IOCTL_IFLAGS(2) 					     Linux Programmer's Manual						   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 '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 imple-
	      ment 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.

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.

SEE ALSO

       chattr(1), lsattr(1), mount(2), btrfs(5), ext4(5), xfs(5), xattr(7), mount(8)

Linux								    2017-09-15							   IOCTL_IFLAGS(2)