mirror of https://github.com/vitalif/e2fsprogs
213 lines
7.5 KiB
Groff
213 lines
7.5 KiB
Groff
.\" -*- nroff -*-
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.TH CHATTR 1 "@E2FSPROGS_MONTH@ @E2FSPROGS_YEAR@" "E2fsprogs version @E2FSPROGS_VERSION@"
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.SH NAME
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chattr \- change file attributes on a Linux file system
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.SH SYNOPSIS
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.B chattr
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[
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.B \-RVf
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]
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[
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.B \-v
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.I version
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]
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[
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.I mode
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]
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.I files...
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.SH DESCRIPTION
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.B chattr
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changes the file attributes on a Linux file system.
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.PP
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The format of a symbolic mode is +-=[aAcCdDeijsStTu].
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.PP
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The operator '+' causes the selected attributes to be added to the
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existing attributes of the files; '-' causes them to be removed; and '='
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causes them to be the only attributes that the files have.
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.PP
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The letters 'aAcCdDeijsStTu' select the new attributes for the files:
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append only (a),
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no atime updates (A),
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compressed (c),
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no copy on write (C),
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no dump (d),
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synchronous directory updates (D),
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extent format (e),
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immutable (i),
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data journalling (j),
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secure deletion (s),
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synchronous updates (S),
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no tail-merging (t),
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top of directory hierarchy (T),
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and undeletable (u).
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.PP
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The following attributes are read-only, and may be listed by
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.BR lsattr (1)
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but not modified by chattr:
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compression error (E),
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huge file (h),
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indexed directory (I),
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inline data (N),
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compression raw access (X),
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and compressed dirty file (Z).
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.PP
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Not all flags are supported or utilized by all filesystems; refer to
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filesystem-specific man pages such as
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.BR btrfs (5),
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.BR ext4 (5),
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and
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.BR xfs (5)
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for more filesystem-specific details.
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.SH OPTIONS
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.TP
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.B \-R
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Recursively change attributes of directories and their contents.
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.TP
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.B \-V
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Be verbose with chattr's output and print the program version.
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.TP
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.B \-f
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Suppress most error messages.
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.TP
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.BI \-v " version"
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Set the file's version/generation number.
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.SH ATTRIBUTES
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A file with the 'a' attribute set can only be open in append mode for writing.
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Only the superuser or a process possessing the CAP_LINUX_IMMUTABLE
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capability can set or clear this attribute.
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.PP
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When a file with the 'A' attribute set is accessed, its atime record is
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not modified. This avoids a certain amount of disk I/O for laptop
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systems.
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.PP
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A file with the 'c' attribute set is automatically compressed on the disk
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by the kernel. A read from this file returns uncompressed data. A write to
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this file compresses data before storing them on the disk. Note: please
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make sure to read the bugs and limitations section at the end of this
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document.
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.PP
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A file with the 'C' attribute set will not be subject to copy-on-write
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updates. This flag is only supported on file systems which perform
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copy-on-write. (Note: For btrfs, the 'C' flag should be
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set on new or empty files. If it is set on a file which already has
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data blocks, it is undefined when the blocks assigned to the file will
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be fully stable. If the 'C' flag is set on a directory, it will have no
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effect on the directory, but new files created in that directory will
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the No_COW attribute.)
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.PP
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A file with the 'd' attribute set is not candidate for backup when the
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.BR dump (8)
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program is run.
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.PP
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When a directory with the 'D' attribute set is modified,
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the changes are written synchronously on the disk; this is equivalent to
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the 'dirsync' mount option applied to a subset of the files.
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.PP
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The 'e' attribute indicates that the file is using extents for mapping
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the blocks on disk. It may not be removed using
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.BR chattr (1).
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.PP
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The 'E' attribute is used by the experimental encryption patches to
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indicate that the file has been encrypted. It may not be
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set or reset using
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.BR chattr (1),
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although it can be displayed by
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.BR lsattr (1).
