Linux 使用chattr设置文件属性

文件的普通属性可以通过ls -l来查看，但还有一些“高级”的文件属性，可以通过chattr来设置、lsattr来查看。这些属性包括 文件是否被自动压缩、文件是否允许修改、删除等。简单的语法如下：

NAME       chattr - change file attributes on a Linux file systemSYNOPSIS       chattr [ -RVf ] [ -v version ] [ mode ] files...DESCRIPTION       chattr changes the file attributes on a Linux file system.       The format of a symbolic mode is +-=[acdeijstuACDST].ATTRIBUTES       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 for       laptop systems.       A file with the `a' attribute set can only be open in append mode for  writing.   Only  the  superuser  or  a  process  possessing  the       CAP_LINUX_IMMUTABLE capability can set or clear this attribute.       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.  Note: please make sure to read the bugs  and  limitations       section at the end of this document.       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.       A file with the `d' attribute set is not candidate for backup when the dump(8) program is run.       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.  Only the superuser or a process possessing the CAP_LINUX_IMMUTABLE capability can set or clear this attribute.       When a file with the `u' attribute set is deleted, its contents are saved.  This allows the user to  ask  for  its  undeletion.   Note:       please make sure to read the bugs and limitations section at the end of this document.

示例1：设置文件只能被追加内容，多用于日志
qingsong@db2a:/tmp$ touch log1
qingsong@db2a:/tmp$ sudo chattr +a log1
qingsong@db2a:/tmp$ echo "line1" >> log1
qingsong@db2a:/tmp$ echo "line2" > log1
-bash: log1: Operation not permitted

示例2：设置文件不能被修改，包括不能被删除、重命名、复制、建立链接文件、修改内容，即使超级用户或者root也没法修改文件
qingsong@db2a:/tmp$ touch log2
qingsong@db2a:/tmp$ sudo chattr +i log2
qingsong@db2a:/tmp$ echo "line1" >> log2
-bash: log2: Permission denied <--无法被修改
qingsong@db2a:/tmp$ sudo echo "line1" >> log2
-bash: log2: Permission denied <--超级用户也无法修改
qingsong@db2a:/tmp$ sudo echo "line1" > log2
-bash: log2: Permission denied
qingsong@db2a:/tmp$ rm log2
rm: remove write-protected regular empty file 'log2'? y
rm: cannot remove 'log2': Operation not permitted <--无法删除
qingsong@db2a:/tmp$ sudo rm log2
rm: cannot remove 'log2': Operation not permitted <--超级用户也无法删除

切换到root之后，也无法删除、重命名、建立硬链接，不过，符号链接还是可以建立的：
qingsong@db2a:/tmp$ sudo su root
root@db2a:/tmp# rm log2
rm: cannot remove log2 Operation not permitted
root@db2a:/tmp# mv log2 log2.bak
mv: cannot move log2 to log2.bak Operation not permitted
root@db2a:/tmp# cp -l log2 log2.bak
cp: cannot create hard link log2.bak to log2 Operation not permitted
root@db2a:/tmp# cp -s log2 log2.bak
root@db2a:/tmp# ls -l log2*
-rw-rw-r-- 1 qingsong qingsong 0 Aug 20 19:57 log2
lrwxrwxrwx 1 root root 4 Aug 20 20:01 log2.bak -> log2

查看特殊属性，由于这些属性都是隐藏的，ls看不出来，需要使用lsattr来查看：
root@db2a:/tmp# lsattr log*
-----a-------e-- log1
----i--------e-- log2
lsattr: Operation not supported While reading flags on log2.bak

所以，有时候明明看起来有权限，却操作不了，不妨看一下隐藏属性。