]> git.ipfire.org Git - thirdparty/util-linux.git/blame - sys-utils/flock.1
man: Use the correct macro for a font change of one argument
[thirdparty/util-linux.git] / sys-utils / flock.1
CommitLineData
baf39af1 1.\" -----------------------------------------------------------------------
e9da7722 2.\"
a120aaa7 3.\" Copyright 2003-2006 H. Peter Anvin - All Rights Reserved
baf39af1
KZ
4.\"
5.\" Permission is hereby granted, free of charge, to any person
6.\" obtaining a copy of this software and associated documentation
7.\" files (the "Software"), to deal in the Software without
8.\" restriction, including without limitation the rights to use,
9.\" copy, modify, merge, publish, distribute, sublicense, and/or
10.\" sell copies of the Software, and to permit persons to whom
11.\" the Software is furnished to do so, subject to the following
12.\" conditions:
e9da7722 13.\"
baf39af1
KZ
14.\" The above copyright notice and this permission notice shall
15.\" be included in all copies or substantial portions of the Software.
e9da7722 16.\"
baf39af1
KZ
17.\" THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
18.\" EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
19.\" OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
20.\" NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
21.\" HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
22.\" WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
23.\" FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
24.\" OTHER DEALINGS IN THE SOFTWARE.
25.\"
26.\" -----------------------------------------------------------------------
e33ee284 27.TH FLOCK 1 "July 2014" "util-linux" "User Commands"
d162fcb5 28.SH NAME
232dc924 29flock \- manage locks from shell scripts
d162fcb5 30.SH SYNOPSIS
e9da7722 31.B flock
e33ee284
BS
32[options]
33.IR file | "directory command " [ arguments ]
e9da7722
SK
34.br
35.B flock
e33ee284
BS
36[options]
37.IR file | directory
38.BI \-c " command"
e9da7722
SK
39.br
40.B flock
e33ee284 41.RI [options] " number"
d162fcb5 42.SH DESCRIPTION
d162fcb5 43.PP
baf39af1
KZ
44This utility manages
45.BR flock (2)
e33ee284 46locks from within shell scripts or from the command line.
d162fcb5 47.PP
e33ee284
BS
48The first and second of the above forms wrap the lock around the execution of a
49.IR command ,
50in a manner similar to
baf39af1
KZ
51.BR su (1)
52or
53.BR newgrp (1).
e33ee284
BS
54They lock a specified \fIfile\fR or \fIdirectory\fR, which is created (assuming
55appropriate permissions) if it does not already exist. By default, if the
e9da7722
SK
56lock cannot be immediately acquired,
57.B flock
baf39af1 58waits until the lock is available.
e9da7722 59.PP
e33ee284
BS
60The third form uses an open file by its file descriptor \fInumber\fR.
61See the examples below for how that can be used.
baf39af1
KZ
62.SH OPTIONS
63.TP
5e43af7e
BS
64.BR \-c , " \-\-command " \fIcommand
65Pass a single \fIcommand\fR, without arguments, to the shell with
66.BR \-c .
baf39af1 67.TP
b06c1ca6 68.BR \-E , " \-\-conflict\-exit\-code " \fInumber
5e43af7e
BS
69The exit code used when the \fB\-n\fP option is in use, and the
70conflicting lock exists, or the \fB\-w\fP option is in use,
71and the timeout is reached. The default value is \fB1\fR.
72.TP
70325140
TB
73.BR \-F , " \-\-no\-fork"
74Do not fork before executing
75.IR command .
76Upon execution the flock process is replaced by
0bb7e904 77.I command
70325140
TB
78which continues to hold the lock. This option is incompatible with
79\fB\-\-close\fR as there would otherwise be nothing left to hold the lock.
80.TP
5e43af7e 81.BR \-e , " \-x" , " \-\-exclusive"
baf39af1
KZ
82Obtain an exclusive lock, sometimes called a write lock. This is the
83default.
84.TP
5e43af7e 85.BR \-n , " \-\-nb" , " \-\-nonblock"
827b1cee 86Fail rather than wait if the lock cannot be
baf39af1 87immediately acquired.
827b1cee 88See the
e33ee284 89.B \-E
827b1cee 90option for the exit code used.
baf39af1 91.TP
5e43af7e 92.BR \-o , " \-\-close"
baf39af1 93Close the file descriptor on which the lock is held before executing
e33ee284 94.IR command .
e9da7722 95This is useful if
e33ee284 96.I command
e9da7722 97spawns a child process which should not be holding the lock.
baf39af1 98.TP
5e43af7e
BS
99.BR \-s , " \-\-shared"
100Obtain a shared lock, sometimes called a read lock.
