我们使用 linux 文件系统定义的文件属性，能够对linux文件系统进行进一步保护；从而给文件 赋予一些额外的限制；在有些情况下，能够对我们的系统提供保护；
该命令特定用于 linux extended filesystem (ext2, ext3, ext4)，是e2fsprogs 工具的一部分；而e2fsprogs 工具包，包含了创建，检查和维护ext2/3/4-based 文件系统的工具。其也包含badblocks等用于检查文件系统坏块的工具。
chattr命令用来改变文件属性。这项指令可改变存放在ext2文件系统上的文件或目录属性，这些属性共有以下8种模式：详细作用，可以查看man手册；注意该属性不是linux文件系统扩展属性。
a：让文件或目录仅供附加用途；
b：不更新文件或目录的最后存取时间；
c：将文件或目录压缩后存放；
d：将文件或目录排除在倾倒操作之外；
i：不得任意更动文件或目录；
s：保密性删除文件或目录；
S：即时更新文件或目录；
u：预防意外删除。
lsattr - list file attributes on a Linux second extended file system
比如你可以给 /etc/passwd 文件进行修改，这样就是连root用户都不能更改它的代码；
File attributes on a Linux file system according to the chattr(1) Linux man page （该表格转载自维基百科）
|
| Compressed dirty file |
Z |
(unavailable) |
- The
Z attribute is used by the experimental compression patches to indicate a compressed file is "dirty".
|
|---|
| Compression raw access |
X |
(unavailable) |
- The
X attribute is used by the experimental compression patches to indicate that a raw contents of a compressed file can be accessed directly.
|
|---|
| Undeletable |
u |
+u to set
-u to clear[note 2] |
- When a file with the
u attribute set is deleted, its contents are saved.
- This allows the user to ask for its undeletion.
|
|---|
| Top of directory hierarchy |
T |
+T to set
-T to clear |
- A directory with the
T attribute will be deemed to be the top of directory hierarchies for the purposes of the Orlov block allocator.
- This is a hint to the block allocator used by ext3 and ext4 that the subdirectories under this directory are not related, and thus should be spread apart for allocation purposes.
- For example: it is a very good idea to set the
T attribute on the /home directory, so that /home/john and /home/mary are placed into separate block groups.
- For directories where this attribute is not set, the Orlov block allocator will try to group subdirectories closer together where possible.
|
|---|
| No tail-merging |
t |
+t to set
-t to clear |
- For those filesystems that support tail-merging, a file with the
t attribute will not have a partial block fragment at the end of the file merged with other files.
- This is necessary for applications such as LILO, which reads the filesystem directly and doesn't understand tail-merged files.
|
|---|
| Synchronous updates |
S |
+S to set
-S to clear |
- When a file with the
S attribute set is modified, the changes are written synchronously on the disk; this is equivalent to the 'sync' mount option applied to a subset of the files.
- This is equivalent to the
sync mount option, applied to a subset of the files.
|
|---|
| Secure deletion |
s |
+s to set
-s to clear[note 2][note 5] |
|
|---|
| Data journaling |
j |
+j to set
-j to clear[note 4] |
- A file with the
j attribute has all of its data written to the ext3 journal before being written to the file itself, if the filesystem is mounted with the "data=ordered" or "data=writeback" options.
- When the filesystem is mounted with the
"data=journal" option all file data is already journaled, so this attribute has no effect.
|
|---|
| Indexed directory |
I |
(unavailable) |
- The
I attribute is used by the htree program code to indicate that a directory is being indexed using hashed trees.
|
|---|
| Immutable |
i |
+i to set
-i to clear[note 1] |
- A file with the
i attribute cannot be modified.
- It cannot be deleted or renamed, no link can be created to this file and no data can be written to the file.
- When set, prevents, even the superuser, from erasing or changing the contents of the file.
|
|---|
| Huge file |
h |
(unavailable) |
- The
h attribute indicates the file is storing its blocks in units of the filesystem blocksize instead of in units of sectors.
- It means that the file is, or at one time was, larger than 2TB.
|
|---|
| Compression error |
E |
(unavailable) |
- The
E attribute is used by the experimental compression patches to indicate that a compressed file has a compression error.
|
|---|
| Extent format |
e |
(unavailable) |
- The
e attribute indicates that the file is using extents for mapping the blocks on disk.
|
|---|
| Synchronous directory updates |
D |
+D to set
-D to clear |
- When a directory with the
D attribute set is modified, the changes are written synchronously on the disk
- This is equivalent to the
dirsync mount option, applied to a subset of the files.
|
|---|
| No dump |
d |
+d to set
-d to clear |
- A file with the
d attribute set is not candidate for backup when the dump program is run.
|
|---|
| No Copy-on-Write (CoW) |
C |
+C to set
-C to clear[note 3] |
- A file with the
C attribute will not be subject to Copy-on-Write updates.
- Updates to these files may not be subject to atomic snapshots, and may lack some reliability information on some filesystems and kernels.
|
|---|
| Compressed |
c |
+c to set
-c to clear[note 2] |
- A file with the
c attribute set is automatically compressed on the disk by the kernel.
- A read from this file returns uncompressed data.
- A write to this file compresses data before storing them on the disk.
|
|---|
No atime updates |
A |
+A to set
-A to clear |
- When a file with the
A attribute set is accessed, its atime record is not modified.
- This avoids a certain amount of disk I/O operations.
|
|---|
| Append only |
a |
+a to set
-a to clear[note 1] |
- A file with the
a attribute set can only be open in append mode for writing.
|
|---|
| Version / generation number |
-v |
-v version |
- File's version/generation number.
|
|---|
参考链接：
https://en.wikipedia.org/wiki/Chattr （上述表格来自于此）
http://c.biancheng.net/view/874.html
https://www.runoob.com/linux/linux-comm-chattr.html
https://www.runoob.com/linux/linux-comm-lsattr.html
https://www.cnblogs.com/ftl1012/p/chattr.html
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关于文件系统扩展属性内容，请参考：Linux 文件系统扩展属性
