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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | STANDARDS | HISTORY | NOTES | BUGS | SEE ALSO | COLOPHON |
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fanotify_mark(2) System Calls Manual fanotify_mark(2)
fanotify_mark - add, remove, or modify an fanotify mark on a
filesystem object
Standard C library (libc, -lc)
#include <sys/fanotify.h>
int fanotify_mark(int fanotify_fd, unsigned int flags,
uint64_t mask, int dirfd,
const char *_Nullable path);
For an overview of the fanotify API, see fanotify(7).
fanotify_mark() adds, removes, or modifies an fanotify mark on a
filesystem object. The caller must have read permission on the
filesystem object that is to be marked.
The fanotify_fd argument is a file descriptor returned by
fanotify_init(2).
flags is a bit mask describing the modification to perform. It
must include exactly one of the following values:
FAN_MARK_ADD
The events in mask will be added to the mark mask (or to
the ignore mask). mask must be nonempty or the error
EINVAL will occur.
FAN_MARK_REMOVE
The events in argument mask will be removed from the mark
mask (or from the ignore mask). mask must be nonempty or
the error EINVAL will occur.
FAN_MARK_FLUSH
Remove either all marks for filesystems, all marks for
mounts, or all marks for directories and files from the
fanotify group. If flags contains FAN_MARK_MOUNT, all
marks for mounts are removed from the group. If flags
contains FAN_MARK_FILESYSTEM, all marks for filesystems are
removed from the group. Otherwise, all marks for
directories and files are removed. No flag other than, and
at most one of, the flags FAN_MARK_MNTNS, FAN_MARK_MOUNT,
or FAN_MARK_FILESYSTEM can be used in conjunction with
FAN_MARK_FLUSH. mask is ignored.
If none of the values above is specified, or more than one is
specified, the call fails with the error EINVAL.
In addition, zero or more of the following values may be ORed into
flags:
FAN_MARK_DONT_FOLLOW
If path is a symbolic link, mark the link itself, rather
than the file to which it refers. (By default,
fanotify_mark() dereferences path if it is a symbolic
link.)
FAN_MARK_ONLYDIR
If the filesystem object to be marked is not a directory,
the error ENOTDIR shall be raised.
FAN_MARK_MNTNS (since Linux 6.14)
Mark the mount namespace specified by path. If path does
not represent a mount namespace (e.g. /proc/pid/ns/mnt),
the call fails with the error EINVAL. An fanotify group
that was initialized with flag FAN_REPORT_MNT is required.
FAN_MARK_MOUNT
Mark the mount specified by path. If path is not itself a
mount point, the mount containing path will be marked. All
directories, subdirectories, and the contained files of the
mount will be monitored. The events which require that
filesystem objects are identified by file handles, such as
FAN_CREATE, FAN_ATTRIB, FAN_MOVE, and FAN_DELETE_SELF,
cannot be provided as a mask when flags contains
FAN_MARK_MOUNT. Attempting to do so will result in the
error EINVAL being returned. Use of this flag requires the
CAP_SYS_ADMIN capability.
FAN_MARK_FILESYSTEM (since Linux 4.20)
Mark the filesystem specified by path. The filesystem
containing path will be marked. All the contained files
and directories of the filesystem from any mount point will
be monitored. Use of this flag requires the CAP_SYS_ADMIN
capability.
FAN_MARK_IGNORED_MASK
The events in mask shall be added to or removed from the
ignore mask. Note that the flags FAN_ONDIR, and
FAN_EVENT_ON_CHILD have no effect when provided with this
flag. The effect of setting the flags FAN_ONDIR, and
FAN_EVENT_ON_CHILD in the mark mask on the events that are
set in the ignore mask is undefined and depends on the
Linux kernel version. Specifically, prior to Linux 5.9,
setting a mark mask on a file and a mark with ignore mask
on its parent directory would not result in ignoring events
on the file, regardless of the FAN_EVENT_ON_CHILD flag in
the parent directory's mark mask. When the ignore mask is
updated with the FAN_MARK_IGNORED_MASK flag on a mark that
was previously updated with the FAN_MARK_IGNORE flag, the
update fails with EEXIST error.
