Histrionic Progenitor Isn't it obvious?

Access, Modify, and Change

What are Access, Modify, and Change as returned by the ’stat’ command?

What better way than to learn by example?  First, we start with no file:

rwill@rwill-laptop:~$ stat foo

stat: cannot stat `foo': No such file or directory

rwill@rwill-laptop:~$

Next we make our file:

rwill@rwill-laptop:~$ echo "Hello, World" > foo

rwill@rwill-laptop:~$ stat foo

 File: `foo'

 Size: 12            Blocks: 8          IO Block: 4096   regular file

Device: 802h/2050d    Inode: 246126      Links: 1

Access: (0644/-rw-r--r--)  Uid: ( 1000/   rwill)   Gid: ( 1000/   rwill)

Access: 2009-06-29 16:25:21.000000000 -0500

Modify: 2009-06-29 16:25:06.000000000 -0500

Change: 2009-06-29 16:25:06.000000000 -0500

rwill@rwill-laptop:~$

We can now see that our file exists and as expected, Access, Modify, and Change are all the same.  Now, lets read something from the file:

rwill@rwill-laptop:~$ stat foo

 File: `foo'

 Size: 12            Blocks: 8          IO Block: 4096   regular file

Device: 802h/2050d    Inode: 246126      Links: 1

Access: (0644/-rw-r--r--)  Uid: ( 1000/   rwill)   Gid: ( 1000/   rwill)

Access: 2009-06-29 16:25:21.000000000 -0500

Modify: 2009-06-29 16:25:06.000000000 -0500

Change: 2009-06-29 16:25:06.000000000 -0500

rwill@rwill-laptop:~$

We can now see that we Accessed the file (read from it) 15 seconds after it was created.  Now, let’s write to the file:

rwill@rwill-laptop:~$ echo "Hello Foo" >> foo

rwill@rwill-laptop:~$ stat foo

 File: `foo'

 Size: 22            Blocks: 8          IO Block: 4096   regular file

Device: 802h/2050d    Inode: 246126      Links: 1

Access: (0644/-rw-r--r--)  Uid: ( 1000/   rwill)   Gid: ( 1000/   rwill)

Access: 2009-06-29 16:27:05.000000000 -0500

Modify: 2009-06-29 16:27:05.000000000 -0500

Change: 2009-06-29 16:27:05.000000000 -0500

rwill@rwill-laptop:~$

Oh no! Everything changed.  Of course it did.  By writing to the file, it was Accessed, Modified, and Changed.  But don’t “Modify” and “Change” mean the same thing?  Not exactly.  A Modification is always a Change, but a Change is not necessarily a Modification.  Changes that are not Modifications include renaming, changing the permissions, etc:

rwill@rwill-laptop:~$ chmod 644 foo

rwill@rwill-laptop:~$ stat foo

 File: `foo'

 Size: 22            Blocks: 8          IO Block: 4096   regular file

Device: 802h/2050d    Inode: 246126      Links: 1

Access: (0644/-rw-r--r--)  Uid: ( 1000/   rwill)   Gid: ( 1000/   rwill)

Access: 2009-06-29 16:27:05.000000000 -0500

Modify: 2009-06-29 16:27:05.000000000 -0500

Change: 2009-06-29 16:28:26.000000000 -0500

rwill@rwill-laptop:~$ mv foo bar

rwill@rwill-laptop:~$ stat bar

 File: `bar'

 Size: 22            Blocks: 8          IO Block: 4096   regular file

Device: 802h/2050d    Inode: 246126      Links: 1

Access: (0644/-rw-r--r--)  Uid: ( 1000/   rwill)   Gid: ( 1000/   rwill)

Access: 2009-06-29 16:29:29.000000000 -0500

Modify: 2009-06-29 16:27:05.000000000 -0500

Change: 2009-06-29 16:29:28.000000000 -0500

rwill@rwill-laptop:~$

How about a homework assignment?  What happens when you move a file?

rwill@rwill-laptop:~$ mkdir baz

rwill@rwill-laptop:~$ mv bar baz

rwill@rwill-laptop:~$ stat baz/bar

 File: `baz/bar'

 Size: 22            Blocks: 8          IO Block: 4096   regular file

Device: 802h/2050d    Inode: 246126      Links: 1

Access: (0644/-rw-r--r--)  Uid: ( 1000/   rwill)   Gid: ( 1000/   rwill)

Access: 2009-06-29 16:29:29.000000000 -0500

Modify: 2009-06-29 16:27:05.000000000 -0500

Change: 2009-06-29 16:30:29.000000000 -0500

rwill@rwill-laptop:~$

That’s right.  A Change, but not a Modification.  It’s all so clear now, isn’t it?

Cheers –