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INOTIFY(7)                Linux Programmer's Manual               INOTIFY(7)

NAME top

       inotify - monitoring filesystem events

DESCRIPTION top

       The inotify API provides a mechanism for monitoring filesystem       events.  Inotify can be used to monitor individual files, or to       monitor directories.  When a directory is monitored, inotify will       return events for the directory itself, and for files inside the       directory.       The following system calls are used with this API:       *  inotify_init(2) creates an inotify instance and returns a file          descriptor referring to the inotify instance.  The more recent          inotify_init1(2) is like inotify_init(2), but has a flags argument          that provides access to some extra functionality.       *  inotify_add_watch(2) manipulates the "watch list" associated with          an inotify instance.  Each item ("watch") in the watch list          specifies the pathname of a file or directory, along with some set          of events that the kernel should monitor for the file referred to          by that pathname.  inotify_add_watch(2) either creates a new watch          item, or modifies an existing watch.  Each watch has a unique          "watch descriptor", an integer returned by inotify_add_watch(2)          when the watch is created.       *  When events occur for monitored files and directories, those          events are made available to the application as structured data          that can be read from the inotify file descriptor using read(2)          (see below).       *  inotify_rm_watch(2) removes an item from an inotify watch list.       *  When all file descriptors referring to an inotify instance have          been closed (using close(2)), the underlying object and its          resources are freed for reuse by the kernel; all associated          watches are automatically freed.          With careful programming, an application can use inotify to          efficiently monitor and cache the state of a set of filesystem          objects.  However, robust applications should allow for the fact          that bugs in the monitoring logic or races of the kind described          below may leave the cache inconsistent with the filesystem state.          It is probably wise to to do some consistency checking, and          rebuild the cache when inconsistencies are detected.   Reading events from an inotify file descriptor       To determine what events have occurred, an application read(2)s from       the inotify file descriptor.  If no events have so far occurred,       then, assuming a blocking file descriptor, read(2) will block until       at least one event occurs (unless interrupted by a signal, in which       case the call fails with the error EINTR; see signal(7)).       Each successful read(2) returns a buffer containing one or more of       the following structures:           struct inotify_event {               int      wd;       /* Watch descriptor */               uint32_t mask;     /* Mask of events */               uint32_t cookie;   /* Unique cookie associating related                                     events (for rename(2)) */               uint32_t len;      /* Size of name field */               char     name[];   /* Optional null-terminated name */           };       wd identifies the watch for which this event occurs.  It is one of       the watch descriptors returned by a previous call to       inotify_add_watch(2).       mask contains bits that describe the event that occurred (see below).       cookie is a unique integer that connects related events.  Currently       this is used only for rename events, and allows the resulting pair of       IN_MOVED_FROM and IN_MOVED_TO events to be connected by the       application.  For all other event types, cookie is set to 0.       The name field is present only when an event is returned for a file       inside a watched directory; it identifies the file pathname relative       to the watched directory.  This pathname is null-terminated, and may       include further null bytes ('\0') to align subsequent reads to a       suitable address boundary.       The len field counts all of the bytes in name, including the null       bytes; the length of each inotify_event structure is thus       sizeof(struct inotify_event)+len.       The behavior when the buffer given to read(2) is too small to return       information about the next event depends on the kernel version: in       kernels before 2.6.21, read(2) returns 0; since kernel 2.6.21,       read(2) fails with the error EINVAL.  Specifying a buffer of size           sizeof(struct inotify_event) + NAME_MAX + 1       will be sufficient to read at least one event.   inotify events       The inotify_add_watch(2) mask argument and the mask field of the       inotify_event structure returned when read(2)ing an inotify file       descriptor are both bit masks identifying inotify events.  The       following bits can be specified in mask when calling       inotify_add_watch(2) and may be returned in the mask field returned       by read(2):           IN_ACCESS (*)                  File was accessed (e.g., read(2), execve(2)).           IN_ATTRIB (*)                  Metadata changed—for example, permissions (e.g.,                  chmod(2)), timestamps (e.g., utimensat(2)), extended                  attributes (setxattr(2)), link count (since Linux 2.6.25;                  e.g., for the target of link(2) and for unlink(2)), and                  user/group ID (e.g., chown(2)).           IN_CLOSE_WRITE (*)                  File opened for writing was closed.           IN_CLOSE_NOWRITE (*)                  File not opened for writing was closed.           IN_CREATE (*)                  File/directory created in watched directory (e.g., open(2)                  O_CREAT, mkdir(2), link(2), symlink(2), bind(2) on a UNIX                  domain socket).           IN_DELETE (*)                  File/directory deleted from watched directory.           IN_DELETE_SELF                  Watched file/directory was itself deleted.  (This event                  also occurs if an object is moved to another filesystem,                  since mv(1) in effect copies the file to the other                  filesystem and then deletes it from the original                  filesystem.)  