# phpman > man > lockmail.maildrop(1)


*Source: tldr-pages*

---

[LOCKMAIL(1)](https://www.chedong.com/phpMan.php/man/LOCKMAIL/1/markdown)                            Double Precision, Inc.                            [LOCKMAIL(1)](https://www.chedong.com/phpMan.php/man/LOCKMAIL/1/markdown)



## NAME
       lockmail - create mail lock files

## SYNOPSIS
       **lockmail** [-r] [-t _timeout_] {_lockfile_} {_program_} [argument...]

## DESCRIPTION
       **lockmail** is a helper utility for working with mailbox files. Mailbox files must be locked to
       prevent other applications from modifying the mailbox at the same time. Different system use
       different locking conventions.  **lockmail** uses two of the most common locking mechanisms in
       use, which should work reliably on most systems.

       _lockfile_ is the pathname to an existing mailbox file. By default, **lockmail** tries to lock the
       mailbox every five seconds (if the mailbox is already locked), and will give up after three
       minutes. After the mailbox is successfully locked, **lockmail** runs _program_ as a child process,
       with any optional _argument_s. When _program_ terminates, **lockmail** removes the mailbox lock, and
       terminates itself.

## OPTIONS
### -r
           If a regular lock fails, try a read-only lock. Use this option to lock mailbox files in a
           read-only directory.

       -t _timeout_
           If the lock attempt fails, try again for up to _timeout_ seconds. The actual timeout is
           rounded up to the next five second interval (a lock attempt is tried every five seconds).

## DESCRIPTION
       This section briefly describes the locking mechanism used by **lockmail**.  **lockmail** uses three
       different locking conventions in order to maximize compatibility with other mail software:
       C-Client folder locks, dot-locks, and file locks.

### C-Client folder locks
       Mail software based on the C-Client library creates lock files named /tmp/._dddddd_._iiiiii_.
       Here, _dddddd_ and _iiiiii_ are the device number and the inode number of the mailbox file (the
       _st_dev_ and _st_ino_ fields in the inode), in hexadecimal. If the process ID saved in the
       C-Client folder lock file is not valid, **lockmail** concludes that it's a stale lock file, and
       will remove it.

           **Note**
           A race condition exists where a C-Client process is killed after it creates a lock file,
           but before saving its process ID in the lock file. The race window is very small, but it
           exists. The C-Client library does not appear to ever clear out the lock file.

           **lockmail** attempts to resolve this race condition by deleting zero-length lock files that
           are at least five minutes old.

### dot-locks
       **lockmail** also creates, and honors dot-lock files. Dot-lock files are first created as
       temporary files, then linked to _lockfile_.lock. The link operation fails if the dot-lock file
       already exists.  **lockmail** uses an enhanced method of dot-locking, where its process ID, and
       the name of the server where **lockmail** is running is also saved in its dot-lock file. If the
       operation fails due to an existing dot-lock file that was created by another **lockmail** process
       on the same server, and the process ID no longer exists, this stale dot-lock file is removed
       immediately. In all other situations a dot-lock file older than five minutes is considered
       stale, and removed.

           **Note**
           A failure to create a dot-lock file is silently ignored if the reason for the failure is
           because **lockmail** does not have the write permission in the dot-lock file's directory. The
           incoming mail spool directory (usually /var/mail) typically does not have global write
           permissions, so the attempt to create the dot-lock file in the spool directory will fail,
           and **lockmail** will be content with using file-locking only.

### File locks
       The final locking mechanism **lockmail** uses is the operating system's file locking facility. If
       **lockmail** fails to obtain all three locks, **lockmail** will sleep for five seconds and try again.
       The only exception is a failure to create a dot-lock because of no write access to the
       dot-lock file's directory, which is ignored. If **lockmail** still fails to obtain all required
       locks in the amount of time specified by the **-t** option (or its default value), **lockmail** will
       terminate with the EX_TEMPFAIL exit code.

       **lockmail** runs _program_ after obtaining the last file lock, waits until _program_ terminates, and
       releases all locks.  _program_ must terminate before any of the locks obtained by **lockmail**
       expire, and are considered stale.  **lockmail** will then terminate with the same exit code as
       _program_.

## EXIT STATUS
       **lockmail** terminates with the same exit status as _program_ **lockmail** terminates with the
       EX_TEMPFAIL exit status if it was unable to obtain a lock, or if _program_ was killed by a
       signal.

## SEE ALSO
       [**maildrop**(1)](https://www.chedong.com/phpMan.php/man/maildrop/1/markdown)[1], [**sendmail**(8)](https://www.chedong.com/phpMan.php/man/sendmail/8/markdown).

## AUTHOR
### Sam Varshavchik
           Author

## NOTES
        1. [**maildrop**(1)](https://www.chedong.com/phpMan.php/man/maildrop/1/markdown)
           <http://www.courier-mta.org/maildrop.html>



Courier Mail Server                          07/24/2017                                  [LOCKMAIL(1)](https://www.chedong.com/phpMan.php/man/LOCKMAIL/1/markdown)