NAME(名稱)

chattr - 修改文件在Linux第二擴展文件系統(tǒng)(E2fs)上的特有屬性  

SYNOPSIS(總覽)

chattr [ -RV ] [ -v version ] [ mode ] files...  

DESCRIPTION(描述)

chattr 修改文件在Linux第二擴展文件系統(tǒng)(E2fs)上的特有屬性

符號模式有+-=[ASacdisu]幾種格式.

操作符`+'用來在文件已有屬性的基礎(chǔ)上增加選定的屬性; `-'用來去掉文件上的選定的屬性;而`='用來指定該文件的唯一屬性.

字符`ASacdisu'用作文件新屬性的選項: 不更新atime(A),同步更新(S),只能添加(a), 壓縮(c),不可變(i),不可轉(zhuǎn)移(d),刪除保護(s)以及不可刪除(u).  

OPTIONS(選項)

-R

遞歸地修改目錄以及其下內(nèi)容的屬性. 如果在遞歸目錄時遇到了符號鏈接,遍歷將跳過.

-V

詳盡地給出chattr的輸出信息并打印出程序的版本.

-v version

設(shè)置文件系統(tǒng)的版本.

ATTRIBUTES(屬性)

當(dāng)修改設(shè)置了'A'屬性的文件時,它的atime記錄不會改變. 這可以在筆記本電腦系統(tǒng)中避免某些磁盤I/O處理.

設(shè)置了`a'屬性的文件只能在添加模式下打開用于寫入. 只有超級用戶可以設(shè)置或清除該屬性.

設(shè)置了`c'屬性的文件在磁盤上由內(nèi)核自動進行壓縮處理. 從該文件讀取時返回的是未壓縮的數(shù)據(jù). 對該文件的一次寫入會在保存它們到磁盤之前進行數(shù)據(jù)壓縮.

設(shè)置了`d'屬性的文件不能對其運行 dump(8) 程序進行備份.

設(shè)置了`i'屬性的文件不能進行修改:你既不能刪除它, 也不能給它重新命名,你不能對該文件創(chuàng)建鏈接, 而且也不能對該文件寫入任何數(shù)據(jù). 只有超級用戶可以設(shè)置或清除該屬性.

當(dāng)刪除設(shè)置了`s'屬性的文件時,將對其數(shù)據(jù)塊清零并寫回到磁盤上.

當(dāng)修改設(shè)置了`S'屬性的文件時, 修改會同步寫入到磁盤上;這與應(yīng)用到文件子系統(tǒng)上的`sync'掛載選項有相同的效果.

當(dāng)刪除設(shè)置了`u'屬性的文件時, 將會保存其內(nèi)容. 這使得用戶可以請求恢復(fù)被刪除的文件.

AUTHOR(作者)

chattr 的作者為Remy Card <card@masi.ibp.fr>, 他是ext2 fs的開發(fā)和維護者.  

BUGS AND LIMITATIONS(BUGS和局限性)

對于ext2 fs 0.5a來說,`c'和`u'屬性是不被內(nèi)核代碼所承認的. 對于Linux 2.0內(nèi)核而言,'A'屬性也是不被內(nèi)核代碼所支持的. (noatime代碼仍在測試中.)

這些屬性將在未來的ext2 fs版本中實現(xiàn).  

AVAILABILITY(怎樣獲取)

chattr 是e2fsprogs包的一部分, 你可以通過對tsx-11.mit.edu的匿名ftp訪問在 /pub/linux/packages/ext2fs下找到它.  

SEE ALSO(另見)

lsattr(1)  

#p#

NAME

chattr - change file attributes on a Linux second extended file system  

SYNOPSIS

chattr [ -RV ] [ -v version ] [ mode ] files...  

DESCRIPTION

chattr changes the file attributes on a Linux second extended file system.

The format of a symbolic mode is +-=[ASacDdIijsTtu].

The operator `+' causes the selected attributes to be added to the existing 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).  

OPTIONS

-R

Recursively change attributes of directories and their contents. Symbolic links encountered during recursive directory traversals are ignored.

-V

Be verbose with chattr's output and print the program version.

-v version

Set the file's version/generation number.

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.

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.

The 'E' attribute is used by the experimental compression patches to indicate that a compressed file has a compression error. It may not be set or reset using chattr(1), although it can be displayed by lsattr(1).

The 'I' attribute is used by the htree code to indicate that a directory is behind indexed using hashed trees. It may not be set or reset using chattr(1), although it can be displayed by lsattr(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. Only the superuser or a process possessing the CAP_LINUX_IMMUTABLE capability can set or clear this attribute.

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 journalled and this attribute has no effect. Only the superuser or a process possessing the CAP_SYS_RESOURCE capability can set or clear this attribute.

When a file with the `s' attribute set is deleted, its blocks are zeroed and written back to the disk.

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.

A directory with the 'T' attribute will be deemed to be the top of directory 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 at the end of the file merged with other files (for those filesystems which support tail-merging). This is necessary for applications such as LILO which read the filesystem directly, and which don't understand tail-merged files. 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 to indicate that a raw contents of a compressed file can be accessed directly. It currently may not be set or reset using chattr(1), although it can be displayed by lsattr(1).

The 'Z' attribute is used by the experimental compression patches to indicate a compressed file is dirty. It may not be set or reset using chattr(1), although it can be displayed by lsattr(1).

AUTHOR

chattr was written by Remy Card <Remy.Card@linux.org>. It is currently being maintained by Theodore Ts'o <tytso@alum.mit.edu>.  

BUGS AND LIMITATIONS

The `c', 's', and `u' attributes are not honored by the ext2 and ext3 filesystems as implemented in the current mainline Linux kernels. These attributes may be implemented in future versions ext2 and ext3.

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.  

AVAILABILITY

chattr is part of the e2fsprogs package and is available from http://e2fsprogs.sourceforge.net.  

SEE ALSO

lsattr(1)