Command copy exited with code 4 when building - Visual Studio restart solves it

Question

Every now and then when I build my solution here (with 7 projects in it) I get the dreaded \'Command copy exited with code 4\' error, in Visual Studio 2010 Premium ed.

Answer 1

As mentioned in many sites, there are various reasons for this. For me it was due to the length of Source and Destination (Path length). I tried xcopy in the command prompt and I was unable to type the complete source and path (after some characters it wont allow you to type). I then reduced the path length and was able to run. Hope this helps.

Answer 2

I am getting something similar using an xcopy with the /exclude option. In my case, I found that editing the post-build event (something harmless like a newline after the command) and saving the project causes the error to happen. Re-saving the file specified in the /exclude option causes it to work again.

Answer 3

Error code 4 can mean a lot of things, so I recommend reading the other answers as well until you find a solution that works for you AND you understand WHY it works (some solutions only disable error handling, which may only mask the problem but not solve it).

This can be a file locking issue related to parallel building. A workaround is to not use parallel building. This is the default behavior, but if you are using the -m option, then projects will be built in parallel. The following variations should not build projects in parallel, so you will not run into the file locking problem.

msbuild -m:1
msbuild -maxcpucount:1
msbuild

Note that, contrary to what has been said here, this even happens with the "latest" version of MSBuild (from Build Tools for Visual Studio 2019).

The best solution is probably to make sure you don't need to copy files in a post-build step. In some situations, you can also disable post-build steps when building with MSBuild on a build server: https://stackoverflow.com/a/55899347/2279059

Answer 4

In case the post build event contains copy/xcopy command for copying build output to some directory(which usually is the most common post build operation) the problem can occur in case the full directory path either of source or target destinations contain folder names which include spaces. Remove space for the directory name(s) and try.

Answer 5

If you are here because your project fails to build on a build server, but builds fine "manually" on a dev machine, and you are doing xcopy only for debugging and to emulate a production environment on a dev machine, then you may want to look at this solution:

https://stackoverflow.com/a/1732478/2279059

You simply turn off post build events on the build server using

msbuild foo.sln /p:PostBuildEvent=

This is not good enough if you have other post build events that also need to run on the build server, and it is not a general solution. However, since there are so many different causes of this problem, there cannot be a general solution. One of the many answers to this question (and its duplicates) will probably help, but be careful with approaches that only somehow circumvent error handling (such as xcopy /C). Those may work for you, particularly also in the build server scenario, but I think this one is more reliable, IF it can be used.

It has also been suggested that with newer versions of Visual Studio, the problem no longer exists, so if you are using an old version, consider updating your build tools.

Answer 6

I found that setting the file's Copy To Output Directory parameter to Copy Always seems to have cleared up the locking issue. Although now I have 2 copies of the files and need to delete one.