1.\" 2.\" Copyright (C) 1998 John D. Polstra. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 13.\" THIS SOFTWARE IS PROVIDED BY JOHN D. POLSTRA AND CONTRIBUTORS ``AS IS'' AND 14.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 15.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 16.\" ARE DISCLAIMED. IN NO EVENT SHALL JOHN D. POLSTRA OR CONTRIBUTORS BE LIABLE 17.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 18.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 19.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 20.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 21.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 22.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 23.\" SUCH DAMAGE. 24.\" 25.\" $FreeBSD$ 26.\" 27.Dd June 18, 2020 28.Dt LOCKF 1 29.Os 30.Sh NAME 31.Nm lockf 32.Nd execute a command while holding a file lock 33.Sh SYNOPSIS 34.Nm 35.Op Fl kns 36.Op Fl t Ar seconds 37.Ar file 38.Ar command 39.Op Ar arguments 40.Sh DESCRIPTION 41The 42.Nm 43utility acquires an exclusive lock on a 44.Ar file , 45creating it if necessary, 46.Bf Em 47and removing the file on exit unless explicitly told not to. 48.Ef 49While holding the lock, it executes a 50.Ar command 51with optional 52.Ar arguments . 53After the 54.Ar command 55completes, 56.Nm 57releases the lock, and removes the 58.Ar file 59unless the 60.Fl k 61option is specified. 62.Bx Ns -style 63locking is used, as described in 64.Xr flock 2 ; 65the mere existence of the 66.Ar file 67is not considered to constitute a lock. 68.Pp 69If the 70.Nm 71utility is being used to facilitate concurrency between a number 72of processes, it is recommended that the 73.Fl k 74option be used. 75This will guarantee lock ordering, as well as implement 76a performance enhanced algorithm which minimizes CPU load associated 77with concurrent unlink, drop and re-acquire activity. 78It should be noted 79that if the 80.Fl k 81option is not used, then no guarantees around lock ordering can be made. 82.Pp 83The following options are supported: 84.Bl -tag -width ".Fl t Ar seconds" 85.It Fl k 86Causes the lock file to be kept (not removed) after the command 87completes. 88.It Fl s 89Causes 90.Nm 91to operate silently. 92Failure to acquire the lock is indicated only in the exit status. 93.It Fl n 94Causes 95.Nm 96to fail if the specified lock 97.Ar file 98does not exist. 99If 100.Fl n 101is not specified, 102.Nm 103will create 104.Ar file 105if necessary. 106.It Fl t Ar seconds 107Specifies a timeout for waiting for the lock. 108By default, 109.Nm 110waits indefinitely to acquire the lock. 111If a timeout is specified with this option, 112.Nm 113will wait at most the given number of 114.Ar seconds 115before giving up. 116A timeout of 0 may be given, in which case 117.Nm 118will fail unless it can acquire the lock immediately. 119When a lock times out, 120.Ar command 121is 122.Em not 123executed. 124.El 125.Pp 126In no event will 127.Nm 128break a lock that is held by another process. 129.Sh EXIT STATUS 130If 131.Nm 132successfully acquires the lock, it returns the exit status produced by 133.Ar command . 134Otherwise, it returns one of the exit codes defined in 135.Xr sysexits 3 , 136as follows: 137.Bl -tag -width ".Dv EX_CANTCREAT" 138.It Dv EX_TEMPFAIL 139The specified lock file was already locked by another process. 140.It Dv EX_CANTCREAT 141The 142.Nm 143utility 144was unable to create the lock file, e.g., because of insufficient access 145privileges. 146.It Dv EX_UNAVAILABLE 147The 148.Fl n 149option is specified and the specified lock file does not exist. 150.It Dv EX_USAGE 151There was an error on the 152.Nm 153command line. 154.It Dv EX_OSERR 155A system call (e.g., 156.Xr fork 2 ) 157failed unexpectedly. 158.It Dv EX_SOFTWARE 159The 160.Ar command 161did not exit normally, 162but may have been signaled or stopped. 163.El 164.Sh EXAMPLES 165The first job takes a lock and sleeps for 5 seconds in the background. 166The second job tries to get the lock and timeouts after 1 second (PID numbers 167will differ): 168.Bd -literal -offset indent 169$ lockf mylock sleep 5 & lockf -t 1 mylock echo "Success" 170[1] 94410 171lockf: mylock: already locked 172.Ed 173.Pp 174The first job takes a lock and sleeps for 1 second in the background. 175The second job waits up to 5 seconds to take the lock and echoes the message on 176success (PID numbers will differ): 177.Bd -literal -offset indent 178$ lockf mylock sleep 1 & lockf -t 5 mylock echo "Success" 179[1] 19995 180Success 181[1]+ Done lockf mylock sleep 1 182.Ed 183.Sh SEE ALSO 184.Xr flock 2 , 185.Xr lockf 3 , 186.Xr sysexits 3 187.Sh HISTORY 188A 189.Nm 190utility first appeared in 191.Fx 2.2 . 192.Sh AUTHORS 193.An John Polstra Aq Mt jdp@polstra.com 194