May 4th

10.1 Use w to view system load

1. Use w to view the system load (mainly view the CPU load)

Explanation: The most common command used by Linux administrators is this w, which displays a wealth of information. The information displayed in the first row from left to right is: time, system running time, number of logged-in users, and average load.

All the lines starting from the second line tell us: the currently logged in user name and its login address, etc.

Note: The most important thing to pay attention to here is the load average: the last three values in the first line.

The first value represents the average load value of the system in one minute.

The second value represents the average load value of the system over five minutes.

The third value represents the average load value of the system over fifteen minutes.

Remarks: We focus on the first value, which indicates the number of active processes using cpu in a unit time period (in this case, it is actually within one minute). The larger the value, the greater the pressure on the server. Under normal circumstances, this value does not matter as long as it does not exceed the number of CPUs of the server. If the number of CPUs of the server is 8, then the value is less than that means that the current server is not under pressure. Otherwise, pay attention.

1.1 Check how many CPU cores the server has (logical CPU)

The processor count here starts from 0, that is, the first one is displayed as 0, and the second is displayed as 1

Command: cat /proc/cpuinfo

1.1.1 Check how many CPUs the current system has

：： Grep -c 'processor' / proc / cpuinfo

10.2 The vmstat command

1. The meaning of the 1.vmstat command is to display the virtual memory status ("Viryual Memor Statics"), which can report the overall operating status of the system such as processes, memory, and I/O. Let us know where the usage bottleneck of the system is.

Explain the role of related processes, focusing on the columns of information r, b, si, so, bi, and bo:

2. procs displays information about the process.

2.1 r (run): Indicates the number of processes running or waiting for CPU time slices. Note: Do not mistakenly think that waiting for the CPU time slice means that the process is not in progress. In fact, at a certain time, there can only be one process on a CPU, and other processes can only wait in line. At this time, these processes waiting for CPU resources are still Operating status. If the value is greater than the number of server CPUs for a long time, it indicates that the CPU resources are insufficient.

2.2 b (block): Indicates the number of processes waiting for resources, such as I/O, memory, etc. For example: when the disk reads and writes very frequently, writing data will be very slow. At this time, the CPU operation will end soon, but the process needs to write the result of the calculation to the disk, so that the task of the process is completed, then this When the process can only wait slowly, so the process is the b state. If the value is greater than 1 for a long time, you need to pay attention.

3. memory Displays information about memory

swpd: Indicates the amount of memory switched to the swap partition, in KB.

free: Indicates the current amount of free memory, in KB.

buff: Indicates the buffer size (to be written to disk), in KB.

cache: Indicates the size of the cache (read from disk), in KB.

4. swap shows the swap of memory.

si: Indicates the amount of data written into memory by the swap area, in KB.

so: Indicates the amount of data written into the swap area from memory, in KB.

5. io displays disk usage.

bi: Indicates the amount of data read from the block device (read disk), in KB.

bo: Indicates the amount of data written from the block device (write to disk), in KB.

6. The system displays the number of interrupts that occurred within the acquisition interval.

in: Indicates the number of device interruptions per second observed in a certain time interval.

cs: Indicates the number of context switches generated per second.

7. cpu shows the usage status of the CPU.

us: Displays the percentage of time spent on CPU under the user.

sy: Displays the percentage of time the system spends CPU time.

id: Indicates the percentage of time the CPU is idle.

wa: Indicates the percentage of CPU time occupied by I/O waiting.

st: Indicates the percentage of stolen CPU (usually 0, do not pay attention)

Second, pay attention to the r column, the b column, and the wa column

In addition, when the values of the two columns of si and so are relatively high and keep changing, it means that the memory is not enough.

10.3 top command

1.top command to view the resource usage of the process

The top command is used to dynamically monitor the system resources occupied by processes , which changes every 3 seconds . Its characteristic is to put the processes that occupy the highest system resources ( cpu , memory, hard disk I/O , etc.) to the front .

There are just a few items of concern: %CPU, %MEM, COMMAND , load average , tasks

2. The top -c command displays detailed process command information

3. The top -bn1 command statically displays all processes

Remark:

q exit top , the number 1 shows all core cpu

Capital M to sort by memory usage

Capital P to sort by cpu usage

kill+pid kills the process

RES represents the amount of memory occupied by the process.

10.4 The sar command

1. sar monitors system status ( mainly view historical network card traffic )

The ar command is very powerful and is nicknamed Swiss ×××. It can monitor the status of almost all resources of the system , such as average load, network traffic, disk status, memory usage, etc. Different from other system status monitoring tools, it can mainly print historical information , and can display the system status information from zero o'clock to the current moment of the day.

2. Use yum to install sysstat to obtain, command: yum install -y sysstat installation

( The first time you use the sar command, an error will be reported, because the sar tool has not yet generated the corresponding database file (data is generated every 10 minutes). Its database file is in the "/var/log/sa/" directory, which is saved for one month by default )