In addition, an IN_IGNORED event will                  subsequently be generated for the watch descriptor.           IN_MODIFY (*)                  File was modified (e.g., write(2), truncate(2)).           IN_MOVE_SELF                  Watched file/directory was itself moved.           IN_MOVED_FROM (*)                  Generated for the directory containing the old filename                  when a file is renamed.           IN_MOVED_TO (*)                  Generated for the directory containing the new filename                  when a file is renamed.           IN_OPEN (*)                  File was opened.       When monitoring a directory, the events marked with an asterisk (*)       above can occur for files in the directory, in which case the name       field in the returned inotify_event structure identifies the name of       the file within the directory.       The IN_ALL_EVENTS macro is defined as a bit mask of all of the above       events.  This macro can be used as the mask argument when calling       inotify_add_watch(2).       Two additional convenience macros are defined:           IN_MOVE                  Equates to IN_MOVED_FROM | IN_MOVED_TO.           IN_CLOSE                  Equates to IN_CLOSE_WRITE | IN_CLOSE_NOWRITE.       The following further bits can be specified in mask when calling       inotify_add_watch(2):           IN_DONT_FOLLOW (since Linux 2.6.15)                  Don't dereference pathname if it is a symbolic link.           IN_EXCL_UNLINK (since Linux 2.6.36)                  By default, when watching events on the children of a                  directory, events are generated for children even after                  they have been unlinked from the directory.  This can                  result in large numbers of uninteresting events for some                  applications (e.g., if watching /tmp, in which many                  applications create temporary files whose names are                  immediately unlinked).  Specifying IN_EXCL_UNLINK changes                  the default behavior, so that events are not generated for                  children after they have been unlinked from the watched                  directory.           IN_MASK_ADD                  Add (OR) events to watch mask for this pathname if it                  already exists (instead of replacing mask).           IN_ONESHOT                  Monitor pathname for one event, then remove from watch                  list.           IN_ONLYDIR (since Linux 2.6.15)                  Only watch pathname if it is a directory.       The following bits may be set in the mask field returned by read(2):           IN_IGNORED                  Watch was removed explicitly (inotify_rm_watch(2)) or                  automatically (file was deleted, or filesystem was                  unmounted).  See also BUGS.           IN_ISDIR                  Subject of this event is a directory.           IN_Q_OVERFLOW                  Event queue overflowed (wd is -1 for this event).           IN_UNMOUNT                  Filesystem containing watched object was unmounted.  In                  addition, an IN_IGNORED event will subsequently be                  generated for the watch descriptor.   Examples       Suppose an application is watching the directory dir and the file       dir/myfile for all events.  The examples below show some events that       will be generated for these two objects.           fd = open("dir/myfile", O_RDWR);                  Generates IN_OPEN events for both dir and dir/myfile.           read(fd, buf, count);                  Generates IN_ACCESS events for both dir and dir/myfile.           write(fd, buf, count);                  Generates IN_MODIFY events for both dir and dir/myfile.           fchmod(fd, mode);                  Generates IN_ATTRIB events for both dir and dir/myfile.           close(fd);                  Generates IN_CLOSE_WRITE events for both dir and                  dir/myfile.       Suppose an application is watching the directories dir1 and dir2, and       the file dir1/myfile.  The following examples show some events that       may be generated.           link("dir1/myfile", "dir2/new");                  Generates an IN_ATTRIB event for myfile and an IN_CREATE                  event for dir2.           rename("dir1/myfile", "dir2/myfile");                  Generates an IN_MOVED_FROM event for dir1, an IN_MOVED_TO                  event for dir2, and an IN_MOVE_SELF event for myfile.  The                  IN_MOVED_FROM and IN_MOVED_TO events will have the same                  cookie value.       Suppose that dir1/xx and dir2/yy are (the only) links to the same       file, and an application is watching dir1, dir2, dir1/xx, and       dir2/yy.  Executing the following calls in the order given below will       generate the following events:           unlink("dir2/yy");                  Generates an IN_ATTRIB event for xx (because its link                  count changes) and an IN_DELETE event for dir2.           unlink("dir1/xx");                  Generates IN_ATTRIB, IN_DELETE_SELF, and IN_IGNORED events                  for xx, and an IN_DELETE event for dir1.       Suppose an application is watching the directory dir and (the empty)       directory dir/subdir.  The following examples show some events that       may be generated.           mkdir("dir/new", mode);                  Generates an IN_CREATE | IN_ISDIR event for dir.           rmdir("dir/subdir");                  Generates IN_DELETE_SELF and IN_IGNORED events for subdir,                  and an IN_DELETE | IN_ISDIR event for dir.   /proc interfaces       The following interfaces can be used to limit the amount of kernel       memory consumed by inotify:       /proc/sys/fs/inotify/max_queued_events              The value in this file is used when an application calls              inotify_init(2) to set an upper limit on the number of events              that can be queued to the corresponding inotify instance.              Events in excess of this limit are dropped, but an              IN_Q_OVERFLOW event is always generated.       /proc/sys/fs/inotify/max_user_instances              This specifies an upper limit on the number of inotify              instances that can be created per real user ID.       /proc/sys/fs/inotify/max_user_watches              This specifies an upper limit on the number of watches that              can be created per real user ID.

