A program is a static collection of executable machine code and data (code stored statically in a file) stored in an external storage medium (such as hard disk, CD)
A process is a computer program that is dynamically executed in the CPU and memory
In the Linux system, one or more processes can be created after each program is started
1. View process information-ps
The ps command is the most common process viewing tool in Linux systems. It is mainly used to display static snapshots containing complete information about the currently running processes.
Through different command options, you can selectively view process information
1.1 Method 1: ps -aux
a: Display all process information under the current terminal, including processes of other users. When combined with the "x" option, all process information in the system will be displayed
u: Output process information in a user-oriented format
x: Display the process information of the current user in all terminals
The process information will be displayed in the form of a simple list
The amount of virtual memory used by the process (KB)
RSS
The amount of physical memory used by the process (KB)
TYY
The name of the terminal that started the process; if the process is not started from the terminal, it will be displayed as "?"
STAT
The state of the process (D: non-interruptible dormant state; R: running state; S: dormant state and can be awakened; s, parent process; T: stopped state, which may be suspended in the background or the process is in a tracking debugging state ; Z: zombie process, the process has been terminated, but most of the programs are still in memory; <: high priority state; +: foreground process) 7
START
The process was triggered to start time
TIME
The time the process actually uses the CPU to run
COMMAND
Process start command
Term explanation (zombie process): A process has ended, but it still occupies memory, which is also called zombie
1.2 Method 2: ps -elf
e: Display all process information in the system
l: Use long format to display process information
f: Use complete format to display process information
Will display the process information in the system in a long format and contain richer content
##例：
[root@localhost ~]# ps -elf
F S UID PID PPID C PRI NI ADDR SZ WCHAN STIME TTY TIME CMD
4 S root 1 0 0 80 0 - 32068 ep_pol 16:47 ? 00:00:01 /usr/lib/systemd/systemd --switched-root --system --deserialize 22
1 S root 2 0 0 80 0 - 0 kthrea 16:47 ? 00:00:00 [kthreadd]
1 S root 4 2 0 60 -20 - 0 worker 16:47 ? 00:00:00 [kworker/0:0H]
1 S root 5 2 0 80 0 - 0 worker 16:47 ? 00:00:00 [kworker/u256:0]
##省略...
noun
Explanation
F
System tag assigned by the kernel to the process
S
Process status
UID
The user who started these processes
PID
Process ID of the process
PPID
The process number of the parent process (if the process was started by another process)
C
CPU utilization in the life cycle of a process
PRI
The priority of the process (the larger the number, the lower the priority)
NI
Modesty value is used to participate in determining priority
ADDR
Memory address of the process
SZ
If the process is swapped out, the approximate size of the swap space required
WCHAN
If the process is sleeping, display the name of the system function in sleep
ESTIMATES
System time when the process started
TTY
Terminal device when the process starts
TIME
Cumulative CPU time required to run the process
CMD
Process start command
In CentOs7 system, tty1 represents the graphical interface, tty2-tty6 represents the text interface, you can use Ctrl+Alt+(F1-F6) to switch
1.3 Other examples
When directly executing the ps command without any options, only the processes opened in the current user session will be displayed
Due to the large number of processes running in the system, when you need to query the information of a certain process, you can combine the pipe symbol and the grep command to filter
Use the ps command to view a static process information, and can not continuously feedback the running status of the current process
If you want to display the status information of each process in a dynamic refresh mode, you can use this command
Refresh every three seconds by default
2.1 Example diagram
[root@localhost ~]# top
2.2 System task (first line) and process (second line) information
Related Information
meaning
/
/
18:55:08
system time
Tasks
Total number of processes
up 2:07
System running time
running
Number of running processes
1 user
Number of currently logged in users
sleeping
Number of sleeping processes
load average：0.00,0.01,0.05
System load, that is, the number of tasks processed by the system in a unit time, the following three values are the average value of 1 minute, 5 minutes, and 15 minutes to the present
stopped
Number of aborted processes
/
/
zombie
Number of zombie processes
2.3 CPU (third line), memory (fourth line) information and swap space (fifth line) information
Related Information
meaning
/
/
/
/
us
User occupation
total
Total memory space
total
Total swap space
his
Kernel occupation
free
Free memory
free
