semctl(2) System Calls semctl(2)NAMEsemctl - 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 opera‐
tions 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 oper‐
ations 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 cor‐
responding 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 exe‐
cuted, the semadj values corresponding to each speci‐
fied 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 exe‐
cuted 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 fol‐
lows:
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 com‐
mand 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(5) for descriptions of the following attributes:
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│Interface Stability │Standard │
└─────────────────────────────┴─────────────────────────────┘
SEE ALSOipcs(1), intro(2), semget(2), semop(2), attributes(5), privileges(5),
standards(5)SunOS 5.10 1 Feb 2003 semctl(2)