VERSIONS top

       Inotify was merged into the 2.6.13 Linux kernel.  The required       library interfaces were added to glibc in version 2.4.       (IN_DONT_FOLLOW, IN_MASK_ADD, and IN_ONLYDIR were added in glibc       version 2.5.)

CONFORMING TO top

       The inotify API is Linux-specific.

NOTES top

Inotify file descriptors can be monitored using select(2), poll(2), and epoll(7). When an event is available, the file descriptor indicates as readable. Since Linux 2.6.25, signal-driven I/O notification is available for inotify file descriptors; see the discussion of F_SETFL (for setting the O_ASYNC flag), F_SETOWN, and F_SETSIG in fcntl(2). The siginfo_t structure (described in sigaction(2)) that is passed to the signal handler has the following fields set: si_fd is set to the inotify file descriptor number; si_signo is set to the signal number; si_code is set to POLL_IN; and POLLIN is set in si_band. If successive output inotify events produced on the inotify file descriptor are identical (same wd, mask, cookie, and name), then they are coalesced into a single event if the older event has not yet been read (but see BUGS). This reduces the amount of kernel memory required for the event queue, but also means that an application can't use inotify to reliably count file events. The events returned by reading from an inotify file descriptor form an ordered queue. Thus, for example, it is guaranteed that when renaming from one directory to another, events will be produced in the correct order on the inotify file descriptor. The FIONREAD ioctl(2) returns the number of bytes available to read from an inotify file descriptor. Limitations and caveats The inotify API provides no information about the user or process that triggered the inotify event. In particular, there is no easy way for a process that is monitoring events via inotify to distinguish events that it triggers itself from those that are triggered by other processes. Inotify reports only events that a user-space program triggers through the filesystem API. As a result, it does not catch remote events that occur on network filesystems. (Applications must fall back to polling the filesystem to catch such events.) Furthermore, various pseudo-filesystems such as /proc, /sys, and /dev/pts are not monitorable with inotify. The inotify API does not report file accesses and modifications that may occur because of mmap(2), msync(2), and munmap(2). The inotify API identifies affected files by filename. However, by the time an application processes an inotify event, the filename may already have been deleted or renamed. The inotify API identifies events via watch descriptors. It is the application's responsibility to cache a mapping (if one is needed) between watch descriptors and pathnames. Be aware that directory renamings may affect multiple cached pathnames. Inotify monitoring of directories is not recursive: to monitor subdirectories under a directory, additional watches must be created. This can take a significant amount time for large directory trees. If monitoring an entire directory subtree, and a new subdirectory is created in that tree or an existing directory is renamed into that tree, be aware that by the time you create a watch for the new subdirectory, new files (and subdirectories) may already exist inside the subdirectory. Therefore, you may want to scan the contents of the subdirectory immediately after adding the watch (and, if desired, recursively add watches for any subdirectories that it contains). Note that the event queue can overflow. In this case, events are lost. Robust applications should handle the possibility of lost events gracefully. For example, it may be necessary to rebuild part or all of the application cache. (One simple, but possibly expensive, approach is to close the inotify file descriptor, empty the cache, create a new inotify file descriptor, and then re-create watches and cache entries for the objects to be monitored.) Dealing with rename() events As noted above, the IN_MOVED_FROM and IN_MOVED_TO event pair that is generated by rename(2) can be matched up via their shared cookie value. However, the task of matching has some challenges. These two events are usually consecutive in the event stream available when reading from the inotify file descriptor. However, this is not guaranteed. If multiple processes are triggering events for monitored objects, then (on rare occasions) an arbitrary number of other events may appear between the IN_MOVED_FROM and IN_MOVED_TO events. Matching up the IN_MOVED_FROM and IN_MOVED_TO event pair generated by rename(2) is thus inherently racy. (Don't forget that if an object is renamed outside of a monitored directory, there may not even be an IN_MOVED_TO event.) Heuristic approaches (e.g., assume the events are always consecutive) can be used to ensure a match in most cases, but will inevitably miss some cases, causing the application to perceive the IN_MOVED_FROM and IN_MOVED_TO events as being unrelated. If watch descriptors are destroyed and re-created as a result, then those watch descriptors will be inconsistent with the watch descriptors in any pending events. (Re-creating the inotify file descriptor and rebuilding the cache may be useful to deal with this scenario.) Applications should also allow for the possibility that the IN_MOVED_FROM event was the last event that could fit in the buffer returned by the current call to read(2), and the accompanying IN_MOVED_TO event might be fetched only on the next read(2).

