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Linux distributions tend (but are not required) to include free from procps, which allows a nice concise display of memory consumption:

# free -m total used free shared buff/cache available Mem: 7688 5027 180 827 2479 1589 Swap: 8189 2082 6106

In order to approximate this in BSD, I've tried a number of different items, but they all give me different answers (presumably because they have different contexts?). For example:

# sysctl -a |grep Memory Virtual Memory: (Total: 1077397132K, Active 3458308K) Real Memory: (Total: 1171952K Active 975744K) Shared Virtual Memory: (Total: 56264K Active: 38652K) Shared Real Memory: (Total: 22184K Active: 19700K) Free Memory Pages: 1664588K # sysctl hw |awk '/mem:/ { printf "%s %.0fM\n", $1, $2/1024^2 }' hw.physmem: 32756M hw.usermem: 29102M hw.realmem: 33792M # grep memory /var/run/dmesg.boot usable memory = 34346901504 (32755 MB) avail memory = 33139134464 (31603 MB) # top |grep -Em2 '^(Mem|Swap):' Mem: 980M Active, 25G Inact, 3654M Wired, 948M Cache, 3285M Buf, 678M Free Swap: 9216M Total, 363M Used, 8853M Free, 3% Inuse

I'm not the first person to have this inquiry; almost 7y ago, it was posted to the FreeBSD-questions list and a perl script was proposed out of it, offering freebsd-memory.pl (output was narrowed to fit here):

# perl freebsd-memory.pl SYSTEM MEMORY INFORMATION: mem_wire: 3831771136 ( 3654MB) [ 11%] Wired: disabled for paging out mem_active: + 1028284416 ( 980MB) [ 3%] Active: recently referenced mem_inactive:+ 26741092352 ( 25502MB) [ 80%] Inactive: recently not referenced mem_cache: + 993902592 ( 947MB) [ 2%] Cached: almost avail. for allocation mem_free: + 710340608 ( 677MB) [ 2%] Free: fully available for allocation mem_gap_vm: + 995328 ( 0MB) [ 0%] Memory gap: UNKNOWN -------------- ----------- ---------- ------ mem_all: = 33306386432 ( 31763MB) [100%] Total real memory managed mem_gap_sys: + 1040515072 ( 992MB) Memory gap: Kernel?! -------------- ----------- ---------- mem_phys: = 34346901504 ( 32755MB) Total real memory available mem_gap_hw: + 12836864 ( 12MB) Memory gap: Segment Mappings?! -------------- ----------- ---------- mem_hw: = 34359738368 ( 32768MB) Total real memory installed SYSTEM MEMORY SUMMARY: mem_used: 5914402816 ( 5640MB) [ 17%] Logically used memory mem_avail: + 28445335552 ( 27127MB) [ 82%] Logically available memory -------------- ----------- ---------- ------ mem_total: = 34359738368 ( 32768MB) [100%] Logically total memory

Update from forquare's answer – yet another method:

# vmstat -h procs memory page disks faults cpu r b w avm fre flt re pi po fr sr da0 da1 in sy cs us sy id 0 2 0 3372M 1627M 39 32 0 0 8 23 0 0 23 25 38 19 9 71 # swapinfo -h Device 1K-blocks Used Avail Capacity /dev/da0s1b 9437184 363M 8.6G 4%

I ran all seven of the above BSD commands (sysctl two ways, /var/run/dmesg.boot, top, freebsd-memory.pl, vmstat, swapinfo) on a single command line, so the output should be pretty consistent, yet I see a lot of conflicting values.

Which of these is "most accurate?" I want a small script (no compilation!) that can be run on pretty much any system (or else just BSD) that concisely display my memory consumption the way procps free does.

I'm using top |grep -Em2 '^(Mem|Swap):' at the moment.

 

Side note 1: Freecolor is almost exactly what I want, but it require compilation and it has a dependency that I don't want to deal with (I'm not the maintainer of these systems), but it may help visitors looking at this question.

Side note 2: The procps (Linux) top command doesn't play well with pipes. You can make it faster with top -d.1 -n1, but it might make your cursor vanish.

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  • 2
    This related question may provide some clues to the differences but not an answer to this question: What do the different memory counters in FreeBSD mean? Commented Mar 8, 2017 at 1:49
  • Why don't you want a compiled program? Commented Mar 8, 2017 at 1:52
  • Too many architectures and too many systems that I use too briefly to justify compiling this (plus its dependencies) for each one, and I don't have control of the deployment mechanisms (I'm not maintaining these systems). I want a drop-in script, ideally brief enough to fit in my .bashrc and .zshrc. Commented Mar 8, 2017 at 2:11

1 Answer 1

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For simple free/active figures, I've always used vmstat:

~ # vmstat procs memory page disks faults cpu r b w avm fre flt re pi po fr sr da0 cd0 in sy cs us sy id 1 0 2 841M 89M 23 0 0 0 29 9 0 0 4 110 93 0 0 100

From the man page:

Information about the usage of virtual and real memory. Virtual pages (reported in units of 1024 bytes) are considered active if they belong to processes which are running or have run in the last 20 seconds.

 avm active virtual pages fre size of the free list

For information on swap usage:

~ # swapinfo -h Device 1K-blocks Used Avail Capacity /dev/da0p2 2097152 25M 2.0G 1%
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  • Okay, so that's yet another set of memory metrics that don't quite line up with the rest. I've added it to the list in the question. My question is which one should I trust and why? Commented Mar 17, 2017 at 21:02
  • The vmstat command here doesn't list the total physical memory of the system and I'm seriously questioning its values; I have a system with 16G of hw.realmem that vmstat -h says has 2.1G active and 350M free (top says it has 318M free plus 12G Inact, so maybe I want that latter value, which presumably means "inactive"?) Commented Oct 29, 2019 at 15:53
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    You might find value reading How does FreeBSD allocate memory? It gives insight into how the memory actually is allocated and you might better understand what you want. Commented Nov 5, 2019 at 14:13

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