Free swap space
ni
Priority scheduling occupation
used
Used memory
used
Swap space used
id
Idle CPU, to understand the percentage of idle CPU, mainly see the %id part
buff / cahe
The sum of the buffers of physical memory and swap memory
avail Mem
Available physical space
wa
I/O waiting to be occupied
/
/
/
/
hi
Hardware interrupt occupation
/
/
/
/
and
Software interrupt occupation
/
/
/
/
st
Virtualization occupancy
/
/
/
/
2.4 Detailed explanation of each column in the process information area
information
Explanation
PID
Process id
USER
User name of the process owner
PR
priority
NI
Modesty value, negative value indicates high priority, positive value indicates low priority
VIRT
The total amount of virtual memory used by the process, in kb
RES
The size of physical memory used by the process, in kb
SHR
Shared memory size, unit kb
S
Process status
%CPU
Percentage of CPU time from the last update to the present
%MEM
The percentage of physical memory used by the process
TIME+
The total CPU time used by the process, in units of 1/100 second
COMMAND
Command name/command line
2.5 TOP commonly used commands
command
Explanation
P
Sort by percentage of CPU usage
M
Sort by size of resident memory
N
Sort by start time
c
Toggle display of command name and full command line
h
Online help information for top program can be obtained
k
Enter the PID number of the specified process as prompted and press Enter to terminate the corresponding process
q
Exit top program
(Number 1
Display the number and status of CPU
3. View process information-pgrep
When using the ps command to query a certain process, it is often necessary to combine the grep command to filter the output results, but this is very inconvenient to use, and the "pgrep" command is a special tool used to query specific process information
[root@localhost ~]# vim tmpfile ##打开vim并挂起以作测试
[1]+ 已停止 vim tmpfile
[root@localhost ~]# jobs -l ##查询目标进程PID号
[1]+ 2028 停止 vim tmpfile
[root@localhost ~]# kill 2028 ##尝试直接终止进程
[root@localhost ~]# jobs -l ##查询后发现并未退出
[1]+ 2028 停止 vim tmpfile
[root@localhost ~]# kill -9 2028 ##结合“-9”选项试试，强制终止目标进程
[root@localhost ~]# jobs -l ##没了，成功
[1]+ 2028 已杀死 vim tmpfile
3.2 killall
用于结束系统中多个相关名称的进程
也可以结合“-9”选项
例：执行“killall -9 vim”命令可将所有名为vim的进程全部强行终止
[root@localhost ~]# vim testfile1
[1]+ 已停止 vim testfile1
[root@localhost ~]# vim testfile2
[2]+ 已停止 vim testfile2
[root@localhost ~]# vim testfile3
[3]+ 已停止 vim testfile3
[root@localhost ~]# jobs -l
[1] 2130 停止 vim testfile1
[2]- 2131 停止 vim testfile2
[3]+ 2132 停止 vim testfile3
[root@localhost ~]# killall -9 vim
[1] 已杀死 vim testfile1
[2]- 已杀死 vim testfile2
[3]+ 已杀死 vim testfile3
1.2 The system default settings, located in the directory: /etc/cron.*/
After the crontabs package is installed, some scheduled task directories set by the system default will be promoted in this directory, and what work the system does every hour and every day is set
1.3 User-defined settings, located in the file: /var/spool/cron/
The cron plan set by the user using the crontab command will be saved in this directory (a file with the same user name will be generated in this directory)
2. Manage crontab scheduled tasks
-u: Specify which user the scheduled task belongs to. By default, it is for the current user (self); generally only the root user has permission to use this option
Edit the scheduled task crontab -e [-u username] (when there is no -u, the default object is the current user)
View the scheduled task crontab -l [-u username]
Delete the scheduled task crontab -r [-u username]
3. The format of crontab task configuration
Field
Description
minute
The value is any integer from 0 to 59
hour
The value is any integer from 0 to 23
date
The value is any integer from 1 to 31
month
The value is any integer from 1 to 12
week
The value is any integer from 0 to 7, 0 or 7 represents Sunday
command
Command or program script to execute
Remember the formula (keep in mind): time-sharing day, month and week
4. Special representation method of time value
"*" means any time within the range
"," means multiple discrete time points in an interval
Because no user login is required to perform tasks, it is recommended to use absolute paths to avoid the situation where commands cannot be executed due to lack of execution paths
When setting the task to be executed every minute, the "minute" field should also be filled in with a specific time value instead of the default "*", otherwise the task will be executed every minute
5. Other
The crontab command set "-l" option can view the current user's scheduled task list. For root users, you can also combine the "-u" option to view other users' scheduled tasks
When you need to delete a scheduled task, you can edit it with the "-e" option
Other examples:
5 * * * * ls ##每个小时的第5分钟执行一次ls命令
30 5 * * * ls ##每天的5:30执行ls命令
30 7 8 * * ls ##每个月8号的7:30执行ls命令
30 5 8 6 * ls ##每个6月8号的5:30执行ls命令
30 6 * * 0 ls ##每个周日的6:30执行ls命令
30 3 10,20 * * ls ##每个月10号和20号的3:30执行ls命令
25 8-11 * * * ls ##每天8点到11点的第25分时执行ls命令
*/15 * * * * ls ##每隔15分钟执行一次ls命令
30 6 */10 * * ls ##月中的每隔10天的6:30时执行一次ls命令
