FILE TYPES
Regular file
Directory file
Character device file
Block device file
Regular file
It may be text or binary file
Both the files are executable provided
execution rights are set
They can be read or written by users with
appropriate permissions
Directory file
Folder that contains other files and
subdirectories
Provides a means to organize files in
hierarchical structure
Block device file : Physical device which
transmits data a block at a time
EX: hard disk drive, floppy disk drive
Character device file : Physical device
which transmits data in a character-based manner
To create : mknod command
mknod filename type major minor
mknod /dev/cdsk c 115 5 /dev/cdsk : name of the device
c -- character device b -- block device
115 — major device number 5 — minor device number
Major device number : an index to the kernel’s file table that contains address of all device drivers
FIFO file
Special pipe device file which provides a temporary buffer for two or more processes to communicate by writing data to and reading data from the buffer
Max size of buffer – PIPE_BUF The storage is temporary
The file exists as long as there is one process in direct connection to the FIFO for data access
To create : mkfifo OR mknod mkfifo /usr/prog/fifo_pipe
mknod /usr/prog/fifo_pipe p
Symbolic link file
A symbolic link file contains a pathname
which references another file in either the local or a remote file system
To create : ln command with –s option
ln –s /usr/abc/original /usr/xyz/slink
cat /usr/xyz/slink
The File System Structure
/
etc bin usr1
faculty
dev tmp
date. . .cal
. . . . . . . . .
File systems
They have a tree-like hierarchical file
system
“/” – denotes the root “.” – current directory “..” – parent directory
NAME_MAX – max number of characters
in a file name
PATH_MAX -- max number of characters
Common UNIX files
/etc : Stores system administrative files
& programs
/etc/passwd : Stores all user information /etc/shadow : Stores user passwords
/etc/group : Stores all group information /bin : Stores all system programs
/dev : Stores all character and
block device files
/usr/include : Stores standard header files /usr/lib : Stores standard libraries
tmp : Stores all temporary files
File attributes
File type : type of file
Access permission : the file access permission for
owner group and others
Hard link count : number of hard links of a file UID : the file owner user ID
GID : the file group ID
File size : the file size in bytes
Last access time : time the file was last accessed Last modify time : the time the file was last modified Last change time : the time the file access
permission UID ,GID or hard link count was last changed
Inode number : system inode number of the file File system ID : the file system ID where the file is
Attributes of a file that remain
unchanged
File type
File inode number
File system ID
Major and minor device number
UNIX
command System call Attributes changed
chmod chmod Changes access
permission, last change time
chown chown Changes UID, last
change time
chgrp chown Changes GID, last
touch utime Changes last access time, modification time
ln link Increases hard link
count
rm unlink Decreases hard link
count .If the hard link
count is zero ,the file will be removed from the file system
vi, emac Changes file size,last
Inodes
UNIX system V has an inode table which keeps track
of all files
Each entry in inode table is an inode record
Inode record contains all attributes of file including inode number and physical address of file
Information of a file is accessed using its inode number
Inode number is unique within a file system
A file record is identified by a file system ID and inode number
Inode record doesnot contain the name of the file The mapping of filenames to inode number is done
112
67 ..
97 abc
234 a.out
To access a file for example /usr/abc, the kernel knows ”/” directory inode number of any process, it will scan “/” directory to
find inode number of “usr” directory it then checks for inode number of abc in usr .
APPLICATION PROGRAM
INTERFACE TO FILES
Files are indentified by path names
Files must must be created before they
can be used.
Files must be opened before they can be
accessed by application programs .open
A process can may open at most
OPEN_MAX number of files
The read and write system calls can be
used to read and write data to opened files
File attributes are queried using stat or
fstat system calls
File attributes are changed using chmod,
chown, utime and link system calls
Hard links are removed by unlink system
Low Level File Access
We can access & control files and directories
using a small number of function known as system calls.
The low level functions used to access file or
device drivers are
open : Open a file or device.
read : Read from an open file or device write : Write to a file or device.
close : Close the file or device
Each running program, called a process, has
a number of file descriptors associated with it.
These are small integers that we can use to
access open files or devices.
When a program starts, it has three
descriptors already opened. These are
0 : Standard Input 1 : Standard Output 2 : Standard Error
We can associate other file descriptors with
Library Functions
The using low level system call directly is inefficient due to
There’s a performance penalty in making a system
call. System calls are therefore expensive
compared to function calls because Linux has to switch from running your program code to
executing its own kernel code and back again.
