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NAME | DESCRIPTION | NOTES | CONFORMING TO | SEE ALSO | COLOPHON |
IOCTL_IFLAGS(2) Linux Programmer's Manual IOCTL_IFLAGS(2)
ioctl_iflags - ioctl() operations for inode flags
Various Linux filesystems support the notion of inode flags—
attributes that modify the semantics of files and directories. These
flags can be retrieved and modified using two ioctl(2) operations:
int attr;
fd = open("pathname", ...);
ioctl(fd, FS_IOC_GETFLAGS, &attr); /* Place current flags
in 'attr' */
attr |= FS_NOATIME_FL; /* Tweak returned bit mask */
ioctl(fd, FS_IOC_SETFLAGS, &attr); /* Update flags for inode
referred to by 'fd' */
The lsattr(1) and chattr(1) shell commands provide interfaces to
these two operations, allowing a user to view and modify the inode
flags associated with a file.
The following flags are supported (shown along with the corresponding
letter used to indicate the flag by lsattr(1) and chattr(1)):
FS_APPEND_FL 'a'
The file can be opened only with the O_APPEND flag. (This
restriction applies even to the superuser.) Only a privileged
process (CAP_LINUX_IMMUTABLE) can set or clear this attribute.
FS_COMPR_FL 'c'
Store the file in a compressed format on disk. This flag is
not supported by most of the mainstream filesystem
implementations; one exception is btrfs(5).
FS_DIRSYNC_FL 'D' (since Linux 2.6.0)
Write directory changes synchronously to disk. This flag
provides semantics equivalent to the mount(2) MS_DIRSYNC
option, but on a per-directory basis. This flag can be
applied only to directories.
FS_IMMUTABLE_FL 'i'
The file is immutable: no changes are permitted to the file
contents or metadata (permissions, timestamps, ownership, link
count and so on). (This restriction applies even to the
superuser.) Only a privileged process (CAP_LINUX_IMMUTABLE)
can set or clear this attribute.
FS_JOURNAL_DATA_FL 'j'
Enable journaling of file data on ext3(5) and ext4(5)
filesystems. On a filesystem that is journaling in ordered or
writeback mode, a privileged (CAP_SYS_RESOURCE) process can
set this flag to enable journaling of data updates on a per-
file basis.
FS_NOATIME_FL 'A'
Don't update the file last access time when the file is
accessed. This can provide I/O performance benefits for
applications that do not care about the accuracy of this
timestamp. This flag provides functionality similar to the
mount(2) MS_NOATIME flag, but on a per-file basis.
FS_NOCOW_FL 'C' (since Linux 2.6.39)
The file will not be subject to copy-on-write updates. This
flag has an effect only on filesystems that support copy-on-
write semantics, such as Btrfs. See chattr(1) and btrfs(5).
FS_NODUMP_FL 'd'
Don't include this file in backups made using dump(8).
FS_NOTAIL_FL 't'
This flag is supported only on Reiserfs. It disables the
Reiserfs tail-packing feature, which tries to pack small files
(and the final fragment of larger files) into the same disk
block as the file metadata.
FS_PROJINHERIT_FL 'P' (since Linux 4.5)
Inherit the quota project ID. Files and subdirectories will
inherit the project ID of the directory. This flag can be
applied only to directories.
FS_SECRM_FL 's'
Mark the file for secure deletion. This feature is not
implemented by any filesystem, since the task of securely
erasing a file from a recording medium is surprisingly
difficult.
FS_SYNC_FL 'S'
Make file updates synchronous. For files, this makes all
writes synchronous (as though all opens of the file were with
the O_SYNC flag). For directories, this has the same effect
as the FS_DIRSYNC_FL flag.
FS_TOPDIR_FL 'T'
Mark a directory for special treatment under the Orlov block-
allocation strategy. See chattr(1) for details. This flag
can be applied only to directories and has an effect only for
ext2, ext3, and ext4.
FS_UNRM_FL 'u'
Allow the file to be undeleted if it is deleted. This feature
is not implemented by any filesystem, since it is possible to
implement file-recovery mechanisms outside the kernel.
In most cases, when any of the above flags is set on a directory, the
flag is inherited by files and subdirectories created inside that
directory. Exceptions include FS_TOPDIR_FL, which is not
inheritable, and FS_DIRSYNC_FL, which is inherited only by
subdirectories.
In order to change the inode flags of a file using the
FS_IOC_SETFLAGS operation, the effective user ID of the caller must
match the owner of the file, or the caller must have the CAP_FOWNER
capability.
Inode flags are a nonstandard Linux extension.
chattr(1), lsattr(1), mount(2), btrfs(5), ext4(5), xfs(5), xattr(7),
mount(8)
This page is part of release 4.12 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
Linux 2017-01-18 IOCTL_IFLAGS(2)
Pages that refer to this page: chmod(2), chown(2), ioctl(2), link(2), setxattr(2), unlink(2), capabilities(7), xattr(7)