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Access time of a file

 
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# 1  
Old 09-04-2008
Access time of a file
I thought that access time of a file is time when the file was run last time (or I read somewhere that it's time when system lookup the file -> but I'm not sure when it really is)

How is it exactly?

Thank you for help!
# 2  
Old 09-04-2008
It's the time a process last accessed it to read/write contents.
# 3  
Old 09-04-2008
Quote:
Originally Posted by aluiken
It's the time a process last accessed it to read/write contents.
i read somewhere the documentation for the c function stat, and describe what type of access changed the mod time.
im sure that tail (awk, head, and surely more) dont change it
# 4  
Old 09-04-2008
2Broli: Well and what is the access time for then? I mean if behaviour of programs is different..
# 5  
Old 09-04-2008
From the POSIX standards:
Quote:
4.7 File Times Update
Each file has three distinct associated time values: st_atime, st_mtime, and st_ctime. The st_atime field is associated with the times that the file data is accessed; st_mtime is associated with the times that the file data is modified; and st_ctime is associated with the times that the file status is changed. These values are returned in the file characteristics structure, as described in <sys/stat.h>.
st_atime == atime
st_ctime == ctime
st_mtime == mtime

Plus if you search the forum for file time you will find a lot of good information.

Broli - the definitions of these have been fixed for years - different apps do not violate those definitions. Things that can change mtime are opening a file for write/append or a call to utime() (e.g., touch). chmod or chown changes ctime, and utime or opening a file for read changes the atime. These values are NOT part of the file, they are file metadata maintained by the filesystem, as accessed thru the kernel.
Last edited by jim mcnamara; 09-04-2008 at 11:08 AM..
# 6  
Old 09-04-2008
I made a simple script and copied the output:

Code:
file=example_1.sh;stat $file; cat $file >/dev/null; stat $file

Code:
  File: `example_1.sh'
  Size: 918             Blocks: 2          IO Block: 4096   regular file
Device: fh/15d  Inode: 2099578354  Links: 1
Access: (0744/-rwxr--r--)  Uid: (13654/vsetm7am)   Gid: (  200/ nofiles)
Access: 2008-09-02 21:47:11.000000000 +0200
Modify: 2008-09-02 21:47:11.000000000 +0200
Change: 2008-09-02 21:47:11.000000000 +0200
  File: `example_1.sh'
  Size: 918             Blocks: 2          IO Block: 4096   regular file
Device: fh/15d  Inode: 2099578354  Links: 1
Access: (0744/-rwxr--r--)  Uid: (13654/vsetm7am)   Gid: (  200/ nofiles)
Access: 2008-09-02 21:47:11.000000000 +0200
Modify: 2008-09-02 21:47:11.000000000 +0200
Change: 2008-09-02 21:47:11.000000000 +0200

How come that access time didn't change when data was accessed?
# 7  
Old 09-04-2008
Quote:
Originally Posted by MartyIX
How come that access time didn't change when data was accessed?

We would need to know the OS and how the file system was mounted. As one example: Sun's mount_ufs man page documents the noatime option:
Quote:
By default, the file system is mounted with normal access time (atime recording. If noatime is specified, the file system will ignore access time updates on files, except when they coincide with updates to the ctime or mtime. See stat(2). This option reduces disk activity on file systems where access times are unimportant (for example, a Usenet news spool). noatime turns off access time recording regardless of dfratime or nodfratime. The POSIX standard requires that access times be marked on files. -noatime ignores them unless the file is also modified.
Another example: the source files might be on cd-rom.
 
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