5 commands to control ram on Linux
Caution
This article was published more than a year ago, there may have been developments.
Please take this into account.
In Linux there are commands pretty much for anything, because the graphical interface cannot always be visible. When working on a server and only shell access exists, everything is available with these commands. So today we will explore the commands that can be used to control memory usage on a Linux system. La memoria include RAM e swap.
It is often important to monitor memory usage and the memory used to make sure you don't run out and continue to provide user access to the server. For example a site. If you have a web server active, the server itself must have enough memory to serve site visitors. Otherwise the site will become very slow, or worse it can “go down” in traffic spikes, simply because the memory would become too little. A dust’ as happens to PCs.
But now let's see the five alternative commands:
1_ The command “free”
The command free it is perhaps the simplest of commands to control memory usage on Linux. Here is a quick example:
$ free -h
total used free shared buff/cache available
Mem: 3,8G 2,7G 157M 267M 915M 565M
Swap: 2,0G 641M 1,4G
The option -h shows the data in a format easily readable by the human eye. The 3.8G total is the total of installed RAM (4GB). The column used shows the ram used by the system, in this case 2.7G. The output is easily explained by itself.
2_ Path “/proc/meminfo”
In the file /proc/meminfo contains all the information about the memory of the connected machine. To read it we will have to launch the command cat. This command prints the contents of a given file to a terminal, as in the following example.
Actually the system directory /proc/ does not contain any files. Content are virtual files that contain dynamic information about your system and the kernel.
$ cat /proc/meminfo MemTotal: 3938504 kB MemFree: 274104 kB MemAvailable: 538012 kB Buffers: 30208 kB Cached: 592216 kB SwapCached: 37948 kB Active: 2583536 kB Inactive: 830584 kB Active(anon): 2364820 kB Inactive(anon): 609264 kB Active(file): 218716 kB Inactive(file): 221320 kB Unevictable: 32 kB Mlocked: 32 kB SwapTotal: 2097148 kB SwapFree: 1186988 kB Dirty: 320 kB Writeback: 0 kB AnonPages: 2777800 kB Mapped: 310684 kB Shmem: 182244 kB Slab: 112400 kB SReclaimable: 56800 kB SUnreclaim: 55600 kB KernelStack: 12032 kB PageTables: 67464 kB NFS_Unstable: 0 kB Bounce: 0 kB WritebackTmp: 0 kB CommitLimit: 4066400 kB Committed_AS: 8606840 kB VmallocTotal: 34359738367 kB VmallocUsed: 0 kB VmallocChunk: 0 kB HardwareCorrupted: 0 kB AnonHugePages: 0 kB ShmemHugePages: 0 kB ShmemPmdMapped: 0 kB CmaTotal: 0 kB CmaFree: 0 kB HugePages_Total: 0 HugePages_Free: 0 HugePages_Rsvd: 0 HugePages_Surp: 0 Hugepagesize: 2048 kB DirectMap4k: 273724 kB DirectMap2M: 3819520 kB
The values relating to MemTotal, MemFree, Buffers, Cached, SwapTotal, SwapFree. They indicate the same values as the command free.
3_ the command “vmstat”
The command vmstat with the option -s shows RAM usage statistics, more or less like the previous command. Here is an example:
$ vmstat -s
3938504 K total memory
3055616 K used memory
2634584 K active memory
824360 K inactive memory
228428 K free memory
35676 K buffer memory
618784 K swap cache
2097148 K total swap
933456 K used swap
1163692 K free swap
323777 non-nice user cpu ticks
1544 nice user cpu ticks
80596 system cpu ticks
506483 idle cpu ticks
24004 IO-wait cpu ticks
0 IRQ cpu ticks
1124 softirq cpu ticks
0 stolen cpu ticks
7303873 pages paged in
5460784 pages paged out
22090 pages swapped in
256081 pages swapped out
14156008 interrupts
32916209 CPU context switches
1589867624 boot time
32561 forks
4_ the command “top”
Top is generally used to check RAM and processor congestion. However, it also reports the total amount of RAM. The first lines of the output show the information that interests us:
top - 10:00:02 up 2:06, 3 users, load average: 0,87, 1,29, 1,35 Tasks: 247 total, 2 running, 202 sleeping, 0 stopped, 0 zombie %Cpu(s): 14,2 us, 5,9 sy, 0,0 ni, 71,5 id, 8,1 wa, 0,0 hi, 0,3 si, 0,0 st KiB Mem : 3938504 total, 496344 free, 2890560 used, 551600 buff/cache KiB Swap: 2097148 total, 1120172 free, 976976 used. 620624 avail Mem
The interesting part are the values related to “KiB Mem” and “KiB Swap“. They indicate the total, the free and used memory.
