files/t_umask.c

This is files/t_umask.c (Listing 15-5, page 302), an example from the book, The Linux Programming Interface.

The source code file is copyright 2022, Michael Kerrisk, and is licensed under the GNU General Public License, version 3.

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/* t_umask.c

   Demonstrate the affect of umask() in conjunction with open() and mkdir().
*/
#include <sys/stat.h>
#include <fcntl.h>
#include "file_perms.h"
#include "tlpi_hdr.h"

#define MYFILE "myfile"
#define MYDIR  "mydir"
#define FILE_PERMS    (S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP)
#define DIR_PERMS     (S_IRWXU | S_IRWXG | S_IRWXO)
#define UMASK_SETTING (S_IWGRP | S_IXGRP | S_IWOTH | S_IXOTH)
int
main(int argc, char *argv[])
{
    int fd;
    struct stat sb;
    mode_t u;

    umask(UMASK_SETTING);

    fd = open(MYFILE, O_RDWR | O_CREAT | O_EXCL, FILE_PERMS);
    if (fd == -1)
        errExit("open-%s", MYFILE);
    if (mkdir(MYDIR, DIR_PERMS) == -1)
        errExit("mkdir-%s", MYDIR);

    u = umask(0);               /* Retrieves (and clears) umask value */

    if (stat(MYFILE, &sb) == -1)
        errExit("stat-%s", MYFILE);
    printf("Requested file perms: %s\n", filePermStr(FILE_PERMS, 0));
    printf("Process umask:        %s\n", filePermStr(u, 0));
    printf("Actual file perms:    %s\n\n", filePermStr(sb.st_mode, 0));

    if (stat(MYDIR, &sb) == -1)
        errExit("stat-%s", MYDIR);
    printf("Requested dir. perms: %s\n", filePermStr(DIR_PERMS, 0));
    printf("Process umask:        %s\n", filePermStr(u, 0));
    printf("Actual dir. perms:    %s\n", filePermStr(sb.st_mode, 0));

    if (unlink(MYFILE) == -1)
        errMsg("unlink-%s", MYFILE);
    if (rmdir(MYDIR) == -1)
        errMsg("rmdir-%s", MYDIR);
    exit(EXIT_SUCCESS);
}

 

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