ioctl_iflags(2) — Linux manual page


IOCTL_IFLAGS(2)           Linux Programmer's Manual          IOCTL_IFLAGS(2)

NAME         top

       ioctl_iflags - ioctl() operations for inode flags

DESCRIPTION         top

       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 implementa‐
              tions; one exception is btrfs(5).

       FS_DIRSYNC_FL 'D' (since Linux 2.6.0)
              Write directory changes synchronously to disk.  This flag pro‐
              vides 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 supe‐
              ruser.)  Only a privileged process (CAP_LINUX_IMMUTABLE) can
              set or clear this attribute.

              Enable journaling of file data on ext3(5) and ext4(5) filesys‐
              tems.  On a filesystem that is journaling in ordered or write‐
              back mode, a privileged (CAP_SYS_RESOURCE) process can set
              this flag to enable journaling of data updates on a per-file

       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 time‐
              stamp.  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 imple‐
              mented 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 inherita‐
       ble, and FS_DIRSYNC_FL, which is inherited only by subdirectories.

CONFORMING TO         top

       Inode flags are a nonstandard Linux extension.

NOTES         top

       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

       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         top

       chattr(1), lsattr(1), mount(2), btrfs(5), ext4(5), xfs(5), xattr(7),

COLOPHON         top

       This page is part of release 5.08 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

Linux                            2019-11-19                  IOCTL_IFLAGS(2)

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