management process
1. View and manage processes
- Kernel functions: process management, memory management, file system, network functions, drivers, security functions, etc. For all operating systems, there are basic functions
- What is the procedure:
- Executable code and data stored in hard disk, CD, etc.
- Code saved statically in the file
- what is a process
- Program code that runs on the CPU and memory
- execute code dynamically
- Parent, child process (each program can create one or more processes)
- A process is a program that is being executed
- The difference between process and thread:
resource allocation and scheduling- Process is the basic unit of resource competition
- Thread is the smallest unit of program execution
1.1 View process
1.1.1PS command – view static process statistics
Common options
| options | Function |
|---|---|
| a | Show all processes on the terminal, including those of other users |
| u | Indicates the user listing the processes |
| x | show all terminal processes |
When executing the ps command directly without any options, the processes open in the current user session will be displayed in
basic format;
ps aux 基本格式
ps aux | wc -l 结合管道符号查询具体的数量
- View current system processes
- View current progress
| name | describe |
|---|---|
| USER | The name of the user account that started the process |
| PID | PID of the process |
| %CPU | The percentage of CPU used by the process |
| %MEM | percentage of memory used |
| VSZ | Amount of virtualized memory used by the process |
| RSS | Amount of physical memory used by the process |
| TTY | The name of the terminal that started the process, or the process that was not started from a terminal is displayed as |
| STAT | status of the process |
| START | The process was falsely triggered to start time |
| TIME | The time the process actually used the CPU to run |
| COMMAND | process start command |
- stat:
- D: Dormant state that cannot be awakened
- R: Running state
- S: Dormant state
- T: Stopped state
- Z: Zombie process, the process has terminated, but some programs are still in memory, but its parent The process was unable to gracefully terminate it - Zombie process: Zombie process is when the child process ends before the parent process, and the second parent process does not recycle the child process and release the resources occupied by the child process. At this time, the child process will become a zombie process. If the parent process exits first, the child process will be killed. init takes over, and after the child process exits, init will reclaim the closed resources it occupies
1.1.2ps -elf command – view static process statistics
| options | Function |
|---|---|
| -e | Display all process information in the system |
| -l | Use long format to display process information |
| -f | Display process information in full format |
- Display the current system process (more information than ps aux display)
| name | representative meaning |
|---|---|
| F | System flags assigned by the kernel to processes |
| s | state of the process |
| UID | start these processes |
| PID | The process ID of the process, each process has a unique PID |
| PPID | The process ID of the parent process |
| C | CPU utilization over process lifetime |
| AT | process priority |
| IN | The humility value is used to participate in determining priorities |
| ADDR | memory address of the process |
| sz | Approximate size of space required |
| ESTIMATIONS | System time when the process started |
| TTY | Terminal device when the process starts |
| CMD | process start command |
1.1.3 grep filter query
Due to the large number of processes running in the system, it is necessary to query the information of a process by combining pipeline operations and grep commands for filtering. For example, do the following to filter out process information that contains "bash"
