Common commands

There are many commands in Linux. With the options of various commands, there are really thousands. How do we remember these commands? The answer is only two words: multi-purpose. We don't have many commonly used linux commands. As long as we use and practice frequently, we will master them quickly. For some uncommon commands, you can use the man command to view the detailed usage and use it.

echo

Output the value of string or variable at the terminal. The echo command has no options.

# Output string
echo string
# Output variable value
echo $SHELL

date

Used to display and set the time or date of the system.

Time formatting

date supports formatted output time, and a "+" sign is required before the format string.

• %a. % a: output day of the week
• %b. % B: output month
• %c: Output current time
• %d: What day of the month
• %D: Output date, same as% m%d%y
• Output full date, same as% Y-%m-%d
• %H. % I: output 24-hour hours and 12 hour hours respectively
• %M: Output minutes
• %S: Output seconds
• %j: Number of days this year

date '+%a' #Output: IV. Thu
date '+%A' #Output: Thursday, Thursday
date '+%b' #Output: September, Sep
date '+%B' #Output: September, September
date '+%c' #Output: Thursday, September 2, 2021 22:23:54
date '+%d' #Output: 02
date '+%D' #Output: 09 / 02 / 21
date '+%F' #Output: 2021-09-02
date '+%H' #Output: 22
date '+%I' #Output: 10
date '+%M' #Output: 34
date '+%S' #Output: 43
date '+%j' #Output: 245

Common options

• -d. -- date = string: output the user-defined time instead of the current time. A time string is required after D.
• -s. -- set = string: set the time, followed by the set time string
• -r. -- Reference = file: the last modification time of the output file
• -u: Output UTC time.

date -d 20230911 #Output: Sunday, September 11, 2023 00:00:00 CST

date -s 20230911
date #Output: Sunday, September 11, 2023 00:00:00 CST

date -r test.txt #Output: Sunday, August 15, 2021 14:10:36 CST

date -u #Output: Sunday, September 11, 2023 00:00:00 CST

reboot

Restart the system

poweroff

Shut down

halt

Notify the hardware to stop all CPU functions, but remain powered on

uname

Used to view the system kernel and version

option

• -a: View the complete kernel name, host name, kernel release and other information

uname -a 
#Output: Linux My-PC 3.10.0-1127.19.1.el7.x86_64 #1 SMP Tue Aug 25 17:23:54 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

who

Displays the terminal information of the currently logged in user.

who #Output: root PTS / 0 2021-09-03 20:40 (125.120.81.36)

last

View login records of all systems

option

• -n NUM, - NUM: number of records displayed
• -F: Output login and logout time and date

last -2
#output
# root   pts/0    39.182.56.184   Thu Sep  2 21:53   still logged in
# root   pts/3    39.182.56.184   Mon Sep 11 00:15   still logged in

last -n 2
#output
# root   pts/0    39.182.56.184   Thu Sep  2 21:53   still logged in
# root   pts/3    39.182.56.184   Mon Sep 11 00:15   still logged in

last -2 -F
#output
# root   pts/0   39.182.56.184   Thu Sep  2 21:53:26 2021   still logged in
# root   pts/2   39.182.56.184   Mon Sep 11 00:07:56 2023 - Mon Sep 11 00:15:05 2023  (00:07)

history

This command is used to display the commands executed in history. The default value is 1000. If 1000 are not enough, you can customize the HISTSIZE variable value in the / etc/profile file. When entering a command, we can quickly use the previous command by pressing the [up] key. These records are obtained from history. If you clear hisotry, press [up] and there will be no content.

history
#output
# 768  history
# 769  man history
# 770  ls
# 771  ll
# 772  man history
# 773  history
# ......

# Empty history
history -c

reference resources
That's how Linux should learn