Files & Directories-II

8/9/2019 Files & Directories-II

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Files & Directories

stat , fstat & lstat functions

> Return information about a le.Syntax :

#include

#include

Int stat(const char*pathname,struct stat *buf);

Int fstat(int ledes,struct stat *buf);

Int lstat(const char

*pathname,struct stat * buf);


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stat > returns a structure of information

fstat > obtains information about te le

%stat > returns information about te symbolic lin!

Second ar is a pointer to a structure tat 'e mustsupply

Structre denition can di(er

struct stat )

mode*t st*mode+ino*t st*ino+

de,*t st*de,+

de,*t st*rde,+

nlin! st*nlin! +

uid*t st*uid+

id*t st*id+

o(*t st*si-e+

time*t st*atime+


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time*t st*mtime+

time*t st*ctime+

lon st*bl!si-e+lon st*bloc!s+


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access Function

0is function is used to test on real user 1D and realroup 1D

* Synta!#include

1nt access2const car patname" int mode3+

*"eturns!

4 if 56 " $ on error 0e mode is te bit'ise 5R of any of te constants.

#ode $escription

R*56 0est for read permission

7*56 0est for 'rite permission8*56 0est for execute permission

F*56 0est for existence of le


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umas% Function

0is function sets te le mode creation mas! for teprocess

9o error ms* Synta!

#include

#include

mode*t umas!2mode*t cmas!3+*"eturns!

pre,ious le mode creation mas!


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chmod and fchmod Functions

sed to cane te le access permissions for an existin le.

* Synta !

#include

#include

1nt cmod 2const car patname"mode*t mode3+

1nt fcmod 2int ledes" mode*t mode3+

* "eturn !

4 if o! " $ on error ;cmod function operates on specied le

;fcmod function operates on already opened le

= conditions to cane te permission bits of a le:

> 0e e(ecti,euser1D of a process o'ner of te le> 0e process must a,e super user permission

?dditional modes are :

> S*1S@AB1D 2?dded set1D constants3

> S*1S08 20e sa,ed 0ext constant3

> S*1R78 20e C combined constants3


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he mode constants for chmod function

#ode $escription

S*1S1D setuser1D on execution

S*1SA1D setroup1D on execution

S*1S08 sa,ed0ext 2Stic!y Eit3

S*1R78 read"'rite"execute by user 2o'ner3

S*1RSR read by user 25'ner3

S*17SR 'rite by user 25'ner3S*18SR xecute by user 25'ner3

S*1R78A Read"'rite" execute by roup

S*1RARG read by roup

S*17ARG 'rite by roup

S*18ARG xecute by roup

S*1R785 Read"'rite" execute by oter 2'orld3

S*1R50H read by oter 2'orld3

S*1750H 'rite by oter 2'orld3

S*1850H xecute by oter 2'orld3


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0e ;cmod function automatically clear = of te permission bitsunder te follo'in conditions:

$. 5nly super user can set te stic!y bit oter'ise stic!y bit turned o(

=. Aroup1D of a le is not eIual to (ecti,eAroup1D of process " ten

setroup1D bit turned o(.. Stic%y 'it

1f it 'as set for an executable proram le " tat le stored in s'aparea.

Jainly used for reduce te time for load le in memory

Eot SRK and K.CLESD allo's te stic!y bit to be set for a directory if te bit is set for a directory " a le in te directory can be remo,edor renamed only if te user as 'rite permission for te directory " andeiter

> 5'ns te le

> 5'ns te directory or

> is te superuser

. chon , fchmod and lchon functions

*;co'n function allo's us to cane te user1D of a le and te

roup*1D of a le.


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*Synta!

#include

#include

int co'n2const car patname"uid*t o'ner" id*t roup3+

int fco'n2int ledes" uid*t o'ner" id*t roup3+int lco'n2const car patname" uid*t o'ner"id*t roup3+

*"eturn!

4 if o! " $ on error

lchon canes te o'ner of te symbolic lin!. 'er%eley based systems super user only can cane teo'nersip of a le

System allo'ed any user can cane te o'nersip of anyles

In +SI-./> 5nly a super user process can cane te user 1D of te le

> ? non super user can cane te roup 1D of te le if

te process o'ns te le

o'ner eIuals te user 1D of te le & roup 1D


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File Si0e

1n stat structure " te eld st*si-e contains si-e of te le in bytes.

0is eld is meanin ful only for

> reular les

> directories> symbolic lin!s

S"1denes te le si-e for a pipe

"e2ular File a le si-e of 4 is allo'ed

$irectory 3 te le si-e is usually a multiple of a number suc as

$M or N$=* Symbolic 4in% 3 te le si-e is actual number of bytes in te

lename

5! usr6lib 3 le si0e is 7

* S"1 and 1.89'S$

st*bl!si-e

st*bloc!s

* :oles in a File

> Reular le can contain ole

> Holes are created by see!in past te current endofle & 'ritinsome data


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File runcation

mptin a le by usin ;5*0R9O Pa in open function ?dditional functions to truncate te data are

Synta!

