In UNIX, quali sono i tipi di processo Ss, Sl e Ssl che vedo con ps aux?

Quando eseguo un ps auxcomando, vedo alcuni processi elencati come Ss, Ssle Sl.

Cosa significano questi?

root     24653  0.0  0.0   2256     8 ?        Ss   Apr12   0:00 /bin/bash -c /usr/bin/python /var/python/report_watchman.py 
root     24654  0.0  0.0  74412    88 ?        Sl   Apr12   0:01 /usr/bin/python /var/python/report_watchman.py
root     21976  0.0  0.0   2256     8 ?        Ss   Apr14   0:00 /bin/bash -c /usr/bin/python /var/python/report_watchman.py 
root     21977  0.0  0.0  73628    88 ?        Sl   Apr14   0:01 /usr/bin/python /var/python/report_watchman.py

Dalla manpage ps :

   S    Interruptible sleep (waiting for an event to complete)

  For BSD formats and when the stat keyword is used, additional
  characters may be displayed:
  s    is a session leader
  l    is multi-threaded (using CLONE_THREAD, like NPTL pthreads do)