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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 | .\" ----------------------------------------------------------------------- | |
e33ee284 | 27 | .TH FLOCK 1 "July 2014" "util-linux" "User Commands" |
d162fcb5 | 28 | .SH NAME |
232dc924 | 29 | flock \- 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 |
44 | This utility manages |
45 | .BR flock (2) | |
e33ee284 | 46 | locks from within shell scripts or from the command line. |
d162fcb5 | 47 | .PP |
e33ee284 BS |
48 | The first and second of the above forms wrap the lock around the execution of a |
49 | .IR command , | |
50 | in a manner similar to | |
baf39af1 KZ |
51 | .BR su (1) |
52 | or | |
53 | .BR newgrp (1). | |
e33ee284 BS |
54 | They lock a specified \fIfile\fR or \fIdirectory\fR, which is created (assuming |
55 | appropriate permissions) if it does not already exist. By default, if the | |
e9da7722 SK |
56 | lock cannot be immediately acquired, |
57 | .B flock | |
baf39af1 | 58 | waits until the lock is available. |
e9da7722 | 59 | .PP |
e33ee284 BS |
60 | The third form uses an open file by its file descriptor \fInumber\fR. |
61 | See the examples below for how that can be used. | |
baf39af1 KZ |
62 | .SH OPTIONS |
63 | .TP | |
5e43af7e BS |
64 | .BR \-c , " \-\-command " \fIcommand |
65 | Pass 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 |
69 | The exit code used when the \fB\-n\fP option is in use, and the |
70 | conflicting lock exists, or the \fB\-w\fP option is in use, | |
71 | and the timeout is reached. The default value is \fB1\fR. | |
72 | .TP | |
70325140 TB |
73 | .BR \-F , " \-\-no\-fork" |
74 | Do not fork before executing | |
75 | .IR command . | |
76 | Upon execution the flock process is replaced by | |
0bb7e904 | 77 | .I command |
70325140 TB |
78 | which 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 |
82 | Obtain an exclusive lock, sometimes called a write lock. This is the |
83 | default. | |
84 | .TP | |
5e43af7e | 85 | .BR \-n , " \-\-nb" , " \-\-nonblock" |
827b1cee | 86 | Fail rather than wait if the lock cannot be |
baf39af1 | 87 | immediately acquired. |
827b1cee | 88 | See the |
e33ee284 | 89 | .B \-E |
827b1cee | 90 | option for the exit code used. |
baf39af1 | 91 | .TP |
5e43af7e | 92 | .BR \-o , " \-\-close" |
baf39af1 | 93 | Close the file descriptor on which the lock is held before executing |
e33ee284 | 94 | .IR command . |
e9da7722 | 95 | This is useful if |
e33ee284 | 96 | .I command |
e9da7722 | 97 | spawns a child process which should not be holding the lock. |
baf39af1 | 98 | .TP |
5e43af7e BS |
99 | .BR \-s , " \-\-shared" |
100 | Obtain a shared lock, sometimes called a read lock. | |
827b1cee | 101 | .TP |
5e43af7e BS |
102 | .BR \-u , " \-\-unlock" |
103 | Drop a lock. This is usually not required, since a lock is automatically | |
104 | dropped when the file is closed. However, it may be required in special | |
105 | cases, for example if the enclosed command group may have forked a background | |
106 | process which should not be holding the lock. | |
a120aaa7 | 107 | .TP |
5e43af7e BS |
108 | .BR \-w , " \-\-wait" , " \-\-timeout " \fIseconds |
109 | Fail if the lock cannot be acquired within | |
110 | .IR seconds . | |
111 | Decimal fractional values are allowed. | |
112 | See the | |
113 | .B \-E | |
c4604c38 | 114 | option for the exit code used. The zero number of |
0bb7e904 | 115 | .I seconds |
c4604c38 | 116 | is interpreted as \fB\-\-nonblock\fR. |
5e43af7e | 117 | .TP |
59dc9f28 SK |
118 | .B \-\-verbose |
119 | Report how long it took to acquire the lock, or why the lock could not be | |
120 | obtained. | |
121 | .TP | |
5e43af7e | 122 | .BR \-V , " \-\-version" |
b4362b6f | 123 | Display version information and exit. |
5e43af7e BS |
124 | .TP |