The hardware has limitations that can impose
To provide a higher-level interface to devices
and disk files, a Linux distribution (and UNIX) provides a number of standard libraries.
These are collections of functions that you can
include in your own programs to handle these problems.
A good example is the standard I/O library that
provides buffered output. You can effectively write data blocks of varying sizes
This dramatically reduces the system call
write
The write system call writes the first nbytes
bytes from buf to the file associated with the file descriptor fildes.
It returns the number of bytes actually written. If
the function returns 0, it means no data was
written; if it returns –1, there has been an error in the write call, and the error will be specified in the errno global variable.
syntax:
#include <unistd.h>
size_t write(int fildes, const void *buf, size_t nbytes);
read
The read system call reads up to nbytes bytes of
data from the file associated with the file
descriptor fildes and places them in the data area buf.
It returns the number of data bytes actually read,
which may be less than the number requested. If a read call returns 0, it had nothing to read.
An error on the call will cause it to return –1.
Syntax
:-#include <unistd.h>
open
To create a new file descriptor, use the open system call. #include <fcntl.h>
#include <sys/types.h> #include <sys/stat.h>
int open(const char *path, int oflags);
int open(const char *path, int oflags, mode_t mode); If successful, it returns a file descriptor (always a
nonnegative integer) that can be used in read, write, and other system calls or –1 if it fails.
The file descriptor is unique and isn’t shared by any other
processes that may be running.
The name of the file or device to be opened is passed as a
The oflags are specified as a combination of a
mandatory file access mode and other optional modes. Mandatory modes are
O_RDONLY Open for read-only O_WRONLY Open for write-only
O_RDWR Open for reading and writing
The call may also include a combination (using a
bitwise OR) of the following optional modes in the oflags parameter:
O_APPEND: Place written data at the end of the file.
O_TRUNC: Set the length of the file to zero, discarding existing
contents.
O_CREAT: Creates the file, if necessary, with permissions given
in mode.
O_EXCL: Used with O_CREAT, ensures that the caller creates
Initial Permissions
When we create a file using the O_CREAT flag with
open, we must use the three-parameter form. mode, the third parameter, is made from a bitwise OR of the flags defined in the header file sys/stat.h. These are:
close
We use close to terminate the association
between a file descriptor, fildes, and its file. The file.
descriptor becomes available for reuse. It
returns 0 if successful and –1 on error.
File Copy Program int in, out; int nread;
in = open(“file.in”, O_RDONLY);
out = open(“file.out”, O_WRONLY|O_CREAT, S_IRUSR|S_IWUSR);
while((nread = read(in,block,sizeof(block))) > 0) write(out,block,nread);
ioctl
It provides an interface for controlling the behavior of
devices and their descriptors and configuring underlying services.
Terminals, file descriptors, sockets, and even tape
drives may have ioctl calls defined for them and we need to refer to the specific device’s man page for details. Here’s the syntax:
#include <unistd.h>
int ioctl(int fildes, int cmd, ...);
ioctl performs the function indicated by cmd on the
object referenced by the descriptor fildes. It may take an optional third argument, depending on the
The Standard I/O Library
The standard I/O library (stdio) and its header
file, stdio.h, provide a versatile interface to low-level I/O system calls.
we look at the following functions: ❑ fopen, fclose
❑ fread, fwrite
❑ fflush
❑ fseek
❑ fgetc, getc, getchar
❑ fputc, putc, putchar
fopen
#include <stdio.h>
FILE *fopen(const char *filename, const char *mode);
fopen opens the file named by the filename parameter and
associates a stream with it. The mode parameter specifies how the file is to be opened. It’s one of the following strings:
“r” or “rb” : Open for reading only
“w” or “wb” : Open for writing, truncate to zero length “a” or “ab” : Open for writing, append to end of file “r+” or “rb+” or “r+b” : Open for update (reading and writing)
“w+” or “wb+” or “w+b”: Open for update, truncate to zero length “a+” or “ab+” or “a+b”: Open for update, append to end of file
If successful, fopen returns a non-null FILE * pointer. If it
fread
The fread library function is used to read data from a
file stream.
Data is read into a data buffer given by ptr from the
stream, stream. Both fread and fwrite deal with data
records. These are specified by a record size, size, and a count, nitems, of records to transfer. The function
returns the number of items (rather than the number of bytes) successfully read into the data buffer.
