To follow the guide, you must have the following:<\/p>\n
- \n
- \n
Access to a Linux user account with sudo privileges<\/p>\n<\/li>\n
- \n
Access to a terminal or command-line interface<\/p>\n<\/li>\n
- \n
Ability to install new packages, such as access to the APT package manager<\/p>\n<\/li>\n<\/ul>\n
Let\u2019s get started.<\/p>\n
Why Learn Commands to Check Memory Usage in Linux?<\/strong><\/h2>\n
Before we start, it is essential to learn about memory usage. In other words, does the knowledge of free and used memory matter?<\/p>\n
Each time you run a process, it consumes Random Access Memory(RAM). Without RAM, a program will not function. So, if you try to run a process that requires more memory than is currently available, it won’t run. Also, running processes in Linux changes memory usage based on users’ actions. If the user tries to do an action, but the system cannot allocate it, it can crash or show an error. All of these become important if you’re running a low-spec machine.<\/p>\n
Sysadmins must also learn about system memory to optimize it for the best performance. This way, they can learn about rouge apps that slow down the whole system by clogging system memory. This can block new applications or even crucial Linux kernel processes.<\/p>\n
In addition, you can use memory usage in Linux commands to learn about the total physical memory installed on the system. It also provides information about Linux swap partitions, including other vital system info.<\/p>\n
On the other hand, web admins can also use these tools to check memory usage in their Linux servers. This way, they can learn whether the server can handle site visitors during peak hours. If memory usage is too high, you can always add more physical memory to handle peak traffic.<\/p>\n
In short, keeping a tab on memory usage in Linux lets you troubleshoot issues with your system. After all, the Linux system depends on memory and how it is utilized. So, if you’re a sysadmin or a developer, you need to know the exact amount of free and used memory alongside the server’s swap memory, kernel’s caches, and buffers.<\/p>\n
cat Command to Show Linux Memory Usage<\/strong><\/h2>\n
The\u00a0cat\u00a0<\/strong>command on Linux lets you read data from files and provides output to the terminal. Here, the\u00a0cat\u00a0<\/strong>command stands for Concatenate.<\/p>\n
On the other hand, Linux stores all the memory usage information in the\u00a0\/proc\/meminfo<\/strong>\u00a0file.<\/p>\n
So, we can combine both of them to reveal information about available and used memory.<\/p>\n
To do so, run the Command below:<\/p>\n
cat \/proc\/meminfo<\/code><\/p>\nIt’ll output the real-time system’s memory usage. Moreover, it’ll also list the shared memory usage in Linux. If you’re looking for buffers’ info, you’ll also get it here.<\/p>\n
cat \/proc\/meminfo<\/code><\/p>\n#output
\nMemTotal: <\/code><\/p>\n8090732 kB
\nMemFree: <\/code><\/p>\n7642496 kB
\nMemAvailable: <\/code><\/p>\n7583008 kB
\nBuffers: <\/code><\/p>\n5912 kB
\nCached: <\/code><\/p>\n119512 kB
\nSwapCached: <\/code><\/p>\n0 kB
\nActive: <\/code><\/p>\n20964 kB
\nInactive: <\/code><\/p>\n141668 kB
\nActive(anon): <\/code><\/p>\n1812 kB
\nInactive(anon): <\/code><\/p>\n37632 kB
\nActive(file): <\/code><\/p>\n19152 kB
\nInactive(file): <\/code><\/p>\n104036 kB
\nUnevictable: <\/code><\/p>\n0 kB
\nMlocked: <\/code><\/p>\n0 kB
\nSwapTotal: <\/code><\/p>\n2097152 kB
\nSwapFree: <\/code><\/p>\n2097152 kB
\nDirty: <\/code><\/p>\n0 kB
\nWriteback: <\/code><\/p>\n0 kB
\nAnonPages:<\/code><\/p>\n<\/code><\/code>37208 kB
\nMapped: <\/code><\/p>\n63220 kB
\nShmem: <\/code><\/p>\n2236 kB
\nKReclaimable: <\/code><\/p>\n21148 kB
\nSlab: <\/code><\/p>\n67344 kB
\nSReclaimable: <\/code><\/p>\n21148 kB
\nSUnreclaim: <\/code><\/p>\n46196 kB
\nKernelStack: <\/code><\/p>\n3184 kB
\nPageTables: <\/code><\/p>\n1216 kB
\nNFS_Unstable: <\/code><\/p>\n0 kB
\nBounce: <\/code><\/p>\n0 kB
\nWritebackTmp: <\/code><\/p>\n0 kB
