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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 mod‐
       ified 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 re‐
              striction 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 directo‐
              ries, 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  directo‐
              ries 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 mech‐
              anisms 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.

       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  in‐
       clude/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                                                                          2019-11-19                                                                IOCTL_IFLAGS(2)