int getgrouplist(const char *, gid_t, gid_t *, int *);
int setgroups(size_t, const gid_t *);
int initgroups(const char *, gid_t);
int getgrouplist(const char *, gid_t, gid_t *, int *);
int setgroups(size_t, const gid_t *);
int initgroups(const char *, gid_t);