NAME

       sem_open - initialize and open a named semaphore

SYNOPSIS

       #include <fcntl.h>           /* For O_* constants */
       #include <sys/stat.h>        /* For mode constants */
       #include <semaphore.h>

       sem_t *sem_open(const char *name, int oflag);
       sem_t *sem_open(const char *name, int oflag,
                       mode_t mode, unsigned int value);

       Link with -pthread.

DESCRIPTION

       sem_open()  creates a new POSIX semaphore or opens an existing semaphore.  The semaphore is identified by
       name.  For details of the construction of name, see sem_overview(7).

       The oflag argument specifies flags that control the operation of the call.   (Definitions  of  the  flags
       values  can be obtained by including <fcntl.h>.)  If O_CREAT is specified in oflag, then the semaphore is
       created if it does not already exist.  The owner (user ID) of the semaphore is set to the effective  user
       ID  of  the  calling  process.   The  group  ownership (group ID) is set to the effective group ID of the
       calling process.  If both O_CREAT and O_EXCL are specified in oflag, then  an  error  is  returned  if  a
       semaphore with the given name already exists.

       If  O_CREAT  is  specified  in  oflag, then two additional arguments must be supplied.  The mode argument
       specifies the permissions to be placed on the new semaphore, as for open(2).  (Symbolic  definitions  for
       the  permissions  bits  can  be obtained by including <sys/stat.h>.)  The permissions settings are masked
       against the process umask.  Both read and write permission should be granted to each class of  user  that
       will  access  the  semaphore.   The value argument specifies the initial value for the new semaphore.  If
       O_CREAT is specified, and a semaphore with the given  name  already  exists,  then  mode  and  value  are
       ignored.

RETURN VALUE

       On  success, sem_open() returns the address of the new semaphore; this address is used when calling other
       semaphore-related functions.  On error, sem_open() returns SEM_FAILED, with errno  set  to  indicate  the
       error.

ERRORS

       EACCES The semaphore exists, but the caller does not have permission to open it.

       EEXIST Both O_CREAT and O_EXCL were specified in oflag, but a semaphore with this name already exists.

       EINVAL value was greater than SEM_VALUE_MAX.

       EINVAL name consists of just "/", followed by no other characters.

       EMFILE The process already has the maximum number of files and open.

       ENAMETOOLONG
              name was too long.

       ENFILE The system limit on the total number of open files has been reached.

       ENOENT The  O_CREAT  flag  was not specified in oflag and no semaphore with this name exists; or, O_CREAT
              was specified, but name wasn't well formed.

       ENOMEM Insufficient memory.

CONFORMING TO

       POSIX.1-2001.

SEE ALSO

       sem_close(3), sem_getvalue(3), sem_post(3), sem_unlink(3), sem_wait(3), sem_overview(7)

COLOPHON

       This page is part of release 3.54 of the Linux man-pages project.  A  description  of  the  project,  and
       information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.