How ChatGPT Diagnosed the ‘No Such File’ Error

Recently, I encountered a strange problem when executing the binary file protoc, which resulted in the error “no such file or directory: ./protoc”. The file was clearly there, but the error persisted, making me wonder if there was a bug in the system.

Whenever I face such bizarre issues, I tend to doubt the operating system or the compiler, but usually, I find that I am the one at fault. This time was no exception. After several attempts, I discovered that this was actually a feature of the system.

If a beginner encounters this problem for the first time, they would generally be at a loss with no idea how to troubleshoot. Before reading on, you might want to guess what could cause this error when executing a binary file.

Answers from the search engine

The binary file truly exists, and the permissions are correct, yet the execution throws an error. Encountering this for the first time, I had no idea where to start troubleshooting, as this seemed like something that should not occur.

$ ./protoc
zsh: no such file or directory: ./protoc
$ ls -alh protoc
-rwxr-xr-x 1 test users 1.1M Jun 17 10:20 protoc

Before ChatGPT, when faced with an unsolvable problem, the first step would be to search online for “no such file or directory but file exists”, which would yield many results.

One of the first search results, “No such file or directory? But the file exists!” matched my issue. The highly upvoted answer suggested the cause might be running a 32-bit binary on a 64-bit machine that does not support 32-bit. Indeed, the binary file was transferred from an old machine to a 64-bit machine. I used the file command to check the file format, which confirmed this:

$ file protoc
protoc: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux.so.2, for GNU/Linux 2.6.4, stripped

It appeared to be the cause, but why was this error happening? How did others diagnose this issue? The search engine provided a conclusion but not the troubleshooting steps or an explanation of the root cause. For further insight, it would be necessary to search with different keywords and dig deeper.

Conversation with ChatGPT

Since ChatGPT became available, my first instinct when encountering a problem is to ask ChatGPT.

When I shared the command error with ChatGPT and asked why it was reporting a nonexistent file when the file was clearly there with the correct permissions, it provided several troubleshooting directions.

After a preliminary check, none of them were the issue.

So, I asked further:

What other methods can be used to troubleshoot this problem?

ChatGPT listed many directions, one of which seemed enlightening, “Debug with strace”: using strace ./protoc to trace system calls to see if any errors occur during execution.

I knew about the strace command and had used it before, but I had not thought to use it for this issue. After ChatGPT’s suggestion, I tried it and indeed found an error:

$ strace -f ./protoc
execve("./protoc", ["./protoc"], 0x7fff2cd172f8 /* 40 vars */) = -1 ENOENT (No such file or directory)
strace: exec: No such file or directory
+++ exited with 1 +++

It appears that the execve command returned ENOENT, which is the root of the command line execution error. I pasted the error directly to ChatGPT and asked it to continue explaining.

The response from ChatGPT was comprehensive. The output from strace showed that the execve system call failed. The execve is used to execute a program, and in this case, it attempted to execute ./protoc. There are several possible reasons for the missing file error, such as:

Mismatched Architecture: If protoc was compiled for a different hardware architecture (for example, running a 32-bit program on a 64-bit system without the necessary library support), this could cause the error.

Dynamic Link Library Issues: If the dynamic link library (.so files) that protoc depends on is missing or the path is incorrect, this could also cause the error. You can use the ldd ./protoc command to check dependencies.

So there’s one last question: why does this error occur when running a 32-bit program on a 64-bit system without the necessary library support? Are there any documents that explain this situation?

I asked ChatGPT, and it did not provide a detailed document source, but it did offer its explanation: By default, many 64-bit systems may not have 32-bit compatibility libraries pre-installed because modern software is mainly 64-bit. If you try to run a 32-bit program, the system requires these 32-bit libraries. If these libraries are not present, the operating system’s loader cannot load the required 32-bit dynamic link libraries, resulting in execution failure and a “No such file or directory” error.

Although ChatGPT did not find the relevant explanation in the documentation, now that execve has been identified as the error, you can directly read the man manual. Searching the manual directly for the error code ENOENT, the following explanation is found:

ENOENT: The file pathname or a script or ELF interpreter does not exist.

If the executable is a dynamically linked ELF executable, the interpreter named in the PT_INTERP segment is used to load the needed shared objects. This interpreter is typically /lib/ld-linux.so.2 for binaries linked with glibc (see ld-linux.so(8)).

It can be seen that this error is reported because there is no ELF interpreter in my current 64-bit machine environment. With this, the fundamental cause of the error is completely understood.

Conclusion

In summary, when facing this peculiar problem, search engines, ChatGPT, and individuals each play an indispensable role. Search engines, like Google, provide a broad pool of information that allows us to quickly access various possible solutions and historical cases. However, the limitation of search engines is that they usually only provide ready-made information, not customized advice for specific situations.

In contrast, ChatGPT is more interactive and targeted in providing solutions. It can offer more customized solutions based on the specific problem, help narrow down the scope of solutions, and provide guidance on logic and steps during the troubleshooting process. In the future, ChatGPT should gradually replace search engines and become the biggest helper for individuals.