#include <linux/nsfs.h> /* Definition of NS_GET_OWNER_UID */ #include <sys/ioctl.h> int ioctl(int fd, NS_GET_OWNER_UID, uid_t *uid);
DESCRIPTION
The NS_GET_OWNER_UID operation can be used to discover the
owner user ID of a user namespace (i.e., the effective user ID of the
process that created the user namespace).
fd refers to a /proc/pid/ns/user file.
The owner user ID is returned in the uid_t pointed to by
the third argument.
RETURN VALUE
On success, 0 is returned. On error, -1 is returned, and
errno is set to indicate the error.