Difference between Access Modify Change ?

hq4ever · 06-04-2005, 09:01 AM

What is the meaning of these three ?
Please note that Modify & Change are exactly the same.
I just don't get the idea here, what information each of the A, M, C gives me about the file ?

Code:

stat access_log
  File: `access_log'
  Size: 1176201         Blocks: 2306       IO Block: 131072 regular file
Device: 303h/771d       Inode: 868798      Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2005-05-13 21:50:51.000000000 +0300
Modify: 2005-06-04 16:29:55.000000000 +0300
Change: 2005-06-04 16:29:55.000000000 +0300

Thank you.

btmiller · 06-04-2005, 12:11 PM

Pretty easy (and available from the ls or stat man pages) -- access is the last time the file was accessed (unless the partition was mounted with the noatime option, in which case it's meaningless), modify is the time the file was last modified, and change time is the last time file status change (i.e. inode number etc.).

hq4ever · 06-04-2005, 08:29 PM

Either I got something wrong here or I got something wrong here

(will provide examples when I return to the machine).

In the mean time, could you please tell me if a "read" from a file cosidered "access" ?
As well as "modify", is it a "write" to file ?
What about "change", will writing data to file automaticly updates the files change time, or maybe only a change in permissions (i.e. meta data) will cause the files (or to be more correctly - the inodes) change field to be set ?

b.t.w : I looked at the stat man page, haven't found it there, the ls page I didn't checked.

Thank you,
Maxim.

EnoksrD · 07-10-2005, 08:16 PM

Quote:

Pretty easy (and available from the ls or stat man pages)

Quote:

b.t.w : I looked at the stat man page, haven't found it there, the ls page I didn't checked.

Had the same confusion my self. I couldn't find any sort of explanation (just said change was for status change, but not what a status change was) in the stat or ls man pages in the user commands section of the manual (mine are from coreutils 5.2.1 and 4 respectively).

However, if you look in the system call manual page for stat you'll find the info you are looking for (look at the descriptions of the st_atime, st_mtime, and st_ctime fields). To do that type

Code:

man -s 2 stat

to specify you want the stat manual from section 2 (System Calls).

If you want to know which sections of the manual a particular command appears in you can type

Code:

whatis <command>

e.g.

Code:

whatis ls

to see that there is no ls system call.

Hope that helps.

7655cjc · 08-26-2008, 10:47 AM

What is the difference between UNIX Access, Modify, and Change Times?

This is a silly little thing that I consistently forget … or at least forget some of the subtle differences between these three measures.

Here are the definitions of the different UNIX time information on a file with how they are typically referred to in man pages and the option to list the particular time with the ls command.

Access Time | atime | -ul
This is the time that the file was last accessed, read or written to.

Modify Time | mtime | -l
This is the time that the inode information (permissions, name, etc., the metadata, as it were) was last modified.

Change Time | ctime | -cl
This is the last time the actual contents of the file were last modified.

mohammednv · 01-17-2010, 02:42 AM

You got it wrong 7655cjc.

You interchanged mtime and ctime :-)