BUGS top

       In kernels before 2.6.16, the IN_ONESHOT mask flag does not work.       As originally designed and implemented, the IN_ONESHOT flag did not       cause an IN_IGNORED event to be generated when the watch was dropped       after one event.  However, as an unintended effect of other changes,       since Linux 2.6.36, an IN_IGNORED event is generated in this case.       Before kernel 2.6.25, the kernel code that was intended to coalesce       successive identical events (i.e., the two most recent events could       potentially be coalesced if the older had not yet been read) instead       checked if the most recent event could be coalesced with the oldest       unread event.

EXAMPLE top

       The following program demonstrates the usage of the inotify API.  It       marks the directories passed as a command-line arguments and waits       for events of type IN_OPEN, IN_CLOSE_NOWRITE and IN_CLOSE_WRITE.       The following output was recorded while editing the file       /home/user/temp/foo and listing directory /tmp.  Before the file and       the directory were opened, IN_OPEN events occurred.  After the file       was closed, an IN_CLOSE_WRITE event occurred.  After the directory       was closed, an IN_CLOSE_NOWRITE event occurred.  Execution of the       program ended when the user pressed the ENTER key.   Example output           $ ./a.out /tmp /home/user/temp           Press enter key to terminate.           Listening for events.           IN_OPEN: /home/user/temp/foo [file]           IN_CLOSE_WRITE: /home/user/temp/foo [file]           IN_OPEN: /tmp/ [directory]           IN_CLOSE_NOWRITE: /tmp/ [directory]           Listening for events stopped.   Program source       #include <errno.h>       #include <poll.h>       #include <stdio.h>       #include <stdlib.h>       #include <sys/inotify.h>       #include <unistd.h>       /* Read all available inotify events from the file descriptor 'fd'.          wd is the table of watch descriptors for the directories in argv.          argc is the length of wd and argv.          argv is the list of watched directories.          Entry 0 of wd and argv is unused. */       static void       handle_events(int fd, int *wd, int argc, char* argv[])       {           /* Some systems cannot read integer variables if they are not              properly aligned. On other systems, incorrect alignment may              decrease performance. Hence, the buffer used for reading from              the inotify file descriptor should have the same alignment as              struct inotify_event. */           char buf[4096]               __attribute__ ((aligned(__alignof__(struct inotify_event))));           const struct inotify_event *event;           int i;           ssize_t len;           char *ptr;           /* Loop while events can be read from inotify file descriptor. */           for (;;) {               /* Read some events. */               len = read(fd, buf, sizeof buf);               if (len == -1 && errno != EAGAIN) {                   perror("read");                   exit(EXIT_FAILURE);               }               /* If the nonblocking read() found no events to read, then                  it returns -1 with errno set to EAGAIN. In that case,                  we exit the loop. */               if (len <= 0)                   break;               /* Loop over all events in the buffer */               for (ptr = buf; ptr < buf + len;                       ptr += sizeof(struct inotify_event) + event->len) {                   event = (const struct inotify_event *) ptr;                   /* Print event type */                   if (event->mask & IN_OPEN)                       printf("IN_OPEN: ");                   if (event->mask & IN_CLOSE_NOWRITE)                       printf("IN_CLOSE_NOWRITE: ");                   if (event->mask & IN_CLOSE_WRITE)                       