Sudden loss of permissions

[ExAmerican]

Hi,

I'm new to Linux, C programming and this forum, so I apologize if my question is out of place here but I'm hoping some of you could help me out.

I've been writing some simple C programs under Linux for a class I'm taking. Since I'm not a Linux user, I've been running Ubuntu in a virtual machine (VMare in case that's somehow relevant). Everything has been working fine until today I start up the VM and try to execute one of my programs ("mydiff" - one of the assignments for my course), only to get the following:

bash: ./mydiff: Permission denied

The first thing I tried was changing the file permissions, though I have no idea why they would have changed themselves, but I still have read and write permissions on the file. I noticed there was a checkbox for "allow executing file as program," which I enabled. Upon doing so I now receive this:

bash: ./mydiff: cannot execute binary file

So at this point I was pretty confused and since I only run the virtual machine for the purpose of C programming and don't have anything else on it, I decided to just copy my C programs over to Windows, delete the entire virtual machine and create a new one. I did that, copied the C files over again and am still getting the same error!

Note: this is NOT just happening with that one mydiff program but with ALL of my C programs. When I delete the binaries and compile new ones using the makefiles, I still get the same error.

Does anyone have an idea what is the cause of this?

Taylor

[Bayint Naung]

Is your executable compiled on linux with gcc?
What's the output of ls -l myprogram ? # myprogram is your executable

[ExAmerican]

Thanks for the quick response!

Is your executable compiled on linux with gcc?
What's the output of ls -l myprogram ? # myprogram is your executable

The program is compiled with gcc. We have very strict coding guidelines in this course so actually we have to compile with: -ansi -pedantic -Wall -c -g -D_XOPEN_SOURCE=500 (not sure if that may be relevant or not).

ls -l mydiff gives me:
-rwxr-xr-x 1 taylor taylor 5920 2010-12-12 17:58 mydiff

[Bayint Naung]

It seems you've execute permission.
If your code is compiled with gcc(on your vm), ./mydiff should work...

[ExAmerican]

Hah yes I also agree that it SHOULD work but for some reason it doesn't!

Yes the code is compiled on my vm. Like I said, I have also tried rebuilding it by deleting the binaries and recompiling the source but I always have the same problem.

taylor@ubuntu:~/SysProg/1A$ ls -l mydiff
-rw-rw-rw- 1 taylor taylor 5920 2010-12-12 21:13 mydiff
taylor@ubuntu:~/SysProg/1A$ ./mydiff
bash: ./mydiff: Permission denied

taylor@ubuntu:~/SysProg/1A$ ls -l mydiff
-rwxrwxrwx 1 taylor taylor 5920 2010-12-12 21:13 mydiff
taylor@ubuntu:~/SysProg/1A$ ./mydiff
bash: ./mydiff: cannot execute binary file

[whiteflags]

Just to verify, the current working directory is also the directory where mydiff is located, correct? You need to cd to the place where mydiff is before ./mydiff works.

[Salem]

You've got -c in the command line.

linux - gcc compiled binaries give "cannot execute binary file" - Stack Overflow

Example

$ gcc foo.c -lm
$ ls -l a.out 
-rwxr-xr-x 1 sc sc 7221 2010-12-13 05:18 a.out
$ file a.out 
a.out: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.15, not stripped
$ gcc -c foo.c
$ ls -l foo.o
-rw-r--r-- 1 sc sc 1520 2010-12-13 05:18 foo.o
$ file foo.o
foo.o: ELF 32-bit LSB relocatable, Intel 80386, version 1 (SYSV), not stripped

[Bayint Naung]

Maybe can you create simple C file.
say hello.c
and type

#include <stdio.h>

int main(void)
{
  printf("Hello World!\n");
  return 0;
}

and compile with
> gcc hello.c
> ./a.out

[ExAmerican]

@ Salem - yes you are correct, I just came to the same conclusion myself.

Compiling with just "-ansi -pedantic -Wall -g -D_XOPEN_SOURCE=500" creates a working binary that runs without problems.

Thanks to everyone for your input!