Linux System Calls

When successful exec will not return, it will start

executing the new program

However if there is an- error exec returns -1 and sets the

errno to the appropriate value

Linux implements fork() via the clone() system call.

The clone() system call, in turn, calls do_fork().

The bulk of the work in forking is handled by do_fork(),

which is defined in kernel/fork.c.This function calls

copy_process() and then starts the process running.

If copy_process() returns successfully, the new child is

woken up and run. Deliberately, the kernel runs the child

process first.

You need to install an SSL certificate in apahce to secure

the transactions.

It contains all the kernel modules that needed to be loaded

into kernel (booting etc). there will some .map, .dep

(dependency files) files present.

When the kernel needs a feature that is not resident in the

kernel, the kernel module daemon kmod[1] execs modprobe to

load the module in.

You can see what modules are already loaded into the kernel

by running lsmod, which gets its information by reading the

file /proc/modules

Mainly hardware related information such as CPU

information, Memory (RAM) information stored under /proc

directory

example:

# cat /proc/cpuinfo (show the information of CPU of that

particular hardware)

# cat /proc/meminfo (show the information of Memory i.e.

RAM of that particular hardware)

kernel 2.6 introduces a new file naming convention: kernel

modules now have a .ko extension (in place of the old .o

extension) which easily distinguishes them from conventional

object files. The reason for this is that they contain an

additional .modinfo section that where additional

information about the module is kept.

Linux program modpost can be used to convert .o files into

.ko files.

ext3 is also same as the ext2, but journaling concept is introduced in ext3.

Compared to ext2, ext3 is slow. ext2 less secure compared to ext3. ext2 is less

Performance where as ext3 is very good performance.

resize2fs is only for ext2 filesystem but not ext3.

first unmount the partition

#umount /dev/sda1

#tune2fs -O ^has_journal /dev/sda1 #to remove journal from /dev/sda1

#e2fsck -f /dev/sda1

#resize2fs /dev/sda1 600M #resize the partition

ssh is secured shell, allows the user to login remotely with more secured.

whereas telnet also same but authentications like passwords, transfers over a network as text mode. so it is not good to use.

mainly spinlock used in threads to avoid synchronization,where as semaphore and mutex used to avoid process synchronization.

1.spinlock is something like polling.it spins for resouce until aloocated resouce releases.

2.binary semaphore and mutex are similar.

umask value = 022

Without a umask in effect,any file created will have 666

permissions.

666

022

---------

644

---------

A umask of 022 will result in files created with 666 permission.

atomic variables are the variables which can only be

manipulated atomically using atomic APIs. Linux declares

variable as atomic by using the type atomic_t. Basically

used a way to achieve synchronization.

an atomic operation is one which cannot be (or is not)

interrupted by concurrent operations and cannot be broken up

into smaller parts that could be performed by different

processors.

Atomic function is a function which is executed to

completion without interruption. Atomic function can also be

seen as a small critical section which is executed without

interruption, locking.

There are 2 situations when Linux can switch from user Space

to Kernel Space:-

1) by doing System calls

2) When interrupt comes (to handle interrupt)

3) by executing 128 (0x80 ) instruction or doing sysenter

Linux can switch from kernel Space to User space:-

1) process in kernel mode is preempted.

2) After completion of Interrupt handler / System call

3) performing sysexit sys call

insmod: insmod is a tool used to attach a module to the

running linux kernel. This will take the kernel object(.ko)

and takes all executable code and data sections of the .ko

and attach it to the running linux kernel.

rmmod: used to remove or deattach a module code from the

running kernel

RAID 1 is disk striping. no mirroring no parity. Minimum 2 disks required. If any

One disk fails all the data get lost.

RAID 5 is disk striping with parity. Minimum 3 disks required. if anyone disk fails

Data is safe, if two fails data get lost.