cat后atime的问题

发现cat命令cat一个系统本来就有的文件，cat 后atime时间没有变。如果cat一个自己创建的文件，atime会改变。

如下：1.txt，使用cat查看后，atime改变；/etc/selinux/config文件使用cat命令后atime不变。纠结了！有知道是什么情况的朋友告诉我下，邮箱:[email protected]

 当前环境：

[root@backup ~]# cat /etc/redhat-release 
CentOS Linux release 7.6.1810 (Core) 
[root@backup ~]# uname -r
3.10.0-957.el7.x86_64

r[root@backup ~]# echo "hello" >1.txt
[root@backup ~]# ll
total 4
-rw-r--r-- 1 root root 6 Apr 13 20:35 1.txt
[root@backup ~]# stat 1.txt 
  File: ‘1.txt’
  Size: 6             Blocks: 8          IO Block: 4096   regular file
Device: 802h/2050d    Inode: 33559406    Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2020-04-13 20:35:35.469055828 +0800    #cat前
Modify: 2020-04-13 20:35:35.469055828 +0800
Change: 2020-04-13 20:35:35.469055828 +0800
 Birth: -
[root@backup ~]# cat 1.txt 
hello
[root@backup ~]# stat 1.txt 
  File: ‘1.txt’
  Size: 6             Blocks: 8          IO Block: 4096   regular file
Device: 802h/2050d    Inode: 33559406    Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2020-04-13 20:36:11.916457040 +0800    #atime改变
Modify: 2020-04-13 20:35:35.469055828 +0800
Change: 2020-04-13 20:35:35.469055828 +0800
 Birth: -
[root@backup ~]# stat /etc/selinux/config 
  File: ‘/etc/selinux/config’
  Size: 542           Blocks: 8          IO Block: 4096   regular file
Device: 802h/2050d    Inode: 101726835   Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2020-04-13 13:22:18.506554335 +0800  #cat前
Modify: 2019-04-19 12:35:11.658922642 +0800
Change: 2019-04-19 12:35:11.658922642 +0800
 Birth: -
[root@backup ~]# cat /etc/selinux/config

# This file controls the state of SELinux on the system.
# SELINUX= can take one of these three values:
#     enforcing - SELinux security policy is enforced.
#     permissive - SELinux prints warnings instead of enforcing.
#     disabled - No SELinux policy is loaded.
SELINUX=disabled
# SELINUXTYPE= can take one of three values:
#     targeted - Targeted processes are protected,
#     minimum - Modification of targeted policy. Only selected processes are protected. 
#     mls - Multi Level Security protection.
SELINUXTYPE=targeted 


[root@backup ~]# stat /etc/selinux/config 
  File: ‘/etc/selinux/config’
  Size: 542           Blocks: 8          IO Block: 4096   regular file
Device: 802h/2050d    Inode: 101726835   Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2020-04-13 13:22:18.506554335 +0800   #cat后
Modify: 2019-04-19 12:35:11.658922642 +0800
Change: 2019-04-19 12:35:11.658922642 +0800
 Birth: -