misc/chattr.1.in

   1 .\" -*- nroff -*-
   2 .TH CHATTR 1 "@E2FSPROGS_MONTH@ @E2FSPROGS_YEAR@" "E2fsprogs version @E2FSPROGS_VERSION@"
   3 .SH NAME
   4 chattr \- change file attributes on a Linux file system
   5 .SH SYNOPSIS
   6 .B chattr
   7 [
   8 .B \-RVf
   9 ]
  10 [
  11 .B \-v
  12 .I version
  13 ]
  14 [
  15 .I mode
  16 ]
  17 .I files...
  18 .SH DESCRIPTION
  19 .B chattr
  20 changes the file attributes on a Linux file system.
  21 .PP
  22 The format of a symbolic mode is +-=[acdeijstuADST].
  23 .PP
  24 The operator `+' causes the selected attributes to be added to the
  25 existing attributes of the files; `-' causes them to be removed; and
  26 `=' causes them to be the only attributes that the files have.
  27 .PP
  28 The letters `acdeijstuADST' select the new attributes for the files:
  29 append only (a), compressed (c), no dump (d), extent format (e), immutable (i),
  30 data journalling (j), secure deletion (s), no tail-merging (t),
  31 undeletable (u), no atime updates (A), synchronous directory updates (D),
  32 synchronous updates (S), and top of directory hierarchy (T).
  33 .PP
  34 The following attributes are read-only, and may be listed by
  35 .BR lsattr (1)
  36 but not modified by chattr: huge file (h), compression error (E),
  37 indexed directory (I), compression raw access (X), and compressed dirty
  38 file (Z).
  39 .SH OPTIONS
  40 .TP
  41 .B \-R
  42 Recursively change attributes of directories and their contents.
  43 .TP
  44 .B \-V
  45 Be verbose with chattr's output and print the program version.
  46 .TP
  47 .B \-f
  48 Suppress most error messages.
  49 .TP
  50 .BI \-v " version"
  51 Set the file's version/generation number.
  52 .SH ATTRIBUTES
  53 When a file with the 'A' attribute set is accessed, its atime record is
  54 not modified.  This avoids a certain amount of disk I/O for laptop
  55 systems.
  56 .PP
  57 A file with the `a' attribute set can only be open in append mode for writing.
  58 Only the superuser or a process possessing the CAP_LINUX_IMMUTABLE
  59 capability can set or clear this attribute.
  60 .PP
  61 A file with the `c' attribute set is automatically compressed on the disk
  62 by the kernel.  A read from this file returns uncompressed data.  A write to
  63 this file compresses data before storing them on the disk.  Note: please
  64 make sure to read the bugs and limitations section at the end of this
  65 document.
  66 .PP
  67 A file with the 'C' attribute set will not be subject to copy-on-write
  68 updates.  This flag is only supported on file systems which perform
  69 copy-on-write.  (Note: For btrfs, the 'C' flag should be
  70 set on new or empty files.  If it is set on a file which already has
  71 data blocks, it is undefined when the blocks assigned to the file will
  72 be fully stable.  If the 'C' flag is set on a directory, it will have no
  73 effect on the directory, but new files created in that directory will
  74 the No_COW attribute.)
  75 .PP
  76 When a directory with the `D' attribute set is modified,
  77 the changes are written synchronously on the disk; this is equivalent to
  78 the `dirsync' mount option applied to a subset of the files.
  79 .PP
  80 A file with the `d' attribute set is not candidate for backup when the
  81 .BR dump (8)
  82 program is run.
  83 .PP
  84 The 'E' attribute is used by the experimental compression patches to
  85 indicate that a compressed file has a compression error.  It may not be
  86 set or reset using
  87 .BR chattr (1),
  88 although it can be displayed by
  89 .BR lsattr (1).
  90 .PP
  91 The 'e' attribute indicates that the file is using extents for mapping
  92 the blocks on disk.  It may not be removed using
  93 .BR chattr (1).
  94 .PP
  95 The 'I' attribute is used by the htree code to indicate that a directory
  96 is being indexed using hashed trees.  It may not be set or reset using
  97 .BR chattr (1),
  98 although it can be displayed by
  99 .BR lsattr (1).
