MAILOCK(3)						     Linux Programmer's Manual							MAILOCK(3)

NAME

       maillock, mailunlock, touchlock - manage mailbox lockfiles

SYNOPSIS

       #include <maillock.h>

       cc [ flag ... ] file ... -llockfile [ library ]

       int maillock( const char *user, int retrycnt );
       void mailunlock( void );
       void touchlock( void );

DESCRIPTION

       The  maillock  function	tries to create a lockfile for the users mailbox in an NFS-safe (or resistant) way. The algorithm is documented in
       lockfile_create(3).

       The mailbox is typically located in /var/mail.  The name of the lockfile then becomes /var/mail/USERNAME.lock.  If the environment variable
       $MAIL  is  set,	and  it  ends  with the same username as the username passed to maillock(), then that file is taken as the mailbox to lock
       instead.

       There is no good way to see if a lockfile is stale. Therefore if the lockfile is older then 5 minutes, it will be removed. That is why  the
       touchlock function is provided: while holding the lock, it needs to be refreshed regulary (every minute or so) by calling touchlock ()  .

       Finally the mailunlock function removes the lockfile.

RETURN VALUES

       maillock returns one of the following status codes:

	  #define L_SUCCESS   0    /* Lockfile created			   */
	  #define L_NAMELEN   1    /* Recipient name too long (> 13 chars) */
	  #define L_TMPLOCK   2    /* Error creating tmp lockfile	   */
	  #define L_TMPWRITE  3    /* Can't write pid int tmp lockfile	   */
	  #define L_MAXTRYS   4    /* Failed after max. number of attempts */
	  #define L_ERROR     5    /* Unknown error; check errno	   */

NOTES

       These  functions are not thread safe. If you need thread safe functions, or you need to lock other mailbox (like) files that are not in the
       standard location, use lockfile_create(3) instead.

       These functions call lockfile_create(3) to do the work. That function might spawn a set group-id executable to do the actual locking if the
       current process doesn't have enough priviliges.

       There are some issues with flushing the kernels attribute cache if you are using NFS - see the lockfile_create(3) manpage.

FILES

       /var/mail/user.lock,
       /usr/lib/liblockfile.so.1

AUTHOR

       Miquel van Smoorenburg <miquels@cistron.nl>

SEE ALSO

       lockfile_create(3), lockfile_touch (3), lockfile_remove(3)

Linux Manpage							   28 March 2001							MAILOCK(3)