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  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 con-
	      tents 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.

       FS_JOURNAL_DATA_FL 'j'
	      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 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 appli-
	      cations that do not care about the accuracy of  this  timestamp.
	      This flag provides functionality similar to the mount(2) MS_NOA-
	      TIME 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	 Reis-
	      erfs  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 inheritable,
       and FS_DIRSYNC_FL, which is inherited only by subdirectories.

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.

CONFORMING TO
       Inode flags are a nonstandard Linux extension.

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 4.10 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/.



Linux				  2017-01-18		       IOCTL_IFLAGS(2)