.\" Copyright (C) 2013, Heinrich Schuchardt .\" .\" %%%LICENSE_START(VERBATIM) .\" Permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" Permission is granted to copy and distribute modified versions of .\" this manual under the conditions for verbatim copying, provided that .\" the entire resulting derived work is distributed under the terms of .\" a permission notice identical to this one. .\" .\" Since the Linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. The author(s) assume. .\" no responsibility for errors or omissions, or for damages resulting. .\" from the use of the information contained herein. The author(s) may. .\" not have taken the same level of care in the production of this. .\" manual, which is licensed free of charge, as they might when working. .\" professionally. .\" .\" Formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%LICENSE_END .TH FANOTIFY_INIT 2 2014-04-24 "Linux" "Linux Programmer's Manual" .SH NAME fanotify_init \- create and initialize fanotify group .SH SYNOPSIS .B #include .br .B #include .sp .BI "int fanotify_init(unsigned int " flags ", unsigned int " event_f_flags ); .SH DESCRIPTION For an overview of the fanotify API, see .BR fanotify (7). .PP .BR fanotify_init () initializes a new fanotify group and returns a file descriptor for the event queue associated with the group. .PP The file descriptor is used in calls to .BR fanotify_mark (2) to specify the files, directories, and mounts 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. .PP Multiple programs may be using the fanotify interface at the same time to monitor the same files. .PP In the current implementation, the number of fanotify groups per user is limited to 128. This limit cannot be overridden. .PP Calling .BR fanotify_init () requires the .B CAP_SYS_ADMIN capability. This constraint might be relaxed in future versions of the API. Therefore, certain additional capability checks have been implemented as indicated below. .PP The .I 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. .PP If multiple listeners for permission events exist, the notification class is used to establish the sequence in which the listeners receive the events. .PP Only one of the following notification classes may be specified in .IR flags : .TP .B 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. .TP .B 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. .TP .B 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. .PP Listeners with different notification classes will receive events in the order .BR FAN_CLASS_PRE_CONTENT , .BR FAN_CLASS_CONTENT , .BR FAN_CLASS_NOTIF . The order of notification for listeners of the same value is undefined. .PP The following bit mask values can be set additionally in .IR flags : .TP .B FAN_CLOEXEC This flag sets the close-on-exec flag .RB ( FD_CLOEXEC ) on the new file descriptor. See the description of the .B O_CLOEXEC flag in .BR open (2). .TP .B FAN_NONBLOCK This flag enables the nonblocking flag .RB ( O_NONBLOCK ) for the file descriptor. Reading from the file descriptor will not block. Instead, if no data is available, .BR read (2) will fail with the error .BR EAGAIN . .TP .B FAN_UNLIMITED_QUEUE This flag removes the limit of 16384 events for the event queue. It requires the .B CAP_SYS_ADMIN capability. .TP .B FAN_UNLIMITED_MARKS This flag removes the limit of 8192 marks. It requires the .B CAP_SYS_ADMIN capability. .PP The argument .I event_f_flags defines the file flags with which file descriptors for fanotify events shall be created. For explanations of possible values, see the argument .I flags of the .BR open (2) system call. Useful values are: .TP .B O_RDONLY This value allows only read access. .TP .B O_WRONLY This value allows only write access. .TP .B O_RDWR This value allows read and write access. .TP .B O_CLOEXEC This flag enables the close-on-exec flag for the file descriptor. .TP .B O_LARGEFILE This flag enables support for files exceeding 2 GB. Failing to set this flag will result in an .B EOVERFLOW error when trying to open a large file which is monitored by an fanotify group on a 32-bit system. .SH RETURN VALUE On success, .BR fanotify_init () returns a new file descriptor. On error, \-1 is returned, and .I errno is set to indicate the error. .SH ERRORS .TP .B EINVAL An invalid value was passed in .IR flags . .B FAN_ALL_INIT_FLAGS defines all allowable bits. .TP .B EMFILE The number of fanotify groups of the user exceeds 128. .TP .B ENOMEM The allocation of memory for the notification group failed. .TP .B ENOSYS This kernel does not implement .BR fanotify_init (). To make the fanotify API available, .B CONFIG_FANOTIFY has to be enabled in the Linux configuration. .TP .B EPERM The operation is not permitted because the caller lacks the .B CAP_SYS_ADMIN capability. .SH VERSIONS .BR fanotify_init () was introduced in version 2.6.36 of the Linux kernel and enabled in version 2.6.37. .SH "CONFORMING TO" This system call is Linux-specific. .SH BUGS As of Linux 3.15, the following bug exists: .IP * 3 .\" FIXME: Patch proposed. The .I event_f_flags argument is not checked for invalid flags. Flags that are intended only for internal use, such as .BR FMODE_EXEC , can be set, and will consequently be set for the file descriptors returned when reading from the fanotify file descriptor. .SH "SEE ALSO" .BR fanotify_mark (2), .BR fanotify (7)