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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 | .\" ----------------------------------------------------------------------- | |
e9da7722 | 27 | .TH FLOCK 1 "September 2011" "util-linux" "User Commands" |
d162fcb5 | 28 | .SH NAME |
232dc924 | 29 | flock \- manage locks from shell scripts |
d162fcb5 | 30 | .SH SYNOPSIS |
e9da7722 | 31 | .B flock |
295dd902 | 32 | [options] <file|directory> <command> [command args] |
e9da7722 SK |
33 | .br |
34 | .B flock | |
295dd902 | 35 | [options] <file|directory> -c <command> |
e9da7722 SK |
36 | .br |
37 | .B flock | |
38 | [options] <file descriptor number> | |
d162fcb5 | 39 | .SH DESCRIPTION |
d162fcb5 | 40 | .PP |
baf39af1 KZ |
41 | This utility manages |
42 | .BR flock (2) | |
43 | locks from within shell scripts or the command line. | |
d162fcb5 | 44 | .PP |
387bae93 | 45 | The first and second forms wrap the lock around the executing a command, in |
e9da7722 | 46 | a manner similar to |
baf39af1 KZ |
47 | .BR su (1) |
48 | or | |
49 | .BR newgrp (1). | |
e9da7722 SK |
50 | It locks a specified file or directory, which is created (assuming |
51 | appropriate permissions), if it does not already exist. By default, if the | |
52 | lock cannot be immediately acquired, | |
53 | .B flock | |
baf39af1 | 54 | waits until the lock is available. |
e9da7722 SK |
55 | .PP |
56 | The third form uses open file by file descriptor number. See examples how | |
1f338fe1 | 57 | that can be used. |
baf39af1 KZ |
58 | .SH OPTIONS |
59 | .TP | |
60 | \fB\-s\fP, \fB\-\-shared\fP | |
61 | Obtain a shared lock, sometimes called a read lock. | |
62 | .TP | |
a120aaa7 | 63 | \fB\-x\fP, \fB\-e\fP, \fB\-\-exclusive\fP |
baf39af1 KZ |
64 | Obtain an exclusive lock, sometimes called a write lock. This is the |
65 | default. | |
66 | .TP | |
67 | \fB\-u\fP, \fB\-\-unlock\fP | |
e9da7722 SK |
68 | Drop a lock. This is usually not required, since a lock is automatically |
69 | dropped when the file is closed. However, it may be required in special | |
70 | cases, for example if the enclosed command group may have forked a background | |
71 | process which should not be holding the lock. | |
baf39af1 | 72 | .TP |
a120aaa7 | 73 | \fB\-n\fP, \fB\-\-nb\fP, \fB\-\-nonblock\fP |
827b1cee | 74 | Fail rather than wait if the lock cannot be |
baf39af1 | 75 | immediately acquired. |
827b1cee JYK |
76 | See the |
77 | .I \-E | |
78 | option for the exit code used. | |
baf39af1 | 79 | .TP |
a120aaa7 | 80 | \fB\-w\fP, \fB\-\-wait\fP, \fB\-\-timeout\fP \fIseconds\fP |
827b1cee | 81 | Fail if the lock cannot be acquired within |
e9da7722 SK |
82 | .IR seconds . |
83 | Decimal fractional values are allowed. | |
827b1cee JYK |
84 | See the |
85 | .I \-E | |
86 | option for the exit code used. | |
baf39af1 KZ |
87 | .TP |
88 | \fB\-o\fP, \fB\-\-close\fP | |
89 | Close the file descriptor on which the lock is held before executing | |
e9da7722 SK |
90 | .BR command\ . |
91 | This is useful if | |
92 | .B command | |
93 | spawns a child process which should not be holding the lock. | |
baf39af1 | 94 | .TP |
827b1cee JYK |
95 | \fB\-E\fP, \fB\-\-conflict\-exit\-code\fP \fInumber\fP |
96 | The exit code used when the \fB\-n\fP option is in use, and the | |
97 | conflicting lock exists, or the \fB\-w\fP option is in use, | |
98 | and the timeout is reached. The default value is 1. | |
99 | .TP | |
