shmget (2)
Leading comments
Copyright (c) 1995 David Hovemeyer <daveho@infocom.com> All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the d...
NAME
shmget - obtain a shared memory identifierLIBRARY
Lb libcSYNOPSIS
In sys/types.h In sys/ipc.h In sys/shm.h Ft int Fn shmget key_t key size_t size int flagDESCRIPTION
Based on the values of Fa key and Fa flag , Fn shmget returns the identifier of a newly created or previously existing shared memory segment. The key is analogous to a filename: it provides a handle that names an IPC object. There are three ways to specify a key:- IPC_PRIVATE may be specified, in which case a new IPC object will be created.
- An integer constant may be specified. If no IPC object corresponding to Fa key is specified and the IPC_CREAT bit is set in Fa flag , a new one will be created.
- The ftok(3) may be used to generate a key from a pathname.
The mode of a newly created IPC object is determined by OR 'ing the following constants into the Fa flag argument:
- S_IRUSR
- Read access for owner.
- S_IWUSR
- Write access for owner.
- S_IRGRP
- Read access for group.
- S_IWGRP
- Write access for group.
- S_IROTH
- Read access for other.
- S_IWOTH
- Write access for other.
When creating a new shared memory segment, Fa size indicates the desired size of the new segment in bytes. The size of the segment may be rounded up to a multiple convenient to the kernel (i.e., the page size).
RETURN VALUES
Upon successful completion, Fn shmget returns the positive integer identifier of a shared memory segment. Otherwise, -1 is returned and errno set to indicate the error.ERRORS
The Fn shmget system call will fail if:- Bq Er EINVAL
- Size specified is greater than the size of the previously existing segment. Size specified is less than the system imposed minimum, or greater than the system imposed maximum.
- Bq Er ENOENT
- No shared memory segment was found matching Fa key , and IPC_CREAT was not specified.
- Bq Er ENOSPC
- The kernel was unable to allocate enough memory to satisfy the request.
- Bq Er EEXIST
- IPC_CREAT and IPC_EXCL were specified, and a shared memory segment corresponding to Fa key already exists.