Inode and Ist Structure:
Inode stands for index node. As soon as the file is created, the kernel allocates a unique inode number to that file. An inode number is a positive number whose maximum value depends on the total inode numbers of the file system. The total number of inode, a file system can have is decided by the person who create the file system. The inode for the file system are kept together in inode table or inode structure. An inode describes which blocks of data a file occupies as will as the access rights of the file, file modification times and type of the file. This is the file system, inode is the basic building block, every file and dilatory in the file system is described by one and only one inode. The inode structures are housed is a separate block called the inode block on secondary storage medium. Each inode has a nugget of secondary storage area associated with it which in 64 byte long. As soon as the inode is allocated to a file, the corresponding inode structure gets filled up with all relevant information such as file type, link information and many more. Thus, an inode number is nothing but a file descriptor. Neither the filename nor the inode number are stored in the inode structure, they are present in the corresponding directory file. These inode can also describe special device files. These are not real file but handle those programs that can be used to access devices. The inode structure is & known below:
Inode stands for index node. As soon as the file is created, the kernel allocates a unique inode number to that file. An inode number is a positive number whose maximum value depends on the total inode numbers of the file system. The total number of inode, a file system can have is decided by the person who create the file system. The inode for the file system are kept together in inode table or inode structure. An inode describes which blocks of data a file occupies as will as the access rights of the file, file modification times and type of the file. This is the file system, inode is the basic building block, every file and dilatory in the file system is described by one and only one inode. The inode structures are housed is a separate block called the inode block on secondary storage medium. Each inode has a nugget of secondary storage area associated with it which in 64 byte long. As soon as the inode is allocated to a file, the corresponding inode structure gets filled up with all relevant information such as file type, link information and many more. Thus, an inode number is nothing but a file descriptor. Neither the filename nor the inode number are stored in the inode structure, they are present in the corresponding directory file. These inode can also describe special device files. These are not real file but handle those programs that can be used to access devices. The inode structure is & known below:
1. File type: This field shows the type associated with each file. If this field contains a hyphen “-“ Here it is an ordinary file, if it contains a letter “d” here it is a directory file.
2. Link Information: This field shown the number of links associated with each file. This is actually the number of filenames maintained by the system of that file. It also contains information about whether the file contains hard links or soft links.
3. UID of the owner: This field displays the UID or user identification number of the owner of the file. This allows the file system to correctly allow the right sort of accesses.
4. GID of the owner: The owner of a file also belongs to some group. However the group does not have same permissions as that after owner who created the file. This field identifies the group of the owner of the file or directory.
5. Size in bytes: This field shown the size of the file in bytes that is the amount of data it contains. It is a measure of only the character space of the file and not a measure of disk space it occupies. Disk space is casually large than the file size because or disks, data is shored is blocks of 1024 bytes which means that of the size of a file is 200 bytes then or a disk it will occupy 1024 bytes.
6. Access time: This field shown the time when the file was last accessed for reading the contents. The contents are not modified in any way.
7. Modification time: This field contains the last modification time of the file. A file is said to be modified if its contents have changed in any way. If only the permissions or ownership of the file is changed then the modification time of the files remains unchanged.
8. Time the inode was last changed: This field contains the time when any of the fields on inode change such as access time, UID and many more.
9. Generation Number: This field contains the number which is generated when an inode is created. It is also incremented every time or existing inode reused.
10. Address of data blocks: This field contains the pointers to the blocks that contains the data the inode is describing. The first 12 are pointers to the physical blocks containing the data described by the inode and the last 3 pointers contain more and more levels of indirection. For example, the double indirect block pointer points at a block of pointers to data blocks. This means that files less than or equal to 12 data blocks is length are more easily accessed than larger files. Also, the inode value of a file can be known by using “ls” command with “-i” option as shown below:
$ ls –i ishan.txt
106 ishan.txt
$
2. Link Information: This field shown the number of links associated with each file. This is actually the number of filenames maintained by the system of that file. It also contains information about whether the file contains hard links or soft links.
3. UID of the owner: This field displays the UID or user identification number of the owner of the file. This allows the file system to correctly allow the right sort of accesses.
4. GID of the owner: The owner of a file also belongs to some group. However the group does not have same permissions as that after owner who created the file. This field identifies the group of the owner of the file or directory.
5. Size in bytes: This field shown the size of the file in bytes that is the amount of data it contains. It is a measure of only the character space of the file and not a measure of disk space it occupies. Disk space is casually large than the file size because or disks, data is shored is blocks of 1024 bytes which means that of the size of a file is 200 bytes then or a disk it will occupy 1024 bytes.
6. Access time: This field shown the time when the file was last accessed for reading the contents. The contents are not modified in any way.
7. Modification time: This field contains the last modification time of the file. A file is said to be modified if its contents have changed in any way. If only the permissions or ownership of the file is changed then the modification time of the files remains unchanged.
8. Time the inode was last changed: This field contains the time when any of the fields on inode change such as access time, UID and many more.
9. Generation Number: This field contains the number which is generated when an inode is created. It is also incremented every time or existing inode reused.
10. Address of data blocks: This field contains the pointers to the blocks that contains the data the inode is describing. The first 12 are pointers to the physical blocks containing the data described by the inode and the last 3 pointers contain more and more levels of indirection. For example, the double indirect block pointer points at a block of pointers to data blocks. This means that files less than or equal to 12 data blocks is length are more easily accessed than larger files. Also, the inode value of a file can be known by using “ls” command with “-i” option as shown below:
$ ls –i ishan.txt
106 ishan.txt
$
File type
|
Link information
|
UID of the owner
|
GID of the owner
|
Size in bytes
|
Access time
|
Modification time
|
Time the inode was last changed
|
Generation number
|
Address of first 10 blocks and than of 3 indirect blocks
|
Fig. : Inode Structure
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