There are different kind of memory measurement metrics in Linux. These are the differences:
| Code | Name | Description |
|---|---|---|
vsz |
virtual memory size | Total amount of memory a process may hypothetically access. Includes swapped memory, memory from external libraries and allocated memory that’s not used. |
rss |
resident set size | Total amount of non-swapped used physical memory. Includes memory from external shared libraries. |
pss |
proportional share size | Total amount of non-swapped physical memory with shared memory proportionally accounted. |
uss |
unique set size | Total amount of the non-swapped physical memory which is not shared with an another task. |
- First choice for metrics is
pss - Second choice (due to the lack of Ubuntu support for
pss) isrss
Commands
ps and
smem
Show archive.org snapshot
can be used to display the metrics. The default ps version in Ubuntu does not support all of them. smem can be used to access all metrics on older Ubuntu versions. However the syntax is a bit clunky. You can use -P as filter but not for the PID.
| Code |
ps command |
smem command |
Ubuntu ps support |
|---|---|---|---|
vsz |
ps -p "${pid}" -o vsz |
smem -c "pid vss" | grep "${pid}" | awk '{ print $2}' |
Yes |
rss |
ps -p "${pid}" -o rss |
smem -c "pid rss" | grep "${pid}" | awk '{ print $2}' |
Yes |
pss |
ps -p "${pid}" -o pss |
smem -c "pid pss" | grep "${pid}" | awk '{ print $2}' |
Ubuntu 24.04+ |
uss |
ps -p "${pid}" -o uss |
smem -c "pid uss" | grep "${pid}" | awk '{ print $2}' |
Ubuntu 24.04+ |