At the end of a file, fewer than nitems may be returned,
including zero. Here’s the syntax:
#include <stdio.h>
fwrite
The fwrite library call has a similar interface to
fread.
It takes data records from the specified data buffer
and writes them to the output stream. It returns the number of records successfully written.
Here’s the syntax:
#include <stdio.h>
fclose
The fclose library function closes the specified
stream, causing any unwritten data to be written.
It’s important to use fclose because the stdio library
will buffer data. If the program needs to be sure that data has been completely written, it should call
fclose. Here’s the syntax:
#include <stdio.h>
fflush
The fflush library function causes all outstanding
data on a file stream to be written immediately.
You can use this to ensure that, for example, an
interactive prompt has been sent to a terminal before any attempt to read a response. It’s also useful for ensuring that important data has been committed to disk before continuing.
Here’s the syntax:
#include <stdio.h>
fseek
The fseek function sets the position in the stream
for the next read or write on that stream.
Here’s the syntax:
#include <stdio.h>
int fseek(FILE *stream, long int offset, int whence);
The offset parameter is used to specify the position,
and the whence parameter specifies how the offset is used. whence can be one of the following:
SEEK_SET: offset is an absolute position
fgetc, getc, and getchar
The fgetc function returns the next byte, as a
character, from a file stream. When it reaches the end of the file or there is an error, it returns EOF.
The getc function is equivalent to fgetc, except that
it may be implemented as a macro.
The getchar function is equivalent to getc(stdin)
and reads the next character from the standard input. Here’s the syntax:
#include <stdio.h>
fputc, putc, and putchar
The fputc function writes a character to an output
file stream. It returns the value it has written, or EOF on failure.
#include <stdio.h>
fgets and gets
The fgets function reads a string from an input file
stream.
#include <stdio.h>
char *fgets(char *s, int n, FILE *stream); char *gets(char *s);
fgets writes characters to the string pointed to by s
until a newline is encountered, n-1 characters have been transferred, or the end of file is reached,
whichever occurs first.
The gets function is similar to fgets, except that it
reads from the standard input and discards any
Formatted Input and Output
printf, fprintf, and sprintf
printf, fprintf, and sprintf
The printf family of functions format and output a
variable number of arguments of different types.
The way each is represented in the output stream
is controlled by the format parameter, which is a string that contains ordinary characters to be
printed and codes called conversion specifiers, which indicate how and where the remaining arguments are to be printed.
#include <stdio.h>
int printf(const char *format, ...);
int sprintf(char *s, const char *format, ...);
The printf function produces its output on the
standard output.
The fprintf function produces its output on a
specified stream.
The sprintf function writes its output and a
terminating null character into the string s passed as a parameter.
Here are some of the most commonly used
conversion specifiers:
❑ %d, %i : Print an integer in decimal
❑ %o, %x : Print an integer in octal, hexadecimal
❑ %c : Print a character
❑ %s : Print a string
❑ %f : Print a floating-point (single precision) number
❑ %e : Print a double precision number, in fixed format
Format Argument |Output|
%10s “Hello” | Hello|
%-10s “Hello” |Hello |
%10d 1234 | 1234|
%-10d 1234 |1234 |
%010d 1234 |0000001234 |
%10.4f 12.34 | 12.3400|
%*s 10,”Hello” | Hello|
scanf, fscanf, and sscanf
The scanf family of functions works in a way similar
to the printf group, except that these functions read items from a stream and place values into variables at the addresses they’re passed as pointer
parameters.
They use a format string to control the input
conversion in the same way, and many of the conversion specifiers are the same.
#include <stdio.h>
int scanf(const char *format, ...);
The conversion specifiers are
❑ %d : Scan a decimal integer
❑ %o, %x : Scan an octal, hexadecimal integer
❑ %f, %e, %g : Scan a floating-point number
❑ %c : Scan a character (whitespace not skipped)
string of capital letters. If the first character in the set is a caret, ^, the specifier reads a string that
consists of characters not in the set. So, to read a string with spaces in it, but stopping at the first
Stream Errors
To indicate an error, many stdio library
functions return out-of-range values, such as null pointers or the constant EOF.
In these cases, the error is indicated in the
external variable errno:
We can also interrogate the state of a file stream to
determine whether an error has occurred, or the end of file has been reached.
#include <stdio.h>
int ferror(FILE *stream); int feof(FILE *stream);
void clearerr(FILE *stream);
The ferror function tests the error indicator for a stream
and returns nonzero if it’s set, but zero otherwise.
