# sysvipc(7) - man - phpman [SVIPC(7)](https://www.chedong.com/phpMan.php/man/SVIPC/7/markdown) Linux Programmer's Manual [SVIPC(7)](https://www.chedong.com/phpMan.php/man/SVIPC/7/markdown) ## NAME sysvipc - System V interprocess communication mechanisms ## DESCRIPTION System V IPC is the name given to three interprocess communication mechanisms that are widely available on UNIX systems: message queues, semaphore, and shared memory. ### Message queues System V message queues allow data to be exchanged in units called messages. Each messages can have an associated priority, POSIX message queues provide an alternative API for achiev‐ ing the same result; see **mq**___**[overview**(7)](https://www.chedong.com/phpMan.php/man/overview/7/markdown). The System V message queue API consists of the following system calls: [**msgget**(2)](https://www.chedong.com/phpMan.php/man/msgget/2/markdown) Create a new message queue or obtain the ID of an existing message queue. This call returns an identifier that is used in the remaining APIs. [**msgsnd**(2)](https://www.chedong.com/phpMan.php/man/msgsnd/2/markdown) Add a message to a queue. [**msgrcv**(2)](https://www.chedong.com/phpMan.php/man/msgrcv/2/markdown) Remove a message from a queue. [**msgctl**(2)](https://www.chedong.com/phpMan.php/man/msgctl/2/markdown) Perform various control operations on a queue, including deletion. ### Semaphore sets System V semaphores allow processes to synchronize their actions System V semaphores are al‐ located in groups called sets; each semaphore in a set is a counting semaphore. POSIX sema‐ phores provide an alternative API for achieving the same result; see **sem**___**[overview**(7)](https://www.chedong.com/phpMan.php/man/overview/7/markdown). The System V semaphore API consists of the following system calls: [**semget**(2)](https://www.chedong.com/phpMan.php/man/semget/2/markdown) Create a new set or obtain the ID of an existing set. This call returns an identifier that is used in the remaining APIs. [**semop**(2)](https://www.chedong.com/phpMan.php/man/semop/2/markdown) Perform operations on the semaphores in a set. [**semctl**(2)](https://www.chedong.com/phpMan.php/man/semctl/2/markdown) Perform various control operations on a set, including deletion. ### Shared memory segments System V shared memory allows processes to share a region a memory (a "segment"). POSIX shared memory is an alternative API for achieving the same result; see **shm**___**[overview**(7)](https://www.chedong.com/phpMan.php/man/overview/7/markdown). The System V shared memory API consists of the following system calls: [**shmget**(2)](https://www.chedong.com/phpMan.php/man/shmget/2/markdown) Create a new segment or obtain the ID of an existing segment. This call returns an identifier that is used in the remaining APIs. [**shmat**(2)](https://www.chedong.com/phpMan.php/man/shmat/2/markdown) Attach an existing shared memory object into the calling process's address space. [**shmdt**(2)](https://www.chedong.com/phpMan.php/man/shmdt/2/markdown) Detach a segment from the calling process's address space. [**shmctl**(2)](https://www.chedong.com/phpMan.php/man/shmctl/2/markdown) Perform various control operations on a segment, including deletion. ### IPC namespaces For a discussion of the interaction of System V IPC objects and IPC namespaces, see **ipc**___**name**‐‐ [**spaces**(7)](https://www.chedong.com/phpMan.php/man/spaces/7/markdown). ## SEE ALSO [**ipcmk**(1)](https://www.chedong.com/phpMan.php/man/ipcmk/1/markdown), [**ipcrm**(1)](https://www.chedong.com/phpMan.php/man/ipcrm/1/markdown), [**ipcs**(1)](https://www.chedong.com/phpMan.php/man/ipcs/1/markdown), [**lsipc**(1)](https://www.chedong.com/phpMan.php/man/lsipc/1/markdown), [**ipc**(2)](https://www.chedong.com/phpMan.php/man/ipc/2/markdown), [**msgctl**(2)](https://www.chedong.com/phpMan.php/man/msgctl/2/markdown), [**msgget**(2)](https://www.chedong.com/phpMan.php/man/msgget/2/markdown), [**msgrcv**(2)](https://www.chedong.com/phpMan.php/man/msgrcv/2/markdown), [**msgsnd**(2)](https://www.chedong.com/phpMan.php/man/msgsnd/2/markdown), [**semctl**(2)](https://www.chedong.com/phpMan.php/man/semctl/2/markdown), [**semget**(2)](https://www.chedong.com/phpMan.php/man/semget/2/markdown), [**semop**(2)](https://www.chedong.com/phpMan.php/man/semop/2/markdown), [**shmat**(2)](https://www.chedong.com/phpMan.php/man/shmat/2/markdown), [**shmctl**(2)](https://www.chedong.com/phpMan.php/man/shmctl/2/markdown), [**shmdt**(2)](https://www.chedong.com/phpMan.php/man/shmdt/2/markdown), [**shmget**(2)](https://www.chedong.com/phpMan.php/man/shmget/2/markdown), [**ftok**(3)](https://www.chedong.com/phpMan.php/man/ftok/3/markdown), **ipc**___**name**‐‐ [**spaces**(7)](https://www.chedong.com/phpMan.php/man/spaces/7/markdown) ## COLOPHON This page is part of release 5.10 of the Linux _man-pages_ project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at . Linux 2020-04-11 [SVIPC(7)](https://www.chedong.com/phpMan.php/man/SVIPC/7/markdown)