I recently noticed that htop displays a much lower ‘memory in use’ number than free -h, top, or fastfetch on my Ubuntu 25.04 server.
I am using ZFS on this server and I’ve read that ZFS will use a lot of RAM. I also read a forum where someone commented that htop doesn’t show caching used by the kernel but I’m not sure how to confirm ZFS is what’s causing the discrepancy.
I’m also running a bunch of docker containers and am concerned about stability since I don’t know what number I should be looking at. I either have a usable ~22GB of available memory left, ~4GB, or ~1GB depending on what tool I’m using. Is htop the better metric to use when my concern is available memory for new docker containers or are the other tools better?
Server Memory Usage:
- htop =
8.35G / 30.6G - free -h =
total used free shared buff/cache available
Mem: 30Gi 26Gi 1.3Gi 730Mi 4.2Gi 4.0Gi
- top =
MiB Mem : 31317.8 total, 1241.8 free, 27297.2 used, 4355.9 buff/cache - fastfetch =
26.54GiB / 30.6GiB
I’ve always used free -mh to check memory, so I would say you have 4gb available.
Fuck. This is a bad time to need more ram
Depending on the workload, compression may be an option. You can use zram or zswap to basically get more RAM at the expense of increased CPU usage.
On a modern CPU, the cost should be insignificant.