The feof function tests the end-of-file indicator within a
stream and returns nonzero if it is set, zero otherwise.
The clearerr function clears the end-of-file and error
File Copy Program
#include <stdio.h> #include <stdlib.h> int main()
{
int c;
FILE *in, *out;
in = fopen(“file.in”,”r”);
out = fopen(“file.out”,”w”); while((c = fgetc(in)) != EOF) fputc(c,out);
UNIX KERNEL SUPPORT FOR FILES
The kernel has a file table that keeps the track
of all opened files in the system.
There is also an inode table that contains a
copy of the file inodes most recently accessed.
Whenever a user executes a command, a
process is created by the kernel to carry out the command execution.
Each process has its own data structures: file
descriptor table is one among them
File descriptor table has OPEN_MAX entries,
Kernel support : open system call
Whenever an open function is called the kernel will resolve the pathname to file inode
Open call fails and returns -1 if the file inode does not exist or the process lacks appropriate
permissions
Else a series of steps follow
1. The kernel will search the file descriptor table and look for first unused entry, which is returned as file descriptor of the opened file
2. The kernel will scan the file table in its kernel space to find an unused entry that can be assigned to
reference the file.
a) The process’s file descriptor table entry will be set to point to file table entry
b)The file table entry will be set to point to inode table entry where the inode record of file is
present
c) The file table entry will contain the current file pointer of the open file
d)The file table entry will contain an open mode which specifies the file is opened for read-only, write-only etc.
e) Reference count of file table is set to 1.
rc=1
rc=2 r
rc=1
rw rc=1
w rc=1
File descriptor table
File table Inode table
Kernel support : read system call
The kernel will use the file descriptor to index the
process’s file descriptor table to find file table entry to opened file
It checks the file table entry to make sure that the file is opened with appropriate mode
The kernel will use the file pointer used in file table entry to determine where the read operation should occur in file
The kernel will check the type of file in the inode record and invokes an appropriate driver function to initiate the actual data transfer with a physical file
If the process calls lseek function then the changes
are made provided the file is not a character device file, a FIFO file, or a symbolic link file as they follow only
Kernel support : close system call
When a process calls the close function to close an opened file, the sequence of events are as follows: 1.The kernel will set the corresponding descriptor table entry to unused
2.It decrements the reference count in file table entry by 1. If reference count !=0 then go to 6
3.File table entry is marked unused
4.The reference count in file inode table entry by 1. If reference count !=0 then go to 6
5.If hard link count is non zero, it returns a success status, otherwise marks the inode table entry as
Hard and symbolic links
A hard link is a UNIX path name for a file To create hard link ln command is used
ln /usr/abc/old.c /usr/xyz/new.c
Symbolic link is also a means of
referencing a file
To create symbolic link ln command is
used with option –s
Cp command creates a duplicated copy of
file to another file with a different path name
Where as ln command saves space by not
duplicating the copy here the new file will have same inode number as original file.
Difference : hard link and symbolic
link
Hard link Symbolic link
Does not create a new
inode Create a new inode
Cannot link directories
unless it is done by root Can link directories Cannot link files across
file systems Can link files across file system Increase hard link count
open Opens a file for data access read Reads data from file
write Writes data into file
lseek Allows random access of data in a file close Terminates connection to a file
stat,fstat Queries attributes of a file
chmod Changes access permissions of a file chown Changes UID and/or GID of a file
Utime Changes last modification time and access time stamps of a file
link creates a hard link to a file
ulink Deletes a hard link to a file
umask Sets default file creation mask
Open
The function establishes connection
between process and a file or to create a new file.
The prototype of the function
#include <sys/types.h> #include <fcntl.h>
int open (const char *pathname, int access mode, mode_t permission);
Access_mode : An integer which specifies how file is to be accessed by calling process, use one of these flag
O_RDONLY Opens file for read-only
O_WRONLY Opens file for write only
O_RDWR Opens file for read & write
One or more Access modifier flag can be used with these
O_APPEND Appends data to the end of the file
O_CREAT Create the file if doesn’t exists.
O_EXCL This causes open to fail, if file already exist.
O_TRUNC If file exists, set file size to zero.
O_NONBLOCK Any subsequent read/write on file should be nonblocking
O_NOCTTY Specifies not to use the named terminal device file as calling process control terminal.
Permission required only if O_CREAT flag is set.
