fanotify_init(2) - Linux manual page (original) (raw)
fanotifyinit(2) System Calls Manual fanotifyinit(2)
NAME top
fanotify_init - create and initialize fanotify groupLIBRARY top
Standard C library (_libc_, _-lc_)SYNOPSIS top
**#include <fcntl.h>** /* Definition of **O_*** constants */
**#include <sys/fanotify.h>**
**int fanotify_init(unsigned int** _flags_**, unsigned int** _eventfflags_**);**DESCRIPTION top
For an overview of the fanotify API, see [fanotify(7)](../man7/fanotify.7.html).
**fanotify_init**() initializes a new fanotify group and returns a
file descriptor for the event queue associated with the group.
The file descriptor is used in calls to [fanotify_mark(2)](../man2/fanotify%5Fmark.2.html) to
specify the files, directories, mounts, or filesystems for which
fanotify events shall be created. These events are received by
reading from the file descriptor. Some events are only
informative, indicating that a file has been accessed. Other
events can be used to determine whether another application is
permitted to access a file or directory. Permission to access
filesystem objects is granted by writing to the file descriptor.
Multiple programs may be using the fanotify interface at the same
time to monitor the same files.
The number of fanotify groups per user is limited. See
[fanotify(7)](../man7/fanotify.7.html) for details about this limit.
The _flags_ argument contains a multi-bit field defining the
notification class of the listening application and further single
bit fields specifying the behavior of the file descriptor.
If multiple listeners for permission events exist, the
notification class is used to establish the sequence in which the
listeners receive the events.
Only one of the following notification classes may be specified in
_flags_:
**FAN_CLASS_PRE_CONTENT**
This value allows the receipt of events notifying that a
file has been accessed and events for permission decisions
if a file may be accessed. It is intended for event
listeners that need to access files before they contain
their final data. This notification class might be used by
hierarchical storage managers, for example. Use of this
flag requires the **CAP_SYS_ADMIN** capability.
**FAN_CLASS_CONTENT**
This value allows the receipt of events notifying that a
file has been accessed and events for permission decisions
if a file may be accessed. It is intended for event
listeners that need to access files when they already
contain their final content. This notification class might
be used by malware detection programs, for example. Use of
this flag requires the **CAP_SYS_ADMIN** capability.
**FAN_CLASS_NOTIF**
This is the default value. It does not need to be
specified. This value only allows the receipt of events
notifying that a file has been accessed. Permission
decisions before the file is accessed are not possible.
Listeners with different notification classes will receive events
in the order **FAN_CLASS_PRE_CONTENT**, **FAN_CLASS_CONTENT**,
**FAN_CLASS_NOTIF**. The order of notification for listeners in the
same notification class is undefined.
The following bits can additionally be set in _flags_:
**FAN_CLOEXEC**
Set the close-on-exec flag (**FD_CLOEXEC**) on the new file
descriptor. See the description of the **O_CLOEXEC** flag in
[open(2)](../man2/open.2.html).
**FAN_NONBLOCK**
Enable the nonblocking flag (**O_NONBLOCK**) for the file
descriptor. Reading from the file descriptor will not
block. Instead, if no data is available, [read(2)](../man2/read.2.html) fails
with the error **EAGAIN**.
**FAN_UNLIMITED_QUEUE**
Remove the limit on the number of events in the event
queue. See [fanotify(7)](../man7/fanotify.7.html) for details about this limit. Use
of this flag requires the **CAP_SYS_ADMIN** capability.
**FAN_UNLIMITED_MARKS**
Remove the limit on the number of fanotify marks per user.
See [fanotify(7)](../man7/fanotify.7.html) for details about this limit. Use of this
flag requires the **CAP_SYS_ADMIN** capability.
