1FANOTIFY_INIT(2) Linux Programmer's Manual FANOTIFY_INIT(2)
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7 fanotify_init - create and initialize fanotify group
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10 #include <fcntl.h> /* Definition of O_* constants */
11 #include <sys/fanotify.h>
12 int fanotify_init(unsigned int flags, unsigned int event_f_flags);
14
16 For an overview of the fanotify API, see fanotify(7).
17 fanotify_init() initializes a new fanotify group and returns a file de‐
19 scriptor for the event queue associated with the group.
20 The file descriptor is used in calls to fanotify_mark(2) to specify the
22 files, directories, mounts, or filesystems for which fanotify events
23 shall be created. These events are received by reading from the file
24 descriptor. Some events are only informative, indicating that a file
25 has been accessed. Other events can be used to determine whether an‐
26 other application is permitted to access a file or directory. Permis‐
27 sion to access filesystem objects is granted by writing to the file de‐
28 scriptor.
29 Multiple programs may be using the fanotify interface at the same time
31 to monitor the same files.
32 In the current implementation, the number of fanotify groups per user
34 is limited to 128. This limit cannot be overridden.
35 Calling fanotify_init() requires the CAP_SYS_ADMIN capability. This
37 constraint might be relaxed in future versions of the API. Therefore,
38 certain additional capability checks have been implemented as indicated
39 below.
40 The flags argument contains a multi-bit field defining the notification
42 class of the listening application and further single bit fields speci‐
43 fying the behavior of the file descriptor.
44 If multiple listeners for permission events exist, the notification
46 class is used to establish the sequence in which the listeners receive
47 the events.
48 Only one of the following notification classes may be specified in
50 flags:
51 FAN_CLASS_PRE_CONTENT
53 This value allows the receipt of events notifying that a file
54 has been accessed and events for permission decisions if a file
55 may be accessed. It is intended for event listeners that need
56 to access files before they contain their final data. This no‐
57 tification class might be used by hierarchical storage managers,
58 for example.
59 FAN_CLASS_CONTENT
61 This value allows the receipt of events notifying that a file
62 has been accessed and events for permission decisions if a file
63 may be accessed. It is intended for event listeners that need
64 to access files when they already contain their final content.
65 This notification class might be used by malware detection pro‐
66 grams, for example.
67 FAN_CLASS_NOTIF
69 This is the default value. It does not need to be specified.
70 This value only allows the receipt of events notifying that a
71 file has been accessed. Permission decisions before the file is
72 accessed are not possible.
73 Listeners with different notification classes will receive events in
75 the order FAN_CLASS_PRE_CONTENT, FAN_CLASS_CONTENT, FAN_CLASS_NOTIF.
76 The order of notification for listeners in the same notification class
77 is undefined.
78 The following bits can additionally be set in flags:
80 FAN_CLOEXEC
82 Set the close-on-exec flag (FD_CLOEXEC) on the new file descrip‐
83 tor. See the description of the O_CLOEXEC flag in open(2).
84 FAN_NONBLOCK
86 Enable the nonblocking flag (O_NONBLOCK) for the file descrip‐
87 tor. Reading from the file descriptor will not block. Instead,
88 if no data is available, read(2) fails with the error EAGAIN.
89 FAN_UNLIMITED_QUEUE
91 Remove the limit of 16384 events for the event queue. Use of
92 this flag requires the CAP_SYS_ADMIN capability.
93 FAN_UNLIMITED_MARKS
95 Remove the limit of 8192 marks. Use of this flag requires the
96 CAP_SYS_ADMIN capability.
97 FAN_REPORT_TID (since Linux 4.20)
99 Report thread ID (TID) instead of process ID (PID) in the pid
100 field of the struct fanotify_event_metadata supplied to read(2)
101 (see fanotify(7)).
102 FAN_ENABLE_AUDIT (since Linux 4.15)
104 Enable generation of audit log records about access mediation
105 performed by permission events. The permission event response
106 has to be marked with the FAN_AUDIT flag for an audit log record
107 to be generated.
108 FAN_REPORT_FID (since Linux 5.1)
110 This value allows the receipt of events which contain additional
111 information about the underlying filesystem object correlated to
112 an event. An additional record of type FAN_EVENT_INFO_TYPE_FID
113 encapsulates the information about the object and is included
114 alongside the generic event metadata structure. The file de‐
115 scriptor that is used to represent the object correlated to an
116 event is instead substituted with a file handle. It is intended
117 for applications that may find the use of a file handle to iden‐
118 tify an object more suitable than a file descriptor. Addition‐
119 ally, it may be used for applications monitoring a directory or
120 a filesystem that are interested in the directory entry modifi‐
121 cation events FAN_CREATE, FAN_DELETE, and FAN_MOVE, or in events
122 such as FAN_ATTRIB, FAN_DELETE_SELF, and FAN_MOVE_SELF. All the
123 events above require an fanotify group that identifies filesys‐
124 tem objects by file handles. Note that for the directory entry
125 modification events the reported file handle identifies the mod‐
126 ified directory and not the created/deleted/moved child object.
127 The use of FAN_CLASS_CONTENT or FAN_CLASS_PRE_CONTENT is not
128 permitted with this flag and will result in the error EINVAL.
