mkdir in C++ setting wrong permissions

fcdev · 01-13-2008, 05:27 AM

Within a C++ program, I am creating a new directory to store log files. The problem is that when I use this code ...

mkdir("logs",0777);

The created directory has it's permissions set to 755. This is catastrophic for my application as the logs directory is shared by all users on the system, and once the logs are initially created by the first user, no other user is able to enable logging.

I am hoping to avoid the need to create a separate logs directory for each user, as this will require substantial modification of the code I'm porting (It was originally a Windows application).

I need to avoid use of the system() function. Also, there is no sensitive information being stored in the logs folder that needs to be kept secret. It is merely diagnostic data to assist in error handling.

Any help would be greatly appreciated.

zaichik · 01-13-2008, 08:35 AM

I'm not sure you can throw octal at it like that when setting the permission bits. I'm not sure you can't, either, but try ORing the permission bits, like

mkdir("logs", S_IRWXU | S_IRWXG | S_IRWXO );

Another thought is that perhaps the umask is being applied after the directory is being created. If the above does not work, trying temporarily resetting umask to 000.

Hope that helps!

h/w · 01-13-2008, 09:50 AM

Code:

// g++ -Wall -o mymkdir mymkdir.cpp

#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <sys/stat.h>
#include <sys/types.h>

#define MY_MASK 0777

int main()
{
  int temp;

  printf("Default mask: %o\n", MY_MASK & ~022 & MY_MASK);

  temp = umask(0);
  printf("Previous umask = %o\n", temp);
  if ((temp = mkdir("foodir", MY_MASK)) != 0) {
    fprintf(stderr, "ERROR %d: unable to mkdir; %s\n", errno, strerror(errno));
  }

  return 0;
}

fcdev · 01-13-2008, 05:47 PM

Thanks, it was fixed by a call to umask(0). I'd never encountered that function before, and had trouble finding documentation on it. I also changed the permissions to S_IRWXU | S_IRWXG | S_IRWXO instead of 0777. This was another problem of not being able to find any documentation on what flags were used by mkdir. Once I read that S_IRWXU ... I knew exactly where to look.

Thanks again guys.

h/w · 01-13-2008, 05:57 PM

Glad to be of help.

man 2 umask
man 2 stat