Adding upstream version 2.36.1.upstream/2.36.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 206 insertions, 0 deletions

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+.\" -----------------------------------------------------------------------
+.\"
+.\"   Copyright 2003-2006 H. Peter Anvin - All Rights Reserved
+.\"
+.\"   Permission is hereby granted, free of charge, to any person
+.\"   obtaining a copy of this software and associated documentation
+.\"   files (the "Software"), to deal in the Software without
+.\"   restriction, including without limitation the rights to use,
+.\"   copy, modify, merge, publish, distribute, sublicense, and/or
+.\"   sell copies of the Software, and to permit persons to whom
+.\"   the Software is furnished to do so, subject to the following
+.\"   conditions:
+.\"
+.\"   The above copyright notice and this permission notice shall
+.\"   be included in all copies or substantial portions of the Software.
+.\"
+.\"   THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+.\"   EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+.\"   OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+.\"   NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+.\"   HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+.\"   WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+.\"   FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+.\"   OTHER DEALINGS IN THE SOFTWARE.
+.\"
+.\" -----------------------------------------------------------------------
+.TH FLOCK 1 "July 2014" "util-linux" "User Commands"
+.SH NAME
+flock \- manage locks from shell scripts
+.SH SYNOPSIS
+.B flock
+[options]
+.IR file | "directory command " [ arguments ]
+.br
+.B flock
+[options]
+.IR file | directory
+.BI \-c " command"
+.br
+.B flock
+.RI [options] " number"
+.SH DESCRIPTION
+This utility manages
+.BR flock (2)
+locks from within shell scripts or from the command line.
+.PP
+The first and second of the above forms wrap the lock around the execution of a
+.IR command ,
+in a manner similar to
+.BR su (1)
+or
+.BR newgrp (1).
+They lock a specified \fIfile\fR or \fIdirectory\fR, which is created (assuming
+appropriate permissions) if it does not already exist.  By default, if the
+lock cannot be immediately acquired,
+.B flock
+waits until the lock is available.
+.PP
+The third form uses an open file by its file descriptor \fInumber\fR.
+See the examples below for how that can be used.
+.SH OPTIONS
+.TP
+.BR \-c , " \-\-command " \fIcommand
+Pass a single \fIcommand\fR, without arguments, to the shell with
+.BR \-c .
+.TP
+.BR \-E , " \-\-conflict\-exit\-code " \fInumber
+The exit status used when the \fB\-n\fP option is in use, and the
+conflicting lock exists, or the \fB\-w\fP option is in use,
+and the timeout is reached.  The default value is \fB1\fR.
+The \fInumber\fR has to be in the range of 0 to 255.
+.TP
+.BR \-F , " \-\-no\-fork"
+Do not fork before executing
+.IR command .
+Upon execution the flock process is replaced by
+.I command
+which continues to hold the lock. This option is incompatible with
+\fB\-\-close\fR as there would otherwise be nothing left to hold the lock.
+.TP
+.BR \-e , " \-x" , " \-\-exclusive"
+Obtain an exclusive lock, sometimes called a write lock.  This is the
+default.
+.TP
+.BR \-n , " \-\-nb" , " \-\-nonblock"
+Fail rather than wait if the lock cannot be
+immediately acquired.
+See the
+.B \-E
+option for the exit status used.
+.TP
+.BR \-o , " \-\-close"
+Close the file descriptor on which the lock is held before executing
+.IR command .
+This is useful if
+.I command
+spawns a child process which should not be holding the lock.
+.TP
+.BR \-s , " \-\-shared"
+Obtain a shared lock, sometimes called a read lock.
+.TP
+.BR \-u , " \-\-unlock"
+Drop a lock.  This is usually not required, since a lock is automatically
+dropped when the file is closed.  However, it may be required in special
+cases, for example if the enclosed command group may have forked a background
+process which should not be holding the lock.
+.TP
+.BR \-w , " \-\-wait" , " \-\-timeout " \fIseconds
+Fail if the lock cannot be acquired within
+.IR seconds .
+Decimal fractional values are allowed.
+See the
+.B \-E
+option for the exit status used. The zero number of
+.I seconds
+is interpreted as \fB\-\-nonblock\fR.
+.TP
+.B \-\-verbose
+Report how long it took to acquire the lock, or why the lock could not be
+obtained.
+.TP
+.BR \-V , " \-\-version"
+Display version information and exit.
+.TP
+.BR \-h , " \-\-help"
+Display help text and exit.
+.SH EXIT STATUS
+The command uses
+.B sysexits.h
+exit status values for everything, except when using either of the options
+.B \-n
+or
+.B \-w
+which report a failure to acquire the lock with a exit status given by the
+.B \-E
+option, or 1 by default.  The exit status given by
+.B \-E has to be in the range of 0 to 255.
+.PP
+When using the \fIcommand\fR variant, and executing the child worked, then
+the exit status is that of the child command.
+.SH EXAMPLES
+Note that "shell> " in examples is a command line prompt.
+.TP
+shell1> flock /tmp \-c cat
+.TQ
+shell2> flock \-w .007 /tmp \-c echo; /bin/echo $?
+Set exclusive lock to directory /tmp and the second command will fail.
+.TP
+shell1> flock \-s /tmp \-c cat
+.TQ
+shell2> flock \-s \-w .007 /tmp \-c echo; /bin/echo $?
+Set shared lock to directory /tmp and the second command will not fail.
+Notice that attempting to get exclusive lock with second command would fail.
+.TP
+shell> flock \-x local-lock-file echo 'a b c'
+Grab the exclusive lock "local-lock-file" before running echo with 'a b c'.
+.TP
+(
+.TQ
+  flock \-n 9 || exit 1
+.TQ
+  # ... commands executed under lock ...
+.TQ
+) 9>/var/lock/mylockfile
+The form is convenient inside shell scripts.  The mode used to open the file
+doesn't matter to
+.BR flock ;
+using
+.I >
+or
+.I >>
+allows the lockfile to be created if it does not already exist, however,
+write permission is required.  Using
+.I <
+requires that the file already exists but only read permission is required.
+.TP
+[ "${FLOCKER}" != "$0" ] && exec env FLOCKER="$0" flock \-en "$0" "$0" "$@" || :
+This is useful boilerplate code for shell scripts.  Put it at the top of the
+shell script you want to lock and it'll automatically lock itself on the first
+run.  If the env var $FLOCKER is not set to the shell script that is being run,
+then execute flock and grab an exclusive non-blocking lock (using the script
+itself as the lock file) before re-execing itself with the right arguments.  It
+also sets the FLOCKER env var to the right value so it doesn't run again.
+.TP
+shell> exec 4<>/var/lock/mylockfile
+.TQ
+shell> flock -n 4
+This form is convenient for locking a file without spawning a subprocess.
+The shell opens the lock file for reading and writing as file descriptor 4,
+then flock is used to lock the descriptor.
+.SH AUTHORS
+.UR hpa@zytor.com
+H. Peter Anvin
+.UE
+.SH COPYRIGHT
+Copyright \(co 2003\-2006 H. Peter Anvin.
+.br
+This is free software; see the source for copying conditions.  There is NO
+warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+.SH SEE ALSO
+.BR flock (2)
+.SH AVAILABILITY
+The flock command is part of the util-linux package and is available from
+.UR https://\:www.kernel.org\:/pub\:/linux\:/utils\:/util-linux/
+Linux Kernel Archive
+.UE .