Why does linux change the inode number after editing the file?
Hello, I am wondering why does linux change the inode number after editing the file? if I open a text/conf file in linux and edit it then I find that it has changed the inode number. It does affect my application but it has made me curious.
Please let me know if someone can answer this behavior. Thanks!
Please let me know if someone can answer this behavior. Thanks!
Papertrip
Because file size, physical location on disk, ctime/mtime/atime are all stored in the inode, amongst other things of course.
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I wanted to expand on the "other things" from my first answer. Check out the man page for the stat() function.
struct stat {
dev_t st_dev; /* ID of device containing file */
ino_t st_ino; /* inode number */
mode_t st_mode; /* protection */
nlink_t st_nlink; /* number of hard links */
uid_t st_uid; /* user ID of owner */
gid_t st_gid; /* group ID of owner */
dev_t st_rdev; /* device ID (if special file) */
off_t st_size; /* total size, in bytes */
blksize_t st_blksize; /* blocksize for filesystem I/O */
blkcnt_t st_blocks; /* number of blocks allocated */
time_t st_atime; /* time of last access */
time_t st_mtime; /* time of last modification */
time_t st_ctime; /* time of last status change */
};
struct stat {
dev_t st_dev; /* ID of device containing file */
ino_t st_ino; /* inode number */
mode_t st_mode; /* protection */
nlink_t st_nlink; /* number of hard links */
uid_t st_uid; /* user ID of owner */
gid_t st_gid; /* group ID of owner */
dev_t st_rdev; /* device ID (if special file) */
off_t st_size; /* total size, in bytes */
blksize_t st_blksize; /* blocksize for filesystem I/O */
blkcnt_t st_blocks; /* number of blocks allocated */
time_t st_atime; /* time of last access */
time_t st_mtime; /* time of last modification */
time_t st_ctime; /* time of last status change */
};
Found an explanation that is less technical. I've never seen it written out so nicely :)
The inode contains all the information necessary for a process to access the file, such as file ownership, access rights, file size, time of last access or modification, and the location of the file’s data on disk. Since a file’s data is spread across disk blocks, the inode contains a “table of contents” to help locate this data. Good analogy.
It is important to note the distinction between changing the contents of an inode and changing the contents of a file. The contents of a file only change on a write operation.
The contents of an inode change when
(1) the contents of the corresponding file change (because when you update the file contents, you change the time of last modification. This is what you can search for with the find command using the -mtime flag, but I digress), or
(2) when its owner (e.g. using chown), permissions (chmod or chgrp), or any of the other information that is maintained as part of the inode changes.
Thus, changing the contents of a file automatically implies a change to the inode, whereas a change to the inode does not imply that the contents of the file have changed.
The inode contains all the information necessary for a process to access the file, such as file ownership, access rights, file size, time of last access or modification, and the location of the file’s data on disk. Since a file’s data is spread across disk blocks, the inode contains a “table of contents” to help locate this data. Good analogy.
It is important to note the distinction between changing the contents of an inode and changing the contents of a file. The contents of a file only change on a write operation.
The contents of an inode change when
(1) the contents of the corresponding file change (because when you update the file contents, you change the time of last modification. This is what you can search for with the find command using the -mtime flag, but I digress), or
(2) when its owner (e.g. using chown), permissions (chmod or chgrp), or any of the other information that is maintained as part of the inode changes.
Thus, changing the contents of a file automatically implies a change to the inode, whereas a change to the inode does not imply that the contents of the file have changed.
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Apologies I misread your original question and got stuck on my lil tangent. At least you know all about inodes now though :p
arnold and hfraser are probably on the right track.
arnold and hfraser are probably on the right track.
I agree that it's likely the file is being copied. If you need further assistance, it would help to know which editor you are using.