153 lines
4.7 KiB
Groff
153 lines
4.7 KiB
Groff
.\" Hey, EMACS: -*- nroff -*-
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.\" First parameter, NAME, should be all caps
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.\" other parameters are allowed: see man(7), man(1)
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.TH EXIM_LOCK 8 "May 12, 2020"
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.\" Please adjust this date whenever revising the manpage.
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.\" \(oqthis text is enclosed in single quotes\(cq
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.\" \(lqthis text is enclosed in double quotes\(rq
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.SH NAME
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exim_lock \- Mailbox maintenance
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.SH SYNOPSIS
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.B exim_lock
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.RI [ options ] mailbox-file
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.SH DESCRIPTION
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The
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.B exim_lock
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utility locks a mailbox file using the same algorithm as Exim.
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For a discussion of locking issues, see section "appendfile transport",
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subsection "Operational details for appending" the Exim specification.
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.B exim_lock
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can be used to prevent any modification of a mailbox by Exim or a user
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agent while investigating a problem.
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The utility requires the name of the file as its first argument.
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If the locking is successful, the second argument is run as a command
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(using C's \(lqsystem()\(rq function); if there is no second argument, the value
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of the SHELL environment variable is used; if this is unset or empty,
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/bin/sh is run.
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When the command finishes, the mailbox is unlocked and the utility ends.
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The following options are available:
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.TP
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.I \-fcntl
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Use \(lqfcntl()\(rq locking on the open mailbox.
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.TP
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.I \-flock
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Use \(lqflock()\(rq locking on the open mailbox, provided the operating
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system supports it.
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.TP
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.I \-interval
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This must be followed by a number, which is a number of seconds; it
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sets the interval to sleep between retries (default 3).
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.TP
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.I \-lockfile
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Create a lock file before opening the mailbox.
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.TP
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.I \-mbx
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Lock the mailbox using MBX rules.
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.TP
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.I \-q
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Suppress verification output.
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.TP
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.I \-retries
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This must be followed by a number; it sets the number of times to try
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to get the lock (default 10).
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.TP
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.I \-restore_time
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This option causes exim_lock to restore the modified and read times to the
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locked file before exiting. This allows you to access a locked mailbox (for
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example, to take a backup copy) without disturbing the times that the user
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subsequently sees.
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.TP
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.I \-timeout
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This must be followed by a number, which is a number of seconds; it
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sets a timeout to be used with a blocking \(lqfcntl()\(rq lock.
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If it is not set (the default), a non-blocking call is used.
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.TP
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.I \-v
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Generate verbose output.
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If none of
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.I \-fcntl, \-flock, \-lockfile
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or
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.I \-mbx
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are given, the default is to create a lock file and also use \(lqfcntl()\(rq
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locking on the mailbox, which is the same as
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.B Exim's
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default.
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The use of
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.I \-fcntl
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or
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.I \-flock
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requires that the file be writable; the use of
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.I \-lockfile
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requires that the directory containing the file be writable.
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Locking by lock file does not last for ever; Exim assumes that a lock file
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is expired if it is more than 30 minutes old.
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The
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.I \-mbx
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can be used with either or both of
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.I \-fcntl
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or
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.I \-flock.
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It assumes
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.I \-fcntl
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by default. MBX locking causes a shared lock to be taken out on the open
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mailbox, and an exclusive lock on the file /tmp/.n.m where n and m are the
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device number and inode number of the mailbox file. When the locking is
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released, if an exclusive lock can be obtained for the mailbox, the file
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in /tmp is deleted.
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The default output contains verification of the locking that takes place.
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The
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.I \-v
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option causes some additional information to be given.
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The
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.I \-q
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option suppresses all output except error messages.
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.PP
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A command such as
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exim_lock /var/spool/mail/spqr
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runs an interactive shell while the file is locked, whereas
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exim_lock \-q /var/spool/mail/spqr <<End
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<some commands>
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End
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runs a specific non-interactive sequence of commands while the file is
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locked, suppressing all verification output.
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A single command can be run by a command such as
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exim_lock \-q /var/spool/mail/spqr \
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"cp /var/spool/mail/spqr /some/where"
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Note that if a command is supplied, it must be entirely contained within
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the second argument - hence the quotes.
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.SH BUGS
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This manual page needs a major re-work. If somebody knows better groff
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than us and has more experience in writing manual pages, any patches
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would be greatly appreciated.
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.SH SEE ALSO
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.BR exim (8),
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/usr/share/doc/exim4\-base/
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.SH AUTHOR
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This manual page was stitched together from spec.txt by
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Andreas Metzler <ametzler at downhill.at.eu.org>,
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for the Debian GNU/Linux system (but may be used by others).
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