top shows a priority of 20 for most processes, including (for example firefox-bin).

Whilst ps -o pid,lwp,pri,nice,start,stat,bsdtime,cmd,comm -C firefox-bin shows:

  PID   LWP PRI  NI  STARTED STAT   TIME CMD                         COMMAND
 9798  9798  19   0 14:03:47 Sl     2:17 /opt/firefox/firefox        firefox-bin

Since both top & ps are ancient commands, this seems unlikely to be a bug. Why the discrepancy?

  • Does this answer your question? What is the difference between ps and top command?
    – taliezin
    Oct 9 '20 at 15:19
  • @taliezin, that suggested duplicate says nothing about the priority value displayed in each command. Oct 9 '20 at 15:23
  • The ps command displays a snapshot of typically just one process, whilst top is typically used to repeatedly display many processes and their effect on machine load. Oct 9 '20 at 15:29
  • 1
    @user4556274, I see, so this might be helpful.
    – taliezin
    Oct 9 '20 at 15:30
  • So its a reported issue? It seems a process can have many priorities... Oct 9 '20 at 15:42

They do so because they're different programs.


Looks like top shows priority as 20 + nice value but ps shows 19 - nice value so both shows priority as value from 0 to 39 but in top 0 means highest priority but in ps 39 means highest priority.

I'm not sure why is this different and it is possible this is a bug in ps because its man page says "Higher number means lower priority."

  • If I use ps -o pri then this statement is also true, but as @user431397 points out, I am using the wrong kind of priority. Oct 9 '20 at 16:00
  • 1
    Interesting, ps manpage mentions only pri (and rprio for real time priority) not priority option/column. Oct 9 '20 at 16:07

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