125 | .BR \-h , " \-\-help" | |
126 | Display help text and exit. | |
e9da7722 SK |
127 | .SH EXAMPLES |
128 | .TP | |
1c4c6024 | 129 | shell1> flock /tmp \-c cat |
e9da7722 | 130 | .TQ |
1c4c6024 | 131 | shell2> flock \-w .007 /tmp \-c echo; /bin/echo $? |
e9da7722 SK |
132 | Set exclusive lock to directory /tmp and the second command will fail. |
133 | .TP | |
1c4c6024 | 134 | shell1> flock \-s /tmp \-c cat |
e9da7722 | 135 | .TQ |
1c4c6024 | 136 | shell2> flock \-s \-w .007 /tmp \-c echo; /bin/echo $? |
e9da7722 SK |
137 | Set shared lock to directory /tmp and the second command will not fail. |
138 | Notice that attempting to get exclusive lock with second command would fail. | |
139 | .TP | |
1c4c6024 | 140 | shell> flock \-x local-lock-file echo 'a b c' |
295dd902 MF |
141 | Grab the exclusive lock "local-lock-file" before running echo with 'a b c'. |
142 | .TP | |
e9da7722 SK |
143 | ( |
144 | .TQ | |
1c4c6024 | 145 | flock \-n 9 || exit 1 |
e9da7722 SK |
146 | .TQ |
147 | # ... commands executed under lock ... | |
148 | .TQ | |
149 | ) 9>/var/lock/mylockfile | |
150 | The form is convenient inside shell scripts. The mode used to open the file | |
151 | doesn't matter to | |
152 | .BR flock ; | |
153 | using | |
154 | .I > | |
155 | or | |
156 | .I >> | |
157 | allows the lockfile to be created if it does not already exist, however, | |
158 | write permission is required. Using | |
159 | .I < | |
160 | requires that the file already exists but only read permission is required. | |
295dd902 | 161 | .TP |
1c4c6024 | 162 | [ "${FLOCKER}" != "$0" ] && exec env FLOCKER="$0" flock \-en "$0" "$0" "$@" || : |
295dd902 MF |
163 | This is useful boilerplate code for shell scripts. Put it at the top of the |
164 | shell script you want to lock and it'll automatically lock itself on the first | |
165 | run. If the env var $FLOCKER is not set to the shell script that is being run, | |
166 | then execute flock and grab an exclusive non-blocking lock (using the script | |
167 | itself as the lock file) before re-execing itself with the right arguments. It | |
168 | also sets the FLOCKER env var to the right value so it doesn't run again. | |
966bcac3 J |
169 | .TP |
170 | .TQ | |
171 | exec 4<>/var/lock/mylockfile | |
172 | .TQ | |
173 | flock -n 4 | |
174 | This form is convenient for locking a file without spawning a subprocess. | |
175 | The shell opens the lock file for reading and writing as file descriptor 4, | |
176 | then flock is used to lock the descriptor. | |
e9da7722 SK |
177 | .SH "EXIT STATUS" |
178 | The command uses | |
179 | .B sysexits.h | |
3523ca7d | 180 | return values for everything, except when using either of the options |
e33ee284 | 181 | .B \-n |
e9da7722 | 182 | or |
e33ee284 | 183 | .B \-w |
3523ca7d | 184 | which report a failure to acquire the lock with a return value given by the |
e33ee284 | 185 | .B \-E |
827b1cee | 186 | option, or 1 by default. |
ce6d69dd | 187 | .PP |
e33ee284 | 188 | When using the \fIcommand\fR variant, and executing the child worked, then |
ce6d69dd | 189 | the exit status is that of the child command. |
d162fcb5 | 190 | .SH AUTHOR |
e9da7722 SK |
191 | .UR hpa@zytor.com |
192 | H. Peter Anvin | |
193 | .UE | |
baf39af1 | 194 | .SH COPYRIGHT |
a120aaa7 | 195 | Copyright \(co 2003\-2006 H. Peter Anvin. |
baf39af1 KZ |
196 | .br |
197 | This is free software; see the source for copying conditions. There is NO | |
198 | warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. | |
199 | .SH "SEE ALSO" | |
200 | .BR flock (2) | |
86d62711 | 201 | .SH AVAILABILITY |
601d12fb | 202 | The flock command is part of the util-linux package and is available from |
d673b74e | 203 | .UR https://\:www.kernel.org\:/pub\:/linux\:/utils\:/util-linux/ |
e9da7722 SK |
204 | Linux Kernel Archive |
205 | .UE . |