So, what can you do with a process ID?

On Linux one of my favourite tools to display metrics about a process in real time, such as cpu/memory/io utilisation, which can also be broken down per thread (with friendly thread names displayed if your application sets them), is pidstat from the sysstat package.

Re: So, what can you do with a process ID?

#5

Post by daniel-s » Fri, Dec 16, 2022, 8:40 PM UTC

For a moment I thought the topic was about PID controllers. That would have been cool.

If the blogging gods take requests I just made one.

Re: So, what can you do with a process ID?

#6

Post by crossingTime » Fri, Dec 16, 2022, 10:13 PM UTC

When I was a chemist we used photoionization detectors to detect VOCs in groundwater.

Re: So, what can you do with a process ID?

#7

Post by dang » Fri, Dec 16, 2022, 10:42 PM UTC

daniel-s wrote: post #5

For a moment I thought the topic was about PID controllers. That would have been cool. If the blogging gods take requests I just made one.

In the meantime, we've macroexpanded that acronym in the title above.

Re: So, what can you do with a process ID?

#8

Post by ghostpepper » Fri, Dec 16, 2022, 10:48 PM UTC

My go-to incantation is `ps ajxf`, (truncated and edited) sample output below

   PPID   PID  PGID   SID TTY      TPGID STAT   UID   TIME COMMAND
      0     1     1     1 ?           -1 Ss       0   0:57 /sbin/init splash
      1   978   978   978 ?           -1 Ss       0   0:00 /usr/sbin/sshd -D
    978 11441 11441 11441 ?           -1 Ss       0   0:00  \_ sshd: ghostpepper [priv]
  11441 11445 11441 11441 ?           -1 S     1000   0:00      \_ sshd: ghostpepper@pts/4
  11445 11446 11446 11446 pts/4    11641 Ss    1000   0:00          \_ -bash
  11446 11641 11641 11446 pts/4    11641 R+    1000   0:00              \_ ps ajxf

Another thing some might not know is that kill (the command / syscall) can send a lot of other signals than KILL (the signal). Not all processes know how to gracefully handle them, so you need to be careful, but for example a lot of daemons can catch SIGHUP and re-load their config file from disk.

Re: So, what can you do with a process ID?

#9

Post by gregw2 » Sat, Dec 17, 2022, 12:43 AM UTC

hsfzxjy wrote: post #3

And with strace -p pid you can somewhat "spy" on what a process is doing.

This. (Combine with sudo too!)

Now if I could just track NFS client traffic on a client associated with a PID (without having NFS server access). All I can get is all-PID/client-kernel data info vi nfsstat, nothing tying to a PID, filename, directory or inode to tell me which PID is causing all the NFS traffic!

Re: So, what can you do with a process ID?

#10

Post by fragmede » Sat, Dec 17, 2022, 3:29 AM UTC

gregw2 wrote: post #9

hsfzxjy wrote: post #3

And with strace -p pid you can somewhat "spy" on what a process is doing.

This. (Combine with sudo too!) Now if I could just track NFS client traffic on a client associated with a PID (without having NFS server access). All I can get is all-PID/client-kernel data info vi nfsstat, nothing tying to a PID, filename, directory or inode to tell me which PID is causing all the NFS traffic!

    iotop?