Foundation

[20:31:34]

[20:31:34] Ignite documentation: http://ignite.apache.org

[20:31:34]

[20:31:34] Quiet mode.

[20:31:34] ^-- To see **FULL** console log here add -DIGNITE_QUIET=false or "-v" to ignite.{sh|bat}

[20:31:34]

[20:31:34] OS: Windows 7 6.1 x86

[20:31:34] VM information: Java(TM) SE Runtime Environment 1.7.0_80-b15 Oracle Corporation Java HotSpot(TM) Client VM 24.80-b11

[20:31:37] Configured plugins:

[20:31:37] ^-- None

[20:31:37]

[20:31:38] Security status [authentication=off, tls/ssl=off]

[20:31:51] Performance suggestions for grid (fix if possible)

[20:31:51] To disable, set -DIGNITE_PERFORMANCE_SUGGESTIONS_DISABLED=true

[20:31:51] ^-- Disable peer class loading (set 'peerClassLoadingEnabled' to false)

[20:31:51] ^-- Disable grid events (remove 'includeEventTypes' from configuration)

[20:31:51]

[20:31:51] To start Console Management & Monitoring run ignitevisorcmd.{sh|bat}

[20:31:51]

[20:31:51] Ignite node started OK (id=c9abb969)

[20:31:51] Topology snapshot [ver=1, servers=1, clients=0, CPUs=4, heap=1.0GB]

Sunday, 28 February 2016

How to build Role-Based Access Control in SQL?

Role-based access control (RBAC) is a method of regulating access to computer or network resources based on the roles of individual users within an enterprise. (see here for more detail)

In above diagram, we model the relationship between User (u), Group/Role (g), and Permission (p) by three tables, i.e. u_g, g_p, and g_g, which are flexible enough to cover any trees or networks. All the following statements are true in this model:

a user can be linked to many groups;
a group can be linked to many users;
a permission can be linked to many groups;
a group can be linked to many permissions;
a group can be linked to many children groups;
a group can be linked to many parent groups;

However, the difficult part of this model is how to deal with hierarchies of roles/groups in SQL (see here, here, and here for detail) due to the recursive nature of navigating between group (g_g) relationship.

One solution is to use SQL stored routines. Followings are my design in MySQL and you can simply:

call get_permisions('u2');
call get_users('p1');

to get all permissions of a user or all users who have a permission.

-----------------------------------------------------------------------------------------------------

DROP PROCEDURE IF EXISTS test.get_users;
CREATE PROCEDURE test.`get_users`(p VARCHAR(20))
BEGIN
SELECT group_concat(gID)
INTO @groups
FROM g_p
WHERE pID = p;

SELECT DISTINCT uID
FROM u_g
WHERE FIND_IN_SET(gID, parents(@groups)) > 0;
END;

DROP PROCEDURE IF EXISTS test.get_permisions;

CREATE PROCEDURE test.`get_permisions`(u VARCHAR(20))

BEGIN

SELECT group_concat(gID)

INTO @groups

FROM u_g

WHERE uID = u;

SELECT DISTINCT pID

FROM g_p

WHERE FIND_IN_SET(gID, children(@groups)) > 0;

END;

DROP FUNCTION IF EXISTS test.children;

CREATE FUNCTION test.`children`(parents VARCHAR(255)) RETURNS varchar(255) CHARSET utf8

BEGIN

DECLARE x VARCHAR(255);

SET @@SESSION.max_sp_recursion_depth = 25;

CALL get_children(parents, x);

RETURN x;

END;

DROP PROCEDURE IF EXISTS test.get_children;
CREATE PROCEDURE test.`get_children`(IN parents VARCHAR(255),
OUT children VARCHAR(255))
BEGIN
DECLARE x VARCHAR(255);
SET children = parents;

SELECT group_concat(DISTINCT child)
INTO x
FROM g_g
WHERE FIND_IN_SET(parent, parents);

IF (x IS NOT NULL)
THEN
CALL get_children(x, x);
SET children = concat(parents, ',', x);
END IF;
END;

DROP FUNCTION IF EXISTS test.parents;

CREATE FUNCTION test.`parents`(children VARCHAR(255)) RETURNS varchar(255) CHARSET utf8

BEGIN

DECLARE x VARCHAR(255);

SET @@SESSION.max_sp_recursion_depth = 25;

CALL get_parents(children, x);

RETURN x;

END;

DROP PROCEDURE IF EXISTS test.get_parents;

CREATE PROCEDURE test.`get_parents`(IN children VARCHAR(255),

OUT parents VARCHAR(255))

BEGIN

DECLARE x VARCHAR(255);

SET parents = children;

SELECT group_concat(DISTINCT parent)

INTO x

FROM g_g

WHERE FIND_IN_SET(child, children);

IF (x IS NOT NULL)

THEN

CALL get_parents(x, x);

SET parents = concat(children, ',', x);

END IF;

END;

Sunday, 10 January 2016

How to install Windows 7 on a computer that has no CD drive?

create an ISO image of Windows 7 DVD
download "Windows USB/DVD Download Tool"
install above tool on a Windows computer
run the tool and pick up the ISO as the source and an USB stick as destination to build the bootable USB
insert the bootable USB stick into the computer that has no CD drive
boot the computer from the USB stick

Tuesday, 18 August 2015

How to use Java 7 Pattern & Matcher to extract values from a String?

public static void main(String[] args) {
String txt = "\"199.47.181.213\" \"NULL-AUTH-USER\" \"06/Oct/2014:11:19:54 +0000\" \"GET /site/\" 'HTTP/1.0\" 200 20668 ";
String rgx = "\"(.*)\" \"(.*)\" \"(.*)\" \"(.*)\" ([0-9]+) ([0-9]+) ";
SimpleDateFormat dateFormat = new SimpleDateFormat("dd/MMM/yyyy:hh:mm:ss +SSSS");
Pattern p = Pattern.compile(rgx);
Matcher m = p.matcher(txt);
boolean b = m.matches();
if (b) {
int groupCount = m.groupCount();
for (int i = 0; i <= groupCount; i++) {
String g = m.group(i);
System.out.print("matched group " + i + ":\t");
if (i == 3) {
Date parsedDate;
try {
parsedDate = dateFormat.parse(g);
Timestamp timestamp = new java.sql.Timestamp(parsedDate.getTime());
System.out.println(timestamp);
} catch (ParseException ex) {
Logger.getLogger(PatternTester.class.getName()).log(Level.SEVERE, g, ex);
}
} else {
System.out.println(g);
}
}
} else {
System.out.println(txt + "\nDOES NOT MATCH\n" + rgx);
}
}

below is the output:

matched group 0: "199.47.181.213" "NULL-AUTH-USER" "06/Oct/2014:11:19:54 +0000" "GET /site/" 'HTTP/1.0" 200 20668
matched group 1: 199.47.181.213
matched group 2: NULL-AUTH-USER
matched group 3: 2014-10-06 11:19:54.0
matched group 4: GET /site/" 'HTTP/1.0
matched group 5: 200
matched group 6: 20668