**FAN_REPORT_TID** (since Linux 4.20)
Report thread ID (TID) instead of process ID (PID) in the
_pid_ field of the _struct fanotifyeventmetadata_ supplied to
[read(2)](../man2/read.2.html) (see [fanotify(7)](../man7/fanotify.7.html)). Use of this flag requires the
**CAP_SYS_ADMIN** capability.
**FAN_ENABLE_AUDIT** (since Linux 4.15)
Enable generation of audit log records about access
mediation performed by permission events. The permission
event response has to be marked with the **FAN_AUDIT** flag for
an audit log record to be generated. Use of this flag
requires the **CAP_AUDIT_WRITE** capability.
**FAN_REPORT_FID** (since Linux 5.1)
This value allows the receipt of events which contain
additional information about the underlying filesystem
object correlated to an event. An additional record of
type **FAN_EVENT_INFO_TYPE_FID** encapsulates the information
about the object and is included alongside the generic
event metadata structure. The file descriptor that is used
to represent the object correlated to an event is instead
substituted with a file handle. It is intended for
applications that may find the use of a file handle to
identify an object more suitable than a file descriptor.
Additionally, it may be used for applications monitoring a
directory or a filesystem that are interested in the
directory entry modification events **FAN_CREATE**, **FAN_DELETE**,
**FAN_MOVE**, and **FAN_RENAME**, or in events such as **FAN_ATTRIB**,
**FAN_DELETE_SELF**, and **FAN_MOVE_SELF**. All the events above
require an fanotify group that identifies filesystem
objects by file handles. Note that without the flag
**FAN_REPORT_TARGET_FID**, for the directory entry modification
events, there is an information record that identifies the
modified directory and not the created/deleted/moved child
object. The use of **FAN_CLASS_CONTENT** or
**FAN_CLASS_PRE_CONTENT** is not permitted with this flag and
will result in the error **EINVAL**. See [fanotify(7)](../man7/fanotify.7.html) for
additional details.
**FAN_REPORT_DIR_FID** (since Linux 5.9)
Events for fanotify groups initialized with this flag will
contain (see exceptions below) additional information about
a directory object correlated to an event. An additional
record of type **FAN_EVENT_INFO_TYPE_DFID** encapsulates the
information about the directory object and is included
alongside the generic event metadata structure. For events
that occur on a non-directory object, the additional
structure includes a file handle that identifies the parent
directory filesystem object. Note that there is no
guarantee that the directory filesystem object will be
found at the location described by the file handle
information at the time the event is received. When
combined with the flag **FAN_REPORT_FID**, two records may be
reported with events that occur on a non-directory object,
one to identify the non-directory object itself and one to
identify the parent directory object. Note that in some
cases, a filesystem object does not have a parent, for
example, when an event occurs on an unlinked but open file.
In that case, with the **FAN_REPORT_FID** flag, the event will
be reported with only one record to identify the non-
directory object itself, because there is no directory
associated with the event. Without the **FAN_REPORT_FID**
flag, no event will be reported. See [fanotify(7)](../man7/fanotify.7.html) for
additional details.
**FAN_REPORT_NAME** (since Linux 5.9)
Events for fanotify groups initialized with this flag will
contain additional information about the name of the
directory entry correlated to an event. This flag must be
provided in conjunction with the flag **FAN_REPORT_DIR_FID**.
