Objective: View threads of a process on Linux.
Threads (also known as Lightweight Processes (LWP)) are created within a program that will have the same “thread group ID” as the program’s PID. They share their address space and system resources with other LWPs within the same process. Command-line tools such as ps or top, display only process level information by default, but they can be instructed to display thread-level information.
View Threads Using ps
Use either the “-T” or “-L” option of ps to display the threads of a process. The command below displays the threads of the mysqld process.
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# pidof mysqld 3692 # ps -T -p 3692 PID SPID TTY TIME CMD 3692 3692 ? 00:00:27 mysqld 3692 3707 ? 00:02:26 mysqld 3692 3708 ? 00:02:30 mysqld 3692 3709 ? 00:02:31 mysqld 3692 3710 ? 00:02:36 mysqld 3692 3711 ? 00:02:36 mysqld 3692 3712 ? 00:02:31 mysqld 3692 3713 ? 00:02:31 mysqld 3692 3714 ? 00:02:33 mysqld # ps -L -p 3692 PID LWP TTY TIME CMD 3692 3692 ? 00:00:27 mysqld 3692 3707 ? 00:02:26 mysqld 3692 3708 ? 00:02:30 mysqld 3692 3709 ? 00:02:31 mysqld 3692 3710 ? 00:02:36 mysqld 3692 3711 ? 00:02:36 mysqld 3692 3712 ? 00:02:31 mysqld 3692 3713 ? 00:02:31 mysqld 3692 3714 ? 00:02:33 mysqld |
If you would like to view the thread id field, use the following syntax.
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# ps -To pid,tid,tgid,tty,time,comm -p 3692 PID TID TGID TT TIME COMMAND 3692 3692 3692 ? 00:00:27 mysqld 3692 3707 3692 ? 00:02:26 mysqld 3692 3708 3692 ? 00:02:30 mysqld 3692 3709 3692 ? 00:02:31 mysqld 3692 3710 3692 ? 00:02:36 mysqld 3692 3711 3692 ? 00:02:36 mysqld 3692 3712 3692 ? 00:02:31 mysqld 3692 3713 3692 ? 00:02:31 mysqld 3692 3714 3692 ? 00:02:33 mysqld |
View Threads Using top
Use the “-H” option of top to view threads. The command below will run top in batch mode and will exit after one iteration.
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# top -Hbn1 -p 3692 top - 22:20:52 up 48 days, 1:13, 1 user, load average: 0.03, 0.05, 0.05 Threads: 22 total, 0 running, 22 sleeping, 0 stopped, 0 zombie %Cpu(s): 0.6 us, 0.4 sy, 0.0 ni, 98.9 id, 0.0 wa, 0.0 hi, 0.0 si, 0.2 st KiB Mem: 2047496 total, 1953516 used, 93980 free, 158964 buffers KiB Swap: 524284 total, 8252 used, 516032 free. 1246584 cached Mem PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 3692 mysql 20 0 886964 72944 6912 S 0.0 3.6 0:27.23 mysqld 3707 mysql 20 0 886964 72944 6912 S 0.0 3.6 2:26.93 mysqld 3708 mysql 20 0 886964 72944 6912 S 0.0 3.6 2:30.84 mysqld 3709 mysql 20 0 886964 72944 6912 S 0.0 3.6 2:31.88 mysqld 3710 mysql 20 0 886964 72944 6912 S 0.0 3.6 2:36.61 mysqld 3711 mysql 20 0 886964 72944 6912 S 0.0 3.6 2:36.66 mysqld 3712 mysql 20 0 886964 72944 6912 S 0.0 3.6 2:31.58 mysqld 3713 mysql 20 0 886964 72944 6912 S 0.0 3.6 2:31.40 mysqld 3714 mysql 20 0 886964 72944 6912 S 0.0 3.6 2:33.09 mysqld |
htop is also capable of displaying threads, but it’s interactive and not suitable for batch mode.
View Threads Using proc Filesystem
The proc filesystem will list threads under the /proc/[pid]/task (where [pid] is the pid of the process that we are interested in) directory.
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# ls -l /proc/3692/task total 0 dr-xr-xr-x 7 mysql mysql 0 Apr 17 21:30 3692 dr-xr-xr-x 7 mysql mysql 0 Apr 17 21:30 3707 dr-xr-xr-x 7 mysql mysql 0 Apr 17 21:30 3708 dr-xr-xr-x 7 mysql mysql 0 Apr 17 21:30 3709 dr-xr-xr-x 7 mysql mysql 0 Apr 17 21:30 3710 dr-xr-xr-x 7 mysql mysql 0 Apr 17 21:30 3711 dr-xr-xr-x 7 mysql mysql 0 Apr 17 21:30 3712 dr-xr-xr-x 7 mysql mysql 0 Apr 17 21:30 3713 dr-xr-xr-x 7 mysql mysql 0 Apr 17 21:30 3714 |
Mohamed Ibrahim
ibrahim = { interested_in(unix, linux, android, open_source, reverse_engineering); coding(c, shell, php, python, java, javascript, nodejs, react); plays_on(xbox, ps4); linux_desktop_user(true); }