#include

#include

int truncate2const car patname" o(*t lent3+

int ftruncate2int ledes"o(*t lent3+

*"eturn!4 if 56 " $ on error

0e = functions truncate an existin le to ;lent bytes.

0ese = functions are pro,ided by

> SRK

> K.CLESD


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File Systems

Gartition Gartition Gartition

ilistDirectory bloc!s and

data bloc!s

inode inode QQ.. inode


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ilistDatabloc!

Directory bloc!

Databloc!

Directory bloc!

inode inodei

node

i

node

i

nodeno.

File

9ame

i

nodeno.

File

9ame


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arious le implementation types

1n SRK supports = di(erent types of dis! le systems

> 0e traditional 918 system le system 2SN3

> 0e unied File System 2FS3 FS Eased on te Eer!ley fast le system

SRK supports additional nondis! lesystems

> = distributed le systems

> ? bootstrap le system ? dis! dri,e di,ided into $ or more partitions

ac partition contains a le system

inode contains information about te le

1n te stat structure " te lin! count is contained in test*lin! member. 1ts primiti,e system data type in nlin!*t .0ese types of lin!s are calledhard lin%.

Symbolic 4in% 0e actual content of te le

contains te name of te le tat te symbolic lin! pointto it.


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1f te le type in i*node S*1F%96 " tat le issymbolic lin! le

i*node contains

> File type> File ?ccess Germission bits

>File Si-e

> Gointer to te data bloc!s for te le

stat structure information obtain from i*node Directory contains

> File 9ame

>i*node number

9o directory entry point to an i*node in a di(erentle systems


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lin% , unlin%, remoe, & rename Functions

?ny le can a,e multiple directory entries pointin to itsi*node

lin% Function

> sed to create a lin! to an existin le

3


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unlin% Function

> Remo,e an existin directory entry

3 0is function remo,es te directory entry & decrementste lin! count of te referenced by ;patname

> 1f oter lin! points to te le and data of te le is stillaccessible " ten le is not caned & error occurs

> 0o unlin! a le " 'e must a,e

> 7rite permission

> xecute permission> 1f stic!y bit is set to te directory " 'e must a,e

> 7rite permission and eiter of follo'in

> 5'n te le > 5'n te directory > Super userpermission

> lin! count 4 ten te content of te le 'ill be deleted

* F ti


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* remoe Function

> unilin! a le or directory 'it tis function

3 For a le ;remo,e ; unlin!

>For a directory ;remo,e ;rmdir> In =>SI ? 3 0is function used for delete a le

* rename Function

> sed to rename a directory or le

3< Synta !#include

int rename2const car oldname" const car ne'name3+

3< "eturns !

o if o!" $ on errror

S b li 4i %


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Symbolic 4in%s

1s an indirect pointer to a le

%imitations of Hard lin!:

> Hard reIuired " lin! & le reside in te same lesystem

>5nly super user can create a ard lin! to adirectory

9o limitations for symbolic lin! 0is is used for

> Jo,e a le

> Jo,e an entire directory ierarcy

1ntroduced 'it K.CLESD 7it SRK " symbolic lin!s are supported for

> 0e 0raditional System FileSystem 2SN3

> nied FileSystem 2FS3

li % & dli % F ti


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symlin% & readlin% Functions

symlin% Function

> Oreate a Symbolic lin!

3


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File imes

C time elds are maintained for eac le

Field $escription 5ample ls(/) option

st*atime lastaccess time of le data read u

st*mtime last*modication time of ledata 'rite default

st*ctime lastcane time of i*node status cmod " co'n c

Jany operations a(ect i*node 'itour canin te actual contents of te le :

> canin te le access permissions

> Oanin te user 1D

> Oanin te number of lin!s 0e system does not maintain te lastaccess time for an i*node

0e ;ls command displays or sorts only one of te C time ,alues.

ls l or lst options uses te modication time of a le

u option causes it to use te access time

c option causes it to use te canestatus time

utime Function


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utime Function

sed to cane access time & modication time of a le

*Synta !

#include

#includeint utime2const car patname" const struct utimebuf times3+

* "eturns!

4 if 56 " $ on errror

0e Structure used by tis function is

struct utimebuf

@

timeAt actime;

timeAt modtime;

B

0ese = time ,alues in te structure are calendar times " 'iccount seconds .

1f time is a null pointer " access time & modication time currenttime

1f time is a null pointer " access time & modication time structure pointed ,alue

%di & di F ti


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m%dir & rmdir Functions m%dir Function

>Oreate an empty directory

3< Synta!

#include#include

1nt m!dir2const car patname"mode*t mode3+

3 0e automatic entires are

dot 2.3 dotdot 2..3

rmdir Function

>Delete an empty directory

3< Synta!

#include

int rmdir2cosnt car patname3+

3< "eturns!

4 if 56 " $ on error

"eadin2 $irectories


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"eadin2 $irectories

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