Introduction
The top command is a common performance analysis tool under Linux that shows the resource usage of individual processes in the system in real time, similar to the Task Manager for Windows.
Top display system current process and other conditions, is a dynamic display process, that is, you can continue to refresh the current state through the user keys. If the command is executed in the foreground, it will monopolize the foreground until the user terminates the program. More accurately, the top command provides real-time status monitoring of the system's processor. It will display the most "sensitive" CPU in the system Task List. This command can be used by CPU. Memory usage and execution time to sort tasks, and many of the features of the command can be set through interactive commands or in personal customization files.
Here is a detailed description of how it is used.
parameter meaningtop-01:06:48 up 1:22, 1 user, load average:0.06, 0.60, 0.48
tasks:29 Total, 1 running, sleeping, 0 stopped, 0 zombie
Cpu (s): 0.3% us, 1.0% sy, 0.0% ni, 98.7% ID, 0.0% wa, 0.0% Hi, 0.0% si
mem:191272k Total, 173656k used, 17616k free, 22052k buffers
swap:192772k Total, 0k used, 192772k free, 123988k cached
PID USER PR NI VIRT RES SHR S%cpu%MEM time+ COMMAND
1379 Root 0 7976 2456 1980 S 0.7 1.3 0:11.03 sshd
14704 Root 0 2128 980 796 R 0.7 0.5 0:02.72 Top
1 Root 0 1992 632 544 S 0.0 0.3 0:00.90 Init
2 Root 0 0 0 s 0.0 0.0 0:00.00 ksoftirqd/03 root RT 0 0 0 0 S 0.0 0.0 0:00. XX watchdog/0
The first five elements of the statistical information area are the statistical information of the whole system. The first line is the task queue information, with the execution result of the uptime command. The contents are as follows:
01:06:48 Current Time
Up 1:22 system run time, format last: minutes
1 user Current number of users logged on
Load average:0.06, 0.60, 0.48 system payload, which is the average length of the task queue. The three values were 1 minutes, 5 minutes, and 15 minutes ago to the present average.
The second to third behavior process and CPU information. When there are multiple CPUs, the content may be more than two lines. The contents are as follows: Total process totals
Running number of processes that are running
Sleeping the number of sleep processes
Stopped number of processes stopped
Zombie Number of zombie processes
Cpu (s):
0.3% US user space consumes CPU percentage
1.0% SY core space CPU percent occupied
0.0% CPU Percentage of processes that have changed priority within NI user process space
98.7% ID Idle CPU percent
0.0% wa wait for the input output CPU time percentage
0.0%hi: Hardware CPU Interrupt occupancy percentage
0.0%si: Soft interrupt occupancy percent 0.0%st: percent of Virtual machine occupancy
The last two behavior memory information. The contents are as follows: Mem:
Total physical memory of 191272k
Total physical memory used by 173656k used
17616k free Memory Total
The amount of memory that 22052k buffers uses as the kernel cache
Swap:
Total Swap Area 192772k
Total swap area used by 0k used
192772k Free Swap area Total 123988k Cached buffer The total amount of swap, in-memory content is swapped out to the swap area, and then swapped into memory, but the used swap area has not been overwritten, the value is that the content already exists in the memory of the swap area size, When the corresponding memory is swapped out again, it is no longer necessary to write to the swap area. How do you see how much memory is free? Totalfree = free17616 + buffers22052 + cached123988
The details of each process are shown below the process information area statistics area. Let's start by understanding the meaning of the columns. Ordinal column name meaning
A PID process ID
b PPID Parent Process ID
C ruser Real User name
D UID Process Owner's user ID
e username of user process Owner
Group name of the F group Process owner
The terminal name of the G TTY boot process. Processes that are not started from the terminal are displayed as?
H PR-Priority
I NI nice value. Negative values indicate high priority, positive values indicate low priority
The last CPU used by J P is meaningful only in a multi-CPU environment
K%cpu CPU time consumption percentage last updated to current
The total CPU time, in seconds, used by the timing process
The total CPU time used by the M time+ process, in units 1/100 seconds
n the percentage of physical memory used by the%MEM process
o The total amount of virtual memory used by the VIRT process, in kilobytes. Virt=swap+res
The P swap process uses the size of the virtual memory, which is swapped out, in kilobytes.
