open() not setting file permissions correctly

Question

I create a file using the code below:

#include <stdio.h> #include <stdlib.h> #include <sys/stat.h> #include <sys/types.h> #include <errno.h> #include <fcntl.h> #include <unistd.h> int main() { const char* filename = "./test.out"; int fd; if(-1 == (fd = open(filename, O_CREAT|O_RDWR, 0666))) { perror("Error"); errno = 0; } else puts("File opened"); if(-1 == (close(fd))) { perror("Error"); errno = 0; } else puts("File closed"); return 0; }

I specify the mode argument as 0666, which should grant read,write access to everyone. However, an ls -l shows

-rw-r--r-- 1 kmehta users 0 2012-01-29 16:29 test.out

As you can see, write permissions are only granted to the owner of the file. I do not know why everyone else is not granted permissions correctly. chmod a+w test.out sets the permissions correctly though.

Code compiled as gcc -Wall test.c

Specs: gcc v 4.5.0 on Opensuse 11.3 64 bit

Did you try using constants for flags, e.g. S_IRUSR, S_IRGRP, etc.?
@dasblinkenlight Using constants didnt help. It was a umask issue, using fchmod after file open now as shown in the answer

Zan Lynx 16.8k 1 23 53 · Accepted Answer · Jan 29 '12 at 22:43

The mode argument to open specifies the maximum allowed permissions. The umask setting is then applied to further restrict the permissions.

If you need to make the permissions be 0666 specifically you will need to use fchmod on the file handle after the open succeeds.

Daniel Kamil Kozar 3,378 1 6 18 · Answer 2 · Jan 29 '12 at 22:48

Executing this code :

#include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> int main(void) { int fd; if((fd = open("new.file",O_CREAT,S_IRWXU | S_IRWXG | S_IRWXO)) == -1) { perror("open"); return 1; } close(fd); return 0; }

on my Linux box, where umask returns 0022, gives me a file with the following attributes :

-rwxr-xr-x 1 daniel daniel 0 Jan 29 23:46 new.file

So, as you can see, the umask masks out the write bits in my case. It looks like it's the same on your system, too.

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open() not setting file permissions correctly

open() not setting file permissions correctly

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