\nCommitLimit: <\/code><\/p>\n6142516 kB
\nCommitted_AS: <\/code><\/p>\n390148 kB
\nVmallocTotal: <\/code><\/p>\n34359738367 kB
\nVmallocUsed: <\/code><\/p>\n23376 kB
\nVmallocChunk: <\/code><\/p>\n0 kB
\nPercpu:<\/code><\/p>\n<\/code>4352 kB
\nAnonHugePages: <\/code><\/p>\n14336 kB
\nShmemHugePages: <\/code><\/p>\n0 kB
\nShmemPmdMapped: <\/code><\/p>\n0 kB
\nFileHugePages: <\/code><\/p>\n0 kB
\nFilePmdMapped: <\/code><\/p>\n0 kB
\nHugePages_Total: <\/code><\/p>\n0
\nHugePages_Free: <\/code><\/p>\n0
\nHugePages_Rsvd: <\/code><\/p>\n0
\nHugePages_Surp: <\/code><\/p>\n0
\nHugepagesize: <\/code><\/p>\n2048 kB
\nHugetlb: <\/code><\/p>\n0 kB
\nDirectMap4k: <\/code><\/p>\n19456 kB
\nDirectMap2M: <\/code><\/p>\n4128768 kB
\nDirectMap1G: <\/code><\/p>\n13631488 kB<\/code><\/p>\n![\"top](\"https:\/\/www.servergigabit.com\/blog\/wp-content\/uploads\/2023\/03\/cat_proc_meminfo-243x300.jpg\")
<\/p>\nAs you can notice, the \/proc\/meminfo lists all the processes, buffers, and shared memory usage in\u00a0kilobytes. The\u00a0MemTotal\u00a0is the total memory of your system. The\u00a0MemFree, on the other hand, lists free memory. You’ll also see\u00a0MemAvailiable, which is similar to\u00a0MemFree. It lets you know how much memory is available for new processes.<\/p>\n
The other values are as below:<\/p>\n
- \n
- \n
- \n
- Buffers:\u00a0The amount of memory used by buffers.<\/li>\n
- Cached:\u00a0The amount of memory used as cache memory.<\/li>\n
- SwapTotal: The total amount of swap memory.<\/li>\n
- SwapFree:\u00a0The available swap memory.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n
If you want to know more about \/proc\/meminfo values, read this:\u00a0Explanation\u00a0of \/proc\/meminfo values.<\/p>\n
You can also use the following commands to show fewer values.<\/p>\n
less \/proc\/meminfo<\/code><\/code><\/code><\/p>\nmore \/proc\/meminfo<\/code><\/p>\nFree Command to see free and used memory in Linux<\/strong><\/h2>\n
The\u00a0free\u00a0Command is a neat way to learn about your system’s physical and swap memory status. It lists the total, used, and free memory usage, alongside shared and buff\/cache values. Lastly, it also lists available memory.<\/p>\n
To run the Command, type the following in the terminal.<\/p>\n
free<\/code><\/p>\nBy default, it’ll show the values in Kilobytes. If you need the output in Megabytes(MB), use the -m flag.<\/p>\n
free -m<\/code><\/p>\nThe output is:<\/p>\n
total used free shared buff\/cache available
\nMem: 7901 303 7452 2 145 7395
\nSwap: 2048 0 2048<\/code><\/p>\n![\"free](\"https:\/\/www.servergigabit.com\/blog\/wp-content\/uploads\/2023\/03\/free-command-300x115.jpg\")
<\/p>\nUnderstanding the free Command displays information is accessible. Under the entire tab, you’ll see the Mem and Swap values. Similarly, it also lists the used and free values. Let’s list them below.<\/p>\n
- \n
- \n
- \n
- \n
- \n
- Total:\u00a0<\/strong>Shows the system’s total RAM. In our case, it is 7901 MB.<\/li>\n
- Used:<\/strong>\u00a0Shows the system’s used RAM. In our case, it is 303 MB.<\/li>\n
- Free:<\/strong>\u00a0Shows the system’s free memory. In our case, it is 7452 MB.<\/li>\n
- Shared:\u00a0<\/strong>Here, you’ll find the memory usage by the tmpfs file system.<\/li>\n
- Buff\/cache:\u00a0<\/strong>It lists the memory used by the buffer and cache.<\/li>\n
- Available:<\/strong>\u00a0System’s available memory for new apps. In other words, any app can use the available memory without relying on swap memory.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n
The Memory column list all the above information. As for Swap, you only get Total, Used, and Free values.<\/p>\n
Lastly, if you want to display it in line, then you need to use the following Command.<\/p>\n
free -t -m<\/code><\/p>\nvmstat Command to Report Virtual Memory Statistics in Linux system<\/strong><\/h2>\n
If you only want to learn about virtual memory statistics, use\u00a0the vmstat\u00a0Command. The command syntax is:<\/p>\n
