- Process Management ps, top
- Task Scheduler crontab
Process Management
Concept: the process is a separate program in its own virtual address space to run.
Processes and procedures difference: the program is just a static set of commands, not the operation of the system resources; and the process is a likely change at any time, dynamic, using the system resources to run the program. A program can start multiple processes. And processes in comparison. Job is a series of commands executed in a certain order. A simple command may involve multiple processes, especially when using pipes and redirection. The process has the following characteristics:
- Dynamics: the essence of the process is executed once the program is in the process of multi-channel programming system, the initial process is dynamic, dynamic extinction.
- Concurrency: any process can be executed concurrently along with other processes.
- Independence: the process is a basic unit can operate independently, but also the system of allocation of resources and scheduling of independent units.
- Asynchronous: As mutual restraint between processes, the process is carried out with a discontinuity, that is, the process by independent, unpredictable pace to move forward.
- Structure: the process control block of three parts by a program, data and processes.
- Different processes can comprise a plurality of the same program: a program in a different data set constitute a different process, different results can be obtained; however, during execution, a program change can not occur.
In linux system consists of three processes:
- Interactive process: a shell and started the process control, interactive process running in the foreground can also be run in the background.
- Batch process: regardless of the terminal, arrange a series of processes at a specified time to complete.
- Daemon: start at boot the system to perform real-time operating system tasks, such as crond, rsyslogd, named and so on.
View system processes
- ps Command syntax: ps [options]
| Options | meaning |
|---|---|
| -A | Show all the process |
| -N | Select all processes except those specified criteria symbol |
| -a | Showing negative session leaders and processes not all processes associated with the terminal |
| -d | Show all the process (exclude the session leader) |
| -e | Show all the process |
| T | Show all processes in the current terminal |
| a | All W / tty, including other users |
| r | Display process runs only in |
| x | Treatment w / o control ttys |
| -c | Show different scheduling information for the -l option |
| c | When listing process, showing each process real command name, and does not include a path identifier, parameter or resident services |
| -C <command name> | Press the command name display process |
| -G <real GID of the user or group name> | Show real progress by group GID or group name |
| -U <user real UID or user name> | According to the real user UID or user name display process |
| -g <group name> | Select the session or a valid group name display process |
| -p <process ID> | Process by process id display |
| -s <Session ID> | Displays the session ID of the process. |
| -t <Terminal> | Press the terminal display process |
| -u <valid user name or user UID> | By a valid user UID display process |
| U <user name> | Display belonging to the user process |
| t <Terminal> | Press the terminal display process |
| -f | Display UID, PPID, C and STIME field |
| -j or j | The display format using job control process |
| s | Adoption process signal format process |
| v | Processes to display virtual memory format |
| -l or l | Using the procedure detailed display format |
| in | To display user-oriented format process |
| p <process ID> | Display specified process ID of the process, and the same effect as the -p option, just in different formats list |
| L | List information output fields |
| f | The results show a tree with ASCII characters, expressing the relationship between processes. |
| r | Show only the termination of the process of |
| e | When listing process, display environment variables used by each process |
| -w some w | Press wide format display output |
| -u | Users print format, display start time username and processes |
| -x | Process display without control terminal |
| -t <terminal ID> | Specifies the number of terminal display process |
| n | With figures to show USER and WCHAN field |
| h | Does not display the title bar |
| -H | Display tree structure, the relationship between the representation process |
| -m or m | Display thread behind the process |
| -Y | When used with the -l option is not displayed F (flag) output field, and to replace the field ADDR field RSS |
Examples: View crond process is running
[root@localhost ~]# ps -ef|grep crond
