1FANOTIFY_INIT(2) Linux Programmer's Manual FANOTIFY_INIT(2)
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6 fanotify_init - create and initialize fanotify group
7
9 #include <fcntl.h>
10 #include <sys/fanotify.h>
11 int fanotify_init(unsigned int flags, unsigned int event_f_flags);
13
15 For an overview of the fanotify API, see fanotify(7).
16 fanotify_init() initializes a new fanotify group and returns a file
18 descriptor for the event queue associated with the group.
19 The file descriptor is used in calls to fanotify_mark(2) to specify the
21 files, directories, and mounts for which fanotify events shall be cre‐
22 ated. These events are received by reading from the file descriptor.
23 Some events are only informative, indicating that a file has been
24 accessed. Other events can be used to determine whether another appli‐
25 cation is permitted to access a file or directory. Permission to
26 access filesystem objects is granted by writing to the file descriptor.
27 Multiple programs may be using the fanotify interface at the same time
29 to monitor the same files.
30 In the current implementation, the number of fanotify groups per user
32 is limited to 128. This limit cannot be overridden.
33 Calling fanotify_init() requires the CAP_SYS_ADMIN capability. This
35 constraint might be relaxed in future versions of the API. Therefore,
36 certain additional capability checks have been implemented as indicated
37 below.
38 The flags argument contains a multi-bit field defining the notification
40 class of the listening application and further single bit fields speci‐
41 fying the behavior of the file descriptor.
42 If multiple listeners for permission events exist, the notification
44 class is used to establish the sequence in which the listeners receive
45 the events.
46 Only one of the following notification classes may be specified in
48 flags:
49 FAN_CLASS_PRE_CONTENT
51 This value allows the receipt of events notifying that a file
52 has been accessed and events for permission decisions if a file
53 may be accessed. It is intended for event listeners that need
54 to access files before they contain their final data. This
55 notification class might be used by hierarchical storage man‐
56 agers, for example.
57 FAN_CLASS_CONTENT
59 This value allows the receipt of events notifying that a file
60 has been accessed and events for permission decisions if a file
61 may be accessed. It is intended for event listeners that need
62 to access files when they already contain their final content.
63 This notification class might be used by malware detection pro‐
64 grams, for example.
65 FAN_CLASS_NOTIF
67 This is the default value. It does not need to be specified.
68 This value only allows the receipt of events notifying that a
69 file has been accessed. Permission decisions before the file is
70 accessed are not possible.
71 Listeners with different notification classes will receive events in
73 the order FAN_CLASS_PRE_CONTENT, FAN_CLASS_CONTENT, FAN_CLASS_NOTIF.
74 The order of notification for listeners in the same notification class
75 is undefined.
76 The following bits can additionally be set in flags:
78 FAN_CLOEXEC
80 Set the close-on-exec flag (FD_CLOEXEC) on the new file descrip‐
81 tor. See the description of the O_CLOEXEC flag in open(2).
82 FAN_NONBLOCK
84 Enable the nonblocking flag (O_NONBLOCK) for the file descrip‐
85 tor. Reading from the file descriptor will not block. Instead,
86 if no data is available, read(2) fails with the error EAGAIN.
87 FAN_UNLIMITED_QUEUE
89 Remove the limit of 16384 events for the event queue. Use of
90 this flag requires the CAP_SYS_ADMIN capability.
91 FAN_UNLIMITED_MARKS
93 Remove the limit of 8192 marks. Use of this flag requires the
94 CAP_SYS_ADMIN capability.
95 The event_f_flags argument defines the file status flags that will be
97 set on the open file descriptions that are created for fanotify events.
98 For details of these flags, see the description of the flags values in
99 open(2). event_f_flags includes a multi-bit field for the access mode.
100 This field can take the following values:
101 O_RDONLY
103 This value allows only read access.
104 O_WRONLY
106 This value allows only write access.
107 O_RDWR This value allows read and write access.
109 Additional bits can be set in event_f_flags. The most useful values
111 are:
112 O_LARGEFILE
114 Enable support for files exceeding 2 GB. Failing to set this
115 flag will result in an EOVERFLOW error when trying to open a
116 large file which is monitored by an fanotify group on a 32-bit
117 system.
118 O_CLOEXEC (since Linux 3.18)
120 Enable the close-on-exec flag for the file descriptor. See the
121 description of the O_CLOEXEC flag in open(2) for reasons why
122 this may be useful.
123 The following are also allowable: O_APPEND, O_DSYNC, O_NOATIME, O_NON‐
125 BLOCK, and O_SYNC. Specifying any other flag in event_f_flags yields
126 the error EINVAL (but see BUGS).
127
129 On success, fanotify_init() returns a new file descriptor. On error,
130 -1 is returned, and errno is set to indicate the error.
131
133 EINVAL An invalid value was passed in flags or event_f_flags.
134 FAN_ALL_INIT_FLAGS defines all allowable bits for flags.
135 EMFILE The number of fanotify groups for this user exceeds 128.
137 EMFILE The per-process limit on the number of open file descriptors has
139 been reached.
140 ENOMEM The allocation of memory for the notification group failed.
142 ENOSYS This kernel does not implement fanotify_init(). The fanotify
144 API is available only if the kernel was configured with CON‐
145 FIG_FANOTIFY.
146 EPERM The operation is not permitted because the caller lacks the
148 CAP_SYS_ADMIN capability.
149
151 fanotify_init() was introduced in version 2.6.36 of the Linux kernel
152 and enabled in version 2.6.37.
153
155 This system call is Linux-specific.
156
158 The following bug was present in Linux kernels before version 3.18:
159 * The O_CLOEXEC is ignored when passed in event_f_flags.
161 The following bug was present in Linux kernels before version 3.14:
163 * The event_f_flags argument is not checked for invalid flags. Flags
165 that are intended only for internal use, such as FMODE_EXEC, can be
166 set, and will consequently be set for the file descriptors returned
167 when reading from the fanotify file descriptor.
168
170 fanotify_mark(2), fanotify(7)
171
173 This page is part of release 4.16 of the Linux man-pages project. A
174 description of the project, information about reporting bugs, and the
175 latest version of this page, can be found at
176 https://www.kernel.org/doc/man-pages/.
177Linux 2017-09-15 FANOTIFY_INIT(2)