fanotify_mark(2) System Calls Manual fanotify_mark(2)
NAME
fanotify_mark - add, remove, or modify an fanotify mark on a filesystem
object
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#include <sys/fanotify.h>
int fanotify_mark(int fanotify_fd, unsigned int flags,
uint64_t mask, int dirfd,
const char *_Nullable pathname);
DESCRIPTION
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 fan-
otify_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 ig-
nore mask). mask must be nonempty or the error EINVAL will oc-
cur.
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 re-
moved from the group. If flags contains FAN_MARK_FILESYSTEM,
all marks for filesystems are removed from the group. Other-
wise, all marks for directories and files are removed. No flag
other than, and at most one of, the flags 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 speci-
fied, 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 pathname is a symbolic link, mark the link itself, rather
than the file to which it refers. (By default, fanotify_mark()
dereferences pathname 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_MOUNT
Mark the mount specified by pathname. If pathname is not itself
a mount point, the mount containing pathname will be marked.
All directories, subdirectories, and the contained files of the
mount will be monitored. The events which require that filesys-
tem 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 pathname. The filesystem con-
taining pathname will be marked. All the contained files and
directories of the filesystem from any mount point will be moni-
tored. 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 set-
ting 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 previ-
ously updated with the FAN_MARK_IGNORE flag, the update fails
with EEXIST error.
FAN_MARK_IGNORE (since Linux 6.0)
This flag has a similar effect as setting the FAN_MARK_IG-
NORED_MASK flag. The events in mask shall be added to or re-
moved 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_IG-
NORE, events on directories will not be ignored. If the flag
FAN_EVENT_ON_CHILD is set with FAN_MARK_IGNORE, events on chil-
dren 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. Fail-
ure 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 use-
ful 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_IG-
NORED_SURV_MODIFY).
FAN_MARK_EVICTABLE (since Linux 5.19)
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 ob-
ject 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 ob-
jects, 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 com-
bination 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 direc-
tory. 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 ig-
nored). It is a bit mask composed of the following values:
FAN_ACCESS
Create an event when a file or directory (but see BUGS) is ac-
cessed (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 exe-
cuted. 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_FS_ERROR (since Linux 5.16)
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_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)
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 re-
quired. If the filesystem object to be marked is not a direc-
tory, 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_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_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 directo-
ries. Note that the events FAN_DELETE_SELF and FAN_MOVE_SELF
are not generated for children of marked directories. To moni-
tor complete directory trees it is necessary to mark the rele-
vant 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 pathname:
• If pathname is NULL, dirfd defines the filesystem object to be
marked.
• If pathname is NULL, and dirfd takes the special value AT_FDCWD, the
current working directory is to be marked.
• If pathname is absolute, it defines the filesystem object to be
marked, and dirfd is ignored.
• If pathname is relative, and dirfd does not have the value AT_FDCWD,
then the filesystem object to be marked is determined by interpret-
ing pathname relative the directory referred to by dirfd.
• If pathname is relative, and dirfd has the value AT_FDCWD, then the
filesystem object to be marked is determined by interpreting path-
name relative to the current working directory. (See openat(2) for
an explanation of why the dirfd argument is useful.)
RETURN VALUE
On success, fanotify_mark() returns 0. On error, -1 is returned, and
errno is set to indicate the error.
ERRORS
EBADF An invalid file descriptor was passed in fanotify_fd.
EBADF pathname is relative but dirfd is neither AT_FDCWD nor a valid
file descriptor.
EEXIST The filesystem object indicated by dirfd and pathname 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 pathname has a mark
that was updated with the FAN_MARK_IGNORE flag, and the user at-
tempted to update the mark with FAN_MARK_IGNORED_MASK flag.
EEXIST The filesystem object indicated by dirfd and pathname has a mark
that was updated with the FAN_MARK_IGNORE and FAN_MARK_IG-
NORED_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_IG-
NORED_SURV_MODIFY.
EISDIR flags contains FAN_MARK_IGNORE, but does not contain
FAN_MARK_IGNORED_SURV_MODIFY, and dirfd and pathname specify a
directory.
ENODEV The filesystem object indicated by dirfd and pathname is not as-
sociated with a filesystem that supports fsid (e.g., fuse(4)).
tmpfs(5) did not support fsid prior to Linux 5.13. This error
can be returned only with an fanotify group that identifies
filesystem objects by file handles.
ENOENT The filesystem object indicated by dirfd and pathname 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 fan-
otify(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 CON-
FIG_FANOTIFY.
ENOTDIR
flags contains FAN_MARK_ONLYDIR, and dirfd and pathname do not
specify a directory.
ENOTDIR
mask contains FAN_RENAME, and dirfd and pathname do not specify
a directory.
ENOTDIR
flags contains FAN_MARK_IGNORE, or the fanotify group was ini-
tialized with flag FAN_REPORT_TARGET_FID, and mask contains di-
rectory entry modification events (e.g., FAN_CREATE,
FAN_DELETE), or directory event flags (e.g., FAN_ONDIR,
FAN_EVENT_ON_CHILD), and dirfd and pathname do not specify a di-
rectory.
EOPNOTSUPP
The object indicated by pathname 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_han-
dle_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 re-
quired capability.
EXDEV The filesystem object indicated by pathname 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.
STANDARDS
Linux.
HISTORY
Linux 2.6.37.
NOTES
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 ex-
ecve(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
BUGS
The following bugs were present in before Linux 3.16:
• If flags contains FAN_MARK_FLUSH, dirfd, and pathname 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.
SEE ALSO
fanotify_init(2), fanotify(7)
Linux man-pages 6.7 2023-10-31 fanotify_mark(2)
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