MLOCK(1)MLOCK(1)NAME
mlock -- lock a mailbox
SYNOPSIS
/usr/bin/mlock
DESCRIPTION
If libc-client.so is unable to create a mailbox lock file, it will call this program. This makes using the mailbox safe over i.e. NFS.
There is no reason to call mlock yourself or through another program. It is setgid mail so there is no need to change the permissions of
/var/mail to 1777.
BUGS
No documentation other than this crappy man page,
AUTHOR
mlock was written by Mark Crispin <mrc@cac.washington.edu> This man page was written for Debian GNU/Linux by Jaldhar H. Vyas
<jaldhar@debian.org>
UW IMAP 2007f~dfsg-2 2008-08-19 MLOCK(1)
Check Out this Related Man Page
MLOCK(2) BSD System Calls Manual MLOCK(2)NAME
mlock, munlock -- lock (unlock) physical pages in memory
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <sys/mman.h>
int
mlock(void *addr, size_t len);
int
munlock(void *addr, size_t len);
DESCRIPTION
The mlock system call locks into memory the physical pages associated with the virtual address range starting at addr for len bytes. The
munlock call unlocks pages previously locked by one or more mlock calls. The entire range of memory must be allocated.
After an mlock call, the indicated pages will cause neither a non-resident page nor address-translation fault until they are unlocked. They
may still cause protection-violation faults or TLB-miss faults on architectures with software-managed TLBs. The physical pages remain in
memory until all locked mappings for the pages are removed. Multiple processes may have the same physical pages locked via their own virtual
address mappings. A single process may likewise have pages multiply-locked via different virtual mappings of the same pages or via nested
mlock calls on the same address range. Unlocking is performed explicitly by munlock or implicitly by a call to munmap which deallocates the
unmapped address range. Locked mappings are not inherited by the child process after a fork(2).
Since physical memory is a potentially scarce resource, processes are limited in how much they can lock down. A single process can mlock the
minimum of a system-wide ``wired pages'' limit and the per-process RLIMIT_MEMLOCK resource limit.
Portable code should ensure that the addr and len parameters are aligned to a multiple of the page size, even though the NetBSD implementa-
tion will round as necessary.
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
mlock() will fail if:
[EAGAIN] Locking the indicated range would exceed either the system or per-process limit for locked memory.
[EINVAL] The length is negative; or the address or length given is not page aligned and the implementation does not round.
[ENOMEM] Some portion of the indicated address range is not allocated. There was an error faulting/mapping a page.
[EPERM] mlock() was called by non-root on an architecture where locked page accounting is not implemented.
munlock() will fail if:
[EINVAL] The length is negative; or the address or length given is not page aligned and the implementation does not round.
[ENOMEM] Some portion of the indicated address range is not allocated. Some portion of the indicated address range is not locked.
SEE ALSO fork(2), mincore(2), mmap(2), munmap(2), setrlimit(2), getpagesize(3)STANDARDS
The mlock() and munlock() functions conform to IEEE Std 1003.1b-1993 (``POSIX.1'').
HISTORY
The mlock() and munlock() functions first appeared in 4.4BSD.
BUGS
The per-process resource limit is a limit on the amount of virtual memory locked, while the system-wide limit is for the number of locked
physical pages. Hence a process with two distinct locked mappings of the same physical page counts as 2 pages against the per-process limit
and as only a single page in the system limit.
BSD February 28, 2011 BSD