a120aaa7 | 100 | \fB\-c\fP, \fB\-\-command\fP \fIcommand\fP |
e9da7722 SK |
101 | Pass a single |
102 | .IR command , | |
103 | without arguments, to the shell with | |
104 | .BR -c . | |
a120aaa7 | 105 | .TP |
baf39af1 | 106 | \fB\-h\fP, \fB\-\-help\fP |
b4362b6f | 107 | Display help text and exit. |
e9da7722 | 108 | .IP "\fB\-V, \-\-version\fP" |
b4362b6f | 109 | Display version information and exit. |
e9da7722 SK |
110 | .SH EXAMPLES |
111 | .TP | |
112 | shell1> flock /tmp -c cat | |
113 | .TQ | |
114 | shell2> flock -w .007 /tmp -c echo; /bin/echo $? | |
115 | Set exclusive lock to directory /tmp and the second command will fail. | |
116 | .TP | |
117 | shell1> flock -s /tmp -c cat | |
118 | .TQ | |
119 | shell2> flock -s -w .007 /tmp -c echo; /bin/echo $? | |
120 | Set shared lock to directory /tmp and the second command will not fail. | |
121 | Notice that attempting to get exclusive lock with second command would fail. | |
122 | .TP | |
295dd902 MF |
123 | shell> flock -x local-lock-file echo 'a b c' |
124 | Grab the exclusive lock "local-lock-file" before running echo with 'a b c'. | |
125 | .TP | |
e9da7722 SK |
126 | ( |
127 | .TQ | |
128 | flock -n 9 || exit 1 | |
129 | .TQ | |
130 | # ... commands executed under lock ... | |
131 | .TQ | |
132 | ) 9>/var/lock/mylockfile | |
133 | The form is convenient inside shell scripts. The mode used to open the file | |
134 | doesn't matter to | |
135 | .BR flock ; | |
136 | using | |
137 | .I > | |
138 | or | |
139 | .I >> | |
140 | allows the lockfile to be created if it does not already exist, however, | |
141 | write permission is required. Using | |
142 | .I < | |
143 | requires that the file already exists but only read permission is required. | |
295dd902 MF |
144 | .TP |
145 | [ "${FLOCKER}" != "$0" ] && exec env FLOCKER="$0" flock -en "$0" "$0" "$@" || : | |
146 | This is useful boilerplate code for shell scripts. Put it at the top of the | |
147 | shell script you want to lock and it'll automatically lock itself on the first | |
148 | run. If the env var $FLOCKER is not set to the shell script that is being run, | |
149 | then execute flock and grab an exclusive non-blocking lock (using the script | |
150 | itself as the lock file) before re-execing itself with the right arguments. It | |
151 | also sets the FLOCKER env var to the right value so it doesn't run again. | |
e9da7722 SK |
152 | .SH "EXIT STATUS" |
153 | The command uses | |
154 | .B sysexits.h | |
3523ca7d | 155 | return values for everything, except when using either of the options |
e9da7722 SK |
156 | .I \-n |
157 | or | |
158 | .I \-w | |
3523ca7d | 159 | which report a failure to acquire the lock with a return value given by the |
827b1cee JYK |
160 | .I \-E |
161 | option, or 1 by default. | |
d162fcb5 | 162 | .SH AUTHOR |
e9da7722 SK |
163 | .UR hpa@zytor.com |
164 | H. Peter Anvin | |
165 | .UE | |
baf39af1 | 166 | .SH COPYRIGHT |
a120aaa7 | 167 | Copyright \(co 2003\-2006 H. Peter Anvin. |
baf39af1 KZ |
168 | .br |
169 | This is free software; see the source for copying conditions. There is NO | |
170 | warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. | |
171 | .SH "SEE ALSO" | |
172 | .BR flock (2) | |
86d62711 | 173 | .SH AVAILABILITY |
601d12fb | 174 | The flock command is part of the util-linux package and is available from |
e9da7722 SK |
175 | .UR ftp://\:ftp.kernel.org\:/pub\:/linux\:/utils\:/util-linux/ |
176 | Linux Kernel Archive | |
177 | .UE . |