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.PP
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The 'h' attribute indicates the file is storing its blocks in units of the
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filesystem blocksize instead of in units of sectors, and means that the file
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is (or at one time was) larger than 2TB. It may not be set or reset using
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.BR chattr (1),
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although it can be displayed by
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.BR lsattr (1).
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.PP
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A file with the 'i' attribute cannot be modified: it cannot be deleted or
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renamed, no link can be created to this file and no data can be written
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to the file. Only the superuser or a process possessing the
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CAP_LINUX_IMMUTABLE capability can set or clear this attribute.
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.PP
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The 'I' attribute is used by the htree code to indicate that a directory
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is being indexed using hashed trees. It may not be set or reset using
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.BR chattr (1),
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although it can be displayed by
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.BR lsattr (1).
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.PP
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A file with the 'j' attribute has all of its data written to the ext3
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or ext4 journal before being written to the file itself, if the filesystem
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is mounted with the "data=ordered" or "data=writeback" options. When the
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filesystem is mounted with the "data=journal" option all file data
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is already journalled and this attribute has no effect. Only
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the superuser or a process possessing the CAP_SYS_RESOURCE
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capability can set or clear this attribute.
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.PP
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A file with the 'N' attribute set indicates that the file has data
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stored inline, within the inode itself. It may not be set or reset using
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.BR chattr (1),
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although it can be displayed by
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.BR lsattr (1).
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.PP
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When a file with the 's' attribute set is deleted, its blocks are zeroed
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and written back to the disk. Note: please make sure to read the bugs
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and limitations section at the end of this document.
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.PP
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When a file with the 'S' attribute set is modified,
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the changes are written synchronously on the disk; this is equivalent to
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the 'sync' mount option applied to a subset of the files.
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.PP
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A file with the 't' attribute will not have a partial block fragment at
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the end of the file merged with other files (for those filesystems which
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support tail-merging). This is necessary for applications such as LILO
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which read the filesystem directly, and which don't understand tail-merged
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files. Note: As of this writing, the ext2 or ext3 filesystems do not
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(yet, except in very experimental patches) support tail-merging.
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.PP
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A directory with the 'T' attribute will be deemed to be the top of
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directory hierarchies for the purposes of the Orlov block allocator.
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This is a hint to the block allocator used by ext3 and ext4 that the
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subdirectories under this directory are not related, and thus should be
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spread apart for allocation purposes. For example it is a very good
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idea to set the 'T' attribute on the /home directory, so that /home/john
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and /home/mary are placed into separate block groups. For directories
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where this attribute is not set, the Orlov block allocator will try to
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group subdirectories closer together where possible.
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.PP
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When a file with the 'u' attribute set is deleted, its contents are
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saved. This allows the user to ask for its undeletion. Note: please
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make sure to read the bugs and limitations section at the end of this
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document.
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.PP
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The 'X' attribute is used by the experimental compression patches to
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indicate that the raw contents of a compressed file can be accessed
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directly. It currently may not be set or reset using
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.BR chattr (1),
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although it can be displayed by
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.BR lsattr (1).
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.PP
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The 'Z' attribute is used by the experimental compression patches to
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indicate a compressed file is dirty. It may not be set or reset using
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.BR chattr (1),
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although it can be displayed by
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.BR lsattr (1).
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.PP
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.SH AUTHOR
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.B chattr
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was written by Remy Card <Remy.Card@linux.org>. It is currently being
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maintained by Theodore Ts'o <tytso@alum.mit.edu>.
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.SH BUGS AND LIMITATIONS
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The 'c', 's', and 'u' attributes are not honored
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by the ext2, ext3, and ext4 filesystems as implemented in the current
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mainline Linux kernels.
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.PP
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The 'j' option is only useful if the filesystem is mounted as ext3 or ext4.
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.PP
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The 'D' option is only useful on Linux kernel 2.5.19 and later.
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.SH AVAILABILITY
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.B chattr
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is part of the e2fsprogs package and is available from
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http://e2fsprogs.sourceforge.net.
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.SH SEE ALSO
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.BR lsattr (1),
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.BR btrfs (5),
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.BR ext4 (5),
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.BR xfs (5).
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