1FLOCK(1)                        H. Peter Anvin                        FLOCK(1)
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NAME

6       flock - Manage locks from shell scripts
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SYNOPSIS

9       flock [-sxon] [-w timeout] lockfile [-c] command...
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11       flock [-sxun] [-w timeout] fd
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DESCRIPTION

14       This  utility  manages  flock(2) locks from within shell scripts or the
15       command line.
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17       The first form wraps the lock around the executing a command, in a man‐
18       ner similar to su(1) or newgrp(1).  It locks a specified file, which is
19       created (assuming appropriate permissions),  if  it  does  not  already
20       exist.
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22       The  second  form  is  conveninent inside shell scripts, and is usually
23       used the following manner:
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25       (
26         flock -s 200
27         # ... commands executed under lock ...
28       ) 200>/var/lock/mylockfile
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30       The mode used to open the file doesn't matter to flock; using >  or  >>
31       allows  the  lockfile  to be created if it does not already exist, how‐
32       ever, write permission is required; using  <  requires  that  the  file
33       already exists but only read permission is required.
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35       By  default,  if  the  lock cannot be immediately acquired, flock waits
36       until the lock is available.
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OPTIONS

39       -s, --shared
40              Obtain a shared lock, sometimes called a read lock.
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42       -x, -e, --exclusive
43              Obtain an exclusive lock, sometimes called a write  lock.   This
44              is the default.
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46       -u, --unlock
47              Drop  a  lock.   This  is  usually not required, since a lock is
48              automatically dropped when the file is closed.  However, it  may
49              be  required  in special cases, for example if the enclosed com‐
50              mand group may have forked a background process which should not
51              be holding the lock.
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53       -n, --nb, --nonblock
54              Fail  (with an exit code of 1) rather than wait if the lock can‐
55              not be immediately acquired.
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57       -w, --wait, --timeout seconds
58              Fail (with an exit code of 1) if the  lock  cannot  be  acquired
59              within seconds seconds.  Decimal fractional values are allowed.
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61       -o, --close
62              Close  the file descriptor on which the lock is held before exe‐
63              cuting command.  This  is  useful  if  command  spawns  a  child
64              process which should not be hold ing the lock.
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66       -c, --command command
67              Pass a single command to the shell with -c.
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69       -h, --help
70              Print a help message.
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AUTHOR

73       Written by H. Peter Anvin <hpa@zytor.com>.
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76       Copyright © 2003-2006 H. Peter Anvin.
77       This is free software; see the source for copying conditions.  There is
78       NO warranty; not even for MERCHANTABILITY or FITNESS FOR  A  PARTICULAR
79       PURPOSE.
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SEE ALSO

82       flock(2)
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84
85
86flock utility                     4 Feb 2006                          FLOCK(1)
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