Providing this flag value without **FAN_REPORT_DIR_FID** will
result in the error **EINVAL**. This flag may be combined with
the flag **FAN_REPORT_FID**. An additional record of type
**FAN_EVENT_INFO_TYPE_DFID_NAME**, which encapsulates the
information about the directory entry, is included
alongside the generic event metadata structure and
substitutes the additional information record of type
**FAN_EVENT_INFO_TYPE_DFID**. The additional record includes a
file handle that identifies a directory filesystem object
followed by a name that identifies an entry in that
directory. For the directory entry modification events
**FAN_CREATE**, **FAN_DELETE**, and **FAN_MOVE**, the reported name is
that of the created/deleted/moved directory entry. The
event **FAN_RENAME** may contain two information records. One
of type **FAN_EVENT_INFO_TYPE_OLD_DFID_NAME** identifying the
old directory entry, and another of type
**FAN_EVENT_INFO_TYPE_NEW_DFID_NAME** identifying the new
directory entry. For other events that occur on a
directory object, the reported file handle is that of the
directory object itself and the reported name is '.'. For
other events that occur on a non-directory object, the
reported file handle is that of the parent directory object
and the reported name is the name of a directory entry
where the object was located at the time of the event. The
rationale behind this logic is that the reported directory
file handle can be passed to [open_by_handle_at(2)](../man2/open%5Fby%5Fhandle%5Fat.2.html) to get an
open directory file descriptor and that file descriptor
along with the reported name can be used to call
[fstatat(2)](../man2/fstatat.2.html). The same rule that applies to record type
**FAN_EVENT_INFO_TYPE_DFID** also applies to record type
**FAN_EVENT_INFO_TYPE_DFID_NAME**: if a non-directory object
has no parent, either the event will not be reported or it
will be reported without the directory entry information.
Note that there is no guarantee that the filesystem object
will be found at the location described by the directory
entry information at the time the event is received. See
[fanotify(7)](../man7/fanotify.7.html) for additional details.
**FAN_REPORT_DFID_NAME**
This is a synonym for (**FAN_REPORT_DIR_FID**|**FAN_REPORT_NAME**).
**FAN_REPORT_TARGET_FID** (since Linux 5.17, 5.15.154, and 5.10.220)
Events for fanotify groups initialized with this flag will
contain additional information about the child correlated
with directory entry modification events. This flag must
be provided in conjunction with the flags **FAN_REPORT_FID**,
**FAN_REPORT_DIR_FID** and **FAN_REPORT_NAME**. or else the error
**EINVAL** will be returned. For the directory entry
modification events **FAN_CREATE**, **FAN_DELETE**, **FAN_MOVE**, and
**FAN_RENAME**, an additional record of type
**FAN_EVENT_INFO_TYPE_FID**, is reported in addition to the
information records of type **FAN_EVENT_INFO_TYPE_DFID**,
**FAN_EVENT_INFO_TYPE_DFID_NAME**,
**FAN_EVENT_INFO_TYPE_OLD_DFID_NAME**, and
**FAN_EVENT_INFO_TYPE_NEW_DFID_NAME**. The additional record
includes a file handle that identifies the filesystem child
object that the directory entry is referring to.
**FAN_REPORT_DFID_NAME_TARGET**
This is a synonym for
(**FAN_REPORT_DFID_NAME**|**FAN_REPORT_FID**|**FAN_REPORT_TARGET_FID**).
**FAN_REPORT_PIDFD** (since Linux 5.15 and 5.10.220)
Events for fanotify groups initialized with this flag will
contain an additional information record alongside the
generic _fanotifyeventmetadata_ structure. This
information record will be of type
**FAN_EVENT_INFO_TYPE_PIDFD** and will contain a pidfd for the
process that was responsible for generating an event. A
pidfd returned in this information record object is no
different to the pidfd that is returned when calling
[pidfd_open(2)](../man2/pidfd%5Fopen.2.html). Usage of this information record are for
applications that may be interested in reliably determining
whether the process responsible for generating an event has
been recycled or terminated. The use of the **FAN_REPORT_TID**
flag along with **FAN_REPORT_PIDFD** is currently not supported
and attempting to do so will result in the error **EINVAL**
being returned. This limitation is currently imposed by
the pidfd API as it currently only supports the creation of
pidfds for thread-group leaders. Creating pidfds for non-
thread-group leaders may be supported at some point in the
future, so this restriction may eventually be lifted. For
more details on information records, see [fanotify(7)](../man7/fanotify.7.html).
The _eventfflags_ argument defines the file status flags that will
be set on the open file descriptions that are created for fanotify
events. For details of these flags, see the description of the
_flags_ values in [open(2)](../man2/open.2.html). _eventfflags_ includes a multi-bit field
for the access mode. This field can take the following values:
**O_RDONLY**
This value allows only read access.
