IPC (Interprocess Communication) implementation example.

This example code illustrates the basic implementation of IPC mechanism that is provided by POSIX API.


#include
#include
#include

int main(int argc, char **argv)
{
int segment_id;
char *shared_mem;
const int size = 5096; // in bytes

//create shared mem.
segment_id = shmget(IPC_PRIVATE, size, S_IRUSR|S_IWUSR);

//attach the shared mem. to the process in Write Read mode.(0 argument)
shared_mem = (char * )shmat(segment_id, NULL, 0);

//write the data to the shared memory.
sprintf(shared_mem, "This is the shared memory example coded by Eren Golge. Regards!!");

//read the data from
printf("*%s \n", shared_mem );

//detach the segment from process
shmdt(shared_mem);

//delete the shared mem. segment form memory
shmctl(segment_id, IPC_RMID, NULL);

printf("End of code");
return 0;
}


Installing MySql to Ubuntu

Here are the steps that you need to follow:

1- Install the files that need to create a mysql database.

$sudo apt-get install mysql-server

2- Open the config file and comment out the line "bind-address = 127.0.0.1" as "#bind-address = 127.0.0.1". It makes your server available from internet.

$gksudo gedit /etc/mysql/my.cnf

3- Set the root password of the server and restart it.

$mysqladmin -u root password your-new-password

$sudo /etc/init.d/mysql restart

4- Install the "MYSql query browser" program

$sudo apt-get install mysql-query-browser

5- Program is installed in Applications > Programming, open it. Then type the necessary infos.

Server Hostname: 127.0.0.1
Username: root
Password: ******
Default Schema: (Empty)
Port : 3306

Compiling Kernel Method 2 (As Debian Package)

Here another compilation method for Kernel installing.

First download wanted kernel source code from kerel.org

then extract the .tar file that comes from the website.

Here the terminal process.

Copy the old config file to the new Kernel to do not try for setting new kernel.
­cp -vi /boot/config-`uname -r` .config

Or if you want to set your kernel type:
sudo make menuconfig

Then compile and create the debian packages of the kernel. You can type anything instead of **** to define your kernel. "fakeroot" commands gives error, maybe you need to download and install from "software center".
fakeroot make-kpkg --initrd --append-to-version=**** kernel-image kernel-headers


There should be created two "debian packages" (most probably in desktop). Go that directory in terminal then type:
sudo dpkg -i linux-ubuntu-modules-2.6.24-16-generic_2.6.24-16.23_i386.deb
sudo dpkg -i linux-headers-lum-2.6.24-16-generic_2.6.24-16.23_i386.deb

Finally go to the boot directory to set the "grub" with your new kernel:

cd /boot
sudo update-initramfs -c -k 2.6.37+QD

sudo update-grub2
reboot

Ubuntu 32-bit and 64-bit comparison bencmark.

http://www.tuxradar.com/content/ubuntu-904-32-bit-vs-64-bit-benchmarks

Good Site to learn commands and some terminal programs to see Process Status of System

http://www.cyberciti.biz/faq/show-all-running-processes-in-linux/

Compiling a kernel source code and use it as the kernel of your linux OS.

get latest kernel source:

$ cd /tmp
$ wget http://www.kernel.org/pub/linux/kernel/v2.6/linux-x.y.z.tar.bz2


extract .tar file:

# tar -xjvf linux-2.6.37.tar.bz2 -C /usr/src
# cd /usr/src


Configure kernel respected to your computer:

# make menuconfig


Compile Kernel:

$ make


Compile Kernel modules:

$ make modules


Install the kernel modules as a root user:

$su -
#make modules_install


Install kernel:

#make install


Create initrd image for Grup program for using at boot time initialization:

#cd /boot
#mkinitrd -o initrd.img-2.6.37 2.6.37


Modify Grup config. file:

# update-grup


Reboot computer:

That's all:)

"grep" Tool.

