fileupdate
l = fileupdate(getgrpath(_GROUP), 0644, grbuf, pfx, l, mode);
return fileupdate(path, 0600, pwbuf, pfx, l, mode) != 0;
rc = fileupdate(getpwpath(_PASSWD), 0644, pwbuf, pfx, l, mode);
rc = fileupdate(getpwpath(_MASTERPASSWD), 0600, pwbuf, pfx, l, mode);
int fileupdate(char const * fname, mode_t fm, char const * nline, char const * pfx, int pfxlen, int updmode);