chattr lsattr linux file system attributes - linux 文件系统文件属性

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）
Attribute	lsattr flag	chattr option	Semantics and rationale
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]}	When a file with the `s` attribute set is deleted, its blocks are zeroed and written back to the disk.
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.