问题:
使用shm_open()
和O_CREAT
和O_RDWR
标志创建,并放在/dev/shm
中,我有以下rxample程序:
#include <stdio.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>
#include <errno.h>
int main()
{
int ret = 0;
errno = 0;
ret = shm_open("/testshm", O_CREAT | O_RDWR, 00666);
fprintf(stderr, "return value %dn", ret);
fprintf(stderr, "result %d: %sn", errno, strerror(errno));
return 0;
}
当我第一次运行它时,它按预期工作,并且创建/dev/shm/testshm
:
$ ls -la /dev/shm
total 0
drwxrwxrwt 2 root root 60 Aug 3 16:34 .
drwxr-xr-x 18 root root 4580 Aug 3 12:41 ..
-rw-rw-r-- 1 krejci krejci 0 Aug 3 14:37 testshm
以相同的用户运行程序可以正常工作,但当我尝试以root运行程序时,我得到" Permission denied" :
# id
uid=0(root) gid=0(root) groups=0(root)
# ./test
return value -1
result 13: Permission denied
答案1:
代码在完成共享内存时缺少调用shm_unlink()
语句
答案2:
./untitled1; ls -la /dev/shm; sudo su; ./untitled1
结果是:
return value 3
result 0: Success
total 0
drwxrwxrwt 2 root root 60 Aug 7 13:19 .
drwxr-xr-x 20 root root 4640 Aug 6 13:26 ..
-rw-r--r-- 1 richard richard 0 Aug 6 18:17 testshm
[sudo] password for richard:
root@richard-desktop:/home/richard/Documents/forum# ./untitled1
return value 3
result 0: Success
注:我已经升级到20,如:
uname -a
Linux richard-desktop 4.15.0-112-generic #113-Ubuntu SMP Thu Jul 9 23:41:39 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux