1. Concept
The top command is often used to monitor the system status of Linux. It is a commonly used performance analysis tool and can display the resource occupancy of each process in the system in real time.
2. Grammar
In the Linux output: top -help, the following situations occur:
Usage : top [-d number] | top [-bnp]
Parameter description :
-d: number represents the number of seconds, which represents the interval between updates of the page displayed by the top command. The default is 5 seconds.
-b: Execute top in batches.
-n: Used in conjunction with -b to indicate that the output of the top command needs to be performed several times.
-p: Specify a specific pid process number for observation.
On the page displayed by the top command, you can also enter the following keys to perform the corresponding functions (note that the case is distinguished):
?: Display the commands that can be entered in top
P: Display in order of CPU usage resources
M: Display in order of memory usage resources
N: display in pid order
T: The time used by the process is cumulatively sorted and displayed
k: Give a signal to a pid. Can be used to kill the process
r: Re-customize a nice value (that is, priority) for a pid. q: Exit top (you can also exit top by using ctrl+c).
Three, example
1. Display process information: top
Output information description :
1. The first line: top-14:21:47 up 7 days, 36 min, 2 users, load average: 0.00, 0.00, 0.00
The first line is the task queue information, the parameters are as follows:
| content |
meaning |
| 14:21:47 |
Indicates the current time |
| up 7 days |
The format of the system running time is: day |
| 36 min |
The format of the system running time is: minutes |
| 2 users |
Number of currently logged in users |
| load average: 0.00, 0.00, 0.00 |
System load, that is, the average length of the task queue. The three values are the average values from 1 minute, 5 minutes, and 15 minutes ago to the present. |
Note: load average: If this number is divided by the number of logical CPUs, when the result is higher than 5, it indicates that the system is overloaded.
2. The second and third lines process and cpu information:
Tasks: 205 total, 1 running, 204 sleeping, 0 stopped, 0 zombie
Cpu (s): 0.3% us, 0.4% sy, 0.0% ni, 99.3% id, 0.0% wa, 0.0% hi, 0.0% si, 0.0% st
| content |
meaning |
| 205 total |
Total number of processes |
| 1 running |
Number of running processes |
| 204 sleeping |
Number of sleeping processes |
| 0 stopped |
Number of stopped processes |
| 0 zombie |
Number of zombie processes |
| 0.3%us |
Percentage of CPU occupied by user space |
| 0.4% sy |
Percentage of CPU occupied by kernel space |
| 0.0% ni |
Percentage of CPU occupied by processes that have changed their priority in the user process space |
| 99.3%id |
Idle CPU percentage |
| 0.0% wa |
Percentage of CPU time waiting for input and output |
| 0.0%hi |
Hard interrupt (Hardware IRQ) occupies the percentage of CPU |
| 0.0% yes |
The percentage of CPU occupied by Software Interrupts |
| 0.0%st |
3. The fourth and fifth lines represent memory information:
Mem: 24564108k total, 24320760k used, 243348k free, 243188k buffers
Swap: 0k total, 0k used, 0k free, 17973516k cached
| content |
meaning |
| Mem: 24564108k total |
Total physical memory |
| 24320760k used |
Total physical memory used |
| 243348k free |
Total amount of free memory |
| 243188k buffers |
Amount of memory used as kernel cache |
| Swap: 0k total |
Total exchange area |
| 0k used |
Total exchange area used |
| 0k free |
Total amount of free swap area |
| 17973516k cached |
The total amount of buffered swap area. |
| 3156100 avail Mem |
Represents the amount of physical memory that can be used for the next allocation of the process |
The total amount of buffered swap area mentioned above, here is an explanation. The so-called total amount of buffered swap area, that is, the content of the memory is swapped out to the swap area, and then swapped into the memory, but the used swap area If it has not been overwritten, the value is the size of the swap area where the content already exists in the memory. When the corresponding memory is swapped out again, it is unnecessary to write to the swap area.
There is an approximate formula for calculating the amount of available memory:
Free in the fourth line + buffers in the fourth line + cached in the fifth line
4. Process information
| Column name |
meaning |
| PID |
Process id |
| PPID |
Parent process id |
| RUSER |
Real user name |
| UID |
The user id of the process owner |
| USER |
The user name of the process owner |
| GROUP |
The group name of the process owner |
| TTY |
The name of the terminal that started the process. Processes that are not started from the terminal are displayed as? |
| PR |
priority |
| NI |
nice value. Negative value indicates high priority, positive value indicates low priority |
| P |
The last CPU used is only meaningful in a multi-CPU environment |
| %CPU |
Percentage of CPU time from the last update to the present |
| TIME |
The total CPU time used by the process, in seconds |
| TIME+ |
The total CPU time used by the process, in units of 1/100 second |
| %MEM |
Percentage of physical memory used by the process |
| VIRT |
The total amount of virtual memory used by the process, in kb. VIRT=SWAP+RES |
| SWAP |
The size of the virtual memory used by the process to be swapped out, in kb |
| RES |
The size of the physical memory used by the process that has not been swapped out, in kb. RES=CODE+DATA |
| CODE |
The size of physical memory occupied by executable code, in kb |
| DATA |
The size of physical memory occupied by parts other than executable code (data segment + stack), in kb |
| SHR |
Shared memory size, unit kb |
| nFLT |
Page faults |
| nDRT |
The number of pages that have been modified since the last write. |
| S |
Process status. D=uninterruptible sleep state R=running S=sleeping T=tracking/stopping Z=zombie process |
| COMMAND |
Command name/command line |
| WCHAN |
If the process is sleeping, display the name of the system function in sleep |
| Flags |
Mission sign |
Study address:
https://blog.csdn.net/yjclsx/article/details/81508455