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NFS-来自两个客户端的mv命令文件损坏？

[英]NFS - mv command from two clients file corruption?

原文 2017-01-10 21:19:02 6 1 linux/ race-condition/ nfs/ corruption/ file-locking

I have a basic script that I want to do the following : 我有一个想要执行以下操作的基本脚本：

if new/file.txt exists 如果new / file.txt存在
mv new/file.txt current/file.txt mv new / file.txt当前/file.txt

Now - if 2 servers were to run this same script at the same exact time (having access to the same NFS file share) : 现在-如果2台服务器要在相同的确切时间运行相同的脚本（可以访问相同的NFS文件共享）：

Server 1 - step 1. checks if file exists. 服务器1-步骤1。检查文件是否存在。 True 真正
Server 2 - step 1. checks if file exists. 服务器2-步骤1.检查文件是否存在。 True 真正
Server 1 - step 2. starts to perform the "mv" command 服务器1-步骤2。开始执行“ mv”命令
Server 2 - step 2. ???? 服务器2-步骤2。

From what I can find online, it looks like an error would just get thrown by Server 2 - but no file corruption or anything should be of concern : http://nfs.sourceforge.net/ 从我在网上可以找到的内容来看，服务器2似乎只会引发错误-但没有文件损坏或任何值得关注的问题： http : //nfs.sourceforge.net/

The file handle refers to a deleted file. 文件句柄是指已删除的文件。 After a file is deleted on the server, clients don't find out until they try to access the file with a file handle they had cached from a previous LOOKUP. 在服务器上删除文件后，客户端只有在尝试使用从上一个LOOKUP缓存的文件句柄来访问文件时，才会发现该文件。 Using rsync or mv to replace a file while it is in use on another client is a common scenario that results in an ESTALE error. 在另一个客户端上使用文件时，使用rsync或mv替换文件是一种常见的情况，会导致ESTALE错误。

I've tried simulating this to confirm but haven't been able to do so successfully - so I wanted to check here before implementing this strategy : 我尝试模拟这一点来进行确认，但未能成功完成-因此，我想在实施此策略之前在此处进行检查：

Question : Is my understanding accurate - or do I need to use a different strategy to ensure the file.txt doesn't get corrupted? 问题： 我的理解正确吗？还是需要使用其他策略来确保file.txt不会损坏？

Additional details : Amazon Linux OS. 其他详细信息：Amazon Linux OS。 The drive is mounted is nsf4 . 驱动器已安装为nsf4 。 The file could be as large as 100MB 该文件可能最大为100MB

1 个解决方案

The check-if-file-exists is a typical TOCTTOU problem. 检查文件是否存在是典型的TOCTTOU问题。

The simplest fix is to just not check, and try to mv . 最简单的解决方法是不检查，然后尝试 mv 。 If there is no file to be moved, the mv will fail (and not do anything). 如果没有要移动的文件，则mv将失败（并且不执行任何操作）。