It is a new tool that I discover and I guess it is also really beneficial for you (The CS'ers). It is to search a String pattern in all kind of documents and the tool gives you the all matching documents and the line numbers of matchings of these documents.
Here is the basic structure of the usage;

grep [options] pattern filieTypes

[options] side to activate some extra functionalities. You can see the documentation in terminal by typing "grep --help"

Here also an example which search "sys_getpid" string in the all file types in directories with subdirectories.

erogol@ubuntu:~/Desktop/linux-2.6.37$ grep -Hrni sys_getPid *
arch/microblaze/kernel/syscall_table.S:27: .long sys_getpid  /* 20 */
arch/mips/kernel/scall64-o32.S:227: PTR sys_getpid   /* 4020 */
arch/mips/kernel/scall64-64.S:168: PTR sys_getpid
arch/mips/kernel/scall64-n32.S:163: PTR sys_getpid
arch/mips/kernel/scall32-o32.S:259: sys sys_getpid  0 /* 4020 */
arch/avr32/kernel/syscall_table.S:36: .long sys_getpid  /* 20 */
arch/xtensa/include/asm/unistd.h:281:__SYSCALL(120, sys_getpid, 0)
arch/xtensa/platforms/iss/include/platform/simcall.h:39:#define SYS_getpid 20
arch/s390/kernel/syscalls.S:31:SYSCALL(sys_getpid,sys_getpid,sys_getpid)   /* 20 */
arch/sparc/kernel/systbls_64.S:25:/*20*/ .word sys_getpid, sys_capget, sys_capset, sys_setuid16, sys_getuid16
arch/sparc/kernel/systbls_64.S:101:/*20*/ .word sys_getpid, sys_capget, sys_capset, sys_setuid, sys_getuid
arch/sparc/kernel/systbls_32.S:23:/*20*/ .long sys_getpid, sys_capget, sys_capset, sys_setuid16, sys_getuid16
arch/frv/kernel/entry.S:1212: .long sys_getpid  /* 20 */
arch/x86/include/asm/unistd_64.h:98:__SYSCALL(__NR_getpid, sys_getpid)
Binary file arch/x86/kernel/syscall_64.o matches
arch/x86/kernel/syscall_table_32.S:22: .long sys_getpid /* 20 */
Binary file arch/x86/kernel/built-in.o matches
Binary file arch/x86/built-in.o matches
arch/x86/ia32/ia32entry.S:533: .quad sys_getpid  /* 20 */
Binary file arch/x86/ia32/built-in.o matches
Binary file arch/x86/ia32/ia32entry.o matches
arch/m68k/kernel/entry.S:451: .long sys_getpid /* 20 */
arch/parisc/hpux/entry_hpux.S:51: ENTRY_NAME(sys_getpid) /* 20 */
arch/sh/kernel/syscalls_32.S:39: .long sys_getpid  /* 20 */
arch/sh/kernel/syscalls_64.S:43: .long sys_getpid  /* 20 */
arch/cris/arch-v10/kernel/entry.S:625: .long sys_getpid /* 20 */
arch/cris/arch-v32/kernel/entry.S:568: .long sys_getpid /* 20 */
arch/h8300/kernel/syscalls.S:37: .long SYMBOL_NAME(sys_getpid)  /* 20 */
arch/ia64/kernel/fsys.S:61:ENTRY(fsys_getpid)
arch/ia64/kernel/fsys.S:92:END(fsys_getpid)
arch/ia64/kernel/fsys.S:782: data8 fsys_getpid  // getpid
arch/ia64/kernel/entry.S:1489: data8 sys_getpid
arch/m32r/kernel/syscall_table.S:22: .long sys_getpid  /* 20 */
arch/mn10300/kernel/entry.S:460: .long sys_getpid /* 20 */
arch/blackfin/mach-common/entry.S:1386: .long _sys_getpid /* 20 */
arch/arm/kernel/calls.S:32:/* 20 */ CALL(sys_getpid)
arch/m68knommu/kernel/syscalltable.S:41: .long sys_getpid /* 20 */
...

