Accessing your Virtualbox Guest from your Host OS

Nine explanation...

Accessing your Virtualbox Guest from your Host OS

Linux I/O Performance Tests using dd

dd if=/dev/zero of=test2.img bs=164K count=100000 oflag=dsync
dd bs=1M count=1024 if=/dev/zero of=test conv=fdatasyn


https://romanrm.net/dd-benchmark

Install Htop 2.0 for CentOS 7

yum groupinstall "Development Tools"
yum install ncurses ncurses-devel
wget http://hisham.hm/htop/releases/2.0.0/htop-2.0.0.tar.gz
tar xvfvz htop-2.0.0.tar.gz
cd htop-2.0.0
./configure
make
make install

Comsol: Tuning the Java heap size

If you get an error message like this: 
                Error in sweep: Java heap space
try to increase the Java heap. Open the comsol.ini file located in the subdirectory bin/$arch in the COMSOL installation directory, where $arch corresponds to the platform you are using. Modify the number in the row that starts with -Xmx, its value is the Java heap size. If you have enough RAM, try doubling the size. This will give the line -Xmx2048m for a 64-bit platform. Repeat this for all *.ini files in the same directory.

If you do not have write permission to the bin/$arch directory, you can instead try the following:

• Copy the comsol.ini file to a folder where you have write permission.
• Open the file and modify it according to the instructions above.
• When you launch COMSOL, add the option -comsolinifile [path] to the COMSOL command, where [path] is the path to your new comsol.ini file.

Also here we can find some recommendations on how to deal with java.lang.OutOfMemoryError in Java, http://javarevisited.blogspot.co.il/2011/09/javalangoutofmemoryerror-permgen-space.html

How to Check Your Disk Quota under Linux

quota -v

du -sh <directory>

df -h <directory>

Color schemes - Midnight Commander

[Colors]

base_color=normal=lightgray,black:input=white,brightred:errors=white,brightred:gauge=yellow,red:selected=gray,lightgray:marked=yellow,black:markselect=yellow,brown:directory=white,black:executable=brightgreen,black:link=green,black:device=brightmagenta,black:special=brown,black:core=brightred,yellow:menu=gray,lightgray:menuhot=yellow,lightgray:menuhotsel=brightred,black:dnormal=white,gray:dfocus=white,brightgreen:dhotnormal=brightred,gray:dhotfocus=brightred,gray:editmarked=white,brightred:editnormal=white,black:editbold=blue,brown:reverse=yellow,black:helpnormal=white,black:helpitalic=brightmagenta,black:helpbold=brightcyan,black:helpslink=yellow,black:helplink=brightblue,black:viewunderline=brightgreen,white

Ubuntu:How to change my MS mouse wheel scroll rate?

Some MS mice have a scrollwheel bug. Try unplugging the USB cable/dongle then plug back in.

VNC server on ubuntu 14.04

#!/bin/sh

# Uncomment the following two lines for
export XKL_XMODMAP_DISABLE=1
unset SESSION_MANAGER
unset DBUS_SESSION_BUS_ADDRESS
# exec /etc/X11/xinit/xinitrc

#[ -x /etc/vnc/xstartup ] && exec /etc/vnc/xstartup
#[ -r $HOME/.Xresources ] && xrdb $HOME/.Xresources
#xsetroot -solid grey
vncconfig -iconic &
#x-terminal-emulator -geometry 80x24+10+10 -ls -title "$VNCDESKTOP Desktop" &
#x-window-manager &

gnome-panel &
gnome-settings-daemon &
metacity &
nautilus &
gnome-terminal &






normal desktop:

Maple: Display plots several plots together

with(plots);
p1 := plot(sin(x), x = 0 .. 2*Pi, color = red);
p2 := plot(cos(y), y = -Pi .. Pi, color = blue);
display({p1, p2});

How to create a bootable USB on Linux

Installation

1. Using UNetbootin

2.

sudo mkdir /media/iso/
sudo mount -o loop /path/to/ubuntu.iso /media/iso

cp -a /media/iso/. /media/xxx/

sudo apt-get install syslinux mtools
sudo syslinux -s /dev/sdd1

Then rename the isolinux directory in media/xxx/ to syslinux, rename the file isolinux.cfg to syslinux.cfg.



In case of the message:

"The installer has tried to mount image #1, but cannot find it on the hard drive.Please copy this image to the drive and click Retry.Click Exit to abort the installation."

press Ctrl-Alt-F2

mount /dev/sdc1 /mnt/foldername

ps -ef | grep sd

copy /mnt/foldername/centos.iso /mnt/isodir/centos.iso

press Ctrl-Alt-F6

How to Repair, Restore, or Reinstall Grub 2 with a Ubuntu Live CD

Mount the partition your Ubuntu Installation is on (with the root partition "/").


sudo mount /dev/sdc2 /mnt

sudo mount --bind /dev /mnt/dev &&
sudo mount --bind /dev/pts /mnt/dev/pts &&
sudo mount --bind /proc /mnt/proc &&
sudo mount --bind /sys /mnt/sys


sudo chroot /mnt

grub-install /dev/sdc # grub-install --recheck /dev/sdc
update-grub

exit &&
sudo umount /mnt/sys &&
sudo umount /mnt/proc &&
sudo umount /mnt/dev/pts &&
sudo umount /mnt/dev &&
sudo umount /mnt



Reboot your computer, and Grub2 screen will be on.