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 '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.

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.

       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)

Linux man-pages 6.7                                2023-10-31                                    ioctl_iflags(2)