Question

Use open syscall to write and create a file ,there’s no attributes with the file. fedora16 gcc-4.6.3

#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>

int main()
{
    char *  str= "helloworld";
    int fd = open("test.db",O_WRONLY|O_CREAT|O_TRUNC|O_APPEND);

    write(fd,str,10);

    close(fd);
    return 0;
}

ll test.db

———-. 1 jiamo jiamo 14 Apr 17 11:34 test.db

While it don’t create file with the default file attributes such like touch test.db

umask : 0002

if drop the O_TRUNC
int fd = open("test1.db",O_WRONLY|O_CREAT|O_APPEND)
the file attributs is :

—-rwx—. 1 jiamo jiamo 14 Apr 17 12:29 test1.db

Answer 1

Add the required permissions to the open() syscall:

int fd = open("test.db",O_WRONLY|O_CREAT|O_TRUNC|O_APPEND, 0666);

From the documentation:

mode must be specified when O_CREAT is in the flags, and is ignored otherwise.
The argument mode specifies the permissions to use in case a new file is created.