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when i do a ps -efT (where -T = Show threads, possibly with SPID column.), i see all the threads have the same PID, which is as expected.

myroot   24958 24958  7942  0 20:20 pts/12   00:00:00 java -jar myapp.jar
myroot   24958 24959  7942  0 20:20 pts/12   00:00:11 java -jar myapp.jar
myroot   24958 24960  7942  0 20:20 pts/12   00:00:00 java -jar myapp.jar
myroot   24958 24961  7942  0 20:20 pts/12   00:00:00 java -jar myapp.jar
myroot   24958 24962  7942  0 20:20 pts/12   00:00:00 java -jar myapp.jar
myroot   24958 24963  7942  0 20:20 pts/12   00:00:00 java -jar myapp.jar
myroot   24958 24964  7942  0 20:20 pts/12   00:00:00 java -jar myapp.jar
myroot   24958 24965  7942  0 20:20 pts/12   00:00:00 java -jar myapp.jar

As it can be seen above, all the threads share/show the same PID 24958.

Now When I do the same with top or htop, i am seeing differnt pid for each thread and this is bothering me. Is there a way to show the same PID for all the threads. Below is the curtailed output for top -H -p 24958 (I am using top with -p, so i could explain and show the problem)

top - 21:42:44 up 9 days, 18:38,  0 users,  load average: 0.00, 0.26, 0.82
Threads:  32 total,   0 running,  32 sleeping,   0 stopped,   0 zombie
%Cpu(s):  0.0 us,  0.1 sy,  0.0 ni, 99.9 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
MiB Mem :  12542.5 total,  10135.3 free,    826.8 used,   1580.4 buff/cache
MiB Swap:   4096.0 total,   4096.0 free,      0.0 used.  11439.4 avail Mem

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
24958 myroot    20   0 7036228 340720  21084 S   0.0   2.7   0:00.00 java
24959 myroot    20   0 7036228 340720  21084 S   0.0   2.7   0:11.99 java
24960 myroot    20   0 7036228 340720  21084 S   0.0   2.7   0:00.43 GC Thread#0
24961 myroot    20   0 7036228 340720  21084 S   0.0   2.7   0:00.00 G1 Main Marker
24962 myroot    20   0 7036228 340720  21084 S   0.0   2.7   0:00.00 G1 Conc#0
--and few more threads.

When i use top -H, i would not have any means to say which all threads belong to same Process unless I see same PID for all of them.
Any guidence on how to get the same PID for all the threads when using top (or htop. As I have observed, htop too has the same issue).

Given @user1686 answer to use TGID column. I am wondering what the PID for the thread is refering to.

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With htop, you want the TGID column (add it through F2 > Columns). It is also available in top with the same name, but I don't know how to configure top.

Linux "processes" are really just thread groups (or task groups), and the "PID" column in top/htop actually shows the thread ID (task ID). The same clone(2) system call is used to create both – check out the part about CLONE_THREAD.

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  • that worked even in top ++1. shift+f takes you there in top. Could you confirm - 1) then what is the PID value actually refering to for these threads. 2) if a process has more than one Thread Groups with in it, then would they all share the same TGID. Is it right? Coz in java i can create Thread Groups ( with some name ) from the program but there seems to be no way to assign or get the Thread Group Id.
    – samshers
    Dec 28, 2021 at 19:17
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    No, a process is a thread group. It can't have more than one; then you would have two processes. The thread groups that you create in Java have nothing to do with thread groups in Linux – only the name is propagated to all grouped threads (and you can see it in htop), but the grouping itself remains internal to the JRE.
    – u1686_grawity
    Dec 28, 2021 at 19:26

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