HP-UX Reference (11i v1 00/12) - 2 System Calls (vol 5)

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semctl(2) semctl(2)

NAME

semctl - semaphore control operations

SYNOPSIS

#include <sys/sem.h>

int semctl(int semid,

int semnum,

int cmd,

union arg

);

union semun {

int val;

struct semid_ds ∗buf;

ushort ∗array;

} arg;

DESCRIPTION

The semctl() system call provides a variety of semaphore control operations as speciﬁed by cmd.For

the meaning of unspeciﬁed variables, see semaphore identiﬁer in glossary(9).

The following values for cmd are executed with respect to the semaphore speciﬁed by semid and semnum:

GETVAL Return the value of semval. Requires semaphore Read permission.

SETVAL Set the value of semval to arg.val, where arg is the fourth argument of semctl()

taken as an int. When this cmd is successfully executed, the semadj value

corresponding to the speciﬁed semaphore in all processes is cleared. Requires sema-

phore Alter permission.

GETPID Return the value of sempid. Requires semaphore Read permission.

GETNCNT Return the value of semncnt. Requires semaphore Read permission.

GETZCNT Return the value of semzcnt. Requires semaphore Read permission.

The following values for cmd return and set, respectively, every semval in the set of semaphores.

GETALL Place semvals into array pointed to by arg.array, where arg is the fourth argument of

semctl() taken as a pointer to unsigned short int. Requires semaphore

Read permission.

SETALL Set semvals according to the array pointed to by arg.array, where arg is the fourth

argument of

semctl() taken as a pointer to unsigned short int. When this

cmd is successfully executed, the semadj values corresponding to each speciﬁed sema-

phore in all processes are cleared. Requires semaphore Alter permission.

The following values for cmd 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, where arg is the fourth argument of

semctl() taken as a pointer to struct semid_ds. The contents of this struc-

ture are deﬁned in glossary(9). Requires semaphore Read permission.

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, where arg is the

fourth argument of

semctl() taken as a pointer to struct semid_ds:

sem_perm.uid

sem_perm.gid

sem_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 superuser or to the value of either sem_perm.uid or

sem_perm.cuid in the data structure associated with semid.

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 cmd can only be exe-

cuted by a process that has an effective user ID equal to either that of superuser or to

the value of either sem_perm.uid or sem_perm.cuid

in the data structure

HP-UX Release 11i: December 2000 − 1 − Section 2−−287

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