Pramod Linux

8/9/2019 Pramod Linux

1/11

INTRODUCTION TO LINUX OPERATING SYSTEM and

FILEs CONCEPTs and PROCESS management

By

KPRAMOD KUMAR REDDY

M!Te"# $DSCE%

R&'' N&!()*((D*+),


2/11

System Ca''s

The kernel provides a set of interfaces for applications running in user mode

to interact with the system. These interfaces, also known as system calls

System calls give applications access to hardware and other kernel

resources.

System calls ensure security and stability.

Use- S.a"e /s Ke-ne' S.a"e


3/11

FILESI/O

"-eate System Ca''

int creat (const char * pathname, int flags)

Flags !"#$!%&', !"#!%&', !"#$#

!"#+T , !"+%$, !"%!%-&!,

!"%!TTT', !"T#/% , !"0&,

!"S'%, !"$1#T!#', !"$1#T,

!"+S'%, !"&+#2F1&

3!$ #+$, #1T, 0/T #31SS1!%

F!# !%#, 2#!/ 33-#S +%$

!T4#S

&.en System Ca''

int open (const char * pathname, int flags)

int open (const char * pathname, int flags, mode"t mode)

Flags !"#$!%&', !"#!%&', !"#$#

!"#+T , !"+%$, !"%!%-&!,

!"%!TTT', !"T#/% , !"0&,!"S'%, !"$1#T!#', !"$1#T, !"+S'%,

!"&+#2F1&

3!$ #+$, #1T, 0/T #31SS1!%

F!# !%#, 2#!/ 33-#S +%$

!T4#S

E0am.'e .-&g-am t& &.en a F1'e

5include 6stdio.h7

5include 6fcntl.h7

5include 6sys8types.h7

5include 6sys8stat.h7

int main( )

9

int fd,count:


4/11

char buf;:

fd?open(@$emo.tAt@,!"#$#):

printf(@new file disciptorBdCn@,fd):

count?read(fd,buf,


5/11

5include 6fcntl.h7

int main()

9

int fd:

char ch:

fd?open(@$emo.tAt@,!"#$!%&'):

while(read(fd,ch,G)H?=)

putchar(ch):

close(fd):

printf(@Cn@):

D


6/11

3-1te System Ca''

ssiEe"t write(int fd, void *buf, siEe"t count)

E0am.'e .-&g-am 2&- 3-1te system "a''

5include6stdio.h7

5include6unistd.h7

5include6fcntl.h7

int main()

9

int fd:

char ch:

fd ? open(@$emoG.tAt@,!"#$#I!"#+T):$#e-e 3e a-e

&.en1ng a 21'e a2te- "-eat1ng 1t4 we can see it from syntaA%

while((ch?getchar())H?!F)

write(fd,ch,G):

close(fd):$It 1s 5sed t& "'&se t#e 21'e 3#1"# #as 6een &.ened%

D


7/11

"'&se system "a''

int close ( int fd )

'see7 System Ca''

!ff"t lseek ( int fd, off"t offset, int where)

here S"ST, S"/#, S"%$

The lseek call enables you to reposition a file descriptor in a file. ass it the

file descriptor and two additional arguments specifying the new position.

1f the third argument is S"ST, lseek interprets the second argument as

a position, in bytes, from the start of the file.

1f the third argument is S"/#, lseek interprets the second argument as

an offset, which may be positive or negative, from the current position. 1f the third argument is S"%$, lseek interprets the second argument as

an offset from the end of the file.+ positive value indicates a position

beyond the end of the file.

E0am.'e .-&g-am 2&- 'see7 synta0

5include6stdio.h7

5include6fcntl.h7

5include6sys8types.h7


8/11

int main()

9

int fd:

char ch:

fd? open(@lsk.tAt@,!"#$#I!"#+T,JJJ):

lseek(fd,K,S"ST):

while((ch?getchar()H?!F)

write(fd,ch,G):

close(fd):

D

P-am&d 75ma-is shown before program is eAecuted


9/11

e can see the appended data after pramod which is pramod reddy

So we can see data as .-am&d.-am&d -eddy

PROCESS MANAGEMENT

fork

fork - create a child process

SYNOPSIS

#include

#include unistd.h>

pid_t fork(void!

"S$%IP&ION

forkcreates a child process that differs from the parent process only in its

PID and PPID, and in the fact that resource utilizations are set to 0. Filelocks and pending signals are not inherited.

Under Linu, forkis implemented using copy-on-!rite pages, so the only

penalty incurred "y fork is the time and memory re#uired to duplicate the

parent$s page ta"les, and to create a uni#ue task structure for the child.


10/11

vfork

%fork - create a child process and "lock parent

SYNOPSIS

#include

#include

pid_t vfork(void!

"S$%IP&ION

&he vfork'( function has the same effect as fork'(, ecept that the

"eha%iour is undefined if the process created "y vfork'( either modifies

any data other than a %aria"le of type pid)t used to store the return %aluefrom vfork'(, or returns from the function in !hich vfork'( !as called, or

calls any other function "efore successfully calling_exit'( or one of

the execfamily of functions.

'it)'itpid

!ait, !aitpid - !ait for process termination

SYNOPSIS

#include sys/types.h>

#include sys/'it.h>

pid_t 'it(int *status!

pid_t 'itpid(pid_tpid) int *status) int options!

"S$%IP&ION

&he 'itfunction suspends eecution of the current process until a child haseited, or until a signal is deli%ered !hose action is to terminate the current

process or to call a signal handling function. If a child has already eited "y

the time of the call 'a so-called *zom"ie* process(, the function returns

immediately. +ny system resources used "y the child are freed.


11/11

e+ecve

eec%e - eecute program

SYNOPSIS

#include

int e+ecve(const chr *filename) chr *const argv,-) chr *const envp,-!

"S$%IP&ION

e+ecve(eecutes the program pointed to "yfilename. filenamemust "e either a

"inary eecuta"le, or a script starting !ith a line of the form *# interpreter arg*.In the latter case, the interpreter must "e a %alid pathname for an eecuta"le !hich

is not itself a script, !hich !ill "e in%oked as interpreterarg filename.

argvis an array of argument strings passed to the ne! program. envpis an array

of strings, con%entionally of the form keyvlue, !hich are passed as en%ironment

to the ne! program. oth, argvand envpmust "e terminated "y a null pointer. &he

argument %ector and en%ironment can "e accessed "y the called program$s main

function, !hen it is defined as int 0in(int r1c) chr *r1v,-) chr *envp,-.

Re2e-en"es4!

Beg1nn1ng L1n50 P-&g-amm1ng 6y! R1"#a-d St&nes and Ne1' Matt#e3

L1n50 Ke-ne' De8e'&.ment 9 R&6e-t L&8e t#1-d ed1t1&n

Documents

Pramod Linux