How to free caches in ubuntu

How to free caches in ubuntu

sudo sync && sudo sysctl -w vm.drop_caches=3

Unable to run a 32-bit program on 64-bit machine

Qs. I compiled a small "hello world" C program on Ubuntu 10.04 32 bit machine. Then I put the executable(a.out) on Ubuntu 12.10(64 bit) VMWare virtual machine and tried to execute it(./a.out). The OS does not identify the file and says 'No such file or directory'. But when I put the same executable on a Ubuntu 12.10(64 bit) running on a 64 bit laptop, it runs fine and I get the desired output. The VM is running on IBM Blade Servers. I wanted to know why the results for a VM?

Ans:
The message No such file or directory does not refer to your executable file: a.out. Instead it refers to a helper program that's needed to run the 32 bit dynamically linked executable a.out.

Source: http://askubuntu.com/questions/351827/unable-to-run-a-32-bit-program-on-64-bit-vm

PHP is running with user ID=33, but this directory is owned by the system user with ID=0

Error:PHP is running with user ID=33, but this directory is owned by the system user with ID=0

Solution:
 sudo chown -R  www-data:www-data  /var/www/X2Engine/

before changes it was

drwxrwxrwx 3 root root    4096 Mar  4 16:24 X2Engine

--
Pranaw Kumar
C-DAC MUMBAI
Ph-(+91) (22) 26201606

How to enable or activate the apache mod_rewrite module

sudo a2enmod rewrite

then restart apache by

/etc/init.d/apache2 restart

How to change Apache Document root Directory in Ubuntu 13.10

http://www.binarytides.com/install-apache-ubuntu-13-10/

“Adding Printer” dialog asks for root password?

start printer configuration window through command line:

sudo system-config-printer

error while loading shared libraries: libtk8.4.so: cannot open shared object file: No such file or directory

Problem: On some Linux systems, launching oommf.tcl yields an error message of the form

error while loading shared libraries: libtk8.4.so: cannot open shared object file: No such file or directory

Solution: This typically happens because the libtk8.x.so (and libtcl8.x.so) files are installed in a directory not included in the ld.so runtime linker/loader search path. One way to fix this is to add that directory (say /usr/local/lib) to the LD_LIBRARY_PATH environment variable. For example, add

export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/usr/local/lib

to your ~/.bashrc file (bash shell users) or

setenv LD_LIBRARY_PATH ${LD_LIBRARY_PATH}:/usr/local/lib

to your ~/.cshrc file (csh or tcsh shell users). Another option is to modify the ld.so cache; see the ld.so and ldconfig man pages for details.

source: http://math.nist.gov/oommf/software-patchsets/oommf12a3/