【Basic command】
1. Gadgets
- man view manual
Commonly used commands:
man name
such as man cd
- date read system date and time
jackgee@ubuntu:~$ date
Thu 30 Apr 2020 04:58:58 PM CST
jackgee@ubuntu:~$ date "+%Y-%m-%d %H:%M:%S 星期%w"
2020-04-30 17:03:11 星期4
jackgee@ubuntu:~$ date "+%j"
121
- cal print calendar
jackgee@ubuntu:~$ cal
April 2020
Su Mo Tu We Th Fr Sa
1 2 3 4
5 6 7 8 9 10 11
12 13 14 15 16 17 18
19 20 21 22 23 24 25
26 27 28 29 30
jackgee@ubuntu:~$ cal 1 2020
January 2020
Su Mo Tu We Th Fr Sa
1 2 3 4
5 6 7 8 9 10 11
12 13 14 15 16 17 18
19 20 21 22 23 24 25
26 27 28 29 30 31
- bc calculator
Advantages:
1) Precision can be customized
2) Support variables, functions, conditions and loops
jackgee@ubuntu:~$ bc
a =10
b = 2
a/b
Output:
5
Use scale to customize precision
scale =6
a/b
Output
5.000000
5. passwd change user password
Ordinary user:
need to verify the original password first
root user:
do not need to verify the original password to set up,
you can also use the passwd username to forcibly modify other user passwords
2. System status
- who determines the users entered in the system
jackgee@ubuntu:~$ who
jackgee :0 2020-05-01 07:57 (:0)
jackgee@ubuntu:~$ whoami
jackgee
- Uptime understands resource startup time and busyness
. The three parameters in load average correspond to CPU:
1-minute average load, 5-minute average load, and 15-minute average load. understand more
jackgee@ubuntu:~$ uptime
09:05:06 up 1:08, 1 user, load average: 0.94, 0.36, 0.21
- top lists the top processes that take up resources
| index | PR | NI | VIRT | RES | SHR | Process status | %CPU | %MEN | TIME+ | COMMAND |
|---|---|---|---|---|---|---|---|---|---|---|
| meaning | Process scheduling priority | The nice value (priority) of the process | Virtual memory used by the process | Resident memory | Shared memory | Common: S sleep R run Z zombie | Percentage of CPU time from the last update to the present | Percentage of physical memory used | CPU time used | Command name |
jackgee@ubuntu:~$ top
进程号 USER PR NI VIRT RES SHR %CPU %MEM TIME+ COMMAND
2679 jackgee 20 0 4789124 207732 90164 S 13.2 7.0 7:00.73 chrome
- ps will selectively print out the process status in the kernel
| command | Options | Features |
|---|---|---|
| ps | Only list the processes started by the current terminal | |
| ps | -e | List all processes in the system |
| ps | -f | List processes in full format |
| ps | -l | List processes in long format |
jackgee@ubuntu:~$ ps
PID TTY TIME CMD
5501 pts/0 00:00:00 bash
12136 pts/0 00:00:00 ps
jackgee@ubuntu:~$ ps -f
UID PID PPID C STIME TTY TIME CMD
jackgee 5501 5487 0 May01 pts/0 00:00:00 bash
jackgee 12138 5501 0 09:43 pts/0 00:00:00 ps -f
jackgee@ubuntu:~$ ps -l
F S UID PID PPID C PRI NI ADDR SZ WCHAN TTY TIME CMD
0 S 1000 5501 5487 0 80 0 - 4878 do_wai pts/0 00:00:00 bash
4 R 1000 12139 5501 0 80 0 - 5009 - pts/0 00:00:00 ps
| parameter name | significance |
|---|---|
| S | Process status |
| UID | User ID |
| PID | Process ID |
| PPID | Parent process ID |
| C | The CPU usage of the process in the last period of time (second level) |
| PRI | Process priority (dynamic kernel update) |
| NI | nice value, priority correction parameter; PRI(new) = PRI(old)+NI |
| ADDR | Specify the location of the program in the memory, the execution program is generally "-" |
| SZ | Process logical memory size |
| WCHAN | "-" process in operation |
| TTY | Terminal name |
| TIME | Used CPU time |
| CMD | Command name |
- Free memory usage management
Linux uses temporarily unused memory to cache read and write disk information to improve reading efficiency.
jackgee@ubuntu:~$ free
总计 已用 空闲 共享 缓冲/缓存 可用
内存： 2954128 2226728 199556 145764 527844 398200
交换： 0 0 0
3. Text processing
- Redirection mechanism
Output redirection:
For example, ls -l> out.txt
input redirection
For example: sort <in.txt
- Pipeline mechanism
For example: ls -l | sort
transfers the output of the ls query result into the input of sort through the pipeline mechanism