LINUX Process memory usage command

In CentOS, we can use the top command to view cpu and memory usage in linux. Next I will give you an example to see if you need to know about it.

(1) top mission

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$ Top-u oracle

1. top Command

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Top-d 1-p pid [, pid...] // set it to delay 1 s. The default value is delay 3 s.

To Sort by memory usage, shift + m (Sort by memory usage)

(2) pmap

You can view the memory occupied by the process information based on the process. (You can view the process number in ps:

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$ Pmaps-d 14596

(3) ps
　　
For example:

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$ Ps-e-o 'pid, comm, args, pcpu, rsz, vsz, stime, user, uid' where rsz is the actual memory $ Ps-e-o 'pid, comm, args, pcpu, rsz, vsz, stime, user, uid' | grep oracle | sort-nrk5

Rsz is the actual memory, and the preceding example is sorted by memory, from large to small.

Static view of memory usage of a process

1. pmap command

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Pmap pid

2. ps command

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Ps aux | grep process_name

3. view the status file in the/proc/process_id/folder.

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Name: php State: R (running) SleepAVG: 0% Tgid: 21574 Pid: 21574 PPid: 10005 TracerPid: 0 Uid: 1000 1000 1000 1000 Gid: 100 100 100 100 FDSize: 256. Groups: 16 100 VmPeak: 161740 kB VmSize: 161740 kB VmLck: 0 kB VmHWM: 107144 kB VmRSS: 107144 kB VmData: 106192 kB VmStk: 84 kB VmExe: 5588 kB VmLib: 7884 kB VmPTE: 268 kB Threads: 1 SigQ: 0/69632 SigPnd: 0000000000000000 ShdPnd: 0000000000000000 SigBlk: 0000000000000000 SigIgn: 0000000000001000 SigCgt: 00000001818040a7 CapInh: 0000000000000000 Cappr: 0000000000000000 CapEff: 0000000000000000 Cpus_allowed: 00000000,00000000, 00000000,000 0000f Mems_allowed: 1

Task virtual address space size VmSize
The physical memory size that the application is using VmRSS

To view the memory, we generally use the free command:

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[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, the memory used is kb, including the + buffers + cached used by the kernel (OS) + Application (X, oracle, etc.
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.

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.

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/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... The meaning of each parameter in each row (in the first behavior example) is:

Parameter description/proc // status

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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

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/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 linux, the memory does not need to be white, so it tries its best to cache and buffer some data for the next use. But in fact, these memories can also be used immediately.

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