Umask
It specifies some access rights to be masked off Prototype:
mode_t umask ( mode_t new_umask);
mode_t old_mask = umask(S_IXGRP|S_IWOTH); /*removes execute permission from others and write
permission from group*/
It is used to create new regular files
Creat
#include <sys/types.h> #include <unistd.h>
Read
This function fetches a fixed size block of
data from a file referenced by a given file descriptor
#include <sys/types.h> #include <unistd.h>
Write
The write function puts a fixed size block
of data to a file referenced by a file descriptor
#include <sys/types.h> #include <unistd.h>
Close
Disconnects a file from a process
Close function frees unused file descriptors.
Close function will deallocate system resources It a process terminates without closing all the
files it has opened, the kernel will close those files for the process.
fcntl
The fcntl function helps to query or set access
control flags and the close-on-exec flag of any file descriptor.
We can also use fcntl to assign multiple file
descriptors to reference the same file
cmd argument specifies which operation to
perform on a file referenced by the fdesc argument.
The third argument value is dependent on the
actual cmd value.
#include <fcntl.h>
Following are the cmd values that can be used.
F_GETFL : returns the access control flags of a file
descriptor fdesc
F_SETFL : sets or clears control flags that are specified
in the third argument. The allowed flags are O_APPEND & O_NONBLOCK
F_GETFD : returns the close-on-exec flag of a file
referenced by fdesc. If return value is 0, flag is off, otherwise if nonzero flag is on.
F_SETFD : sets or clears close-on-exec flag of a file
descriptor fdesc. The third argument is 0 to clear the flag or 1 to set the flag.
F_DUPFD : duplicates the file descriptor fdesc with
lseek
the lseek system call is used to change the
file offset to a different value
Prototype :
#include <sys/types.h> #include <unistd.h>
Pos :
specifies a byte offset to be added to a
reference location in deriving the new file offset value
Whence location reference
SEEK_CUR current file pointer
address
SEEK_SET the beginning of a
file
link
The link function creates a new link for
existing file
Prototype :
Cannot link a directory unless the calling
function has the superuser privilege
#include <unistd.h>
unlink
Deletes link of an existing file
#include <unistd.h>
Stat fstat
Stat and fstat retrieve arguments of a
given file
#include <sys/types.h> #include <unistd.h>
If pathname specified in stast is a
symbolic link then the attributes of the non-symbolic file is obtained
To avoid this lstat system call is used It is used to obtain attribites of the
symbolic link file
int lstat (const char* path_name , struct stat*
/* Program to emulate the UNIX ls -l command */ #include <iostream.h>
#include <sys/types.h> #include <sys/stat.h> #include <unistd.h> #include <pwd.h> #include <grp.h>
static char xtbl[10] = "rwxrwxrwx"; #ifndef MAJOR
#define MINOR_BITS 8
#define MAJOR(dev) ((unsigned)dev >> MINOR_BITS) #define MINOR(dev) ( dev & MINOR_BITS)
/* Show file type at column 1 of an output line */ static void display_file_type ( ostream& ofs, int st_mode )
{
switch (st_mode &S_IFMT) {
case S_IFDIR: ofs << 'd'; return;
/* directory file */
case S_IFCHR:ofs << 'c'; return;
/* character device file */
case S_IFBLK: ofs << 'b'; return;
/* block device file */
case S_IFREG: ofs << ' '; return;
/* regular file */
case S_IFLNK: ofs << 'l'; return;
/* symbolic link file */
case S_IFIFO: ofs << 'p'; return;
/* FIFO file */
/* Show access permission for owner, group, others, and any special flags */
static void display_access_perm ( ostream& ofs, int st_mode ) {
char amode[10];
for (int i=0, j= (1 << 8); i < 9; i++, j>>=1) amode[i] = (st_mode&j) ? xtbl[i] : '-';
/* List attributes of one file */
static void long_list (ostream& ofs, char* path_name) {
struct stat statv; struct group *gr_p; struct passwd *pw_p;
if (stat (path_name, &statv)) { perror( path_name );
return; }
display_file_type( ofs, statv.st_mode );
display_access_perm( ofs, statv.st_mode );
ofs << statv.st_nlink; /* display hard link count */
gr_p = getgrgid(statv.st_gid);
/* convert GID to group name */
pw_p = getpwuid(statv.st_uid); / *convert UID to user name */
if ((statv.st_mode&S_IFMT) == S_IFCHR || (statv.st_mode&S_IFMT)==S_IFBLK) ofs << MAJOR(statv.st_rdev) << ','
<< MINOR(statv.st_rdev); else ofs << statv.st_size;
/* show file size or major/minor no. */
ofs << ' ' << ctime (&statv.st_mtime);/* print last modification time */
ofs << ' ' << path_name << endl; /* show file name */ }
/* Main loop to display file attributes one file at a time */ int main (int argc, char* argv[])
{
if (argc==1)
cerr << "usage: " << argv[0] << " <file path name> ...\n"; else while (--argc >= 1) long_list( cout, *++argv);
FILE AND RECORD LOCKING
UNIX systems allow multiple processes toread and write the same file concurrently.