**O_WRONLY**
This value allows only write access.
**O_RDWR** This value allows read and write access.
Additional bits can be set in _eventfflags_. The most useful
values are:
**O_LARGEFILE**
Enable support for files exceeding 2 GB. Failing to set
this flag will result in an **EOVERFLOW** error when trying to
open a large file which is monitored by an fanotify group
on a 32-bit system.
**O_CLOEXEC** (since Linux 3.18)
Enable the close-on-exec flag for the file descriptor. See
the description of the **O_CLOEXEC** flag in [open(2)](../man2/open.2.html) for
reasons why this may be useful.
The following are also allowable: **O_APPEND**, **O_DSYNC**, **O_NOATIME**,
**O_NONBLOCK**, and **O_SYNC**. Specifying any other flag in
_eventfflags_ yields the error **EINVAL** (but see BUGS).RETURN VALUE top
On success, **fanotify_init**() returns a new file descriptor. On
error, -1 is returned, and _[errno](../man3/errno.3.html)_ is set to indicate the error.ERRORS top
**EINVAL** An invalid value was passed in _flags_ or _eventfflags_.
**FAN_ALL_INIT_FLAGS** (deprecated since Linux 4.20) defines
all allowable bits for _flags_.
**EMFILE** The number of fanotify groups for this user exceeds the
limit. See [fanotify(7)](../man7/fanotify.7.html) for details about this limit.
**EMFILE** The per-process limit on the number of open file
descriptors has been reached.
**ENOMEM** The allocation of memory for the notification group failed.
**ENOSYS** This kernel does not implement **fanotify_init**(). The
fanotify API is available only if the kernel was configured
with **CONFIG_FANOTIFY**.
**EPERM** The operation is not permitted because the caller lacks a
required capability.VERSIONS top
Prior to Linux 5.13 (and 5.10.220), calling **fanotify_init**()
required the **CAP_SYS_ADMIN** capability. Since Linux 5.13 (and
5.10.220), users may call **fanotify_init**() without the
**CAP_SYS_ADMIN** capability to create and initialize an fanotify
group with limited functionality.
The limitations imposed on an event listener created by a user
without the
**CAP_SYS_ADMIN** capability are as follows:
• The user cannot request for an unlimited event queue by
using **FAN_UNLIMITED_QUEUE**.
• The user cannot request for an unlimited number of marks
by using **FAN_UNLIMITED_MARKS**.
• The user cannot request to use either notification
classes **FAN_CLASS_CONTENT** or **FAN_CLASS_PRE_CONTENT**.
This means that user cannot request permission events.
• The user is required to create a group that identifies
filesystem objects by file handles, for example, by
providing the **FAN_REPORT_FID** flag.
• The user is limited to only mark inodes. The ability to
mark a mount or filesystem via **fanotify_mark**() through
the use of **FAN_MARK_MOUNT** or **FAN_MARK_FILESYSTEM** is not
permitted.
• The event object in the event queue is limited in terms
of the information that is made available to the
unprivileged user. A user will also not receive the pid
that generated the event, unless the listening process
itself generated the event.STANDARDS top
Linux.HISTORY top
Linux 2.6.37.BUGS top
The following bug was present before Linux 3.18:
• The **O_CLOEXEC** is ignored when passed in _eventfflags_.
The following bug was present before Linux 3.14:
• The _eventfflags_ argument is not checked for invalid flags.
Flags that are intended only for internal use, such as
**FMODE_EXEC**, can be set, and will consequently be set for the
file descriptors returned when reading from the fanotify file
descriptor.SEE ALSO top
[fanotify_mark(2)](../man2/fanotify%5Fmark.2.html), [fanotify(7)](../man7/fanotify.7.html)COLOPHON top
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man-pages@man7.orgLinux man-pages 6.10 2024-07-23 fanotifyinit(2)
Pages that refer to this page:fanotify_mark(2), syscalls(2), proc_pid_fdinfo(5), capabilities(7), fanotify(7)