printf("IN_CLOSE_WRITE: ");                   /* Print the name of the watched directory */                   for (i = 1; i < argc; ++i) {                       if (wd[i] == event->wd) {                           printf("%s/", argv[i]);                           break;                       }                   }                   /* Print the name of the file */                   if (event->len)                       printf("%s", event->name);                   /* Print type of filesystem object */                   if (event->mask & IN_ISDIR)                       printf(" [directory]\n");                   else                       printf(" [file]\n");               }           }       }       int       main(int argc, char* argv[])       {           char buf;           int fd, i, poll_num;           int *wd;           nfds_t nfds;           struct pollfd fds[2];           if (argc < 2) {               printf("Usage: %s PATH [PATH ...]\n", argv[0]);               exit(EXIT_FAILURE);           }           printf("Press ENTER key to terminate.\n");           /* Create the file descriptor for accessing the inotify API */           fd = inotify_init1(IN_NONBLOCK);           if (fd == -1) {               perror("inotify_init1");               exit(EXIT_FAILURE);           }           /* Allocate memory for watch descriptors */           wd = calloc(argc, sizeof(int));           if (wd == NULL) {               perror("calloc");               exit(EXIT_FAILURE);           }           /* Mark directories for events              - file was opened              - file was closed */           for (i = 1; i < argc; i++) {               wd[i] = inotify_add_watch(fd, argv[i],                                         IN_OPEN | IN_CLOSE);               if (wd[i] == -1) {                   fprintf(stderr, "Cannot watch '%s'\n", argv[i]);                   perror("inotify_add_watch");                   exit(EXIT_FAILURE);               }           }           /* Prepare for polling */           nfds = 2;           /* Console input */           fds[0].fd = STDIN_FILENO;           fds[0].events = POLLIN;           /* Inotify input */           fds[1].fd = fd;           fds[1].events = POLLIN;           /* Wait for events and/or terminal input */           printf("Listening for events.\n");           while (1) {               poll_num = poll(fds, nfds, -1);               if (poll_num == -1) {                   if (errno == EINTR)                       continue;                   perror("poll");                   exit(EXIT_FAILURE);               }               if (poll_num > 0) {                   if (fds[0].revents & POLLIN) {                       /* Console input is available. Empty stdin and quit */                       while (read(STDIN_FILENO, &buf, 1) > 0 && buf != '\n')                           continue;                       break;                   }                   if (fds[1].revents & POLLIN) {                       /* Inotify events are available */                       handle_events(fd, wd, argc, argv);                   }               }           }           printf("Listening for events stopped.\n");           /* Close inotify file descriptor */           close(fd);           free(wd);           exit(EXIT_SUCCESS);       }

COLOPHON top

       This page is part of release 3.69 of the Linux man-pages project.  A       description of the project, information about reporting bugs, and the       latest version of this page, can be found at       http://www.kernel.org/doc/man-pages/.Linux                            2014-05-23                       INOTIFY(7)

INOTIFY_ADD_WATCH(2)      Linux Programmer's Manual     INOTIFY_ADD_WATCH(2)

NAME top

       inotify_add_watch - add a watch to an initialized inotify instance

SYNOPSIS top

       #include <sys/inotify.h>       int inotify_add_watch(int fd, const char *pathname, uint32_t mask);