FAN_MARK_IGNORE (since Linux 6.0, 5.15.154, and 5.10.220)
This flag has a similar effect as setting the
FAN_MARK_IGNORED_MASK flag. The events in mask shall be
added to or removed from the ignore mask. Unlike the
FAN_MARK_IGNORED_MASK flag, this flag also has the effect
that the FAN_ONDIR, and FAN_EVENT_ON_CHILD flags take
effect on the ignore mask. Specifically, unless the
FAN_ONDIR flag is set with FAN_MARK_IGNORE, events on
directories will not be ignored. If the flag
FAN_EVENT_ON_CHILD is set with FAN_MARK_IGNORE, events on
children will be ignored. For example, a mark on a
directory with combination of a mask with FAN_CREATE event
and FAN_ONDIR flag and an ignore mask with FAN_CREATE event
and without FAN_ONDIR flag, will result in getting only the
events for creation of sub-directories. When using the
FAN_MARK_IGNORE flag to add to an ignore mask of a mount,
filesystem, or directory inode mark, the
FAN_MARK_IGNORED_SURV_MODIFY flag must be specified.
Failure to do so will results with EINVAL or EISDIR error.
FAN_MARK_IGNORED_SURV_MODIFY
The ignore mask shall survive modify events. If this flag
is not set, the ignore mask is cleared when a modify event
occurs on the marked object. Omitting this flag is
typically used to suppress events (e.g., FAN_OPEN) for a
specific file, until that specific file's content has been
modified. It is far less useful to suppress events on an
entire filesystem, or mount, or on all files inside a
directory, until some file's content has been modified.
For this reason, the FAN_MARK_IGNORE flag requires the
FAN_MARK_IGNORED_SURV_MODIFY flag on a mount, filesystem,
or directory inode mark. This flag cannot be removed from
a mark once set. When the ignore mask is updated without
this flag on a mark that was previously updated with the
FAN_MARK_IGNORE and FAN_MARK_IGNORED_SURV_MODIFY flags, the
update fails with EEXIST error.
FAN_MARK_IGNORE_SURV
This is a synonym for
(FAN_MARK_IGNORE|FAN_MARK_IGNORED_SURV_MODIFY).
FAN_MARK_EVICTABLE (since Linux 5.19, 5.15.154, and 5.10.220)
When an inode mark is created with this flag, the inode
object will not be pinned to the inode cache, therefore,
allowing the inode object to be evicted from the inode
cache when the memory pressure on the system is high. The
eviction of the inode object results in the evictable mark
also being lost. When the mask of an evictable inode mark
is updated without using the FAN_MARK_EVICATBLE flag, the
marked inode is pinned to inode cache and the mark is no
longer evictable. When the mask of a non-evictable inode
mark is updated with the FAN_MARK_EVICTABLE flag, the inode
mark remains non-evictable and the update fails with EEXIST
error. Mounts and filesystems are not evictable objects,
therefore, an attempt to create a mount mark or a
filesystem mark with the FAN_MARK_EVICTABLE flag, will
result in the error EINVAL. For example, inode marks can
be used in combination with mount marks to reduce the
amount of events from noninteresting paths. The event
listener reads events, checks if the path reported in the
event is of interest, and if it is not, the listener sets a
mark with an ignore mask on the directory. Evictable inode
marks allow using this method for a large number of
directories without the concern of pinning all inodes and
exhausting the system's memory.
mask defines which events shall be listened for (or which shall be
ignored). It is a bit mask composed of the following values:
FAN_ACCESS
Create an event when a file or directory (but see BUGS) is
accessed (read).
FAN_MODIFY
Create an event when a file is modified (write).
FAN_CLOSE_WRITE
Create an event when a writable file is closed.
