SEMCTL

NAME

SYNOPSIS

DESCRIPTION

    int     val;            /* value for SETVAL */
    struct  semid_ds *buf;  /* buffer for IPC_{STAT,SET} */
    u_short *array;         /* array for GETALL & SETALL */

The Bf -literal semid_ds Ef structure used in the IPC_SET and IPC_STAT commands is defined as follows in Aq Pa sys/sem.h :

struct semid_ds {
    struct ipc_perm sem_perm;  /* operation permissions */
    struct  sem *sem_base;     /* semaphore set */
    u_short sem_nsems;         /* number of sems in set */
    time_t  sem_otime;         /* last operation time */
    time_t  sem_ctime;         /* last change time */
};

The Bf -literal ipc_perm Ef structure used inside the Bf -literal semid_ds Ef structure is defined in Aq Pa sys/ipc.h and looks like this:

struct ipc_perm {
    ushort cuid; /* creator user id */
    ushort cgid; /* creator group id */
    ushort uid;  /* user id */
    ushort gid;  /* group id */
    ushort mode; /* r/w permission (see chmod(2)) */
    ushort seq;  /* sequence # (to generate unique msg/sem/shm id) */
    key_t key;   /* user specified msg/sem/shm key */
};

Fn semctl provides the following operations:

GETVAL

Return the value of the semaphore.

SETVAL

Set the value of the semaphore to arg.val

GETPID

Return the pid of the last process that did an operation on this semaphore.

GETNCNT

Return the number of processes waiting to acquire the semaphore.

GETZCNT

Return the number of processes waiting for the value of the semaphore to reach 0.

GETALL

Return the values for all the semaphores associated with Fa semid .

SETALL

Set the values for all the semaphores that are associated with the semaphore identifier Fa semid to the corresponding values in arg.array

IPC_STAT

Gather statistics about a semaphore and place the information in the Bf -literal semid_ds Ef structure pointed to by Fa arg.buf (see above).

IPC_SET

Set the value of the sem_perm.uid sem_perm.gid and sem_perm.mode fields in the structure associated with the semaphore. The values are taken from the corresponding fields in the structure pointed to by Fa arg.buf . This operation can only be executed by the super-user, or a process that has an effective user id equal to either sem_perm.cuid or sem_perm.uid in the data structure associated with the message queue.

IPC_RMID

Remove the semaphores associated with Fa semid from the system and destroy the data structures associated with it. Only the super-user or a process with an effective uid equal to the sem_perm.cuid or sem_perm.uid values in the data structure associated with the semaphore can do this.

The permission to read or change a message queue (see semop(2)) is determined by the sem_perm.mode field in the same way as is done with files (see chmod(2)), but the effective uid can match either the sem_perm.cuid field or the sem_perm.uid field, and the effective gid can match either sem_perm.cgid or sem_perm.gid  

RETURN VALUES

ERRORS

Bq Er EPERM

Fa cmd is equal to IPC_SET or IPC_RMID and the caller is not the super-user, nor does the effective uid match either the sem_perm.uid or sem_perm.cuid fields of the data structure associated with the message queue.

Bq Er EACCESS

The caller has no operation permission for this semaphore.

Bq Er EINVAL

Fa semid is not a valid message semaphore identifier.

cmd is not a valid command.

Bq Er EFAULT

Fa arg.buf specifies an invalid address.

SEE ALSO

Index

NAME

SYNOPSIS

DESCRIPTION

RETURN VALUES

ERRORS

SEE ALSO