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inotify_add_watch() - Unix, Linux System Call

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inotify_add_watch - add a watch to an initialized inotify instance


#include <sys/inotify.h>

int inotify_add_watch(int fd, const char *pathname, uint32_t mask);


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 indicating file system events; the returned watch descriptor identifies the object for which the event occurred.


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


  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 legal events; or fd is not an inotify file descriptor.
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.


Inotify was merged into the 2.6.13 Linux kernel.


This system call is Linux specific.


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