The Prayfor.EE Space.

Error: Virtualbox guest additions: modprobe vboxsf failed

shared folder Error: Virtualbox guest additions: modprobe vboxsf failed

$ sudo apt-get install virtualbox-guest-dkms

$ sudo apt-get install linux-headers-virtual

#Example #Error #Virtualbox #linux

linux "ps" command example

"ps" command example

: If i use "ps" command, I can check working process.

$ ps [-option]

-a : enumerates all processes (total user)

-u : each process of user and usage time

-x: enumerates all processes without a controlling terminal

-l : enumerates the detailed information

-e: Display all processes statuses

Example)
ps -aux

PID : process id

%CPU : cpu usage

%MEM : memory usage
VSZ : virtual memory usage

RSS : real memory usage

Stat : process status ( S : sleep, I : idle, T : stop, …)

Linux : search content (in file) / and search file or folder example

search content
$ grep -r "content" ./*

ex) grep -r "LD_PRELOAD" ./*

search file or folder

$ find ./* -name "file or folder"
ex) find ./* -name "library" or find ./* -name "*lib*"

android pdk make error : Android can only be built by versions 3.81 and 3.82.

This error is caused by an incorrect "make" version.

root@kiwon-VirtualBox:~/pdk/android-4.4.2_r1# make

build/core/main.mk:45: ********************************************************************************

build/core/main.mk:46: * You are using version 4.1 of make.

build/core/main.mk:47: * Android can only be built by versions 3.81 and 3.82.

build/core/main.mk:48: * see https://source.android.com/source/download.html

build/core/main.mk:49: ********************************************************************************

build/core/main.mk:50: *** stopping. Stop.

This error is caused by an incorrect "make" version.

So, Please add "make" version.

$make -v

GNU Make 4.1
.…

Please add "make" version 4.1 .

$ vi ./build/core/main.mk

40 # Check for broken versions of make.

41 # (Allow any version under Cygwin since we don't actually build the platform there.)

42 ifeq (,$(findstring CYGWIN,$(shell uname -sm)))

43 ifeq (0,$(shell expr $$(echo $(MAKE_VERSION) | sed "s/[^0-9\.].*//") = 3.81))

44 ifeq (0,$(shell expr $$(echo $(MAKE_VERSION) | sed "s/[^0-9\.].*//") = 3.82))

45 ifeq (0,$(shell expr $$(echo $(MAKE_VERSION) | sed "s/[^0-9\.].*//") = 4.1))

46 $(warning ********************************************************************************)

47 $(warning * You are using version $(MAKE_VERSION) of make.)

48 $(warning * Android can only be built by versions 3.81 and 3.82.)

49 $(warning * see https://source.android.com/source/download.html)

50 $(warning ********************************************************************************)

51 $(error stopping)

52 endif

53 endif

54 endif

55 endif

Okay .

QT set background image example(QLable_setstylesheet, QPixmap)

QT set background image example(QLable_setstylesheet, QPixmap)
I had a problem about applying image.

This is problem :

My app is working on an embedded system. I have migrated the app from Qt 5.6 to Qt 5.9.3 and it became very slow. I have checked the output of the top command and realized that my app is causing a CPU utilization of 100%.

So, I have check my app and I have found a problem in this part of the code:

MainWidget::MainWidget(QWidget *parent)
    : QWidget(parent)
{
...

    QPixmap bg(BACK_IMG_PATH);
    bg.fill(Qt::transparent);
    QPalette p(palette());
    p.setBrush(QPalette::Background, bg);
    setAutoFillBackground(true);
    setPalette(p);
...
}

The problem is, that if I add the code for the background, my app becomes extremely slow. However, if I remove this code, my app is working as expected. This cannot be a solution though, cause I need the background.

This problem did not exist before the migration.

I have tried to solve this by reimplementing the paintEvent and using QPainter like this:

void MainWidget::paintEvent(QPaintEvent *event)
{
    QPainter painter(this);
    painter.drawImage(QRectF(this->x(), this->y(), this->width(), this->height()), QImage("img/bg_1280_720.png"));
}

This result is slightly faster, but still not satisfactory (the cpu utilization is 50%).

How to solve this problem?

before:

#define BACK_IMG_PATH           "/img/bg_1280_720.png"
    QPixmap bg(BACK_IMG_PATH);
    bg.fill(Qt::transparent);
    QPalette p(palette());
    p.setBrush(QPalette::Background, bg);
    setAutoFillBackground(true);
    setPalette(p);

after:

#define BACK_IMG_PATH           "background-image:url(/img/bg_1280_720.png)"
    QLabel *labelBg = new QLabel(this);
    labelBg->setStyleSheet(BACK_IMG_PATH);
    labelBg->setGeometry(this->geometry());

Java Lotto / get random number example

This code was made in five minutes, so there are many weak point.

this code save that the number from 1 to 45 has been count N times.
finally, i will get 6 numbers.

import java.util.Random;

public class lottonamatja {
public static void main(String[] args) {
Random ranNum = new Random(); // random variable
long[] cloneNum = new long[45];
long[] num = new long[45];
long[] lottoNum = new long[6]; // get real number(I wanted)
long count = 1;
long N = 100000000;

for (long i = 0; i< N ; i++) {
int tempRanNum = ranNum.nextInt(45)+1; // random number of 1~45
num[tempRanNum-1] += count; // count of each number about N times
}

//copy number
cloneNum = num.clone();

// sorting count
for (int i = 0; i < 45; i++) {
for (int j = i + 1; j < 45; j++) {
if (num[i] > num[j]) {
long tmp = 0;
tmp = num[i];
num[i] = num[j];
num[j] = tmp;
}
}
}

// compare sorting number to original number ( this is real number(1~45), num[i] or cloneNum[j] is counting number)
for (int i = 0 ; i < 6; i++) {
for (int j = 0 ; j < 45; j++) {
if (num[i] == cloneNum[j])
lottoNum[i] = j+1; // save result number
}
}

// sorting about 6 number
for (int i = 0; i < 6; i++) {
for (int j = i + 1; j < 6; j++) {
if (lottoNum[i] > lottoNum[j]) {
long tmp = 0;
tmp = lottoNum[i];
lottoNum[i] = lottoNum[j];
lottoNum[j] = tmp;
}
}
System.out.print(lottoNum[i] + " "); //i wanted to real number
}
}
}

RSS(Resident Set Size), VSS(Virtual Set Size)

RSS(Resident Set Size): Number of physical pages associated with the process(the size is calculated with duplicated shared memoy size, so, is calculated lager than the actual size)

VSS(Virtual Set Size): Size of virtual memory associated with the process

But, the amount of memory about the process is unknown exactly.