shmctl(2) System Calls Manual shmctl(2)
NAME
shmctl() - shared memory control operations
SYNOPSIS
DESCRIPTION
The system call provides a variety of shared memory control operations as specified by the cmd argument. cmd can have the following val-
ues:
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 glossary(9).
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 /* only low 9 bits */
This cmd can only be executed by a process that has an effective user ID equal to either that of a user having appro-
priate privileges or to the value of either or in the data structure associated with shmid.
This cmd cannot be executed on a shared memory segment that has been created with relaxed isolation.
Remove the shared memory identifier specified by
shmid from the system and destroy the shared memory segment and data structure associated with it. If the segment is
attached to one or more processes, then the segment key is changed to and the segment is marked removed. The segment
disappears when the last attached process detaches it. This cmd can only be executed by a process that has an effec-
tive user ID equal to either that of a user with appropriate privileges or to the value of either or in the data
structure associated with shmid.
Lock the shared memory segment specified by
shmid in memory. This cmd can only be executed by a process that either has an effective user ID equal to that of a
user having appropriate privileges or has an effective user ID equal to the value of either or in the data structure
associated with shmid and has the privilege (see getprivgrp(2)).
Unlock the shared memory segment specified by
shmid. This cmd can only be executed by a process that either has an effective user ID equal to a user having appro-
priate privileges or has an effective user ID equal to the value of either or in the data structure associated with
shmid and has the privilege (see getprivgrp(2)).
RETURN VALUE
returns the following values:
Successful completion.
Failure.
is set to indicate the error.
ERRORS
If fails, is set to one of the following values.
cmd is equal to and Read operation permission is denied to the calling process (see in glossary(9)).
buf points to an illegal address. The reliable detection of this error is implementation dependent.
cmd is equal to and the shared-memory segment specified by shmid is not locked in memory.
shmid is not a valid shared memory identifier.
cmd is not a valid command, or the command contains invalid parameters.
cmd is equal to and there is not sufficient lockable memory to fill the request.
cmd is equal to The attached process count of a shared memory object is too large for the field in the data structure
provided by the application. Recompile the application with the latest file to resolve this issue.
cmd is equal to or and the effective user ID of the calling process is not equal to that of a user having appropriate
privileges and it is not equal to the value of either or in the data structure associated with shmid.
cmd is equal to and the shared memory segment has
cmd is equal to or and the effective user ID of the calling process is not equal to that of a user having appropriate
privileges and the calling process does not have the privilege (see getprivgrp(2)).
EXAMPLES
The following call to locks in memory the shared memory segment represented by This example assumes the process has a valid shmid, which
can be obtained by calling shmget(2).
The following call to removes the shared memory segment represented by This example assumes the process has a valid shmid, which can be
obtained by calling (see shmget(2).
AUTHOR
was developed by AT&T and HP.
SEE ALSO
ipcrm(1), ipcs(1), shmget(2), shmop(2), stdipc(3C), privileges(5),
STANDARDS CONFORMANCE
shmctl(2)