semctl(2)semctl(2)NAMEsemctl - semaphore control operations
SYNOPSIS
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
union semun {
int val;
struct semid_ds *buf;
ushort *array;
};
int semctl(int semid, int semnum, int cmd, ... /* union semun arg */);
DESCRIPTIONsemctl provides a variety of semaphore control operations as specified by
cmd.
The following cmds 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 cmds 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 cmds 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}
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semctl(2)semctl(2)
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 /* only access permission bits */
This command can be executed only by a process that has
an effective user ID equal to the value of sem_perm.cuid
or sem_perm.uid in the data structure associated with
semid or to a process that has the super-user privilege.
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 an effective user ID
equal to the value of sem_perm.cuid or sem_perm.uid in
the data structure associated with semid or to a process
that has the super-user privilege.
semctl fails if one or more of the following are true:
EACCES Operation permission is denied to the calling process [see
intro(2)].
EINVAL semid is not a valid semaphore identifier.
EINVAL semnum is less than 0 or greater than sem_nsems.
EINVAL cmd is not a valid command.
EINVAL cmd is IPC_SET and sem_perm.uid or sem_perm.gid is not
valid.
EOVERFLOW cmd is IPC_STAT and uid or gid is too large to be stored
in the structure pointed to by arg.buf.
ERANGE cmd is SETVAL or SETALL and the value to which semval is
to be set is greater than the system imposed maximum.
EPERM cmd is equal to IPC_RMID or IPC_SET and 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 the calling process does not
have super-user privilege.
EFAULT arg.buf points to an illegal address.
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semctl(2)semctl(2)SEE ALSOintro(2), semget(2), semop(2).
DIAGNOSTICS
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 others
a value of 0
Otherwise, a value of -1 is returned and errno is set to indicate the
error.
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