root 6571 1 0 03:04 ? 00:00:00 /usr/sbin/crond -n root 7457 7383 0 03:28 pts/0 00:00:00 grep --color=auto crond Show all processes without a console terminal, and displays a user name and start time process.
[root@localhost ~]# ps -aux
Display process under tty1 terminal
[root@localhost ~]# ps -t tty1
PID TTY TIME CMD
6572 tty1 00:00:00 agetty - The top command: displays currently running processes and important information about them including their memory and CPU usage. Use the q key to exit the top command
Command Syntax: top [options]
| Options | meaning |
|---|---|
| -b | Using batch mode |
| -c | When the column process, display the full command for each process, including the command name, path and parameters |
| -d <seconds between> | Interval execution state monitoring process, calculated in units of seconds. |
| -i | Ignore idle or has become a Zombie process |
| -n <executions> | Set the number of update monitoring information |
| -S | 使用累计时间模式 |
| -u<用户名或有效用户UID> | 仅监控指定有效用户UID或用户名匹配的进程 |
| -p<进程PID> | 仅监视指定进程的ID的进程 |
| -U<用户名或用户UID> | 仅监视指定用户UID或用户名匹配的进程 |
例子：只显示root用户的进程
[root@localhost ~]# top -u root
kill命令杀死进程
命令语法：kill [选项] [进程号]
| 选项 | 含义 |
|---|---|
| -s<信号> | 指定发送的信号 |
| -l | 显示信号名称的列表，一共62个 |
例如：强制杀死进程号为6571的进程
[root@localhost ~]# ps -ef|grep crond
root 6571 1 0 03:04 ? 00:00:00 /usr/sbin/crond -n root 7534 7383 0 03:48 pts/0 00:00:00 grep --color=auto crond [root@localhost ~]# kill -9 6571 [root@localhost ~]# ps -ef|grep crond root 7536 7383 0 03:49 pts/0 00:00:00 grep --color=auto crond 任务计划：在固定的时间上触发某个作业，就需要创建任务计划，按时执行该作业。使用cron实现任务计划可以通过修改/etc/crontab文件以及使用crontab命令实现，其结果是一样的。
- 安装crontabs和cronie软件包
[root@localhost ~]# yum -y install vixie-cron
- 控制crond服务 使用以下命令启动crond服务
[root@localhost ~]# systemctl start crond.service
使用以下命令在重新引导系统时自动启动crond服务
[root@localhost ~]# systemctl enable crond.service
[root@localhost ~]# systemctl is-enabled crond.service
enabled
- /etc/crontab文件是cron的默认配置文件，内容如下
[root@localhost ~]# cat /etc/crontab
SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin MAILTO=root # For details see man 4 crontabs # Example of job definition: # .---------------- minute (0 - 59) # | .------------- hour (0 - 23) # | | .---------- day of month (1 - 31) # | | | .------- month (1 - 12) OR jan,feb,mar,apr ... # | | | | .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat # | | | | | # * * * * * user-name command to be executed 其中#号开始的行是注释内容，不会被处理。
前面3行是用来配置cron任务运行环境的变量。/etc/crontab文件中的每一行都表示一项任务，它的格式如下
minute hour day month day of week user-name command | 内容 | 描述 |
|---|---|
| minute | 分钟，0~59的任意整数 |
| hour | 小时，0~23的任意整数 |
| day | 日期，1~31的任意整数(如果指定了月份，则必须是该月份的有效日期) |
| month | 月份，1~12的任意整数(或使用月份的英文简写入Jan、Feb等) |
| day of week | 星期，0~7的任意整数，这里的0或7代表星期日(或使用星期的英文简写入Sun、Mon等) |
| user-name | 执行命令的用户 |
| Command | 要执行的命令或者是自己编写的脚本 |
/etc、crontab文件中可以下表的时间格式
| 时间格式 | 描述 |
|---|---|
| * | 可以用来代表所有有效的值。如月份值中的型号意味着在满足其他制约条件后每月都执行该命令 |
| - | 指定一个整数范围。比如1-4意味着整数1、2、3、4 |
| , | 指定隔开的一系列值指定一个列表。比如3,4,6,8表明这四个指定的整数。 |
| / | 可以用来指定间隔频率。在范围后加上/<integer>意味着在范围内可以跳过integer。如"0-59/2"可以用来在分钟字段上定义时间间隔为两分钟。间隔频率值还可以和星号一起使用，如"*/3"的值可以用在月份字段中表示每3个月运行一次任务。 |
- /etc/crontab文件配置举例 在每天晚上的21:30执行/root、backup.sh
SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root
30 21 * * * root /root/backup.sh 在每星期六、星期日的1:20执行一个find命令，查找相应的文件
20 1 * * 6,0 root /bin/find / -name core -exec rm {} \; - /etc/cron/d目录：在/etc/cron.d目录中创建文件(该目录下所有文和/etc/crontab文件使用一样的配置语法)来实现。例如：
[root@localhost ~]# ls /etc/cron.d
0hourly
[root@localhost ~]# cat /etc/cron.d/0hourly
# Run the hourly jobs SHELL=/bin/bash PATH=/sbin:/bin:/usr/sbin:/usr/bin MAILTO=root 01 * * * * root run-parts /etc/cron.hourly 使用crontab命令实现任务计划
- cronta命令简介 root以外的用户可以使用crontab命令配置cron任务。所有用户定义的crontab都被保存在/varspool/cron目录中，并使用创建它们的用户身份来执行。
- 以某位用户身份一个crontab项目
- 以该用户身份登录
- 然后输入crontab -e命令，就进入编辑器编辑该用户的crontab了。(该编辑器是由VISUAL或EDITOR环境变量指定的，文件格式和/etc/crontab相同)
- 编辑成功保存后，该文件会根据用户名被保存在/var/spool/cron/<username>文件中。
- crond守护进程每分钟都检查/etc/crontab文件、/etc/cron.d目录以及/var/spool/cron目录中的改变。如果发现改变，它们就会被载入内存。
-
命令语法：crontab [选项] crontab [选项] [文件] 选项|含义 ---|--- -u<用户名>|用户名，如果使用自己的用户名登录，就不需要使用该选项 -e|编辑用户的crontab -l|列出用户的crontab中的内容 -r|删除用户的crontab -i|删除用户的crontab前进行提示
-
创建crontab 例子：以用户zhangsan登录系统，创建crontab
[root@localhost ~]# su - wangwu
[wangwu@localhost ~]$ date
Sat Jul 27 05:41:34 EDT 2019 使用crontab -e命令打开vi编辑器，编辑成功后查看，切换为root用户查看（普通用户没有权限打开该文件）
[wangwu@localhost ~]$ su - root
Password:
Last login: Sat Jul 27 05:38:10 EDT 2019 from 192.168.64.1 on pts/0 [root@localhost ~]# cat /var/spool/cron/wangwu - 编辑crontab过程中可以在每个条目指示加一条注释，这样就可以知道它的功能、运行时间，更为重要的是指定这是哪位用户的作业。
- 列出crontab: 以root用户列出wangwu的crontab
[root@localhost ~]# crontab -u wangwu -l
- 删除crontab：删除crontab同时会删除/var/spool/cron目录中指定有用户的文件
例如：以普通用户wangwu删除自己的crontab
[wangwu@localhost ~]$ crontab -r
- 恢复丢失的crontab文件(找到系统自动备份的位置/var/spool/cron/wangwu)
命令语法：crontab [文件] 例如：以wangwu登录恢复丢失的crontab文件
[wangwu@localhost ~]$ crontab /home/wangwu/wangwucron
摘自:《Linux实用教程》人民邮电出版社出版发行 於岳编著