sys-utils/flock.1

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   4 .\"   Copyright 2003-2006 H. Peter Anvin - All Rights Reserved
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  28 .TH FLOCK "1" "4 Feb 2006" "flock utility" "H. Peter Anvin"
  29 .SH NAME
  30 flock \- Manage locks from shell scripts
  31 .SH SYNOPSIS
  32 \fBflock\fP [\fB\-sxon\fP] [\fB\-w\fP \fItimeout\fP] \fIlockfile\fP [\fB\-c\fP] \fIcommand...\fP
  33 .PP
  34 \fBflock\fP [\fB\-sxun\fP] [\fB\-w\fP \fItimeout\fP] \fIfd\fP
  35 .SH DESCRIPTION
  36 .PP
  37 This utility manages
  38 .BR flock (2)
  39 locks from within shell scripts or the command line.
  40 .PP
  41 The first form wraps the lock around the executing a command, in a manner similar to
  42 .BR su (1)
  43 or
  44 .BR newgrp (1).
  45 It locks a specified file, which is created (assuming appropriate
  46 permissions), if it does not already exist.
  47 .PP
  48 The second form is conveninent inside shell scripts, and is usually
  49 used the following manner:
  50 .PP
  51 \fC(
  52 .br
  53   flock -s 200
  54 .br
  55   # ... commands executed under lock ...
  56 .br
  57 ) 200>/var/lock/mylockfile\fP
  58 .PP
  59 The mode used to open the file doesn't matter to \fBflock\fP; using
  60 \fC>\fP or \fP>>\fP allows the lockfile to be created if it does not
  61 already exist, however, write permission is required; using \fC<\fP
  62 requires that the file already exists but only read permission is
  63 required.
  64 .PP
  65 By default, if the lock cannot be immediately acquired, \fBflock\fP
  66 waits until the lock is available.
  67 .SH OPTIONS
  68 .TP
  69 \fB\-s\fP, \fB\-\-shared\fP
  70 Obtain a shared lock, sometimes called a read lock.
  71 .TP
  72 \fB\-x\fP, \fB\-e\fP, \fB\-\-exclusive\fP
  73 Obtain an exclusive lock, sometimes called a write lock.  This is the
  74 default.
  75 .TP
  76 \fB\-u\fP, \fB\-\-unlock\fP
  77 Drop a lock.  This is usually not required, since a lock is
  78 automatically dropped when the file is closed.  However, it may be
  79 required in special cases, for example if the enclosed command group
  80 may have forked a background process which should not be holding the
  81 lock.
  82 .TP
  83 \fB\-n\fP, \fB\-\-nb\fP, \fB\-\-nonblock\fP
  84 Fail (with an exit code of 1) rather than wait if the lock cannot be
  85 immediately acquired.
  86 .TP
  87 \fB\-w\fP, \fB\-\-wait\fP, \fB\-\-timeout\fP \fIseconds\fP
  88 Fail (with an exit code of 1) if the lock cannot be acquired within
  89 \fIseconds\fP seconds.  Decimal fractional values are allowed.
  90 .TP
  91 \fB\-o\fP, \fB\-\-close\fP
  92 Close the file descriptor on which the lock is held before executing
  93 \fIcommand\fP.  This is useful if \fIcommand\fP spawns a child process
  94 which should not be hold ing the lock.
  95 .TP
  96 \fB\-c\fP, \fB\-\-command\fP \fIcommand\fP
  97 Pass a single \fIcommand\fP to the shell with \fB\-c\fP.
  98 .TP
  99 \fB\-h\fP, \fB\-\-help\fP
 100 Print a help message.
 101 .SH AUTHOR
 102 Written by H. Peter Anvin <hpa@zytor.com>.
 103 .SH COPYRIGHT
 104 Copyright \(co 2003\-2006 H. Peter Anvin.
 105 .br
 106 This is free software; see the source for copying conditions.  There is NO
 107 warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 108 .SH "SEE ALSO"
 109 .BR flock (2)