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Management of processes and scheduled tasks in linux

1. The relationship between program and process

Programs: executable code and data stored in media such as hard drives, CDs, etc.; statically saved code

Process: program code that runs in CPU and memory; dynamically executed code; parent and child processes: each process can create one or more processes

Basic command

1): ps command (processes statistc): view static process statistics

Ps-aux: displays process information in the form of a simple list.

The an option means to view all process information

The u option indicates the user information to which the process belongs

The x option indicates that information other than the default information is displayed

Ps-elf: displays the process information in the system in a long format and contains richer content.

The e parameter represents the entire process

The f parameter represents the full format

L parameter represents long format display

PID: the ID of the running process

TTY: where the command runs

TIME: the CPU processing time taken by the running command

CMD: the command that the process runs

2): top command: displays the ranking of processes in a full-screen interactive interface. By default, it is refreshed every three seconds, and it is sorted by cup occupancy by default.

Common option:-d: specify the refresh time (in seconds)

-b: operates in batch processing mode, usually used with-n

-n: specify the number of times to follow the bad display

-u: specify the user name

-p: develop the process number

PID: process ID

USER: the user running the process

PR: the default priority of the system. PR is always 20% larger than NI.

NI: the priority that the user can modify. The range is from-20 to 19, and the smaller the number, the larger the value. When a process is already running, use the renice command to change its priority: renice-n-20 PID. When the process is not running, you can use nice-n 20 httpd to start the process to specify the priority

VIRT: virtual memory

RES: the memory used by the current process

SHR: shared memory

S: status S (sleep) or R (running)

% CPU: proportion of process to CPU

% MEM: the proportion of memory occupied by the process

Time: the time the process is running

COMMAND: instructions for the process

Classification of S status:

S (uppercase): interruptible hibernation process

D: uninterruptible hibernation process

S: parent process

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