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.\" Copyright 2003-2006 H. Peter Anvin - All Rights Reserved
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-.TH FLOCK "1" "4 Feb 2006" "flock utility" "H. Peter Anvin"
+.TH FLOCK 1 "September 2011" "util-linux" "User Commands"
.SH NAME
-flock \- Manage locks from shell scripts
+flock \- manage locks from shell scripts
.SH SYNOPSIS
-\fBflock\fP [\fB\-sxon\fP] [\fB\-w\fP \fItimeout\fP] \fIlockfile\fP [\fB\-c\fP] \fIcommand...\fP
-.PP
-\fBflock\fP [\fB\-sxon\fP] [\fB\-w\fP \fItimeout\fP] \fIlockdir\fP [\fB\-c\fP] \fIcommand...\fP
-.PP
-\fBflock\fP [\fB\-sxun\fP] [\fB\-w\fP \fItimeout\fP] \fIfd\fP
+.B flock
+[options] <file|directory> <command> [command args]
+.br
+.B flock
+[options] <file|directory> -c <command>
+.br
+.B flock
+[options] <file descriptor number>
.SH DESCRIPTION
.PP
This utility manages
.BR flock (2)
locks from within shell scripts or the command line.
.PP
-The first and second forms wraps the lock around the executing a command, in a manner similar to
+The first and second forms wrap the lock around the executing a command, in
+a manner similar to
.BR su (1)
or
.BR newgrp (1).
-It locks a specified file or directory, which is created (assuming appropriate
-permissions), if it does not already exist.
-.PP
-The third form is convenient inside shell scripts, and is usually
-used the following manner:
-.PP
-\fC(
-.br
- flock -n 9
-.br
- # ... commands executed under lock ...
-.br
-) 9>/var/lock/mylockfile\fP
-.PP
-The mode used to open the file doesn't matter to \fBflock\fP; using
-\fC>\fP or \fP>>\fP allows the lockfile to be created if it does not
-already exist, however, write permission is required; using \fC<\fP
-requires that the file already exists but only read permission is
-required.
-.PP
-By default, if the lock cannot be immediately acquired, \fBflock\fP
+It locks a specified file or directory, which is created (assuming
+appropriate permissions), if it does not already exist. By default, if the
+lock cannot be immediately acquired,
+.B flock
waits until the lock is available.
+.PP
+The third form uses open file by file descriptor number. See examples how
+that can be used.
.SH OPTIONS
.TP
\fB\-s\fP, \fB\-\-shared\fP
default.
.TP
\fB\-u\fP, \fB\-\-unlock\fP
-Drop a lock. This is usually not required, since a lock is
-automatically dropped when the file is closed. However, it may be
-required in special cases, for example if the enclosed command group
-may have forked a background process which should not be holding the
-lock.
+Drop a lock. This is usually not required, since a lock is automatically
+dropped when the file is closed. However, it may be required in special
+cases, for example if the enclosed command group may have forked a background
+process which should not be holding the lock.
.TP
\fB\-n\fP, \fB\-\-nb\fP, \fB\-\-nonblock\fP
-Fail (with an exit code of 1) rather than wait if the lock cannot be
+Fail rather than wait if the lock cannot be
immediately acquired.
+See the
+.I \-E
+option for the exit code used.
.TP
\fB\-w\fP, \fB\-\-wait\fP, \fB\-\-timeout\fP \fIseconds\fP
-Fail (with an exit code of 1) if the lock cannot be acquired within
-\fIseconds\fP seconds. Decimal fractional values are allowed.
+Fail if the lock cannot be acquired within
+.IR seconds .
+Decimal fractional values are allowed.
+See the
+.I \-E
+option for the exit code used.
.TP
\fB\-o\fP, \fB\-\-close\fP
Close the file descriptor on which the lock is held before executing
-\fIcommand\fP. This is useful if \fIcommand\fP spawns a child process
-which should not be hold ing the lock.
+.BR command\ .
+This is useful if
+.B command
+spawns a child process which should not be holding the lock.
+.TP
+\fB\-E\fP, \fB\-\-conflict\-exit\-code\fP \fInumber\fP
+The exit code used when the \fB\-n\fP option is in use, and the
+conflicting lock exists, or the \fB\-w\fP option is in use,
+and the timeout is reached. The default value is 1.
.TP
\fB\-c\fP, \fB\-\-command\fP \fIcommand\fP
-Pass a single \fIcommand\fP to the shell with \fB\-c\fP.
+Pass a single
+.IR command ,
+without arguments, to the shell with
+.BR -c .
.TP
\fB\-h\fP, \fB\-\-help\fP
-Print a help message.
+Display help text and exit.
+.IP "\fB\-V, \-\-version\fP"
+Display version information and exit.
+.SH EXAMPLES
+.TP
+shell1> flock /tmp -c cat
+.TQ
+shell2> flock -w .007 /tmp -c echo; /bin/echo $?
+Set exclusive lock to directory /tmp and the second command will fail.
+.TP
+shell1> flock -s /tmp -c cat
+.TQ
+shell2> flock -s -w .007 /tmp -c echo; /bin/echo $?
+Set shared lock to directory /tmp and the second command will not fail.
+Notice that attempting to get exclusive lock with second command would fail.
+.TP
+shell> flock -x local-lock-file echo 'a b c'
+Grab the exclusive lock "local-lock-file" before running echo with 'a b c'.
+.TP
+(
+.TQ
+ flock -n 9 || exit 1
+.TQ
+ # ... commands executed under lock ...
+.TQ
+) 9>/var/lock/mylockfile
+The form is convenient inside shell scripts. The mode used to open the file
+doesn't matter to
+.BR flock ;
+using
+.I >
+or
+.I >>
+allows the lockfile to be created if it does not already exist, however,
+write permission is required. Using
+.I <
+requires that the file already exists but only read permission is required.
+.TP
+[ "${FLOCKER}" != "$0" ] && exec env FLOCKER="$0" flock -en "$0" "$0" "$@" || :
+This is useful boilerplate code for shell scripts. Put it at the top of the
+shell script you want to lock and it'll automatically lock itself on the first
+run. If the env var $FLOCKER is not set to the shell script that is being run,
+then execute flock and grab an exclusive non-blocking lock (using the script
+itself as the lock file) before re-execing itself with the right arguments. It
+also sets the FLOCKER env var to the right value so it doesn't run again.
+.SH "EXIT STATUS"
+The command uses
+.B sysexits.h
+return values for everything else but an options
+.I \-n
+or
+.I \-w
+failures which return either the value given by the
+.I \-E
+option, or 1 by default.
.SH AUTHOR
-Written by H. Peter Anvin <hpa@zytor.com>.
+.UR hpa@zytor.com
+H. Peter Anvin
+.UE
.SH COPYRIGHT
Copyright \(co 2003\-2006 H. Peter Anvin.
.br
.BR flock (2)
.SH AVAILABILITY
The flock command is part of the util-linux package and is available from
-ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
+.UR ftp://\:ftp.kernel.org\:/pub\:/linux\:/utils\:/util-linux/
+Linux Kernel Archive
+.UE .
projects / thirdparty / util-linux.git / blobdiff