ioctl_iflags

<html> <head> <title>ioctl_iflags</title> <META NAME="KEYWORDS" CONTENT="ioctl_iflags"> </head> <body BGCOLOR="#ffffff" LINK="#0000ff" VLINK="#0000ff" ALINK="#0000ff" TEXT="#000000"> <center> <h1>ioctl_iflags</h1></center> <PRE> <A HREF="/man2/IOCTL_IFLAGS">IOCTL_IFLAGS(2)</A> Linux Programmer's Manual <A HREF="/man2/IOCTL_IFLAGS">IOCTL_IFLAGS(2)</A> 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 <A HREF="/man2/ioctl">ioctl(2)</A> 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 <A HREF="/man1/lsattr">lsattr(1)</A> and <A HREF="/man1/chattr">chattr(1)</A> 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 <A HREF="/man1/lsattr">lsattr(1)</A> and <A HREF="/man1/chattr">chattr(1)</A>): 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 <A HREF="/man5/btrfs">btrfs(5)</A>. FS_DIRSYNC_FL 'D' (since Linux 2.6.0) Write directory changes synchronously to disk. This flag pro- vides semantics equivalent to the <A HREF="/man2/mount">mount(2)</A> 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 <A HREF="/man5/ext3">ext3(5)</A> and <A HREF="/man5/ext4">ext4(5)</A> 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 <A HREF="/man2/mount">mount(2)</A> 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 <A HREF="/man1/chattr">chattr(1)</A> and <A HREF="/man5/btrfs">btrfs(5)</A>. FS_NODUMP_FL 'd' Don't include this file in backups made using <A HREF="/man8/dump">dump(8)</A>. 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 <A HREF="/man1/chattr">chattr(1)</A> 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 <A HREF="/man1/chattr">chattr(1)</A>, <A HREF="/man1/lsattr">lsattr(1)</A>, <A HREF="/man2/mount">mount(2)</A>, <A HREF="/man5/btrfs">btrfs(5)</A>, <A HREF="/man5/ext4">ext4(5)</A>, <A HREF="/man5/xfs">xfs(5)</A>, <A HREF="/man7/xattr">xattr(7)</A>, <A HREF="/man8/mount">mount(8)</A> 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 <A HREF="/man2/IOCTL_IFLAGS">IOCTL_IFLAGS(2)</A></PRE> <center> <h6>Man Pages Copyright Respective Owners. Site Copyright (C) 1994 - 2025 <a href="http://www.he.net">Hurricane Electric</a>. All Rights Reserved.</h6></center> </body> </html>

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ioctl_iflags