NAME

       mlockall, munlockall — lock (unlock) the address space of a process

LIBRARY

       Standard C Library (libc, -lc)

SYNOPSIS

       #include <sys/mman.h>

       int
       mlockall(int flags);

       int
       munlockall(void);

DESCRIPTION

       The  mlockall()  system  call locks into memory the physical pages associated with the address space of a
       process until the address space is unlocked, the process exits, or execs another program image.

       The following flags affect the behavior of mlockall():

       MCL_CURRENT  Lock all pages currently mapped into the process's address space.

       MCL_FUTURE   Lock all pages mapped into the process's address space  in  the  future,  at  the  time  the
                    mapping  is established.  Note that this may cause future mappings to fail if those mappings
                    cause resource limits to be exceeded.

       Since physical memory is a potentially scarce resource, processes are limited in how much they  can  lock
       down.   A  single process can lock the minimum of a system-wide “wired pages” limit vm.max_user_wired and
       the per-process RLIMIT_MEMLOCK resource limit.

       If security.bsd.unprivileged_mlock is set to 0 these calls are only  available  to  the  super-user.   If
       vm.old_mlock is set to 1 the per-process RLIMIT_MEMLOCK resource limit will not be applied for mlockall()
       calls.

       The munlockall() call unlocks any locked memory regions in the process address space.  Any regions mapped
       after an munlockall() call will not be locked.

RETURN VALUES

       A  return value of 0 indicates that the call succeeded and all pages in the range have either been locked
       or unlocked.  A return value of -1 indicates an error occurred and the locked status of all pages in  the
       range remains unchanged.  In this case, the global location errno is set to indicate the error.

ERRORS

       mlockall() will fail if:

       [EINVAL]           The flags argument is zero, or includes unimplemented flags.

       [ENOMEM]           Locking  the  indicated  range would exceed either the system or per-process limit for
                          locked memory.

       [EAGAIN]           Some or all of the memory mapped into the process's address space could not be  locked
                          when the call was made.

       [EPERM]            The  calling  process does not have the appropriate privilege to perform the requested
                          operation.

SEE ALSO

       mincore(2), mlock(2), mmap(2), munmap(2), setrlimit(2)

STANDARDS

       The mlockall() and munlockall() functions are believed to conform to IEEE Std 1003.1-2001 (“POSIX.1”).

HISTORY

       The mlockall() and munlockall() functions first appeared in FreeBSD 5.1.

BUGS

       The per-process and system-wide resource limits of locked memory apply to the amount  of  virtual  memory
       locked, not the amount of locked physical pages.  Hence two distinct locked mappings of the same physical
       page  counts  as 2 pages aginst the system limit, and also against the per-process limit if both mappings
       belong to the same physical map.

Debian                                            May 13, 2019                                       MLOCKALL(2)