Linux Process and Thread (LWP - Light Weight Process)

Program  :In Linux, an executable stored on disk is called a program.

Process    :A Program loaded into memory and running is called a process.

Thread    :A little processes called LWP (Light Weight Process) or otherwise known as threads which will be runs by Process

When a process is started, it is given a unique number called process ID (PID) that identifies that process to the system.

If you ever need to kill a process, for example, you can refer to it by its PID. Since each PID is unique, there is no ambiguity or risk of accidentally killing the wrong process (unless you enter the wrong PID).

See the list of Process on server 

[root@gw-server ~]# ps -ef
UID        PID  PPID  C STIME TTY          TIME CMD
root         1     0  0 Aug03 ?        00:23:18 /usr/lib/systemd/systemd --switched-root --system --deserialize 21
root         2     0  0 Aug03 ?        00:00:05 [kthreadd]
root         3     2  0 Aug03 ?        00:05:11 [ksoftirqd/0]
root         7     2  0 Aug03 ?        00:02:17 [migration/0]
root         8     2  0 Aug03 ?        00:00:00 [rcu_bh]
root         9     2  0 Aug03 ?        01:27:07 [rcu_sched]

Total Number of Process running on server 

[root@gw-server ~]# ps -ef -T | wc -l

416

Total Number of Process and Threads  running on server 

[root@gw-server ~]# ps -ef -T | wc -l

783

Check Name of the Process by PID

[root@gw-server ~]# ps -ef | grep 1893

oracle    1893     1  0 Oct28 ?        02:19:03 /oracle/GRID/12102/bin/oraagent.bin

root     25162 18727  0 07:31 pts/1    00:00:00 grep --color=auto 1893

[root@gw-server ~]#  ls -l /proc/1893/exe

lrwxrwxrwx 1 oracle oinstall 0 Nov 12 06:02 /proc/1893/exe -> /oracle/GRID/12102/bin/oraagent.bin

How to check the process runs Threads or not ?

[root@gw-server ~]# top -H -p 1893

  PID USER      PR  NI    VIRT    RES    SHR S %CPU %MEM     TIME+ COMMAND

 1895 oracle    20   0 1213240  55040  22400 S  0.3  0.3  86:45.19 oraagent.bin

 1893 oracle    20   0 1213240  55040  22400 S  0.0  0.3   3:20.88 oraagent.bin

 1896 oracle    20   0 1213240  55040  22400 S  0.0  0.3   0:05.50 oraagent.bin

 1897 oracle    20   0 1213240  55040  22400 S  0.0  0.3   5:12.75 oraagent.bin

 1899 oracle    20   0 1213240  55040  22400 S  0.0  0.3   0:05.83 oraagent.bin

 1902 oracle    20   0 1213240  55040  22400 S  0.0  0.3  11:50.29 oraagent.bin

 1906 oracle    20   0 1213240  55040  22400 S  0.0  0.3   2:29.80 oraagent.bin

 1907 oracle    20   0 1213240  55040  22400 S  0.0  0.3   0:00.06 oraagent.bin

 1911 oracle    20   0 1213240  55040  22400 S  0.0  0.3   0:00.00 oraagent.bin

 1914 oracle    20   0 1213240  55040  22400 S  0.0  0.3   0:00.00 oraagent.bin

 1916 oracle    20   0 1213240  55040  22400 S  0.0  0.3   0:52.09 oraagent.bin

 1917 oracle    20   0 1213240  55040  22400 S  0.0  0.3   0:01.74 oraagent.bin

23257 oracle    20   0 1213240  55040  22400 S  0.0  0.3   0:00.08 oraagent.bin

 2389 oracle    20   0 1213240  55040  22400 S  0.0  0.3   0:01.29 oraagent.bin

28455 oracle    20   0 1213240  55040  22400 S  0.0  0.3   0:00.38 oraagent.bin

[root@gw-server ~]# ps -e -T | grep <application name or pid>

-e show's all processes

-T lists all threads

[root@gw-server ~]# ps -e -T | grep 1893

 PID  SPID TTY          TIME CMD

 1893  1893 ?        00:03:20 oraagent.bin

 1893  1895 ?        01:26:45 oraagent.bin

 1893  1896 ?        00:00:05 oraagent.bin

 1893  1897 ?        00:05:12 oraagent.bin

 1893  1899 ?        00:00:05 oraagent.bin

 1893  1902 ?        00:11:50 oraagent.bin

 1893  1906 ?        00:02:29 oraagent.bin

 1893  1907 ?        00:00:00 oraagent.bin

 1893  1911 ?        00:00:00 oraagent.bin

 1893  1914 ?        00:00:00 oraagent.bin

 1893  1916 ?        00:00:52 oraagent.bin

 1893  1917 ?        00:00:01 oraagent.bin

 1893 23257 ?        00:00:00 oraagent.bin

 1893  2389 ?        00:00:01 oraagent.bin

 1893 28455 ?        00:00:00 oraagent.bin

[root@gw-server ~]#

In above output SPID is thread ID of particular Process 1893, means the process 1893 runs the 15 threads called Light Weight Process (LWP).