[转] stat命令输出结果中, Access，Modify，Change的含义

先建立一个空白文件a.txt

1	[emduser@emd tmp]$ touch a.txt

2

3	[emduser@emd tmp]$ ls -al a.txt

4

5	-rw-rw-r-- 1 emduser emd 0 Dec 14 16:44 a.txt

利用stat命令查看文件a.txt的各种属性

01	[emduser@emd tmp]$ stat a.txt

02

03	File: `a.txt'

04

05	Size: 0               Blocks: 0          IO Block: 4096   regular empty file

06

07	Device: fd00h/64768d    Inode: 654176      Links: 1

08

09	Access: (0664/-rw-rw-r--)  Uid: (  501/ emduser)   Gid: (  506/     emd)

10

11	Access: 2011-12-14 16:44:23.000000000 +0800

12

13	Modify: 2011-12-14 16:44:23.000000000 +0800

14

15	Change: 2011-12-14 16:44:23.000000000 +0800

上述最后三行的含义如下：

Access : 文件最近一次被访问的时间

Modify:  文件内容最近一次被修改的时间

Change: 文件属性最近一次被改变的时间

• 假如用cat命令将文件a.txt的内容输出到终端（ 执行 cat a.txt）, 那么只有a.txt的Access就被刷新了
• 假如我们把当前的时间追加到a.txt(执行 date >> a.txt) ， 那么a.txt的Modify和Change都被刷新
• 假如我们把a.txt的权限改为777(执行 chmod 777 a.txt) , 那么只有a.txt的Change被刷新
• 假如我们用vi命令把文件a.txt打开, 然后保存退出，那么a.txt的Access，Modify和Change都被刷新

PS:  我们可以使用命令touch更新a.txt的Access和Modify时间，比如：

touch -d 1999-01-01 a.txt // 将a.txt的Access和Modify时间改为1999-01-01

touch -a a.txt  // 只将a.txt的Access时间改为当前系统时间

touch -m a.txt // 只将a.txt的Modify时间改为当前系统时间

当我们用ls -l a.txt看到的时间是Modify时间

 

PS: http://unix.stackexchange.com/questions/2464/timestamp-modification-time-and-created-time-of-a-file

There are 3 kind of "timestamps":

• Access - the last time the file was read
• Modify - the last time the file was modified (content has been modified)
• Change - the last time meta data of the file was changed (e.g. permissions)

To display this information, you can use stat which is part of the coreutils.

stat will show you also some more information like the device, inodes, links, etc.

Remember that this sort of information depends highly on the filesystem and mount options. For example if you mount a partition with the noatime option, no access information will be written.

A utility to change the timestamps would be touch. There are some arguments to decide which timestamp to change (e.g. -a for access time, -m for modification time, etc.) and to influence the parsing of a new given timestamp. See man touch for more details.

touch can become handy in combination with cp -u ("copy only when the SOURCE file is newer than the destination file or when the destination file is missing") or for the creation of empty marker files.

The  field  st_atime  is  changed  by  file  accesses,  for example, by execve(2), mknod(2), pipe(2),
utime(2) and read(2) (of more than zero bytes).  Other routines, like mmap(2), may or may not  update
st_atime.

The  field st_mtime is changed by file modifications, for example, by mknod(2), truncate(2), utime(2)
and write(2) (of more than zero bytes).  Moreover, st_mtime of a directory is changed by the creation
or  deletion  of  files  in  that directory.  The st_mtime field is not changed for changes in owner,
group, hard link count, or mode.

The field st_ctime is changed by writing or by setting inode information (i.e.,  owner,  group,  link
count, mode, etc.).