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NAMEioctl_iflags - ioctl() operations for inode flags
DESCRIPTIONVarious 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:
fd = open("pathname", ...);
ioctl(fd, FS_IOC_GETFLAGS, &attr); /* Place current flags
in aqattraq */ attr |= FS_NOATIME_FL; /* Tweak returned bit mask */ ioctl(fd, FS_IOC_SETFLAGS, &attr); /* Update flags for inode
referred to by aqfdaq */
- FS_APPEND_FL aqaaq
- 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 aqcaq
- 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 aqDaq (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 aqiaq
- 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 aqjaq
- 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 aqAaq
- 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 aqCaq (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 aqdaq
- Don't include this file in backups made using dump(8).
- FS_NOTAIL_FL aqtaq
- 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 aqPaq (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 aqsaq
- 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 aqSaq
- 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 aqTaq
- 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 aquaq
- 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.