827b1cee 101.TP
5e43af7e
BS
102.BR \-u , " \-\-unlock"
103Drop a lock. This is usually not required, since a lock is automatically
104dropped when the file is closed. However, it may be required in special
105cases, for example if the enclosed command group may have forked a background
106process which should not be holding the lock.
a120aaa7 107.TP
5e43af7e
BS
108.BR \-w , " \-\-wait" , " \-\-timeout " \fIseconds
109Fail if the lock cannot be acquired within
110.IR seconds .
111Decimal fractional values are allowed.
112See the
113.B \-E
c4604c38 114option for the exit code used. The zero number of
0bb7e904 115.I seconds
c4604c38 116is interpreted as \fB\-\-nonblock\fR.
5e43af7e 117.TP
59dc9f28
SK
118.B \-\-verbose
119Report how long it took to acquire the lock, or why the lock could not be
120obtained.
121.TP
5e43af7e 122.BR \-V , " \-\-version"
b4362b6f 123Display version information and exit.
5e43af7e
BS
124.TP
125.BR \-h , " \-\-help"
126Display help text and exit.
e9da7722
SK
127.SH EXAMPLES
128.TP
129shell1> flock /tmp -c cat
130.TQ
131shell2> flock -w .007 /tmp -c echo; /bin/echo $?
132Set exclusive lock to directory /tmp and the second command will fail.
133.TP
134shell1> flock -s /tmp -c cat
135.TQ
136shell2> flock -s -w .007 /tmp -c echo; /bin/echo $?
137Set shared lock to directory /tmp and the second command will not fail.
138Notice that attempting to get exclusive lock with second command would fail.
139.TP
295dd902
MF
140shell> flock -x local-lock-file echo 'a b c'
141Grab the exclusive lock "local-lock-file" before running echo with 'a b c'.
142.TP
e9da7722
SK
143(
144.TQ
145 flock -n 9 || exit 1
146.TQ
147 # ... commands executed under lock ...
148.TQ
149) 9>/var/lock/mylockfile
150The form is convenient inside shell scripts. The mode used to open the file
151doesn't matter to
152.BR flock ;
153using
154.I >
155or
156.I >>
157allows the lockfile to be created if it does not already exist, however,
158write permission is required. Using
159.I <
160requires that the file already exists but only read permission is required.
295dd902
MF
161.TP
162[ "${FLOCKER}" != "$0" ] && exec env FLOCKER="$0" flock -en "$0" "$0" "$@" || :
163This is useful boilerplate code for shell scripts. Put it at the top of the
164shell script you want to lock and it'll automatically lock itself on the first
165run. If the env var $FLOCKER is not set to the shell script that is being run,
166then execute flock and grab an exclusive non-blocking lock (using the script
167itself as the lock file) before re-execing itself with the right arguments. It
168also sets the FLOCKER env var to the right value so it doesn't run again.
e9da7722
SK
169.SH "EXIT STATUS"
170The command uses
171.B sysexits.h
3523ca7d 172return values for everything, except when using either of the options
e33ee284 173.B \-n
e9da7722 174or
e33ee284 175.B \-w
3523ca7d 176which report a failure to acquire the lock with a return value given by the
e33ee284 177.B \-E
827b1cee 178option, or 1 by default.
ce6d69dd 179.PP
e33ee284 180When using the \fIcommand\fR variant, and executing the child worked, then
ce6d69dd 181the exit status is that of the child command.
d162fcb5 182.SH AUTHOR
e9da7722
SK
183.UR hpa@zytor.com
184H. Peter Anvin
185.UE
baf39af1 186.SH COPYRIGHT
a120aaa7 187Copyright \(co 2003\-2006 H. Peter Anvin.
baf39af1
KZ
188.br
189This is free software; see the source for copying conditions. There is NO
190warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
191.SH "SEE ALSO"
192.BR flock (2)
86d62711 193.SH AVAILABILITY
601d12fb 194The flock command is part of the util-linux package and is available from
d673b74e 195.UR https://\:www.kernel.org\:/pub\:/linux\:/utils\:/util-linux/
e9da7722
SK
196Linux Kernel Archive
197.UE .