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shm_attach — Attaches to a shared memory segment, creating it if necessary.


int shm_attach(key[, memsize][, permissions]);
int key: Unique key for the script's shared memory segment
int memsize (optional): Size of the shared memory segment, in bytes
int permissions (optional): Permissions for the shared memory segment


Shared memory ID on success; FALSE on failure


shm_attach() takes as its first argument a key that it uses to identify the shared memory segment to which you want to attach. Any process can use the same key to attach to this segment, which allows the sharing of the memory. It's a good idea to attempt to make this key unique to the scripts that will be using it, so as not to conflict with other programs that might use the same key.

If supplied, memsize denotes the number of bytes of storage that will be allocated for the shared memory segment. If not given, the value will be that given by the sysvshm.init_mem option in php.ini, or 100000 if sysvshm.init_mem isn't specified.

If supplied, permissions sets the permissions on the shared memory segment, which are expressed in the same fashion as UNIX filesystem permissions. This is usually given in octal, and defaults to 0666.


PHP 3 since 3.0.6, PHP 4


Example 1173. Attach to a shared memory segment

if (!$shm_id = @shm_attach(2000, 10000, 0600)) {
    echo "Could not attach to shared memory; reason: $php_errormsg.\n";

PHP Functions Essential Reference. Copyright © 2002 by New Riders Publishing (Authors: Zak Greant, Graeme Merrall, Torben Wilson, Brett Michlitsch). This material may be distributed only subject to the terms and conditions set forth in the Open Publication License, v1.0 or later (the latest version is presently available at The authors of this book have elected not to choose any options under the OPL. This online book was obtained from and is designed to provide information about the PHP programming language, focusing on PHP version 4.0.4 for the most part. The information is provided on an as-is basis, and no warranty or fitness is implied. All persons and entities shall have neither liability nor responsibility to any person or entity with respect to any loss or damage arising from the information contained in this book.

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