Course Content#
uptime System Uptime and Average Load#
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Used to monitor how long the system has been running, how many users are logged in, and the running status (load)
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Learn to use --help to view command help
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w User List and Running Tasks#
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When the system is slow, you can check the commands currently being executed by the processes.
who Display Current Logged-in User Information#
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A bit like a simplified version of w
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When the --help information is too much, learn to use tldr
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-q View all logged-in users and their count
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-H Display header
whoami, who am i Current Effective/Real Username#
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sudo -i starts the default shell with superuser privileges
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who i am = who am i
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who am i actually belongs to the who command, am i is a parameter
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last Recent Login Information of Users#
Application: Find the three users who logged in most frequently recently.
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Clean empty lines【"^$"】, split by spaces and take the first column, sort in dictionary order [i.e., ASCII order], count, and sort in descending numerical order.
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cut -c 10-15: cut by character, take the 10th to 15th characters of a certain column.
【Extension】Word Frequency Statistics (a.log contains the content of man pages for ls, man, stdio, scanf)
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tr character replacement command
- -c reverse replacement
- -s compress consecutive duplicate characters
uname System Information#
- uname -a very complete system information [use this command first when getting hands-on with the machine]
date Display or Set System Time and Date#
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You can customize string formats; try different cases yourself.
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[PS] NTP—Network Time Protocol, synchronizes time through time zones.
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- From Wikipedia, the distributed structure is similar to DNS, but it is a one-way connection.
- Applications: Banking systems, online shopping.
- Time server configuration can be found in /etc/ntp.conf.
- Time zones can be viewed in /usr/share/zoneinfo.
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- To modify the time zone, you can use the ln -sf [force overwrite soft link] command to link /etc/localtime to the time zone.
- Example: sudo ln -sf /usr/share/zoneinfo/Asia/City /etc/localtime
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Additional Knowledge Points#
- cal Display Calendar
- echo -e can make the backslash \ effective
- For example, echo -e "\033[32m123\033[0m456" outputs color, similar to printf.
- $[] only performs integer calculations.
Points to Consider#
Tips#
- Abbreviations may represent
- -h: help, human, header (w -h)
- -p: pretty
- Spaces in shell scripts are sensitive.
- Variables defined in the shell exist in the process; they disappear when you exit the shell [or disconnect from SSH].
- wget can download document data.