osf1 man page for shmat

shmat(2)							System Calls Manual							  shmat(2)

NAME
       shmat - Attaches a shared memory region

SYNOPSIS
       #include <sys/shm.h>

       void *shmat(
	       int shmid,
	       const void *shmaddr,
	       int shmflg);

       If  programs  are  being developed for multiple platforms, application developers may want to specify #include statements for <sys/types.h>
       and <sys/ipc.h> before the one for <sys/shm.h>.	The additional #include statements are not required on Tru64 UNIX systems  or  by  ISO	or
       X/Open standards, but may be required on other vendors' systems that conform to these standards.

STANDARDS
       Interfaces documented on this reference page conform to industry standards as follows:

       shmat(): XSH4.2

       Refer to the standards(5) reference page for more information about industry standards and associated tags.

PARAMETERS
       Specifies  the  ID  for	the  shared  memory  region.  The ID is typically returned by a previous shmget() function.  Specifies the virtual
       address at which the process wants to attach the shared memory region.  The process can also specify 0 (zero) to have the kernel select	an
       appropriate  address.   Specifies  the attach flags.  Possible values are: If the addr parameter is not 0 (zero), the kernel rounds off the
       address, if necessary.  If the calling process has read permission, the kernel attaches the region for reading only.

DESCRIPTION
       The shmat() function attaches the shared memory region identified by the shmid parameter to  the  virtual  address  space  of  the  calling
       process.   For  the  addr parameter, the process can specify either an explicit address or 0 (zero), to have the kernel select the address.
       If an explicit address is used, the process can set the SHM_RND flag to have the kernel round off the address, if necessary.

       Access to the shared memory region is determined by the operation permissions in the shm_perm.mode member in the region's  shmid_ds  struc-
       ture.  The low-order bits in shm_perm.mode are interpreted as follows:

       Read by user Write by user Read by group Write by group Read by others Write by others

       The  calling  process  is granted read and write permissions on the attached region if at least one of the following is true: The effective
       user ID of the process is superuser.  The effective user ID of the process is equal to shm_perm.cuid  or  shm_perm.uid  and  bit  0600	in
       shm_perm.mode  is  set.	 The effective group ID of the process is equal to shm_perm.cgid or shm_perm.gid and bit 0060  in shm_perm.mode is
       set.  Bit 0006  in shm_perm.mode is set.

       If the process has read permission, it can attach the region as read only by setting the SHM_RDONLY flag.

RETURN VALUES
       Upon successful completion, shmat() increments the value of shm_nattach in the data structure associated with the shared memory ID  of  the
       attached  shared  memory  segment  and returns the segment's start address.  If the shmat() function fails, the shared memory region is not
       attached, a value of -1 is returned, and errno is set to indicate the error.

ERRORS
       The shmat() function sets errno to the specified values for the following conditions: The calling process does  not  have  the  appropriate
       privilege.   The  shmid	parameter  does  not  specify  a valid shared memory region ID; the addr parameter is not 0 (zero) and not a valid
       address; or the addr parameter is not 0 (zero) and not a valid address, and SHM_RND is not set.

	      [Tru64 UNIX]  The shmid refers to a segmented shared memory region and the addr parameter is not aligned at SSM_SIZE (that is, (addr
	      %  SSM_SIZE) != 0).  An attempt to attach a shared memory region exceeded the maximum number of attached regions allowed for any one
	      process.	There was not enough data space available to attach the shared memory region.

	      [Tru64 UNIX]  The shmid refers to a segmented shared memory region whose size is not a multiple of SSM_SIZE  and	where  not  enough
	      data space is available for the rounded-up size.

RELATED INFORMATION
       Commands: sysconfig(8)

       Functions: exec(2), exit(2), fork(2), shmctl(2), shmdt(2), shmget(2)

       Data structures: shmid_ds(4)

       Standards: standards(5) delim off

																	  shmat(2)