FAN_CLOSE_NOWRITE
Create an event when a read-only file or directory is
closed.
FAN_OPEN
Create an event when a file or directory is opened.
FAN_OPEN_EXEC (since Linux 5.0)
Create an event when a file is opened with the intent to be
executed. See NOTES for additional details.
FAN_ATTRIB (since Linux 5.1)
Create an event when the metadata for a file or directory
has changed. An fanotify group that identifies filesystem
objects by file handles is required.
FAN_CREATE (since Linux 5.1)
Create an event when a file or directory has been created
in a marked parent directory. An fanotify group that
identifies filesystem objects by file handles is required.
FAN_DELETE (since Linux 5.1)
Create an event when a file or directory has been deleted
in a marked parent directory. An fanotify group that
identifies filesystem objects by file handles is required.
FAN_DELETE_SELF (since Linux 5.1)
Create an event when a marked file or directory itself is
deleted. An fanotify group that identifies filesystem
objects by file handles is required.
FAN_MOVED_FROM (since Linux 5.1)
Create an event when a file or directory has been moved
from a marked parent directory. An fanotify group that
identifies filesystem objects by file handles is required.
FAN_MOVED_TO (since Linux 5.1)
Create an event when a file or directory has been moved to
a marked parent directory. An fanotify group that
identifies filesystem objects by file handles is required.
FAN_RENAME (since Linux 5.17, 5.15.154, and 5.10.220)
This event contains the same information provided by events
FAN_MOVED_FROM and FAN_MOVED_TO, however is represented by
a single event with up to two information records. An
fanotify group that identifies filesystem objects by file
handles is required. If the filesystem object to be marked
is not a directory, the error ENOTDIR shall be raised.
FAN_MOVE_SELF (since Linux 5.1)
Create an event when a marked file or directory itself has
been moved. An fanotify group that identifies filesystem
objects by file handles is required.
FAN_MNT_ATTACH
FAN_MNT_DETACH (both since Linux 6.14)
Create an event when a mount was attached to or detached
from a marked mount namespace, respectively. An attempt to
set this flag on an inode, mount, or filesystem mark will
result in the error EINVAL. An fanotify group that was
initialized with flag FAN_REPORT_MNT and the mark flag
FAN_MARK_MNTNS are required. An additional information
record of type FAN_EVENT_INFO_TYPE_MNT is returned with the
event. See fanotify(7) for additional details.
FAN_FS_ERROR (since Linux 5.16, 5.15.154, and 5.10.220)
Create an event when a filesystem error leading to
inconsistent filesystem metadata is detected. An
additional information record of type
FAN_EVENT_INFO_TYPE_ERROR is returned for each event in the
read buffer. An fanotify group that identifies filesystem
objects by file handles is required. Events of such type
are dependent on support from the underlying filesystem.
At the time of writing, only the ext4 filesystem reports
FAN_FS_ERROR events. See fanotify(7) for additional
details.
FAN_OPEN_PERM
Create an event when a permission to open a file or
directory is requested. An fanotify file descriptor
created with FAN_CLASS_PRE_CONTENT or FAN_CLASS_CONTENT is
required.
FAN_OPEN_EXEC_PERM (since Linux 5.0)
Create an event when a permission to open a file for
execution is requested. An fanotify file descriptor
created with FAN_CLASS_PRE_CONTENT or FAN_CLASS_CONTENT is
required. See NOTES for additional details.
FAN_ACCESS_PERM
Create an event when a permission to read a file or
directory is requested. An fanotify file descriptor
created with FAN_CLASS_PRE_CONTENT or FAN_CLASS_CONTENT is
required.
FAN_PRE_ACCESS (since Linux 6.14)
Create an event before read or write access to a file
range, that provides an opportunity for the event listener
to modify the content of the file before access to the
content in the specified range. An additional information
record of type FAN_EVENT_INFO_TYPE_RANGE is returned for
each event in the read buffer. An fanotify file descriptor
created with FAN_CLASS_PRE_CONTENT is required.
