shmctl(2) [freebsd man page]
SHMCTL(2) BSD System Calls Manual SHMCTL(2) NAME
shmctl -- shared memory control LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <sys/types.h> #include <sys/ipc.h> #include <sys/shm.h> int shmctl(int shmid, int cmd, struct shmid_ds *buf); DESCRIPTION
Performs the action specified by cmd on the shared memory segment identified by shmid: IPC_STAT Fetch the segment's struct shmid_ds, storing it in the memory pointed to by buf. IPC_SET Changes the shm_perm.uid, shm_perm.gid, and shm_perm.mode members of the segment's struct shmid_ds to match those of the struct pointed to by buf. The calling process's effective uid must match either shm_perm.uid or shm_perm.cuid, or it must have supe- ruser privileges. IPC_RMID Removes the segment from the system. The removal will not take effect until all processes having attached the segment have exited; however, once the IPC_RMID operation has taken place, no further processes will be allowed to attach the segment. For the operation to succeed, the calling process's effective uid must match shm_perm.uid or shm_perm.cuid, or the process must have superuser privileges. The shmid_ds structure is defined as follows: struct shmid_ds { struct ipc_perm shm_perm; /* operation permission structure */ size_t shm_segsz; /* size of segment in bytes */ pid_t shm_lpid; /* process ID of last shared memory op */ pid_t shm_cpid; /* process ID of creator */ int shm_nattch; /* number of current attaches */ time_t shm_atime; /* time of last shmat() */ time_t shm_dtime; /* time of last shmdt() */ time_t shm_ctime; /* time of last change by shmctl() */ }; RETURN VALUES
The shmctl() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error. ERRORS
The shmctl() system call will fail if: [EINVAL] Invalid operation, or no shared memory segment was found corresponding to shmid. [EPERM] The calling process's effective uid does not match the uid of the shared memory segment's owner or creator. [EACCES] Permission denied due to mismatch between operation and mode of shared memory segment. SEE ALSO
shmat(2), shmdt(2), shmget(2), ftok(3) BSD
July 17, 1995 BSD
Check Out this Related Man Page
shmctl(2) System Calls shmctl(2) NAME
shmctl - shared memory control operations SYNOPSIS
#include <sys/types.h> #include <sys/ipc.h> #include <sys/shm.h> int shmctl(int shmid, int cmd, struct shmid_ds *buf); DESCRIPTION
The shmctl() function provides a variety of shared memory control operations as specified by cmd. The permission required for a shared mem- ory control operation is given as {token}, where token is the type of permission needed. The types of permission are interpreted as fol- lows: 00400 READ by user 00200 WRITE by user 00040 READ by group 00020 WRITE by group 00004 READ by others 00002 WRITE by others See the Shared Memory Operation Permissions section of Intro(2) for more information. The following operations require the specified tokens: IPC_STAT Place the current value of each member of the data structure associated with shmid into the structure pointed to by buf. The contents of this structure are defined in Intro(2). {READ} IPC_SET Set the value of the following members of the data structure associated with shmid to the corresponding value found in the structure pointed to by buf: shm_perm.uid shm_perm.gid shm_perm.mode /* access permission bits only */ This command can be executed only by a process that has appropriate privileges or an effective user ID equal to the value of shm_perm.cuid or shm_perm.uid in the data structure associated with shmid. IPC_RMID Remove the shared memory identifier specified by shmid from the system. The segment referenced by the identifier will be destroyed when all processes with the segment attached have either detached the segment or exited. If the segment is not attached to any process when IPC_RMID is invoked, it will be destroyed immediately. This command can be executed only by a process that has appropriate privileges or an effective user ID equal to the value of shm_perm.cuid or shm_perm.uid in the data structure associated with shmid. SHM_LOCK Lock the shared memory segment specified by shmid in memory. This command can be executed only by a process that has appro- priate privileges. SHM_UNLOCK Unlock the shared memory segment specified by shmid. This command can be executed only by a process that has appropriate privileges. A shared memory segment must be explicitly removed using IPC_RMID before the system can deallocate it and the resources it uses. RETURN VALUES
Upon successful completion, 0 is returned. Otherwise, -1 is returned and errno is set to indicate the error. ERRORS
The shmctl() function will fail if: EACCES The cmd argument is equal to IPC_STAT and {READ} operation permission is denied to the calling process. EFAULT The buf argument points to an illegal address. EINVAL The shmid argument is not a valid shared memory identifier; or the cmd argument is not a valid command or is IPC_SET and shm_perm.uid or shm_perm.gid is not valid. ENOMEM The cmd argument is equal to SHM_LOCK and there is not enough memory, or the operation would exceed a limit or resource con- trol on locked memory. EOVERFLOW The cmd argument is IPC_STAT and uid or gid is too large to be stored in the structure pointed to by buf. EPERM The cmd argument is equal to IPC_RMID or IPC_SET, the effective user ID of the calling process is not equal to the value of shm_perm.cuid or shm_perm.uid in the data structure associated with shmid, and {PRIV_IPC_OWNER} is not asserted in the effec- tive set of the calling process. The cmd argument is equal to SHM_LOCK or SHM_UNLOCK and {PRIV_PROC_LOCK_MEMORY} is not asserted in the effective set of the calling process. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ SEE ALSO
ipcs(1), Intro(2), shmget(2), shmop(2), attributes(5), privileges(5), standards(5) SunOS 5.11 10 Apr 2007 shmctl(2)