unexpected result(-wS-wx--T) on file permission with open() function in C
I coded this program to open a file. Everything was OK when I saw this permission(-wS-wx--T) with
ls -lhopen.c
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
#include <string.h>
#define FILE "open_1.txt"
int main()
{
int fd;
int errnum;
fd = open(FILE, O_RDWR | O_CREAT);
if(fd == -1)
{
printf("[error] There is a error\n");
perror("Error printed by perror");
}else {
printf("[succeeded] The process was succeeded\n");
}
return 0;
}
I compiled the program featly. I didn't take any error or warning.
$ ./open
[succeeded] The process was succeeded
$ ls -lh
-rwxrwxr-x 1 arien arien 8.5K Feb 1 23:38 open
--wS-wx--T 1 arien arien 0 Feb 1 23:39 open_1.txt
I haven't ever seen like this permission. I need some explanation.
If you include O_CREAT in the flags passed to open() then you must use the three-arg form of the function, which takes a numeric file mode as the third argument. This requirement is documented in the Linux manual page for the function (emphasis added):
The
modeargument specifies the file mode bits be applied when a new file is created. This argument must be supplied whenO_CREATorO_TMPFILEis specified inflags; if neitherO_CREATnorO_TMPFILEis specified, then mode is ignored.
What mode you actually want is unclear, but perhaps S_IRUSR | S_IWUSR | S_IRGRP would be suitable (== 0640; read and write for the owner, read only for the owner's group, no permission for anyone else).