NAME

       FS_IOC_GETFLAGS, FS_IOC_SETFLAGS - ioctl() operations for inode flags

SYNOPSIS

       #include <linux/fs.h>  /* Definition of FS_* constants */
       #include <sys/ioctl.h>

       int ioctl(int fd, FS_IOC_GETFLAGS, int *attr);
       int ioctl(int fd, FS_IOC_SETFLAGS, const int *attr);

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.  If applied to a directory,
              forbids removing files from the directory (via unlink(), rename(), and  the  like).
              (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.

SEE ALSO

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