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32 .Nd execute a command while holding a file lock
43 utility acquires an exclusive lock on a
45 creating it if necessary,
47 and removing the file on exit unless explicitly told not to.
49 While holding the lock, it executes a
57 releases the lock, and removes the
63 locking is used, as described in
65 the mere existence of the
67 is not considered to constitute a lock.
71 utility is being used to facilitate concurrency between a number
72 of processes, it is recommended that the
75 This will guarantee lock ordering, as well as implement
76 a performance enhanced algorithm which minimizes CPU load associated
77 with concurrent unlink, drop and re-acquire activity.
81 option is not used, then no guarantees around lock ordering can be made.
83 The following options are supported:
84 .Bl -tag -width ".Fl t Ar seconds"
86 Causes the lock file to be kept (not removed) after the command
92 Failure to acquire the lock is indicated only in the exit status.
96 to fail if the specified lock
106 Specifies a timeout for waiting for the lock.
109 waits indefinitely to acquire the lock.
110 If a timeout is specified with this option,
112 will wait at most the given number of
115 A timeout of 0 may be given, in which case
117 will fail unless it can acquire the lock immediately.
118 When a lock times out,
127 break a lock that is held by another process.
131 successfully acquires the lock, it returns the exit status produced by
133 Otherwise, it returns one of the exit codes defined in
136 .Bl -tag -width ".Dv EX_CANTCREAT"
138 The specified lock file was already locked by another process.
143 was unable to create the lock file, e.g., because of insufficient access
145 .It Dv EX_UNAVAILABLE
148 option is specified and the specified lock file does not exist.
150 There was an error on the
160 did not exit normally,
161 but may have been signaled or stopped.
170 utility first appeared in
173 .An John Polstra Aq Mt jdp@polstra.com