It is a means of data sharing among
processes.
Why the need to lock files?
It is needed in some applications like
database access where no other process can write or read a file while a process is accessing a file-locking mechanism.
File locking is applicable only to regular
Shared and exclusive locks
A read lock is also called a shared lock and a
write lock is called an exclusive lock. These locks can be imposed on the whole file or a portion of it.
A write lock prevents other processes from
setting any overlapping read or write locks on the locked regions of the file. The intention is to prevent other processes from both reading and writing the locked region while a process is modifying the region.
A read lock allows processes to set
overlapping read locks but not write locks.
FCNTL file locking
int fcntl (int fdesc, int cmd_flag, …);
Use
Sets a file lock. Do not block if this cannot succeed immediately.
Sets a file lock and blocks the calling process until the lock is acquired.
Queries as to which process locked a specified region of a file.
Cmd_flag
F_SETLK
F_SETLKW
For file locking the third argument is struct flock-typed variable.
struct flock
{
short l_type;
short l_whence;
off_t l_start;
l_type and l_whence fields of flock
l_type value Use
F_RDLCK Sets as a read (shared) lock on a specified region
F_WRLCK Sets a write (exclusive) lock on a specified region
F_UNLCK Unlocks a specified region
l_whence value Use
SEEK_CUR The l_start value is added to the current file pointer address
SEEK_SET The l_start value is added to byte 0 of file
The l_len specifies the size of a locked
region beginning from the start address defined by l_whence and l_start.
If l_len is 0 then the length of the locked is
imposed on the maximum size and also as it extends. It cannot have a –ve value.
When fcntl is called, the variable contains
#include <iostream.h> #include <stdio.h>
#include <sys/types.h> #include <fcntl.h>
#include <unistd.h>
int main (int argc, char* argv[]) {
fvar.l_type = F_WRLCK;
fvar.l_whence = SEEK_SET; fvar.l_start = 0;
fvar.l_len = 0;
/* Attempt to set an exclusive (write) lock on the entire file */
while (fcntl(fdesc, F_SETLK,&fvar)==-1) {
/* Set lock fails, find out who has locked the file */ while (fcntl(fdesc,F_GETLK,&fvar)!=-1 &&
fvar.l_type!=F_UNLCK) {
cout << *argv << " locked by " << fvar.l_pid<< " from " << fvar.l_start << " for "<< fvar.l_len << " byte for " << (fvar.l_type==F_WRLCK ? 'w' : 'r') << endl;
fvar.l_start += fvar.l_len; fvar.l_len = 0;
} /* while there are locks set by other processes */ } /* while set lock un-successful */
// Lock the file OK. Now process data in the file /* Now unlock the entire file */
fvar.l_type = F_UNLCK;
fvar.l_whence = SEEK_SET; fvar.l_start = 0;
fvar.l_len = 0;
if (fcntl(fdesc, F_SETLKW,&fvar)==-1) perror("fcntl");
}
Directory File APIs
Why do need directory files? Uses?
To aid users in organizing their files into some
structure based on the specific use of files
They are also used by the operating system to
convert file path names to their inode numbers
To create
int mkdir (const char* path_name , mode_t mode);
The mode argument specifies the access
A newly created directory has its user ID
set to the effective user ID of the process that creates it.
Directory group ID will be set to either the
effective group ID of the calling process
FUNCTIONS
Opendir:
DIR*opendir (const char* path_name);
This opens the file for read-only
Readdir:
Dirent* readdir(DIR* dir_fdesc);
Closedir :
int closedir (DIR* dir_fdesc);
It terminates the connection between the dir_fdesc handler and a directory file.
Rewinddir :
void rewinddir (DIR* dir_fdesc);
Rmdir API:
int rmdir (const char* path_name);
Used to remove the directory files. Users may also use the unlink API to remove
directories provided they have superuser privileges.
