How to get all process ids without ps command on Linux？
On Linux, all running process have "metadata" stored in the /proc filesystem.
# for exe in /proc/*/exe; do ls -l $exe; done
# man ps
# ps -C sshd --no-header
# ps -C dockerd --no-header
-C cmdlist
Select by command name. This selects the processes whose executable name is given in cmdlist.
you can use the long options --headers and --no-headers to enable printing headers each page or disable headers entirely, respectively.
# ps -eo nlwp,pcpu,user,pid,ppid,args --sort nlwp
注：以 nlwp排序，默认正序
LWP -- 轻量级进程，即线程
NLWP --线程数，即 number of threads in process
# ps -eo pid,cmd,%mem,%cpu --sort=-%mem
Thecommand is highly valuable for system admins during troubleshooting the system.
You can display the processes list in a sorted manner to find out the highest memory usage processes.
# ps -mp ${pid} -o THREAD,tid,time
参数解释：
-m:显示所有的线程
-p:pid进程使用CPU的时间
-o:该参数后是用户自定义格式。
如：THREAD,tid,time表示线程、线程ID号、线程占用的时间。
$ ps -Hp ${pid}
参考ps(1) — Linux manual page
https://man7.org/linux/man-pages/man1/ps.1.html
Linux PS command with examples
https://www.fosslinux.com/43296/linux-ps-command-with-examples.htm
How to get all process ids without ps command on Linux？
https://stackoverflow.com/questions/32913424/how-to-get-all-process-ids-without-ps-command-on-linux
What is the difference between ps and top command?
https://unix.stackexchange.com/questions/62176/what-is-the-difference-between-ps-and-top-command
