2005/06/07 SPID, threads in ps

Modern ps can show thread information:

-L           show threads, possibly with LWP and NLWP columns
-T           show threads, possibly with SPID column
-m           show threads after processes
H            show threads as if they were processes
m            show threads after processes
 

The SPID column is the thread id. As far as I can tell, LWP and SPID are the same thing; I am not sure what the value of NLWP is; it appears to be just the count of threads. Use "ps -Lf" to see that column.

The ps man and info pages

don't tell you much about threads, probably because there's been plenty of confusion and disagreement about how the kernel should expose thread info, how /proc should pick it up, etc. This old thread shows some of that. Also, Uncertainty about implementation details probably didn't help either.

There are some better man pages out there. Here's the threads of mysqld on a Linux system:

$ ps -p 677 -T 
  PID  SPID TTY          TIME CMD
  677   677 ?        00:00:00 mysqld
  677   678 ?        00:00:00 mysqld
  677   679 ?        00:00:00 mysqld
  677   680 ?        00:00:00 mysqld
  677   681 ?        00:00:00 mysqld
  677   682 ?        00:00:00 mysqld
  677   683 ?        00:00:00 mysqld
  677   684 ?        00:00:00 mysqld
  677   685 ?        00:00:00 mysqld
  677   686 ?        00:00:00 mysqld
 

Different Unixes have widely different implementations of how thread info is shown and what is displayed. Be sure to check the man pages carefully.

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