Memory (RAM) usage monitoring on Linux
Monitoring RAM resources of your VPS is very important. Especially, if you use caching systems such as Redis or Memcached. If your server runs out of memory, or runs short on memory, your website or service can stop or may run slow.
Luckily, Linux gives you a few handy tools that you would need to monitor memory usage. These tools can be easily used from the command line. This short (and sweet) article will give you an idea how to use those commands, and you can pick the one that fits your needs the most.
1. vmstat command
Type in vmstat
to your command line and the program will display how much free memory is available.
root@localhost:/# vmstatprocs -----------memory---------- ---swap-- -----io---- -system-- ------cpu----- r b swpd free buff cache si so bi bo in cs us sy id wa st 3 0 0 185332 43880 150176 0 0 2 6 8 7 0 0 100 0 0
If you need more details, run vmstat with the -s
or --stats
parameter. Check the first line of the output to see how much free memory is available on your server.
root@209:/# vmstat -s759872 K total memory575220 K used memory356148 K active memory86168 K inactive memory184652 K free memory44048 K buffer memory149248 K swap cache0 K total swap0 K used swap0 K free swap806545 non-nice user cpu ticks1 nice user cpu ticks533833 system cpu ticks424692262 idle cpu ticks54982 IO-wait cpu ticks244344 IRQ cpu ticks0 softirq cpu ticks0 stolen cpu ticks7190421 pages paged in27240788 pages paged out0 pages swapped in0 pages swapped out335817481 interrupts285597986 CPU context switches1425579890 boot time332134 forks
2. top command
This is a widely known command to check both memory and CPU usage.
top - 03:20:50 up 49 days, 8:55, 1 user, load average: 0.00, 0.01, 0.05Tasks: 87 total, 1 running, 86 sleeping, 0 stopped, 0 zombie%Cpu(s): 0.3 us, 0.3 sy, 0.0 ni, 99.3 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 stKiB Mem: 759872 total, 576156 used, 183716 free, 44628 buffersKiB Swap: 0 total, 0 used, 0 free. 149652 cached MemPID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND1 root 20 0 36284 5312 1192 S 0.0 0.7 0:42.98 init2 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kthreadd3 root 20 0 0 0 0 S 0.0 0.0 0:05.13 ksoftirqd/05 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 kworker/0:0H
3. free command
This is my favorite, and probably the most simple command to view memory stats.
root@209:/# free -m total used free shared buffers cachedMem: 742 562 179 27 43 146-/+ buffers/cache: 372 369Swap: 0 0 0
The example above shows you how much total memory your VPS has (in Megabytes), how much memory is used, and how much memory is free.
4. htop command
This command is similar to the top
command, but in my opinion, it gives you a better idea about the memory state of your server.
Conclusion
The commands listed above can be used to manually monitor memory usage. You can also write a simple script using your preferred programming language to run these commands and alert you (by email, for example) if your memory resources are low.
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