vmstat<\/code><\/p>\nIt reports virtual memory statistics, including processes, paging, block device, memory, traps, disks, and CPU.<\/p>\n
However, its output is not easy to read. You’ll get the following output if you type vmstat in the terminal.<\/p>\n
#output
\nprocs -----------memory---------- ---swap-- -----io---- -system-- ------cpu-----
\n<\/code><\/p>\nr b swpd free buff cache si so bi bo in cs us sy id wa st
\n<\/code><\/p>\n0 0 0 7631484 5912 142568 0 0 1 0 1 19 0 0 100 0 0<\/code><\/p>\n![\"vmstat](\"https:\/\/www.servergigabit.com\/blog\/wp-content\/uploads\/2023\/03\/vmstat-300x141.png\")
<\/p>\nAs you can see, the output is not clear. To circumvent it, you can use the -s switch flag. It forces the\u00a0vmstat\u00a0<\/strong>Command to show values in a single column. This makes it easy to read.<\/p>\n
vmstat -s<\/code><\/p>\n#output
\n<\/code><\/p>\n8090732 K total memory
\n<\/code><\/p>\n310728 K used memory
\n<\/code><\/p>\n22340 K active memory
\n<\/code><\/p>\n144956 K inactive memory
\n<\/code><\/p>\n7631484 K free memory
\n<\/code><\/p>\n5912 K buffer memory<\/code><\/p>\n142608 K swap cache
\n<\/code><\/p>\n2097152 K total swap
\n<\/code><\/p>\n0 K used swap
\n<\/code><\/p>\n2097152 K free swap
\n<\/code><\/p>\n299 non-nice user cpu ticks
\n<\/code><\/p>\n0 nice user cpu ticks
\n<\/code><\/p>\n581 system cpu ticks
\n<\/code><\/p>\n8080176 idle cpu ticks
\n<\/code><\/p>\n51 IO-wait cpu ticks
\n<\/code><\/p>\n0 IRQ cpu ticks
\n<\/code><\/p>\n24 softirq cpu ticks
\n<\/code><\/p>\n0 stolen cpu ticks
\n<\/code><\/p>\n84626 pages paged in
\n<\/code><\/p>\n972 pages paged out
\n<\/code><\/p>\n0 pages swapped in
\n<\/code><\/p>\n0 pages swapped out
\n<\/code><\/p>\n42773 interrupts
\n<\/code><\/p>\n1555675 CPU context switches
\n<\/code><\/p>\n1677583195 boot time
\n<\/code><\/p>\n334 forks<\/code><\/p>\nWith\u00a0vmstat, you can check memory usage on Linux and learn about different system summaries. That’s why\u00a0vmstat\u00a0is more of a system monitor tool that offers more than just checking RAM usage.<\/p>\n
Some of its unique options include:<\/p>\n
- \n
- \n
- \n
- \n
- \n
- – a Active: It lets you discover the system’s active and inactive memory.<\/li>\n
- – f : It lists the number of times the system has been forked since boot.<\/li>\n
- -d : Use it to show disk space and other disk statistics<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n
In short, you can use\u00a0vmstat\u00a0to learn about procs, swap space, operating system’s IO, interrupts, and context switches. Additionally, you can learn about CPU usage, including time running kernel code, non-kernel code, idle time spent, and much more.<\/p>\n
Top Command to Check Memory Use<\/strong><\/h2>\n
The\u00a0top\u00a0Command is another useful command to check memory usage in the Linux operating system. It provides a detailed system summary that offers access to memory and CPU usage.<\/p>\n
The syntax of the top Command is as below.<\/p>\n
top<\/code><\/pre>\nWhen you run the\u00a0top\u00a0<\/strong>Command, it offers access to the following information:<\/p>\n
- \n
- \n
- \n
- \n
- \n
- memory\/ swap system processes<\/li>\n
- number of users logged in<\/li>\n
- Average load on the system<\/li>\n
- System’s uptime<\/li>\n
- Number of tasks running processes<\/li>\n
- The number of CPUs utilization<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n
And the output for the top Command to check memory usage is as below:
<\/code><\/p>\ntop - 19:47:24 up 27 min, 0 users, load average: 0.00, 0.00, 0.00
\n<\/code><\/p>\nTasks: 6 total, 1 running, 5 sleeping, 0 stopped, 0 zombie
\n<\/code><\/p>\n%Cpu(s): 0.0 us, 0.0 sy, 0.0 ni,100.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
\n<\/code><\/p>\n
- \n
- \n
- \n
- Used:<\/strong>\u00a0Shows the system’s used RAM. In our case, it is 303 MB.<\/li>\n
- Total:\u00a0<\/strong>Shows the system’s total RAM. In our case, it is 7901 MB.<\/li>\n
- \n
- \n
- \n