FAN_ONDIR
Create events for directories—for example, when opendir(3),
readdir(3) (but see BUGS), and closedir(3) are called.
Without this flag, events are created only for files. In
the context of directory entry events, such as FAN_CREATE,
FAN_DELETE, FAN_MOVED_FROM, and FAN_MOVED_TO, specifying
the flag FAN_ONDIR is required in order to create events
when subdirectory entries are modified (i.e., mkdir(2)/
rmdir(2)).
FAN_EVENT_ON_CHILD
Events for the immediate children of marked directories
shall be created. The flag has no effect when marking
mounts and filesystems. Note that events are not generated
for children of the subdirectories of marked directories.
More specifically, the directory entry modification events
FAN_CREATE, FAN_DELETE, FAN_MOVED_FROM, and FAN_MOVED_TO
are not generated for any entry modifications performed
inside subdirectories of marked directories. Note that the
events FAN_DELETE_SELF and FAN_MOVE_SELF are not generated
for children of marked directories. To monitor complete
directory trees it is necessary to mark the relevant mount
or filesystem.
The following composed values are defined:
FAN_CLOSE
A file is closed (FAN_CLOSE_WRITE|FAN_CLOSE_NOWRITE).
FAN_MOVE
A file or directory has been moved
(FAN_MOVED_FROM|FAN_MOVED_TO).
The filesystem object to be marked is determined by the file
descriptor dirfd and the pathname specified in path:
• If path is NULL, dirfd defines the filesystem object to be
marked.
• If path is NULL, and dirfd takes the special value AT_FDCWD,
the current working directory is to be marked.
• If path is absolute, it defines the filesystem object to be
marked, and dirfd is ignored.
• If path is relative, and dirfd does not have the value
AT_FDCWD, then the filesystem object to be marked is determined
by interpreting path relative the directory referred to by
dirfd.
• If path is relative, and dirfd has the value AT_FDCWD, then the
filesystem object to be marked is determined by interpreting
path relative to the current working directory. (See openat(2)
for an explanation of why the dirfd argument is useful.)
On success, fanotify_mark() returns 0. On error, -1 is returned,
and errno is set to indicate the error.
EBADF An invalid file descriptor was passed in fanotify_fd.
EBADF path is relative but dirfd is neither AT_FDCWD nor a valid
file descriptor.
EEXIST The filesystem object indicated by dirfd and path has a
mark that was updated without the FAN_MARK_EVICTABLE flag,
and the user attempted to update the mark with
FAN_MARK_EVICTABLE flag.
EEXIST The filesystem object indicated by dirfd and path has a
mark that was updated with the FAN_MARK_IGNORE flag, and
the user attempted to update the mark with
FAN_MARK_IGNORED_MASK flag.
EEXIST The filesystem object indicated by dirfd and path has a
mark that was updated with the FAN_MARK_IGNORE and
FAN_MARK_IGNORED_SURV_MODIFY flags, and the user attempted
to update the mark only with FAN_MARK_IGNORE flag.
EINVAL An invalid value was passed in flags or mask, or
fanotify_fd was not an fanotify file descriptor.
EINVAL The fanotify file descriptor was opened with
FAN_CLASS_NOTIF or the fanotify group identifies filesystem
objects by file handles and mask contains a flag for
permission events (FAN_OPEN_PERM or FAN_ACCESS_PERM).
EINVAL The group was initialized without FAN_REPORT_FID but one or
more event types specified in the mask require it.
EINVAL flags contains FAN_MARK_IGNORE, and either FAN_MARK_MOUNT
or FAN_MARK_FILESYSTEM, but does not contain
FAN_MARK_IGNORED_SURV_MODIFY.
EISDIR flags contains FAN_MARK_IGNORE, but does not contain
FAN_MARK_IGNORED_SURV_MODIFY, and dirfd and path specify a
directory.