DESCRIPTION top

       inotify_add_watch() adds a new watch, or modifies an existing watch,       for the file whose location is specified in pathname; the caller must       have read permission for this file.  The fd argument is a file       descriptor referring to the inotify instance whose watch list is to       be modified.  The events to be monitored for pathname are specified       in the mask bit-mask argument.  See inotify(7) for a description of       the bits that can be set in mask.       A successful call to inotify_add_watch() returns the unique watch       descriptor associated with pathname for this inotify instance.  If       pathname was not previously being watched by this inotify instance,       then the watch descriptor is newly allocated.  If pathname was       already being watched, then the descriptor for the existing watch is       returned.       The watch descriptor is returned by later read(2)s from the inotify       file descriptor.  These reads fetch inotify_event structures (see       inotify(7)) indicating filesystem events; the watch descriptor inside       this structure identifies the object for which the event occurred.

RETURN VALUE top

       On success, inotify_add_watch() returns a nonnegative watch       descriptor.  On error, -1 is returned and errno is set appropriately.

ERRORS top

       EACCES Read access to the given file is not permitted.       EBADF  The given file descriptor is not valid.       EFAULT pathname points outside of the process's accessible address              space.       EINVAL The given event mask contains no valid events; or fd is not an              inotify file descriptor.       ENAMETOOLONG              pathname is too long.       ENOENT A directory component in pathname does not exist or is a              dangling symbolic link.       ENOMEM Insufficient kernel memory was available.       ENOSPC The user limit on the total number of inotify watches was              reached or the kernel failed to allocate a needed resource.

VERSIONS top

       Inotify was merged into the 2.6.13 Linux kernel.

CONFORMING TO top

       This system call is Linux-specific.

COLOPHON top

       This page is part of release 3.69 of the Linux man-pages project.  A       description of the project, information about reporting bugs, and the       latest version of this page, can be found at       http://www.kernel.org/doc/man-pages/.Linux                            2014-03-28             INOTIFY_ADD_WATCH(2)

INOTIFY_INIT(2)           Linux Programmer's Manual          INOTIFY_INIT(2)

NAME top

       inotify_init, inotify_init1 - initialize an inotify instance

SYNOPSIS top

       #include <sys/inotify.h>       int inotify_init(void);       int inotify_init1(int flags);

DESCRIPTION top

       For an overview of the inotify API, see inotify(7).       inotify_init() initializes a new inotify instance and returns a file       descriptor associated with a new inotify event queue.       If flags is 0, then inotify_init1() is the same as inotify_init().       The following values can be bitwise ORed in flags to obtain different       behavior:       IN_NONBLOCK Set the O_NONBLOCK file status flag on the new open file                   description.  Using this flag saves extra calls to                   fcntl(2) to achieve the same result.       IN_CLOEXEC  Set the close-on-exec (FD_CLOEXEC) flag on the new file                   descriptor.  See the description of the O_CLOEXEC flag in                   open(2) for reasons why this may be useful.

RETURN VALUE top

       On success, these system calls return a new file descriptor.  On       error, -1 is returned, and errno is set to indicate the error.

ERRORS top

       EINVAL (inotify_init1()) An invalid value was specified in flags.       EMFILE The user limit on the total number of inotify instances has              been reached.       ENFILE The system limit on the total number of file descriptors has              been reached.       ENOMEM Insufficient kernel memory is available.

VERSIONS top

       inotify_init() first appeared in Linux 2.6.13; library support was       added to glibc in version 2.4.  inotify_init1() was added in Linux       2.6.27; library support was added to glibc in version 2.9.

CONFORMING TO top

       These system calls are Linux-specific.

COLOPHON top

       This page is part of release 3.69 of the Linux man-pages project.  A       description of the project, information about reporting bugs, and the       latest version of this page, can be found at       http://www.kernel.org/doc/man-pages/.Linux                            2014-03-28                  INOTIFY_INIT(2)

INOTIFY_RM_WATCH(2)       Linux Programmer's Manual      INOTIFY_RM_WATCH(2)

NAME top

       inotify_rm_watch - remove an existing watch from an inotify instance

SYNOPSIS top

       #include <sys/inotify.h>       int inotify_rm_watch(int fd, int wd);

DESCRIPTION top

       inotify_rm_watch() removes the watch associated with the watch       descriptor wd from the inotify instance associated with the file       descriptor fd.       Removing a watch causes an IN_IGNORED event to be generated for this       watch descriptor.  (See inotify(7).)

