SEMCTL(2) System Calls SEMCTL(2)
NAME
semctl - semaphore control operations
SYNOPSIS
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
int semctl(
int semid,
int semnum,
int cmd...);
DESCRIPTION
The
semctl() function provides a variety of semaphore control
operations as specified by
cmd. The fourth argument is optional,
depending upon the operation requested. If required, it is of type
union semun, which must be explicitly declared by the application
program.
union semun {
int val;
struct semid_ds *buf;
ushort_t *array;
} arg ;
The permission required for a semaphore operation is given as
{
token}, where
token is the type of permission needed. The types of
permission are interpreted as follows:
00400 READ by user
00200 ALTER by user
00040 READ by group
00020 ALTER by group
00004 READ by others
00002 ALTER by others
See the
Semaphore Operation Permissions subsection of the
DEFINITIONS section of
Intro(2) for more information. The following semaphore
operations as specified by
cmd are executed with respect to the
semaphore specified by
semid and
semnum.
GETVAL Return the value of semval (see
Intro(2)). {READ}
SETVAL Set the value of
semval to
arg.val. {ALTER} When this
command is successfully executed, the
semadj value
corresponding to the specified semaphore in all processes
is cleared.
GETPID Return the value of
(int) sempid. {READ}
GETNCNT Return the value of
semncnt. {READ}
GETZCNT Return the value of
semzcnt. {READ}
The following operations return and set, respectively, every
semval in the set of semaphores.
GETALL Place
semvals into array pointed to by
arg.array. {READ}
SETALL Set
semvals according to the array pointed to by
arg.array.
{ALTER}. When this cmd is successfully executed, the
semadj values corresponding to each specified semaphore in all
processes are cleared.
The following operations are also available.
IPC_STAT Place the current value of each member of the data
structure associated with
semid into the structure
pointed to by
arg.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
semid to the corresponding
value found in the structure pointed to by
arg.
buf:
sem_perm.uid
sem_perm.gid
sem_perm.mode /* access permission bits only */
This command can be executed only by a process that has
either the {
PRIV_IPC_OWNER} privilege or an effective
user
ID equal to the value of
msg_perm.cuid or
msg_perm.uid in the data structure associated with
msqid.
Only a process with the {
PRIV_SYS_IPC_CONFIG} privilege
can raise the value of
msg_qbytes.
IPC_RMID Remove the semaphore identifier specified by
semid from
the system and destroy the set of semaphores and data
structure associated with it. This command can be
executed only by a process that has the {
PRIV_IPC_OWNER}
privilege or an effective user
ID equal to the value of
sem_perm.cuid or
sem_perm.uid in the data structure
associated with
semid.
RETURN VALUES
Upon successful completion, the value returned depends on
cmd as
follows:
GETVAL the value of
semval GETPID the value of
(int) sempid GETNCNT the value of
semncnt GETZCNT the value of
semzcnt All other successful completions return
0; otherwise,
-1 is returned
and
errno is set to indicate the error.
ERRORS
The
semctl() function will fail if:
EACCES Operation permission is denied to the calling process
(see
Intro(2)).
EFAULT The source or target is not a valid address in the user
process.
EINVAL The
semid argument is not a valid semaphore identifier;
the
semnum argument is less than 0 or greater than
sem_nsems -1; or the
cmd argument is not a valid command
or is
IPC_SET and
sem_perm.uid or
sem_perm.gid is not
valid.
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
sem_perm.cuid or
sem_perm.uid in the data
structure associated with
semid, and {
PRIV_IPC_OWNER} is
not asserted in the effective set of the calling
process.
EOVERFLOW The
cmd argument is
IPC_STAT and
uid or
gid is too large
to be stored in the structure pointed to by
arg.buf.
ERANGE The
cmd argument is
SETVAL or
SETALL and the value to
which
semval is to be set is greater than the system
imposed maximum.
ATTRIBUTES
See
attributes(7) for descriptions of the following attributes:
+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Standard |
+--------------------+-----------------+
SEE ALSO
ipcs(1),
Intro(2),
semget(2),
semop(2),
attributes(7),
privileges(7),
standards(7) February 1, 2003 SEMCTL(2)
