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NAME | DESCRIPTION | STANDARDS | NOTES | SEE ALSO |
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ioctl_iflags(2) System Calls 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.
Linux.
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.
The type of the argument given to the FS_IOC_GETFLAGS and
FS_IOC_SETFLAGS operations is int *, notwithstanding the
implication in the kernel source file include/uapi/linux/fs.h
that the argument is long *.
chattr(1), lsattr(1), mount(2), btrfs(5), ext4(5), xfs(5),
xattr(7), mount(8)
Linux man-pages (unreleased) (date) ioctl_iflags(2)
Pages that refer to this page: access(2), chmod(2), chown(2), ioctl(2), ioctl_xfs_fsgetxattr(2), link(2), mount(2), setxattr(2), unlink(2), capabilities(7), xattr(7)
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HTML rendering created 2023-12-22 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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