The size of the physical memory, in kilobytes, that the Q RES process uses and has not been swapped out. Res=code+data
R code executable code occupies the physical memory size, in kilobytes
The amount of physical memory that is used outside of the S data executable code (data segment + stack), in kilobytes
T SHR shared memory size, in kilobytes
U Nflt page Error count
V NDRT the number of pages that have been modified in the last write to now.
W S process status (d= non-interruptible sleep state, r= run, s= sleep, t= track/Stop, z= zombie process)
x command name/command line
Y Wchan If the process is sleeping, the system function name in sleep is displayed Z Flags task flag, reference sched.h
By default, only the more important PID, USER, PR, NI, VIRT, RES, SHR, S,%cpu,%MEM, time+, and COMMAND columns are displayed. You can change the display by using the following shortcut keys.
Change the display by using the F key to select what to display. Press the F key to display a list of columns, press A-Z to show or hide the corresponding column, and then press ENTER to confirm.
Press the o key to change the order in which the columns are displayed. A-Z in the lower case moves the corresponding column to the right, while the uppercase A-Z moves the corresponding column to the left. Finally, press ENTER to confirm.
Press the uppercase F or O key, and then press A-Z to sort the process by the appropriate column. The uppercase R Key can reverse the current sort.
command to use
Top Use Format
Top [-] [d] [P] [Q] [C] [C] [s] [s] [n]
Parameter Description d Specifies the time interval between each two screen information refresh. Of course the user can use the s interactive command to change it.
P only monitors the state of a process by specifying the monitoring process ID.
Q This option will cause top to refresh without any delay. If the calling program has Superuser privileges, top will run at the highest possible priority.
S Specifies the cumulative mode
s enables the top command to run in Safe mode. This removes the potential danger of interactive commands.
I make top not show any idle or zombie processes. C Displays the entire command line instead of just displaying the command name
Other Utility commands The following are some of the interactive commands you can use during the execution of the top command. From a point of view of use, mastering these commands is more important than mastering the options. These commands are single-letter, and if you use the S option in command-line options, some of these commands may be masked out. Ctrl+l Erase and rewrite the screen.
H or? Display the help screen and give a brief summary of the commands.
K Terminates a process. The user will be prompted for the process PID to be terminated and what signal needs to be sent to the process. The normal termination process can use a 15 signal, and if not, use signal 9 to force end the process. The default value is signal 15. This command is masked in safe mode.
I ignore idle and zombie processes. This is a switch-type command.
Q quit the program.
R reschedule the priority level of a process. The user is prompted to enter the process PID that needs to be changed and the process priority value that needs to be set. Entering a positive value lowers the priority and, conversely, it gives the process a higher priority. The default value is 10.
S switch to cumulative mode.
s changes the delay time between two refreshes. The user will be prompted to enter a new time in S. If there are decimals, it is converted into M S. Enter a value of 0 and the system will refresh continuously, the default value is 5 S. It is important to note that if you set too small a time, it is likely to cause a constant refresh, so it is too late to see the display, and the system load will be greatly increased.
F or F Add or remove items from the current display.
O or O change the order in which items are displayed.
L Toggle Display Average load and start time information.
M toggles display memory information.
T toggles the display of process and CPU status information.
The C toggle Displays the command name and the full command line.
M sorts based on the size of the resident memory.
P is sorted according to the percentage size of CPU usage.
T is sorted by time/accumulated time. W writes the current settings to the ~/.TOPRC file. This is the recommended way to write top configuration files.
Common operations:
Top//5-second explicit resource usage for all processes
Top-d 2//every 2 seconds explicit resource usage for all processes
TOP-C//5-second explicit process resource usage and display of process command-line arguments (default to process name only)
Top-p 12345-p 6789//every 5 seconds the PID is 12345 and the PID is 6789 of the resource usage of two processes
top-d 2-c-P 123456//Every 2 seconds shows the PID is 12345 of the resource usage of the process and explicitly the command-line arguments that the process started
Linux-linux top command each parameter detailed
