// RunningFromSystemService tries to detect whether the current process has
// been invoked from a system service. The condition for this is whether the
// process is _not_ a user process. User processes are those running in session
// scopes or under per-user `systemd --user` instances.
//
// To avoid false positives on systems without `pam_systemd` (which is
// responsible for creating user sessions), this function also uses a heuristic
// to detect whether it's being invoked from a session leader process. This is
// the case if the current process is executed directly from a service file
// (e.g. with `ExecStart=/this/cmd`). Note that this heuristic will fail if the
// command is instead launched in a subshell or similar so that it is not
// session leader (e.g. `ExecStart=/bin/bash -c "/this/cmd"`)
//
// This function is a wrapper around the libsystemd C library; if this is
// unable to successfully open a handle to the library for any reason (e.g. it
// cannot be found), an errr will be returned
func RunningFromSystemService() (ret bool, err error) {
var h *libHandle
h, err = getHandle()
if err != nil {
return
}
defer func() {
if err1 := h.Close(); err1 != nil {
err = err1
}
}()
sym := C.CString("sd_pid_get_owner_uid")
defer C.free(unsafe.Pointer(sym))
sd_pid_get_owner_uid := C.dlsym(h.handle, sym)
if sd_pid_get_owner_uid == nil {
err = fmt.Errorf("error resolving sd_pid_get_owner_uid function")
return
}
var uid C.uid_t
errno := C.my_sd_pid_get_owner_uid(sd_pid_get_owner_uid, 0, &uid)
serrno := syscall.Errno(-errno)
// when we're running from a unit file, sd_pid_get_owner_uid returns
// ENOENT (systemd <220) or ENXIO (systemd >=220)
switch {
case errno >= 0:
ret = false
case serrno == syscall.ENOENT, serrno == syscall.ENXIO:
// Since the implementation of sessions in systemd relies on
// the `pam_systemd` module, using the sd_pid_get_owner_uid
// heuristic alone can result in false positives if that module
// (or PAM itself) is not present or properly configured on the
// system. As such, we also check if we're the session leader,
// which should be the case if we're invoked from a unit file,
// but not if e.g. we're invoked from the command line from a
// user's login session
ret = C.am_session_leader() == 1
default:
err = fmt.Errorf("error calling sd_pid_get_owner_uid: %v", syscall.Errno(-errno))
}
return
}
func isRunningFromUnitFile() (ret bool, err error) {
libname := C.CString("libsystemd.so")
defer C.free(unsafe.Pointer(libname))
handle := C.dlopen(libname, C.RTLD_LAZY)
if handle == nil {
// we can't open libsystemd.so so we assume systemd is not
// installed and we're not running from a unit file
return
}
defer func() {
if r := C.dlclose(handle); r != 0 {
err = fmt.Errorf("error closing libsystemd.so")
}
}()
sd_pid_get_owner_uid := C.dlsym(handle, C.CString("sd_pid_get_owner_uid"))
if sd_pid_get_owner_uid == nil {
err = fmt.Errorf("error resolving sd_pid_get_owner_uid function")
return
}
var uid C.uid_t
errno := C.my_sd_pid_get_owner_uid(sd_pid_get_owner_uid, 0, &uid)
// when we're running from a unit file, sd_pid_get_owner_uid returns
// ENOENT (systemd <220) or ENXIO (systemd >=220)
switch {
case errno >= 0:
case syscall.Errno(-errno) == syscall.ENOENT || syscall.Errno(-errno) == syscall.ENXIO:
if C.am_session_leader() == 1 {
ret = true
}
default:
err = fmt.Errorf("error calling sd_pid_get_owner_uid: %v", syscall.Errno(-errno))
}
return
}