IOCTL_IFLAGS(2) (2019-11-19) IOCTL_IFLAGS(2)
NAME
ioctl_iflags - ioctl() operations for inode flags
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 aqattraq */
attr |= FS_NOATIME_FL; /* Tweak returned bit mask */
ioctl(fd, FS_IOC_SETFLAGS, &attr); /* Update flags for inode
referred to by aqfdaq */
The lsattr(1) and chattr(1) shell commands provide inter-
faces 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 cor-
responding letter used to indicate the flag by lsattr(1) and
chattr(1)):
FS_APPEND_FL aqaaq
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 aqcaq
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 aqDaq (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 aqiaq
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 pro-
cess (CAP_LINUX_IMMUTABLE) can set or clear this
attribute.
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IOCTL_IFLAGS(2) (2019-11-19) IOCTL_IFLAGS(2)
FS_JOURNAL_DATA_FL aqjaq
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 aqAaq
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 simi-
lar to the mount(2) MS_NOATIME flag, but on a per-file
basis.
FS_NOCOW_FL aqCaq (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 sup-
port copy-on-write semantics, such as Btrfs. See
chattr(1) and btrfs(5).
FS_NODUMP_FL aqdaq
Don't include this file in backups made using dump(8).
FS_NOTAIL_FL aqtaq
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 aqPaq (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 aqsaq
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 sur-
prisingly difficult.
FS_SYNC_FL aqSaq
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 aqTaq
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.
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FS_UNRM_FL aquaq
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 out-
side 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.
CONFORMING TO
Inode flags are a nonstandard Linux extension.
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.
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 *.
SEE ALSO
chattr(1), lsattr(1), mount(2), btrfs(5), ext4(5), xfs(5),
xattr(7), mount(8)
COLOPHON
This page is part of release 5.10 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/.
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