ioctl_iflags

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  as-
       sociated 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  re-
              striction  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  ac-
              cessed.   This can provide I/O performance benefits for applica-
              tions 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 in-
              herit 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-al-
              location 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  di-
       rectory.   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_SET-
       FLAGS  operations is int *, notwithstanding the implication in the ker-
       nel 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)

COLOPHON
       This  page  is  part of release 5.05 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                             2019-11-19                   IOCTL_IFLAGS(2)