SHMCTL(3)                  POSIX Programmer's Manual                 SHMCTL(3)



PPRROOLLOOGG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

NNAAMMEE
       shmctl -- XSI shared memory control operations

SSYYNNOOPPSSIISS
       #include <sys/shm.h>

       int shmctl(int _s_h_m_i_d, int _c_m_d, struct shmid_ds *_b_u_f);

DDEESSCCRRIIPPTTIIOONN
       The _s_h_m_c_t_l() function operates on XSI shared memory (see the Base
       Definitions volume of POSIX.1-2017, _S_e_c_t_i_o_n _3_._3_4_6, _S_h_a_r_e_d _M_e_m_o_r_y
       _O_b_j_e_c_t).  It is unspecified whether this function interoperates with
       the realtime interprocess communication facilities defined in _S_e_c_t_i_o_n
       _2_._8, _R_e_a_l_t_i_m_e.

       The _s_h_m_c_t_l() function provides a variety of shared memory control
       operations as specified by _c_m_d.  The following values for _c_m_d are
       available:

       IPC_STAT    Place the current value of each member of the sshhmmiidd__ddss data
                   structure associated with _s_h_m_i_d into the structure pointed
                   to by _b_u_f.  The contents of the structure are defined in
                   _<_s_y_s_/_s_h_m_._h_>.

       IPC_SET     Set the value of the following members of the sshhmmiidd__ddss data
                   structure associated with _s_h_m_i_d to the corresponding value
                   found in the structure pointed to by _b_u_f:


                       shm_perm.uid
                       shm_perm.gid
                       shm_perm.mode    Low-order nine bits.

                   Also, the _s_h_m___c_t_i_m_e timestamp shall be set to the current
                   time, as described in _S_e_c_t_i_o_n _2_._7_._1, _I_P_C _G_e_n_e_r_a_l
                   _D_e_s_c_r_i_p_t_i_o_n.

                   IPC_SET can only be executed by a process that has an
                   effective user ID equal to either that of a process with
                   appropriate privileges or to the value of _s_h_m___p_e_r_m_._c_u_i_d or
                   _s_h_m___p_e_r_m_._u_i_d in the sshhmmiidd__ddss data structure associated with
                   _s_h_m_i_d.

       IPC_RMID    Remove the shared memory identifier specified by _s_h_m_i_d from
                   the system and destroy the shared memory segment and
                   sshhmmiidd__ddss data structure associated with it. IPC_RMID can
                   only be executed by a process that has an effective user ID
                   equal to either that of a process with appropriate
                   privileges or to the value of _s_h_m___p_e_r_m_._c_u_i_d or _s_h_m___p_e_r_m_._u_i_d
                   in the sshhmmiidd__ddss data structure associated with _s_h_m_i_d.

RREETTUURRNN VVAALLUUEE
       Upon successful completion, _s_h_m_c_t_l() shall return 0; otherwise, it
       shall return -1 and set _e_r_r_n_o to indicate the error.

EERRRROORRSS
       The _s_h_m_c_t_l() function shall fail if:

       EEAACCCCEESS The argument _c_m_d is equal to IPC_STAT and the calling process
              does not have read permission; see _S_e_c_t_i_o_n _2_._7, _X_S_I _I_n_t_e_r_p_r_o_c_e_s_s
              _C_o_m_m_u_n_i_c_a_t_i_o_n.

       EEIINNVVAALL The value of _s_h_m_i_d is not a valid shared memory identifier, or
              the value of _c_m_d is not a valid command.

       EEPPEERRMM  The argument _c_m_d is equal to IPC_RMID or IPC_SET and the
              effective user ID of the calling process is not equal to that of
              a process with appropriate privileges and it is not equal to the
              value of _s_h_m___p_e_r_m_._c_u_i_d or _s_h_m___p_e_r_m_._u_i_d in the data structure
              associated with _s_h_m_i_d.

       The _s_h_m_c_t_l() function may fail if:

       EEOOVVEERRFFLLOOWW
              The _c_m_d argument is IPC_STAT and the _g_i_d or _u_i_d value is too
              large to be stored in the structure pointed to by the _b_u_f
              argument.

       _T_h_e _f_o_l_l_o_w_i_n_g _s_e_c_t_i_o_n_s _a_r_e _i_n_f_o_r_m_a_t_i_v_e_.

EEXXAAMMPPLLEESS
       None.

AAPPPPLLIICCAATTIIOONN UUSSAAGGEE
       The POSIX Realtime Extension defines alternative interfaces for
       interprocess communication. Application developers who need to use IPC
       should design their applications so that modules using the IPC routines
       described in _S_e_c_t_i_o_n _2_._7, _X_S_I _I_n_t_e_r_p_r_o_c_e_s_s _C_o_m_m_u_n_i_c_a_t_i_o_n can be easily
       modified to use the alternative interfaces.

RRAATTIIOONNAALLEE
       None.

FFUUTTUURREE DDIIRREECCTTIIOONNSS
       None.

SSEEEE AALLSSOO
       _S_e_c_t_i_o_n _2_._7, _X_S_I _I_n_t_e_r_p_r_o_c_e_s_s _C_o_m_m_u_n_i_c_a_t_i_o_n, _S_e_c_t_i_o_n _2_._8, _R_e_a_l_t_i_m_e,
       _s_h_m_a_t(), _s_h_m_d_t(), _s_h_m_g_e_t(), _s_h_m___o_p_e_n(), _s_h_m___u_n_l_i_n_k()

       The Base Definitions volume of POSIX.1-2017, _S_e_c_t_i_o_n _3_._3_4_6, _S_h_a_r_e_d
       _M_e_m_o_r_y _O_b_j_e_c_t, <<ssyyss__sshhmm..hh>>

CCOOPPYYRRIIGGHHTT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  In the event of any discrepancy between this version and the
       original IEEE and The Open Group Standard, the original IEEE and The
       Open Group Standard is the referee document. The original Standard can
       be obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                            SHMCTL(3)
