FS_IOC_SETFLAGS(2const) — Linux manual page
FS_IOC_SETFLAGS(2const) FS_IOC_SETFLAGS(2const)
NAME
FS_IOC_GETFLAGS, FS_IOC_SETFLAGS - ioctl() operations for inode
flags
SYNOPSIS
#include <linux/fs.h> /* Definition of FS_* constants */
#include <sys/ioctl.h>
int ioctl(int fd, FS_IOC_GETFLAGS, int *attr);
int ioctl(int fd, FS_IOC_SETFLAGS, const int *attr);
DESCRIPTION
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. If
applied to a directory, forbids removing files from the
directory (via unlink(), rename(), and the like). (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.
STANDARDS
Linux.
NOTES
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.
SEE ALSO
ioctl(2), chattr(1), lsattr(1), mount(2), btrfs(5), ext4(5),
xfs(5), xattr(7), mount(8)
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Linux man-pages 6.9.1 2024-06-13 FS_IOC_SETFLAGS(2const)
Pages that refer to this page: access(2), chmod(2), chown(2), ioctl_fs(2), link(2), mount(2), setxattr(2), unlink(2), capabilities(7), xattr(7)