Linux memory monitoring: free command

In Windows, it is very easy to view the memory usage. I think everyone is familiar with it. How can I check the memory usage in Linux? The following is a free command for checking memory usage in Linux:

BKJIA recommended for editing: Linux monitoring tools

 
 

  
  
[root@scs-2 tmp]# free  
  
  
total used free shared buffers cached  
  
  
Mem: 3266180 3250004 16176 0 110652 2668236  
  
  
-/+ buffers/cache: 471116 2795064  
  
  
Swap: 2048276 80160 1968116 
 
 

The following is an explanation of these values:

Total: total physical memory size.

Used: used.

Free: available.

Shared: The total memory Shared by multiple processes.

Buffers/cached: disk cache size.

Row 3 (-/+ buffers/cached ):

Used: used.

Free: available.

The fourth line won't be explained much.

Difference: used/free of the second row (mem) differs from used/free of the third row (-/+ buffers/cache. The difference between the two is that from the perspective of usage, the first line is from the OS perspective, because for OS, buffers/cached is used, so its available memory is 16176KB, memory in use is kb, including kernel OS + + Application (X, oracle, etc) + buffers + cached.

The third line indicates that, from the application perspective, for applications, buffers/cached is equivalent to available, because buffer/cached is designed to improve file read performance, when the application needs to use the memory, buffer/cached will be quickly recycled.

From the application perspective, the available memory = system free memory + buffers + cached.

For example:

2795064 = 16176 + 110652 + 2668236

Next, we will explain when the memory will be exchanged and by which side. When the available memory is less than the rated value, a meeting will be held for exchange.

Rating:

 
 

  
  
cat /proc/meminfo  
  
  
[root@scs-2 tmp]# cat /proc/meminfo  
  
  
MemTotal: 3266180 kB  
  
  
MemFree: 17456 kB  
  
  
Buffers: 111328 kB  
  
  
Cached: 2664024 kB  
  
  
SwapCached: 0 kB  
  
  
Active: 467236 kB  
  
  
Inactive: 2644928 kB  
  
  
HighTotal: 0 kB  
  
  
HighFree: 0 kB  
  
  
LowTotal: 3266180 kB  
  
  
LowFree: 17456 kB  
  
  
SwapTotal: 2048276 kB  
  
  
SwapFree: 1968116 kB  
  
  
Dirty: 8 kB  
  
  
Writeback: 0 kB  
  
  
Mapped: 345360 kB  
  
  
Slab: 112344 kB  
  
  
Committed_AS: 535292 kB  
  
  
PageTables: 2340 kB  
  
  
VmallocTotal: 536870911 kB  
  
  
VmallocUsed: 272696 kB  
  
  
VmallocChunk: 536598175 kB  
  
  
HugePages_Total: 0  
  
  
HugePages_Free: 0  
  
  
Hugepagesize: 2048 kB 
 
 

View the result in free-m:

 
 

  
  
[root@scs-2 tmp]# free -m  
  
  
total used free shared buffers cached  
  
  
Mem: 3189 3173 16 0 107 2605  
  
  
-/+ buffers/cache: 460 2729  
  
  
Swap: 2000 78 1921 
 
 

View the memory image of the/proc/kcore file ):

 
 

  
  
[root@scs-2 tmp]# ll -h /proc/kcore  
  
  
-r——– 1 root root 4.1G Jun 12 12:04 /proc/kcore 
 
 

Note:Memory usage Measurement

Measure how much memory a process occupies. Linux provides us with a very convenient method. The/proc Directory provides us with all the information, in fact, the top tool also obtains the corresponding information here.

 
 

  
  
/Proc/meminfo memory usage information of the machine
  
  
/Proc/pid/maps pid is the process number and displays the virtual address occupied by the current process.
  
  
Memory occupied by/proc/pid/statm Process
  
  
[Root @ localhost ~] # Cat/proc/self/statm
  
  
654 57 44 0 0 334 0
 
 

Output description

CPU and CPU 0... For each parameter in each row of, the first behavior is used as an example:

Parameter description/proc // status

Size (pages) task virtual address space Size VmSize/4

The size of the physical memory that the Resident (pages) application is using VmRSS/4

Shared (pages) Shared pages 0

Size of executable virtual memory owned by the Trs (pages) program VmExe/4

The size of the library that the Lrs (pages) is mapped to the virtual memory space of the task. VmLib/4

Drs (pages) Program Data Segment and user-state stack size VmData + VmStk) 4

Dt (pages) 04

View available machine memory

 
 

  
  
/proc/28248/>free  
  
  
total used free shared buffers cached  
  
  
Mem: 1023788 926400 97388 0 134668 503688  
  
  
-/+ buffers/cache: 288044 735744  
  
  
Swap: 1959920 89608 1870312 
 
 

When we run the free command to view the idle memory of the machine, we will find that the free value is very small. This is mainly because there is such an idea in the Linux system that the memory does not need to be white, so it tries its best to cache and buffer some data to facilitate the next use. But in fact, these memories can also be used immediately.

So free memory = free + buffers + cached = total-used