# 前面的工作
update_pkg_on_machine_1
update_pkg_on_machine_2
update_pkg_on_machine_3
# ... 后面的工作

# 前面的工作
update_pkg_on_machine_1 &
update_pkg_on_machine_2 &
update_pkg_on_machine_3 &
sleep 10
# ... 后面的工作

NAME
  flock - Manage locks from shell scripts

SYNOPSIS
  flock [-sxon] [-w timeout] lockfile [-c] command...

  flock [-sxon] [-w timeout] lockdir [-c] command...

  flock [-sxun] [-w timeout] fd
DESCRIPTION
  This utility manages flock(2) locks from within shell scripts or the
  command line.

  The first and second forms wraps the lock around the executing a
  command, in a manner similar to su(1) or newgrp(1). It locks a
  specified file or directory, which is created (assuming appropriate
  permissions), if it does not already exist.

  The third form is convenient inside shell scripts, and is usually used
  the following manner:

  (
   flock -s 200
   # ... commands executed under lock ...
  ) 200>/var/lock/mylockfile

  The mode used to open the file doesn't matter to flock; using > or >>
  allows the lockfile to be created if it does not already exist,
  however, write permission is required; using < requires that the file
  already exists but only read permission is required.

  By default, if the lock cannot be immediately acquired, flock waits
  until the lock is available.

OPTIONS
  -s, --shared
    Obtain a shared lock, sometimes called a read lock.

  -x, -e, --exclusive
    Obtain an exclusive lock, sometimes called a write lock. This
    is the default.

  -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.

  -n, --nb, --nonblock
    Fail (with an exit code of 1) rather than wait if the lock
    cannot be immediately acquired.

  -w, --wait, --timeout seconds
    Fail (with an exit code of 1) if the lock cannot be acquired
    within seconds seconds. Decimal fractional values are allowed.

  -o, --close
    Close the file descriptor on which the lock is held before
    executing command. This is useful if command spawns a child
    process which should not be hold ing the lock.

  -c, --command command
    Pass a single command to the shell with -c.

  -h, --help
    Print a help message.

AUTHOR
  Written by H. Peter Anvin <hpa@zytor.com>.

COPYRIGHT
  Copyright © 2003-2006 H. Peter Anvin.
  This is free software; see the source for copying conditions. There is
  NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
  PURPOSE.

SEE ALSO
  flock(2)

AVAILABILITY
  The flock command is part of the util-linux-ng package and is available
  from ftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/.

#! /bin/bash
sleep 10
date

flock /tmp/demo.lock ~/test.sh

wush@router:~$ flock /tmp/demo.lock ./test.sh

wush@router:~$ flock /tmp/demo.lock ./test.sh

# 前面的工作
flock -s lock_path update_pkg_on_machine_1 &
flock -s lock_path update_pkg_on_machine_2 &
flock -s lock_path update_pkg_on_machine_3 &
flock -x lock_path echo "all done!"
# ... 后面的工作