RETURN VALUE top

       On success, inotify_rm_watch() returns zero.  On error, -1 is       returned and errno is set to indicate the cause of the error.

ERRORS top

       EBADF  fd is not a valid file descriptor.       EINVAL The watch descriptor wd is not valid; or fd is not an inotify              file descriptor.

VERSIONS top

       Inotify was merged into the 2.6.13 Linux kernel.

CONFORMING TO top

       This system call is Linux-specific.

COLOPHON top

       This page is part of release 3.69 of the Linux man-pages project.  A       description of the project, information about reporting bugs, and the       latest version of this page, can be found at       http://www.kernel.org/doc/man-pages/.Linux                            2010-10-15              INOTIFY_RM_WATCH(2)

英文：http://linux.die.net/man/2/inotify_add_watch

notify是什么？用它能干些什么？

通俗点说它是一个内核用于通知用户空间程序文件系统变化的系统，并且它是powerful yet simple的。

inotify的用户接口原型主要有以下3个：
#include <sys/inotify.h>

初始化：int inotify_init(void);

int fd = inotify_init();
添加监视对象：int inotify_add_watch(int fd, const char *path, uint32_t mask);

int wd = inotify_add_watch(fd,path,mask);

fd是inotify_init()的返回值。

const char *path是要监控的文件(目录)的路径。

uint32_t mask是:

如何使用inotify_init，inotify_add_watch,inotify_rm_watch编写程序 - xychenbaihu@yeah - 无影的博客

还有非常多的事件可以使用。使用man inotify可以查看所有可以监听的事件。

mask是上面这些事件的或。例如IN_ACCESS|IN_MODIFY。

返回值:wd表示对那个文件进行监控。
删除监视对象：int inotify_rm_watch(int fd, uint32_t wd);

参数fd是inotify_init的返回值。

wd是inotify_add_watch的返回值。

inotify_rm_watch删除对wd所指向的文件的监控。

读取监控发生的事件:

size_t len = read(fd, buf, BUF_LEN);

读取事件数据，buf应是一个指向inotify_event结构数组的指针。不过要注意的是inotify_event的name成员长度是可变的，这个问题后面再解释。

注意:其中buf是一个指向struct inotify_event数组的指针。

由于struct inotify_event长度是可变的，因此在读取inotify_event数组内容的时候需要动态计算一下时间数据的偏移量。index += sizeof(struct inotify_event)+event->len，len即name成员的长度。

其实还是没有讲的很清楚，不过看了下面的例子，一定非常清楚:

#include <stdio.h>
#include <unistd.h>
#include <sys/select.h>
#include <errno.h>
#include <sys/inotify.h>

static void   _inotify_event_handler(struct inotify_event *event)      //从buf中取出一个事件。
{
         printf("event->mask: 0x%08x\n", event->mask);
         printf("event->name: %s\n", event->name);
}

int  main(int argc, char **argv)
{
  if (argc != 2) {
    printf("Usage: %s <file/dir>\n", argv[0]);
    return -1;
  }

  unsigned char buf[1024] = {0};
  struct inotify_event *event = NULL;

  int fd = inotify_init();                 //初始化
  int wd = inotify_add_watch(fd, argv[1], IN_ALL_EVENTS);                  //监控指定文件的ALL_EVENTS。

  for (;;)

{
       fd_set fds;
       FD_ZERO(&fds);
       FD_SET(fd, &fds);

if (select(fd + 1, &fds, NULL, NULL, NULL) > 0) //监控fd的事件。当有事件发生时，返回值>0

       {
           int len, index = 0;
           while (((len = read(fd, &buf, sizeof(buf))) < 0) && (errno == EINTR));       //没有读取到事件。
           while (index < len)

           {
                  event = (struct inotify_event *)(buf + index);
                  _inotify_event_handler(event);                                             //获取事件。
                  index += sizeof(struct inotify_event) + event->len;             //移动index指向下一个事件。
           }
      }
  }

  inotify_rm_watch(fd, wd);              //删除对指定文件的监控。

  return 0;
}

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linux文件监控（网站拷贝英文仅转存浏览）

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