ENODEV The filesystem object indicated by dirfd and path is
associated with a filesystem that reports zero fsid (e.g.,
fuse(4)). This error can be returned only with an fanotify
group that identifies filesystem objects by file handles.
Since Linux 6.8, this error can be returned when trying to
add a mount or filesystem mark.
ENOENT The filesystem object indicated by dirfd and path does not
exist. This error also occurs when trying to remove a mark
from an object which is not marked.
ENOMEM The necessary memory could not be allocated.
ENOSPC The number of marks for this user exceeds the limit and the
FAN_UNLIMITED_MARKS flag was not specified when the
fanotify file descriptor was created with fanotify_init(2).
See fanotify(7) for details about this limit.
ENOSYS This kernel does not implement fanotify_mark(). The
fanotify API is available only if the kernel was configured
with CONFIG_FANOTIFY.
ENOTDIR
flags contains FAN_MARK_ONLYDIR, and dirfd and path do not
specify a directory.
ENOTDIR
mask contains FAN_RENAME, and dirfd and path do not specify
a directory.
ENOTDIR
flags contains FAN_MARK_IGNORE, or the fanotify group was
initialized with flag FAN_REPORT_TARGET_FID, and mask
contains directory entry modification events (e.g.,
FAN_CREATE, FAN_DELETE), or directory event flags (e.g.,
FAN_ONDIR, FAN_EVENT_ON_CHILD), and dirfd and path do not
specify a directory.
EOPNOTSUPP
The object indicated by path is associated with a
filesystem that does not support the encoding of file
handles. This error can be returned only with an fanotify
group that identifies filesystem objects by file handles.
Calling name_to_handle_at(2) with the flag AT_HANDLE_FID
(since Linux 6.5) can be used as a test to check if a
filesystem supports reporting events with file handles.
EPERM The operation is not permitted because the caller lacks a
required capability.
EXDEV The filesystem object indicated by path resides within a
filesystem subvolume (e.g., btrfs(5)) which uses a
different fsid than its root superblock. This error can be
returned only with an fanotify group that identifies
filesystem objects by file handles. Since Linux 6.8, this
error will be returned when trying to add a mount or
filesystem mark on a subvolume, when trying to add inode
marks in different subvolumes, or when trying to add inode
marks in a btrfs(5) subvolume and in another filesystem.
Since Linux 6.8, this error will also be returned when
trying to add marks in different filesystems, where one of
the filesystems reports zero fsid (e.g., fuse(4)).
Linux.
Linux 2.6.37.
FAN_OPEN_EXEC and FAN_OPEN_EXEC_PERM
When using either FAN_OPEN_EXEC or FAN_OPEN_EXEC_PERM within the
mask, events of these types will be returned only when the direct
execution of a program occurs. More specifically, this means that
events of these types will be generated for files that are opened
using execve(2), execveat(2), or uselib(2). Events of these types
will not be raised in the situation where an interpreter is passed
(or reads) a file for interpretation.
Additionally, if a mark has also been placed on the Linux dynamic
linker, a user should also expect to receive an event for it when
an ELF object has been successfully opened using execve(2) or
execveat(2).
For example, if the following ELF binary were to be invoked and a
FAN_OPEN_EXEC mark has been placed on /:
$ /bin/echo foo
The listening application in this case would receive FAN_OPEN_EXEC
events for both the ELF binary and interpreter, respectively:
/bin/echo
/lib64/ld-linux-x86-64.so.2
The following bugs were present in before Linux 3.16:
• If flags contains FAN_MARK_FLUSH, dirfd, and path must specify
a valid filesystem object, even though this object is not used.
• readdir(2) does not generate a FAN_ACCESS event.
• If fanotify_mark() is called with FAN_MARK_FLUSH, flags is not
checked for invalid values.
fanotify_init(2), fanotify(7)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
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⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
[email protected]
Linux man-pages 6.15 2025-05-17 fanotify_mark(2)
Pages that refer to this page: fanotify_init(2), open(2), syscalls(2), proc_pid_fdinfo(5), fanotify(7)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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