1.1.4 top command – dynamically view process information
- Dynamic view process
- Sort the queried processes according to the memory ratio, and press shift+m after the top command
- View the current process
The first line: task queue information
| 19:11:05 | system time |
|---|---|
| up 1:03 | How long the system has been running |
| 2 users | Currently logged in users |
| load average: 0.00，0.01，0.05 | Average load, that is, the number of tasks processed by the system per unit time, and the last three values are the average values from 1 minute, 5 minutes, and 15 minutes ago to the present |
The second line: system process information
| Tasks | total number of processes |
|---|---|
| running | 正在运行的进程数 |
| sleeping、 休眠的进程数 | |
| stopped | 中止的进程数 |
| zombie | 僵死的进程数 |
第三行：CPU占用信息
| us | 用户占用 |
|---|---|
| sy | 内核占用 |
| ni | 优先级调度占用 |
| id | 空闲CPU，要了解空闲的CPU百分比，主要看%id部分 |
| wa | I/o等待占用 |
| hi | 硬件中断占用 |
| si | 软件中断占用 |
| st | 虚拟化占用 |
第四行内存占用信息
| total | 总空闲内存 |
|---|---|
| free | 空闲内存 |
| used | 己用内存 |
| lbuff/cache | 物理内存和交换内存的缓冲区总和 |
第五行：交换空间swap占用信息
| total | 总交换内存 |
|---|---|
| free | 空闲交换内存 |
| used | 已用交换内存 |
| avail Mem | 可用物理空间 |
- top常用命令
| 命令 | 代表意思 |
|---|---|
| P 键 | 根据CPU使用百分比大小进行排序 |
| M键 | 根据驻留内存大小进行排序 |
| N键 | 根据启动时间进行排序 |
| c键 | 切换显示命令名称和完整命令行 |
| h键 | 可以获得top程序的在线帮助信息 |
| q键 | 退出top程序 |
| 数字键1 | 显示CPU个数状态 |
1.1.5pstree命令-- 查看进程树
pstree命令可以查看当前系统的进程树，包括各个进程对应的pid号，用户名，完整命令等信息
| 选项 | 代表意思 |
|---|---|
| -A | 各进程树之间连接以ASCLL字符来连接 |
| -u | 各进程树之间的连接以Unicode字符来连接，在某些终端界面下可能会有错误 |
| -p | 同时列出每个进程的pid |
| -u | 同时列出每个进程的所属账号名称 |
1.2控制进程方式
进程启动方式为手工启动和调度启动
1.2.1手动启动
- 前台启动：用户在输入命令，直接执行的程序
- 后台启动：在命令行尾加入“&”符号
当使用cp命令从光盘中制作镜像文件时，由于需要复制的数据较多，耗时较长，因此可结合“&”符号将复制操作放到后天运行，以便用户可以继续执行其他命令操作
1.2.2进程的前后台调度
- ctrl+Z组合键：将当前进程挂起，即调入后台并停止执行
- jobs命令：查看处于后台的任务列表
- fg命令：将后天进程恢复到前台运行，可指定任务序列号
1.2.3终止程序的运行
- ctrl+c组合键：中断正在执行的命令
- kill，kallall命令
- kill用于终止指定pid号
- killall用于终止指定名称相关的所有进程
- -9选项用于强制执行
- pkill命令：根据特定条件终止相应的进程
| -u | 根据进程所属的用户名终止相应的进程 |
|---|---|
| -t | 根据进程所在的终端终止相应进程 |
二.计划管理
2.1使用at命令，设置一次性计划任务
- at命令一次性计划任务
2.2使用crontab命令，设置周期性计划任务
2.2.1crontab命令简介
- crontab命令
- 按照预先设置的时间周期重复执行用户的命令操作
- 属于周期性计划任务
- 服务脚本名称
- 主要设置文件
- 全局配置文件，位于文件：/etc/crontab
- 系统默认的设置，位于目录：/etc/cron.*/
- 用户定义的设置，位于文件：/var/spoolcron用户名
2.2.2使用crontab命令管理用户计划任务
编辑计划任务
crontab -e [-u 用户名] #-u缺省时默认是针对当前用户，只有超级用户才可以用-u
查看计划任务
crontab -l [-u 用户名]
删除计划任务
crontab -r [-u 用户名]
- 时间数值的特殊标识方法：
| 特殊字符 | 说明 |
|---|---|
| *(星号) | 代表任何时刻都接受的意思。 |
| ，(逗号) | 代表分隔时段的意思 |
| -(减号) | 代表一段时间范围内 |
| /n(斜杠) | n代表数字，代表每隔n单位间隔的意思 |
| 代表意义 | 分钟 | 小时 | 日期 | 月份 | 周 | 命令 |
|---|---|---|---|---|---|---|
| 数字范围 | 0~59 | 0~23 | 1~31 | 1~12 | 0~7 | 需要执行的命令 |
示例：0 17 * * 1-5 每周一到周五17；00
- crontab计划任务的配置模式
时间周期设置 任务内容设置
命令一定要用绝对路径，例如cp命令，要用/usr/bin/cp，可以使用which查看命令的绝对路径
三、总结
1、掌握程序、进程、线程
2. The command to view the process: ps aux or ps -elf; top; pgrep; pstree;
3. How to check the child process? pstree ap or cd /stat in /proc/numbers file
4. Start the process: start in the foreground; start in the background (add & at the end of the command)
to view the background task list: jobs
call the background process: fg task list number
ctrl+z hang
kill -9 process number PID
pkill -9 process number PID
killall all processes
at hour: minute year-month-day
command: ctrl D to save and run
atq serial number
atrm + serial number
crontab -e -u user (do not write user default current user)
crontab -l -u user
crontab -r -u user
Format: Time-sharing day, month and week If you forget, you can check cat /etc/crontab
* represents any time without interval, such as 1, 2, 4 can be every other week
— continuous time, eg: 1-7
/ frequency of intervals 1/* every minute 1/* every other hour 1/* every other day 1/* every other month