129 See fanotify(7) for additional details.
130 FAN_REPORT_DIR_FID (since Linux 5.9)
132 Events for fanotify groups initialized with this flag will con‐
133 tain (see exceptions below) additional information about a di‐
134 rectory object correlated to an event. An additional record of
135 type FAN_EVENT_INFO_TYPE_DFID encapsulates the information about
136 the directory object and is included alongside the generic event
137 metadata structure. For events that occur on a non-directory
138 object, the additional structure includes a file handle that
139 identifies the parent directory filesystem object. Note that
140 there is no guarantee that the directory filesystem object will
141 be found at the location described by the file handle informa‐
142 tion at the time the event is received. When combined with the
143 flag FAN_REPORT_FID, two records may be reported with events
144 that occur on a non-directory object, one to identify the non-
145 directory object itself and one to identify the parent directory
146 object. Note that in some cases, a filesystem object does not
147 have a parent, for example, when an event occurs on an unlinked
148 but open file. In that case, with the FAN_REPORT_FID flag, the
149 event will be reported with only one record to identify the non-
150 directory object itself, because there is no directory associ‐
151 ated with the event. Without the FAN_REPORT_FID flag, no event
152 will be reported. See fanotify(7) for additional details.
153 FAN_REPORT_NAME (since Linux 5.9)
155 Events for fanotify groups initialized with this flag will con‐
156 tain additional information about the name of the directory en‐
157 try correlated to an event. This flag must be provided in con‐
158 junction with the flag FAN_REPORT_DIR_FID. Providing this flag
159 value without FAN_REPORT_DIR_FID will result in the error EIN‐
160 VAL. This flag may be combined with the flag FAN_REPORT_FID.
161 An additional record of type FAN_EVENT_INFO_TYPE_DFID_NAME,
162 which encapsulates the information about the directory entry, is
163 included alongside the generic event metadata structure and sub‐
164 stitutes the additional information record of type
165 FAN_EVENT_INFO_TYPE_DFID. The additional record includes a file
166 handle that identifies a directory filesystem object followed by
167 a name that identifies an entry in that directory. For the di‐
168 rectory entry modification events FAN_CREATE, FAN_DELETE, and
169 FAN_MOVE, the reported name is that of the created/deleted/moved
170 directory entry. For other events that occur on a directory ob‐
171 ject, the reported file handle is that of the directory object
172 itself and the reported name is '.'. For other events that oc‐
173 cur on a non-directory object, the reported file handle is that
174 of the parent directory object and the reported name is the name
175 of a directory entry where the object was located at the time of
176 the event. The rationale behind this logic is that the reported
177 directory file handle can be passed to open_by_handle_at(2) to
178 get an open directory file descriptor and that file descriptor
179 along with the reported name can be used to call fstatat(2).
180 The same rule that applies to record type
181 FAN_EVENT_INFO_TYPE_DFID also applies to record type
182 FAN_EVENT_INFO_TYPE_DFID_NAME: if a non-directory object has no
183 parent, either the event will not be reported or it will be re‐
184 ported without the directory entry information. Note that there
185 is no guarantee that the filesystem object will be found at the
186 location described by the directory entry information at the
187 time the event is received. See fanotify(7) for additional de‐
188 tails.
189 FAN_REPORT_DFID_NAME
191 This is a synonym for (FAN_REPORT_DIR_FID|FAN_REPORT_NAME).
192 The event_f_flags argument defines the file status flags that will be
194 set on the open file descriptions that are created for fanotify events.
195 For details of these flags, see the description of the flags values in
196 open(2). event_f_flags includes a multi-bit field for the access mode.
197 This field can take the following values:
198 O_RDONLY
200 This value allows only read access.
201 O_WRONLY
203 This value allows only write access.
204 O_RDWR This value allows read and write access.
206 Additional bits can be set in event_f_flags. The most useful values
208 are:
209 O_LARGEFILE
211 Enable support for files exceeding 2 GB. Failing to set this
212 flag will result in an EOVERFLOW error when trying to open a
213 large file which is monitored by an fanotify group on a 32-bit
214 system.
215 O_CLOEXEC (since Linux 3.18)
217 Enable the close-on-exec flag for the file descriptor. See the
218 description of the O_CLOEXEC flag in open(2) for reasons why
219 this may be useful.
220 The following are also allowable: O_APPEND, O_DSYNC, O_NOATIME, O_NON‐
222 BLOCK, and O_SYNC. Specifying any other flag in event_f_flags yields
223 the error EINVAL (but see BUGS).
224
226 On success, fanotify_init() returns a new file descriptor. On error,
227 -1 is returned, and errno is set to indicate the error.
228
230 EINVAL An invalid value was passed in flags or event_f_flags.
231 FAN_ALL_INIT_FLAGS (deprecated since Linux kernel version 4.20)
232 defines all allowable bits for flags.
233 EMFILE The number of fanotify groups for this user exceeds 128.
235 EMFILE The per-process limit on the number of open file descriptors has
237 been reached.
238 ENOMEM The allocation of memory for the notification group failed.
240 ENOSYS This kernel does not implement fanotify_init(). The fanotify
242 API is available only if the kernel was configured with CON‐
243 FIG_FANOTIFY.
244 EPERM The operation is not permitted because the caller lacks the
246 CAP_SYS_ADMIN capability.
247
249 fanotify_init() was introduced in version 2.6.36 of the Linux kernel
250 and enabled in version 2.6.37.
251
253 This system call is Linux-specific.
254
256 The following bug was present in Linux kernels before version 3.18:
257 * The O_CLOEXEC is ignored when passed in event_f_flags.
259 The following bug was present in Linux kernels before version 3.14:
261 * The event_f_flags argument is not checked for invalid flags. Flags
263 that are intended only for internal use, such as FMODE_EXEC, can be
264 set, and will consequently be set for the file descriptors returned
265 when reading from the fanotify file descriptor.
266
268 fanotify_mark(2), fanotify(7)
269
271 This page is part of release 5.13 of the Linux man-pages project. A
272 description of the project, information about reporting bugs, and the
273 latest version of this page, can be found at
274 https://www.kernel.org/doc/man-pages/.
275Linux 2021-03-22 FANOTIFY_INIT(2)