5_ the command “htop”
Very similar to the command top (not only in the name), also htop shows us information about the RAM, but in a more readable and dynamic way.
RAM information with “dmidecode”
One of the commands that ever show the most RAM information is definitely dmidecode.
$ sudo dmidecode -t 17
dmidecode 3.1
Getting SMBIOS data from sysfs.
SMBIOS 2.5 present.
Handle 0x000D, DMI type 17, 27 bytes
Memory Device
Array Handle: 0x000C
Error Information Handle: No Error
Total Width: 64 bits
Data Width: 64 bits
Size: 2048 MB
Form Factor: SODIMM
Set: 1
Locator: M1
Bank Locator: Bank 0
Type: Reserved
Type Detail: Synchronous
Speed: 800 MT/s
Manufacturer: Mfg 0
Serial Number: 1234-B0
Asset Tag: Not Specified
Part Number: SODIMM000
Handle 0x000E, DMI type 17, 27 bytes
Memory Device
Array Handle: 0x000C
Error Information Handle: No Error
Total Width: 64 bits
Data Width: 64 bits
Size: 2048 MB
Form Factor: SODIMM
Set: 1
Locator: M2
Bank Locator: Bank 1
Type: Reserved
Type Detail: Synchronous
Speed: 800 MT/s
Manufacturer: Mfg 1
Serial Number: 1234-B1
Asset Tag: Not Specified
Part Number: SODIMM001
Conclusions
All the solutions mentioned are vital in all areas where the graphical interface is precluded. In case we were working on a classic computer with a gui installed the simplest software are “gnome-system-monitor” for Gnome and “ksysguard” by KDE.
Both show total memory, used, free, The swap, CPU and network load with an easy-to-interpret graphical interface.
4 Comments
Jan · 22 March 2024 at 11:10 AM
Hi Joe,
i found the same translation errors, but i recognized them as such. And i can differenciate between translation errors and content quality. That means: yours is one of the best collections of Linux commands to get infos on RAM usage. Many thanks for that!
BTW: You have reacted perfect on Pauls rude comment – i would have reacted less kind…;-)
TheJoe · 24 March 2024 at 1:44 PM
Hi Jan, thank you for commenting, for being so kind (and thank you for understanding that I don’t speak German at all… eheh).
Paul has been rude to me, it’s true… but you both had the same issue on the site. This pushed me to look for a solution and seems that I’ve found one. Now no preformatted or code tags will be translated anymore.
Paul · 1 February 2023 at 7:30 PM
What a load of rubbish.
The command “frei” doesn’t exist at all, as well as “Top”. I understand that “free” and “top” was ment.
The command “/proc / meminfo” doesn’t exist in any language at all. Everything is wrong here, /proc/meminfo is a path, not a command. And with the spaces it’s just totally garbage.
If you don’t want to or can’t check your posts ( including the translated versions), it would be better to be modestly silent instead of leading help seekers down the wrong path.
TheJoe · 1 February 2023 at 8:33 PM
Hey, Paul! How are you tonight? What a rude comment, I’ve never received such a rude comment!
There’s an error in the post: /proc/meminfo is a path, not a command… I’m going to correct it right now. But if you allow me to, the best way to point something to someone you don’t know would be: “Hi there, I’ve spotted a big mistake in your post. Please doublecheck the part where you write about /proc/meminfo. It’s a path, not a command. Cheers.”.
Coming to the second point… You’re absolutely right: I don’t doublecheck my posts in different languages, simply because I don’t even know a word of German (or Russian). But you don’t seem to be a complete noob, aren’t you? At least you know what the commands “free” and “top” do. Do you think we can collaborate on writing the same articles in our respective languages? Or you can just review my posts for the German audience.
There’s no money involved, we shall do it for the community.
Feel free to contact me with a comment, or via the form.