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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 modified using two ioctl(2) operations:

         int attr; fd = open("pathname", ...);

         ioctl(fd, FS_IOC_GETFLAGS, &attr);  /* Place current flags
                                                in 'attr' */ attr |= FS_NOA-
         TIME_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.

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.