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) Linux Programmer's Manual MLOCK(2)NAME
mlock - disable paging for some parts of memory
SYNOPSIS
#include <sys/mman.h>
int mlock(const void *addr, size_t len);
DESCRIPTION
mlock disables paging for the memory in the range starting at addr with length len bytes. All pages which contain a part of the specified
memory range are guaranteed be resident in RAM when the mlock system call returns successfully and they are guaranteed to stay in RAM until
the pages are unlocked by munlock or munlockall, until the pages are unmapped via munmap, or until the process terminates or starts another
program with exec. Child processes do not inherit page locks across a fork.
Memory locking has two main applications: real-time algorithms and high-security data processing. Real-time applications require determin-
istic timing, and, like scheduling, paging is one major cause of unexpected program execution delays. Real-time applications will usually
also switch to a real-time scheduler with sched_setscheduler. Cryptographic security software often handles critical bytes like passwords
or secret keys as data structures. As a result of paging, these secrets could be transfered onto a persistent swap store medium, where they
might be accessible to the enemy long after the security software has erased the secrets in RAM and terminated.
Memory locks do not stack, i.e., pages which have been locked several times by calls to mlock or mlockall will be unlocked by a single call
to munlock for the corresponding range or by munlockall. Pages which are mapped to several locations or by several processes stay locked
into RAM as long as they are locked at least at one location or by at least one process.
On POSIX systems on which mlock and munlock are available, _POSIX_MEMLOCK_RANGE is defined in <unistd.h> and the value PAGESIZE from <lim-
its.h> indicates the number of bytes per page.
NOTES
With the Linux system call, addr is automatically rounded down to the nearest page boundary. However, POSIX 1003.1-2001 allows an imple-
mentation to require that addr is page aligned, so portable applications should ensure this.
RETURN VALUE
On success, mlock returns zero. On error, -1 is returned, errno is set appropriately, and no changes are made to any locks in the address
space of the process.
ERRORS
ENOMEM Some of the specified address range does not correspond to mapped pages in the address space of the process or the process tried to
exceed the maximum number of allowed locked pages.
EPERM The calling process does not have appropriate privileges. Only root processes are allowed to lock pages.
EINVAL len was not a positive number.
CONFORMING TO
POSIX.1b, SVr4. SVr4 documents an additional EAGAIN error code.
SEE ALSO mlockall(2), munlock(2), munlockall(2), munmap(2), setrlimit(2)Linux 1.3.43 1995-11-26 MLOCK(2)