Check a Process's Memory Usage (RSS) with ps
Report exactly how many kilobytes of physical memory a single process holds, without Activity Monitor.
Run ps -o pid,rss,comm -p 1234 to print the PID, RSS in kilobytes, and the command path for one process.
01Command
Command
$ ps -o pid,rss,comm -p <PID>02What it does
RSS (resident set size) is the physical RAM a process currently occupies — the number Activity Monitor's Memory column is built on. Selecting the pid, rss and comm columns with -o and targeting one PID with -p gives a clean, scriptable answer; divide by 1024 to get megabytes. For a machine-wide view, ps aux -m sorts every process by memory usage.
03Risk
!Warning: RSS double-counts memory that multiple processes share (frameworks, libraries), so summing RSS across all processes overstates real usage. Also note rss is reported in kilobytes on macOS.
04Undo
✓No undo needed — this command does not change persistent state.
05Sources
- PS(1) — macOS man pageEvidence: The man page lists rss among the standard output keywords ("... vsz=SZ, rss, wchan, state=S ...") and documents -o for selecting columns and -p for selecting a single process ID.
- ps(1) man pageEvidence: The page documents the rss output keyword (resident set size, the process's non-swapped physical memory in kilobytes) and the -p pid process-selection option.
Last verified: 2026-09-19 · Category: System & Settings