The top command is often used to monitor Linux system conditions, such as CPU, memory usage, the programmer basically knows this command, but it is strange to use it very few people, such as the top monitoring view of the memory value of the meaning of a lot of distortion.
This article covers the meaning of various data in the top view and the sorting of the fields of each process (task) in the view through top monitoring of a running Web server. Top into view top view 01 "Top View 01" is the basic view that just entered top, and let's combine this view to explain the meaning of each data.
First line:
10:01:23 Current system time
126 days, 14:29 the system has been running for 126 day, 14 hours, 29 minutes (not restarted during this period)
2 users currently have 2 user login systems
The three numbers behind load average:1.15, 1.42, 1.44 load average are 1-minute, 5-minute, 15-minute loads respectively. The load average data is the number of active processes that are checked every 5 seconds and then calculated by a particular algorithm. If this number is divided by the number of logical CPUs, the result above 5 indicates that the system is overloaded.
Second line:
Tasks task (process), the system now has a total of 183 processes, of which there are 1 in the running, 182 in hibernation (sleep), 0 in the stoped state, and 0 in the zombie State (zombie).
Third line: CPU status
6.7% the percentage of CPU occupied by US user space.
0.4% Sy Core Space consumes a percentage of the CPU.
0.0% NI changes the priority of the process to occupy a percentage of the CPU
92.9% ID Idle CPU percent
0.0% wa io waiting for CPU percentage
0.0% Hi Hard Interrupt (Hardware IRQ)% of CPU occupied
0.0% si soft interrupt (software interrupts) The percentage of CPU used here is different from the Windows concept, and if you don't understand user space and kernel space, you need to recharge it.
Line four: Memory status
8306544k Total Physical Memory (8GB)
7775876k used total memory in use (7.7GB)
530668k free Memory Total (530M)
79236k Buffers Cache Memory (79M)
Line five: Swap swap partition
2031608k Total swap area (2GB)
Total swap area used by 2556k used (2.5M)
2029052k Free Swap Area total (2GB)
4231276k cached buffer Swap area total (4GB)
The point here is that this data cannot be understood in terms of the Windows memory concept, which is dangerous if you press windows: The total amount of memory in 8G is only 530M of available memory. The memory management of Linux has its particularity, the complex point needs a book to explain, here is simply to say the point and our traditional concept (Windows) is different.
The total amount of memory in use in row four (used) refers to the amount of memory that is now controlled by the system kernel, and the total amount of free memory that the kernel has not included in its control range. The memory that is included in kernel management is not always in use, but also includes the memory that has been used in the past that can now be reused, and the kernel does not return these reusable memory to free, so there is less memory on Linux, but don't worry about it. If you are accustomed to calculating the number of available memory, here is an approximate formula: The fourth line of Free + fourth row of buffers + fifth row of cached, press this formula for this server's available memory: 530668+79236+4231276 = 4.7GB.
For memory monitoring, in the top we have to monitor the fifth line swap partition used, if this value is constantly changing, indicating that the kernel is constantly in memory and swap data exchange, which is really not enough memory.
Line six is the empty line below line seventh: status monitoring of each process (Task)
PID Process ID
USER Process Owner
PR Process Priority
NI nice value. Negative values indicate high priority, positive values indicate low priority
The total amount of virtual memory used by the VIRT process, in kilobytes. Virt=swap+res
The size, in kilobytes, of the physical memory used by the RES process and not swapped out. Res=code+data
SHR shared memory size, in kilobytes
S process state. d= non-disruptive sleep status r= run s= sleep t= track/stop z= zombie Process
%cpu percentage of CPU time that was last updated to current
Percentage of physical memory used by the%MEM process
Total CPU time used by the time+ process, Unit 1/100 sec
Commands process name (command name/command line) Multi-u multi-core CPU monitoring in the top basic view, press the keypad number 1 to monitor the status of each logical CPU:
Top View 02 observes that the server has 16 logical CPUs, which are actually 4 physical CPUs. Process field sorting default to top, each process is sorted by CPU consumption, in "Top View 01" In the process ID 14210 of the Java process ranked first (CPU occupied 100%), the process ID of 14183 Java process ranked second (CPU occupied 12%). You can change the sort field by keyboard instruction, for example, to monitor which process consumes mem most, I use the following method as follows: 1. Tap Keyboard B (turn on/off highlighting), and the top view changes as follows:
Top View 03 We find that the top process with process ID 10704 is highlighted, the top process is the only running state (runing) that is displayed in the second row of the view, and you can turn off or turn on the highlight effect of the running process by tapping the Y key. 2. Tap keyboard x (Highlight effect on/off column), and the top view changes as follows:
Top View 04 You can see that the top default sort column is%cpu. 3. With SHIFT + > or SHIFT + <, you can change the column to the right or left by pressing SHIFT + > once:
The top view 05 view is now sorted by%mem. Change process display Field 1. Tap the F key and top into another view, where you can orchestrate the display fields in the base view:
Top view 06 Lists all the process fields that can be displayed in the top Basic view, fields with * and uppercase letters are visible, fields without * and lowercase are not displayed. If you want to display the code and data two fields in the basic view, you can tap the R and S keys:
Top View 072. Return to Basic view, you can see more code and data two fields:
The Supplemental top command of the top view 08top command is the preferred command for system monitoring on Linux, but sometimes it does not reach our requirements, such as the current server, where top monitoring has great limitations. This server runs the WebSphere cluster, there are two node services, is "Top view 01" in the eldest, the old 22 Java processes, the top command is the smallest monitoring unit of the process, so I do not see the number of Java threads and customer connections, And these two indicators are very important indicators of Java Web Services, usually I use PS and netstate two commands to supplement the top of the shortcomings.
To monitor the number of Java threads:
ps-elf | grep java | Wc-l Monitoring network client connections:
Netstat-n | grep TCP | grep Listening Port | Wc-l the above two commands, can change the parameters of grep, to achieve more detailed monitoring requirements.
In the Linux system everything is the idea of the implementation of the guidance, all processes running state can be used to obtain files. system root/proc, each digital subdirectory name is the PID of the running process, into any process directory, through which files or directories to observe the process of the various operational indicators, such as the task directory is used to describe the thread of the process, Therefore, you can also get the number of threads running in a process by using the following method (PID refers to the process ID):
Ls/proc/pid/task | Wc-l also has a command pmap in Linux to output the status of process memory, which can be used to analyze the thread stack:
Pmap PID
Graphical use of the top command in Linux
