open() not setting file permissions correctly

最新推荐文章于 2021-12-13 16:33:54 发布

shuixin536

最新推荐文章于 2021-12-13 16:33:54 发布

阅读量1k

点赞数

分类专栏： Linux

Linux 专栏收录该内容

5 篇文章

订阅专栏

http://stackoverflow.com/questions/9057419/open-not-setting-file-permissions-correctly

open() not setting file permissions correctly

up vote 0 down vote favorite

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

edited Jan 29 '12 at 22:42

Kerrek SB
124k 12 170 320

asked Jan 29 '12 at 22:38

KVM
602 6 17

check umask. check umask. – wildplasser Jan 29 '12 at 22:40

Did you try using constants for flags, e.g. S_IRUSR, S_IRGRP, etc.? – dasblinkenlight Jan 29 '12 at 22:41

@dasblinkenlight Using constants didnt help. It was a umask issue, using fchmod after file open now as shown in the answer – KVM Jan 29 '12 at 22:59

2 Answers

active oldest votes

up vote 6 down vote accepted

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.

answered Jan 29 '12 at 22:43

Zan Lynx
16.8k 1 23 53

up vote 1 down vote

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.

answered Jan 29 '12 at 22:48

Daniel Kamil Kozar
3,378 1 6 18

Not the answer you're looking for? Browse other questions tagged c posix or ask your own question.

question feed

Technology			Life / Arts	Culture / Recreation	Science	Other
Stack Overflow Server Fault Super User Web Applications Ask Ubuntu Webmasters Game Development TeX - LaTeX	Programmers Unix & Linux Ask Different (Apple) WordPress Answers Geographic Information Systems Electrical Engineering Android Enthusiasts IT Security	Database Administrators Drupal Answers SharePoint User Experience Mathematica more (14)	Photography Science Fiction & Fantasy Seasoned Advice (cooking) Home Improvement more (13)	English Language & Usage Skeptics Mi Yodeya (Judaism) Travel Arqade (gaming) Bicycles Role-playing Games more (22)	Mathematics Cross Validated (stats) Theoretical Computer Science Physics more (7)	Stack Apps Meta Stack Overflow Area 51 Stack Overflow Careers