 100 .PP
 101 The 'h' attribute indicates the file is storing its blocks in units of the
 102 filesystem blocksize instead of in units of sectors, and means that the file
 103 is (or at one time was) larger than 2TB.  It may not be set or reset using
 104 .BR chattr (1),
 105 although it can be displayed by
 106 .BR lsattr (1).
 107 .PP
 108 A file with the `i' attribute cannot be modified: it cannot be deleted or
 109 renamed, no link can be created to this file and no data can be written
 110 to the file.  Only the superuser or a process possessing the
 111 CAP_LINUX_IMMUTABLE capability can set or clear this attribute.
 112 .PP
 113 A file with the `j' attribute has all of its data written to the ext3
 114 journal before being written to the file itself, if the filesystem is
 115 mounted with the "data=ordered" or "data=writeback" options.  When the
 116 filesystem is mounted with the "data=journal" option all file data
 117 is already journalled and this attribute has no effect.  Only
 118 the superuser or a process possessing the CAP_SYS_RESOURCE
 119 capability can set or clear this attribute.
 120 .PP
 121 When a file with the `s' attribute set is deleted, its blocks are zeroed
 122 and written back to the disk.  Note: please make sure to read the bugs
 123 and limitations section at the end of this document.
 124 .PP
 125 When a file with the `S' attribute set is modified,
 126 the changes are written synchronously on the disk; this is equivalent to
 127 the `sync' mount option applied to a subset of the files.
 128 .PP
 129 A directory with the 'T' attribute will be deemed to be the top of
 130 directory hierarchies for the purposes of the Orlov block allocator.
 131 This is a hint to the block allocator used by ext3 and ext4 that the
 132 subdirectories under this directory are not related, and thus should be
 133 spread apart for allocation purposes.   For example it is a very good
 134 idea to set the 'T' attribute on the /home directory, so that /home/john
 135 and /home/mary are placed into separate block groups.  For directories
 136 where this attribute is not set, the Orlov block allocator will try to
 137 group subdirectories closer together where possible.
 138 .PP
 139 A file with the 't' attribute will not have a partial block fragment at
 140 the end of the file merged with other files (for those filesystems which
 141 support tail-merging).  This is necessary for applications such as LILO
 142 which read the filesystem directly, and which don't understand tail-merged
 143 files.  Note: As of this writing, the ext2 or ext3 filesystems do not
 144 (yet, except in very experimental patches) support tail-merging.
 145 .PP
 146 When a file with the `u' attribute set is deleted, its contents are
 147 saved.  This allows the user to ask for its undeletion.  Note: please
 148 make sure to read the bugs and limitations section at the end of this
 149 document.
 150 .PP
 151 The 'X' attribute is used by the experimental compression patches to
 152 indicate that a raw contents of a compressed file can be accessed
 153 directly.  It currently may not be set or reset using
 154 .BR chattr (1),
 155 although it can be displayed by
 156 .BR lsattr (1).
 157 .PP
 158 The 'Z' attribute is used by the experimental compression patches to
 159 indicate a compressed file is dirty.  It may not be set or reset using
 160 .BR chattr (1),
 161 although it can be displayed by
 162 .BR lsattr (1).
 163 .PP
 164 .SH AUTHOR
 165 .B chattr
 166 was written by Remy Card <Remy.Card@linux.org>.  It is currently being
 167 maintained by Theodore Ts'o <tytso@alum.mit.edu>.
 168 .SH BUGS AND LIMITATIONS
 169 The `c', 's',  and `u' attributes are not honored
 170 by the ext2 and ext3 filesystems as implemented in the current mainline
 171 Linux kernels.
 172 .PP
 173 The `j' option is only useful if the filesystem is mounted as ext3.
 174 .PP
 175 The `D' option is only useful on Linux kernel 2.5.19 and later.
 176 .SH AVAILABILITY
 177 .B chattr
 178 is part of the e2fsprogs package and is available from
 179 http://e2fsprogs.sourceforge.net.
 180 .SH SEE ALSO
 181 .BR lsattr (1)