The format of a symbolic mode is +-=[ASacDdIijsTtu].
The operator `+' causes the selected attributes to be added to theexisting attributes of the files; `-' causes them to be removed; and`=' causes them to be the only attributes that the files have.
The letters `acdijsuADST' select the new attributes for the files:append only (a), compressed (c), no dump (d), immutable (i),data journalling (j), secure deletion (s), no tail-merging (t),undeletable (u), no atime updates (A), synchronous directory updates (D),synchronous updates (S), and top of directory hierarchy (T).
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_IMMUTABLEcapability can set or clear this attribute. ///設置之后只能追加數據而不能刪除
A file with the `c' attribute set is automatically compressed on the diskby the kernel. A read from this file returns uncompressed data. A write tothis file compresses data before storing them on the disk.
When a directory with the `D' attribute set is modified,the changes are written synchronously on the disk; this is equivalent tothe `dirsync' mount option applied to a subset of the files.
A file with the `d' attribute set is not candidate for backup when thedump(8)program is run. 不懂
The 'E' attribute is used by the experimental compression patches toindicate that a compressed file has a compression error. It may not beset or reset usingchattr(1),although it can be displayed bychattr(1),although it can be displayed bylsattr(1).
A file with the `i' attribute cannot be modified: it cannot be deleted orrenamed, no link can be created to this file and no data can be writtento the file. Only the superuser or a process possessing theCAP_LINUX_IMMUTABLE capability can set or clear this attribute.
A file with the `j' attribute has all of its data written to the ext3journal before being written to the file itself, if the filesystem ismounted with the "data=ordered" or "data=writeback" options. When thefilesystem is mounted with the "data=journal" option all file datais already journalled and this attribute has no effect.Only the superuser or a process possessing the CAP_SYS_RESOURCEcapability can set or clear this attribute.
When a file with the `s' attribute set is deleted, its blocks are zeroed andwritten back to the disk.
/////s ：當檔案設定了 s 屬性時(shí)，如果這個(gè)檔案被刪除，他將會(huì )被完全的移除出這個(gè)硬碟
空間，所以如果誤刪了，完全無(wú)法救回來(lái)了喔！
When a file with the `S' attribute set is modified,the changes are written synchronously on the disk; this is equivalent tothe `sync' mount option applied to a subset of the files.
A directory with the 'T' attribute will be deemed to be the top ofdirectory hierarchies for the purposes of the Orlov block allocator(which is used in on systems with Linux 2.5.46 or later).
A file with the 't' attribute will not have a partial block fragment atthe end of the file merged with other files (for those filesystems whichsupport tail-merging). This is necessary for applications such as LILOwhich read the filesystem directly, and which don't understand tail-mergedfiles. Note: As of this writing, the ext2 or ext3 filesystems do not(yet, except in very experimental patches) support tail-merging.
When a file with the `u' attribute set is deleted, its contents are saved.This allows the user to ask for its undeletion.
The 'X' attribute is used by the experimental compression patches toindicate that a raw contents of a compressed file can be accesseddirectly. It currently may not be set or reset usingchattr(1),although it can be displayed bychattr(1),although it can be displayed bylsattr(1).
The `j' option is only useful if the filesystem is mounted as ext3.
The `D' option is only useful on Linux kernel 2.5.19 and later.
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