sofars explanation is very well, and I share his point.
So if you or anyone check for lag,
first he should understand
- * time of data send between server location and client location (gamer)
* time the server need to process the incoming date (change position, build, etc) and process* them, and send them out
* time or ability the clients hardware (CPU, RAM speed, GPU and game Settings) is able to show the received data
THEN the shown lag of /status or /lagcheck or /lag make more sence.
- * MY Server is in Thailand, but very fast, myself logging into the server via home GB Connection show RTT of 0.001 as I have no distance for the data to travel. (Connected via fiber 50 mb / 20 mb to internet)
* The Server itself is also very fast: i7-4770 CPU, all 4 Memory slots used (= faster RAM Speed) and a 2.200 read write M.2 SSD, instead of slow normal 250 HDD readings, also keep most needed parts in fast RAM cache
and as my
* Gaming Maschine is even same CPU, 4 memory slots used, and has GPU GTX 960 2 GB (but 3 monitors) - and remember good working GPU driver is important
- --- so for me my own server is really fast, and i only realize lag when new blocks are generated (lag most near 0.2 even with moretrees, technic, monsters, ... but then getting to 2.5)
--- but if I would sit at my old home in Germany using same PC there, might not change any speed of my Rig or the server, but just the data between have to travel about 7.000 km fiber, what is a not change fact of 220 ms about.
So THIS lag might be a network-transport lag.
And also clients using Wifi, or even have a slow or bad Internet connection (old cable, using 4G, or Wifi at home) have or make there own lag ... not knowing it.
Easy to check your "ping" to the server you like in a dos / cmd box with "ping address" (no port)
So if you have a short ping as inside Germany or USA you and server location (should be about 20-40 ms then), and it is laggy, you might think about your rig or the server, the servers mod and if a lot of players are there - and just ONE of them going to new area (mean activation mapgen) you will get lag again (here from the server).
So what I often here about "this server lags" I don't listen to it anymore - as this gamer sure doesn't understand this basics.
* fake-lag ... the real lag made a break or stop might just happen for 5 seconds, but the algorithm of the servers showed lag is very slow getting down, it is not the reality, that why sometime you feel good, even lag show bad
* like sofar wrote: chose a nearby server - check it with ping
And to answer the starting question:
How to check real lag of server?
the shown lag of server (/status or at me with hud) IS THE REAL SERVER LAG, mean the time the server need to do his work, not mention what clients do and how far they are.
So when the /status lag is low, but you feel lag, see the RTT, then you might understand better and think about distance from you and server, or flooded network.
The ONLY REAL lag the server can show is his own lag (mean get data and offer them), as every player with his distance and lousy network connection is DIFFERENT.
YOUR gamer lag depends basically on your distance to the server and the time your
* wish data (build, dig, movement) had to get the way through wifi, router, provider netork, internet to the server,
* worked out there in the real server lag time
* and send back the same way again to reach your unit
* and need to be worked out by your CPU and GPU
AND that lg is different.
When press F5 you might see your RTT, and if this is over 50 the server is already out of own county, and if more than 200 maybe take another one.
And as the serverlist ping is cheating (as its base is always distance to a server from the Netherlands server itself)
then better check one a month with Minetest-ping-sort
and take only those servers with less than 200, better less than 100 ping. (100 ping = .1 RTT)
and if your using Wifi ... all problems are just there !