shm_open 未设置组写入权限

Question

我正在像这样创建一个新的共享内存对象

  int fd = shm_open("somekey", O_CREAT | O_RDWR, S_IRWXU | S_IRWXG);

return 值很好，我希望在 /dev/shm

中找到类似以下内容

-rwxrwx--- 1 root   group     4096 Jun 27 19:08 somekey

但是文件中的写入权限丢失了，我不知道为什么。

-rwxr-x--- 1 root   group     4096 Jun 27 19:08 somekey

Answer 1

http://man7.org/linux/man-pages/man3/shm_open.3.html

the object's permission bits are set according to the low-order 9 bits of mode, except that those bits set in the process file mode creation mask (see umask(2)) are cleared for the new object.

这只是 umask 的工作，就像它对常规 open 所做的一样。

Answer 2

您的问题与以下线程重复

POSIX shared memory and semaphores permissions set incorrectly by open calls

mode_t old_umask = umask(0);

int fd = shm_open("somekey", O_CREAT | O_RDWR, S_IRWXU | S_IRWXG);

// restore old
umask(old_umask);