.\" Copyright (c) 2017 by Michael Kerrisk .\" .\" SPDX-License-Identifier: Linux-man-pages-copyleft .\" .\" .TH ioctl_iflags 2 2023-03-30 "Linux man-pages 6.04" .SH NAME ioctl_iflags \- ioctl() operations for inode flags .SH DESCRIPTION Various Linux filesystems support the notion of .IR "inode flags" \[em]attributes that modify the semantics of files and directories. These flags can be retrieved and modified using two .BR ioctl (2) operations: .PP .in +4n .EX int attr; fd = open("pathname", ...); ioctl(fd, FS_IOC_GETFLAGS, &attr); /* Place current flags in \[aq]attr\[aq] */ attr |= FS_NOATIME_FL; /* Tweak returned bit mask */ ioctl(fd, FS_IOC_SETFLAGS, &attr); /* Update flags for inode referred to by \[aq]fd\[aq] */ .EE .in .PP The .BR lsattr (1) and .BR chattr (1) shell commands provide interfaces to these two operations, allowing a user to view and modify the inode flags associated with a file. .PP The following flags are supported (shown along with the corresponding letter used to indicate the flag by .BR lsattr (1) and .BR chattr (1)): .TP .BR FS_APPEND_FL " \[aq]a\[aq]" The file can be opened only with the .B O_APPEND flag. (This restriction applies even to the superuser.) Only a privileged process .RB ( CAP_LINUX_IMMUTABLE ) can set or clear this attribute. .TP .BR FS_COMPR_FL " \[aq]c\[aq]" Store the file in a compressed format on disk. This flag is .I not supported by most of the mainstream filesystem implementations; one exception is .BR btrfs (5). .TP .BR FS_DIRSYNC_FL " \[aq]D\[aq] (since Linux 2.6.0)" Write directory changes synchronously to disk. This flag provides semantics equivalent to the .BR mount (2) .B MS_DIRSYNC option, but on a per-directory basis. This flag can be applied only to directories. .\" .TP .\" .BR FS_EXTENT_FL " \[aq]e\[aq]" .\" FIXME Some support on ext4? (EXT4_EXTENTS_FL) .TP .BR FS_IMMUTABLE_FL " \[aq]i\[aq]" 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 .RB ( CAP_LINUX_IMMUTABLE ) can set or clear this attribute. .TP .BR FS_JOURNAL_DATA_FL " \[aq]j\[aq]" Enable journaling of file data on .BR ext3 (5) and .BR ext4 (5) filesystems. On a filesystem that is journaling in .I ordered or .I writeback mode, a privileged .RB ( CAP_SYS_RESOURCE ) process can set this flag to enable journaling of data updates on a per-file basis. .TP .BR FS_NOATIME_FL " \[aq]A\[aq]" 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 .BR mount (2) .B MS_NOATIME flag, but on a per-file basis. .\" .TP .\" .BR FS_NOCOMP_FL " \[aq]\[aq]" .\" FIXME Support for FS_NOCOMP_FL on Btrfs? .TP .BR FS_NOCOW_FL " \[aq]C\[aq] (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 .BR chattr (1) and .BR btrfs (5). .TP .BR FS_NODUMP_FL " \[aq]d\[aq]" Don't include this file in backups made using .BR dump (8). .TP .BR FS_NOTAIL_FL " \[aq]t\[aq]" 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. .TP .BR FS_PROJINHERIT_FL " \[aq]P\[aq] (since Linux 4.5)" .\" commit 040cb3786d9b25293b8b0b05b90da0f871e1eb9b .\" Flag name was added in Linux 4.4 .\" FIXME Not currently supported because not in FS_FL_USER_MODIFIABLE? Inherit the quota project ID. Files and subdirectories will inherit the project ID of the directory. This flag can be applied only to directories. .TP .BR FS_SECRM_FL " \[aq]s\[aq]" 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. .TP .BR FS_SYNC_FL " \[aq]S\[aq]" Make file updates synchronous. For files, this makes all writes synchronous (as though all opens of the file were with the .B O_SYNC flag). For directories, this has the same effect as the .B FS_DIRSYNC_FL flag. .TP .BR FS_TOPDIR_FL " \[aq]T\[aq]" Mark a directory for special treatment under the Orlov block-allocation strategy. See .BR chattr (1) for details. This flag can be applied only to directories and has an effect only for ext2, ext3, and ext4. .TP .BR FS_UNRM_FL " \[aq]u\[aq]" 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. .PP 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 .BR FS_TOPDIR_FL , which is not inheritable, and .BR FS_DIRSYNC_FL , which is inherited only by subdirectories. .SH STANDARDS Linux. .SH NOTES In order to change the inode flags of a file using the .B FS_IOC_SETFLAGS operation, the effective user ID of the caller must match the owner of the file, or the caller must have the .B CAP_FOWNER capability. .PP The type of the argument given to the .B FS_IOC_GETFLAGS and .B FS_IOC_SETFLAGS operations is .IR int\~* , notwithstanding the implication in the kernel source file .I include/uapi/linux/fs.h that the argument is .IR long\~* . .SH SEE ALSO .BR chattr (1), .BR lsattr (1), .BR mount (2), .BR btrfs (5), .BR ext4 (5), .BR xfs (5), .BR xattr (7), .BR mount (8)