这个例子是在man flock中解释的，但它需要一些改进，因为我们应该管理bug和退出代码:

   #!/bin/bash
   #set -e this is useful only for very stupid scripts because script fails when anything command exits with status more than 0 !! without possibility for capture exit codes. not all commands exits >0 are failed.

( #start subprocess
  # Wait for lock on /var/lock/.myscript.exclusivelock (fd 200) for 10 seconds
  flock -x -w 10 200
  if [ "$?" != "0" ]; then echo Cannot lock!; exit 1; fi
  echo $$>>/var/lock/.myscript.exclusivelock #for backward lockdir compatibility, notice this command is executed AFTER command bottom  ) 200>/var/lock/.myscript.exclusivelock.
  # Do stuff
  # you can properly manage exit codes with multiple command and process algorithm.
  # I suggest throw this all to external procedure than can properly handle exit X commands

) 200>/var/lock/.myscript.exclusivelock   #exit subprocess

FLOCKEXIT=$?  #save exitcode status
    #do some finish commands

exit $FLOCKEXIT   #return properly exitcode, may be usefull inside external scripts

你可以用另一种方法，列出我过去用过的过程。但这比上面的方法要复杂得多。你应该按ps列出进程，按其名称过滤，附加过滤器grep -v grep清除寄生虫，最后按grep -c计数。和数字比较。这是复杂而不确定的

您可以使用GNU Parallel，因为它在作为sem调用时是作为互斥量工作的。所以，具体来说，你可以使用:

sem --id SCRIPTSINGLETON yourScript

如果你也想要一个超时，使用:

sem --id SCRIPTSINGLETON --semaphoretimeout -10 yourScript

如果信号量在超时时间内没有释放，Timeout <0表示退出而不运行脚本，>的Timeout表示仍然运行脚本。

注意，您应该给它一个名称(使用——id)，否则它默认为控制终端。

GNU Parallel在大多数Linux/OSX/Unix平台上是一个非常简单的安装程序——它只是一个Perl脚本。

使用flock(1)在文件描述符上创建一个独占作用域锁。通过这种方式，您甚至可以同步脚本的不同部分。

#!/bin/bash

(
  # Wait for lock on /var/lock/.myscript.exclusivelock (fd 200) for 10 seconds
  flock -x -w 10 200 || exit 1

  # Do stuff

) 200>/var/lock/.myscript.exclusivelock

这确保(和)之间的代码一次只由一个进程运行，并且该进程不会为锁等待太长时间。

注意:这个特殊的命令是util-linux的一部分。如果您运行的是Linux以外的操作系统，那么它可能不可用，也可能不可用。

这个例子是在man flock中解释的，但它需要一些改进，因为我们应该管理bug和退出代码:

   #!/bin/bash
   #set -e this is useful only for very stupid scripts because script fails when anything command exits with status more than 0 !! without possibility for capture exit codes. not all commands exits >0 are failed.

( #start subprocess
  # Wait for lock on /var/lock/.myscript.exclusivelock (fd 200) for 10 seconds
  flock -x -w 10 200
  if [ "$?" != "0" ]; then echo Cannot lock!; exit 1; fi
  echo $$>>/var/lock/.myscript.exclusivelock #for backward lockdir compatibility, notice this command is executed AFTER command bottom  ) 200>/var/lock/.myscript.exclusivelock.
  # Do stuff
  # you can properly manage exit codes with multiple command and process algorithm.
  # I suggest throw this all to external procedure than can properly handle exit X commands

) 200>/var/lock/.myscript.exclusivelock   #exit subprocess

FLOCKEXIT=$?  #save exitcode status
    #do some finish commands

exit $FLOCKEXIT   #return properly exitcode, may be usefull inside external scripts

你可以用另一种方法，列出我过去用过的过程。但这比上面的方法要复杂得多。你应该按ps列出进程，按其名称过滤，附加过滤器grep -v grep清除寄生虫，最后按grep -c计数。和数字比较。这是复杂而不确定的

一个有flock(1)但没有subshell的例子。Flock ()ed文件/tmp/foo永远不会被删除，但这没关系，因为它会被Flock()和un-flock()ed。

#!/bin/bash

exec 9<> /tmp/foo
flock -n 9
RET=$?
if [[ $RET -ne 0 ]] ; then
    echo "lock failed, exiting"
    exit
fi

#Now we are inside the "critical section"
echo "inside lock"
sleep 5
exec 9>&- #close fd 9, and release lock

#The part below is outside the critical section (the lock)
echo "lock released"
sleep 5

这将工作，如果你的脚本名称是唯一的:

#!/bin/bash
if [ $(pgrep -c $(basename $0)) -gt 1 ]; then 
  echo $(basename $0) is already running
  exit 0
fi

如果scriptname不是唯一的，这在大多数linux发行版上都有效:

#!/bin/bash
exec 9>/tmp/my_lock_file
if ! flock -n 9  ; then
   echo "another instance of this script is already running";
   exit 1
fi

来源:http://mywiki.wooledge.org/BashFAQ/045