notifyd

notifyd

---

 notifyd [-no_restart] [-no_startup] [-shm_pages   integer   ] 

Description

The notification server for the API described in the notify(3) manpage . (Use man 3 notify to display this page.) Using the API, processes may post notifications associated with arbitrary names , and other processes can register to be informed of such notification events. (A name should follow the convention used for Java classes: the reversed DNS domain name associated with the responsible organization, followed by one or more segments; for example, com.apple.system.timezone .) notifyd sets up the shared memory used for the notify_register_check call, and directly answers notify_check requests for other notification methods (signal, Mach port, and file descriptor).

notifyd also reads a configuration file, /etc/notify.conf . Each line begins with one of two keywords: reserve or monitor . The reserve keyword lays out access restrictions for portions of the namespace. The arguments are a name, a user and a group that "owns" the name, and a set of read /write permissions for the user , the group, and others, similar to those applied to files. For example, the following line:

 reserve com.apple.system. 0 0 rwr-r- 

states that any names starting with com.apple.system. are owned by UID 0 ( root ) and GID 0 ( wheel ), and that anyone can receive notifications for these names, but only root (the owner) can post notifications.

The monitor keyword takes a name and a filename as arguments. When the specified file is changed, a notification is posted for the name. For example, the following line from the stock /etc/notify.conf can be used by processes wishing to keep track of time zone changes:

 monitor com.apple.system.timezone /etc/localtime 

Another use would be to monitor changes to a daemon's configuration file. When the file is changed, the daemon or another process could receive notification and cause the daemon to automatically reread the configuration.

notifyd is started as a bootstrap daemon, from /etc/mach_init.d/notifyd. plist ( processed by register_mach_bootstrap_servers ). It responds to HUP or TERM signals by restarting (unless the - no_restart flag was used), thus rereading /etc/notify.conf . Before notifyd exits, it sends notifications for all registered names; after it restarts, processes registered for notifications must register again, as their tokens become invalid.

Options/Usage

-no_restart

Disables automatic restart. Normally, if notifyd is killed , it's restarted within a few seconds.

-no_startup

Apparently prevents notifyd from issuing notifications, while using all available CPU time. The purpose of this option is unknown.

-shm_pages

Specifies the number of pages (i.e., units of 4096 bytes) to reserve for shared memory (although it appears to use about twice that). Defaults to 1 .

Location

/usr/sbin