A Good Writing About Boot Process for Linux System!

http://harrykar.blogspot.com/2010/03/ubuntu-system-administration.html

Using "strace" to see the Sys. calls executed with your written code.

"strace" is really effective utility for system administrators and coders to see the system calls that your program makes. It is really easy to use, just write to your terminal "strace programName" exp. "strace ./a.out" like ordinary compiled C code. It give output something like this; (I have interesting name of directory "01-um-getpid$" includes the a.out file. Do not be confused!)

erogol@ubuntu:~/Desktop/01-um-getpid$ strace ./a.out
execve("./a.out", ["./a.out"], [/* 39 vars */]) = 0
brk(0)                                  = 0x186e000
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3c3d4d8000
access("/etc/ld.so.preload", R_OK)      = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY)      = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=123841, ...}) = 0
mmap(NULL, 123841, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f3c3d4b9000
close(3)                                = 0
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
open("/lib/libc.so.6", O_RDONLY)        = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\240\356\1\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=1572232, ...}) = 0
mmap(NULL, 3680296, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f3c3cf37000
mprotect(0x7f3c3d0b1000, 2093056, PROT_NONE) = 0
mmap(0x7f3c3d2b0000, 20480, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x179000) = 0x7f3c3d2b0000
mmap(0x7f3c3d2b5000, 18472, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f3c3d2b5000
close(3)                                = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3c3d4b8000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3c3d4b7000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3c3d4b6000
arch_prctl(ARCH_SET_FS, 0x7f3c3d4b7700) = 0
mprotect(0x7f3c3d2b0000, 16384, PROT_READ) = 0
mprotect(0x600000, 4096, PROT_READ)     = 0
mprotect(0x7f3c3d4da000, 4096, PROT_READ) = 0
munmap(0x7f3c3d4b9000, 123841)          = 0
getpid()                                = 9376
exit_group(0)                           = ?

The numbers that are at the end of the lines are the System Call numbers and the beginning of the lines are the sys. call names. That is all...

Here is a basic process on GDB to see the Sys. Assemble codes executed with your C Program's "main" func..

There are the input strings to your terminal in sequence. Follow the order;

gcc demo.c // it compiles and gives a.out.
gdb a.out  //it starts the debugger gdb.
break main //it puts a break point to your code's main function.
run        //it runs the program up to main func.
disassemble //it gives the system assemble codes. 

Here is the process overview from my terminal.

erogol@ubuntu:~/Desktop/01-um-getpid$ gcc demo.c
erogol@ubuntu:~/Desktop/01-um-getpid$ gdb a.out
GNU gdb (GDB) 7.2-ubuntu
Copyright (C) 2010 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later 
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
For bug reporting instructions, please see:
...
Reading symbols from /home/erogol/Desktop/01-um-getpid/a.out...(no debugging symbols found)...done.
(gdb) break main
Breakpoint 1 at 0x4004f8
(gdb) run
Starting program: /home/erogol/Desktop/01-um-getpid/a.out 

Breakpoint 1, 0x00000000004004f8 in main ()
(gdb) disassemble
Dump of assembler code for function main:
   0x00000000004004f4 <+0>: push   %rbp
   0x00000000004004f5 <+1>: mov    %rsp,%rbp
=> 0x00000000004004f8 <+4>: mov    $0x0,%eax
   0x00000000004004fd <+9>: callq  0x400400 
   0x0000000000400502 <+14>: mov    $0x0,%eax
   0x0000000000400507 <+19>: leaveq 
   0x0000000000400508 <+20>: retq   
End of assembler dump.
(gdb) ^CQuit
(gdb) 

About OS!!!!

I just start a new course about Operating Systems concept so after a long time there will be some useful content in the blog about OS for sure!!! Keep up with me