Basic knowledge of Linux three

1. List the user name of all logged-in users on the current system, note: The same user logged in multiple times, only once.

The commands for viewing system users are:
(1)getent passwd

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View all user information on the system

(2) W

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View the process information that the logged-on user is using, and the information used by the command originates from the/var/run/utmp file

The information for the W command output includes:
-User Name
-User's machine name or TTY number
-Remote host Address
-time when the user logged on to the system
-Idle time (small function)
-time spent in a process attached to a TTY (terminal) (Jcpu time)
-time spent in the current process (pcpu time)
-commands that the user is currently using

The W command can also use the following option parameters:
-H Ignores header file information
-U Displays the load time of the result
-S does not show JCPU, PCPU, logon Hours

(3) who

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View (log in) the user name and the process that was started, the output is: User name, TTY number, time date, host address.

View user's user name with who value: Who | Cut-d '-f1

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The users command can be used to output the user name of the login

(4) WhoAmI

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2. Remove information about the user who last logged in to the current system .

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3. Remove the shell that is the user's default shell on the current system.

Command: cut-d:-f7/etc/passwd |uniq-c |sort-n |tail-1

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Uniq usage
Parameters
-C: Displays the number of occurrences of the row next to each column.
-D: Displays only the rows that appear repeatedly.
-F: Ignores the column specified by comparison.
-S: Ignores the comparison of the specified characters.
-U: Show only one row at a time.
-W: Specifies the character to compare.
-N: The first n fields are ignored along with the blanks in front of each field
+n: first n characters are ignored

Sort usage
Parameters
-B ignores whitespace characters that begin before each line.
-C checks whether the files are sorted in order.
-f sort, ignores uppercase and lowercase letters.
-M sorts the first 3 letters according to the abbreviation of the month.
-N Sorts by the size of the numbers.
-o< the output file > The sorted result into the specified file.
-R is sorted in reverse order.
-t< Delimited character > specifies the field separator character to use when sorting.
-K selects which interval to sort.

Tail usage
Parameters
Default to the end of the file, the last 10 lines are shown by default
The-n parameter can set the number of rows displayed,
The-f parameter is displayed automatically when the content of the file increases.

4, the information of the third field in/ETC/PASSW D with the largest number of the first 10 users is changed to uppercase and then saved to the/tmp/maxusers.txt file.

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Sort usage
The sort command helps us sort by different data types, and its syntax and common parameter formats
Parameters
-B ignores whitespace characters that begin before each line.
-C checks whether the files are sorted in order.
-f sort, ignores uppercase and lowercase letters.
-M sorts the first 3 letters according to the abbreviation of the month.
-N Sorts by the size of the numbers.
-o< the output file > The sorted result into the specified file.
-R is sorted in reverse order.
-t< Delimited character > specifies the field separator character to use when sorting.
-K selects which interval to sort.

TR usage
TR Conversion characters

5, take out the IP address of the current host, hint: The result of ifconfig command is sliced.

command: ifconfig | grep ' [0-9]{1,3}.[ 0-9]{1,3}. [0-9] {1,3}. [0-9] {1,3} ' |cut-d '-f10|head-n1

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Head usage
Show start to standard output, the default head command prints the first 10 lines of its corresponding file.
Parameters
-Q Hide file names
-V Show file name
-c< bytes > Display bytes
-n< rows > rows displayed

6. List the file names of all files ending with. conf in/etc directory and convert their names to uppercase and save them to the/tmp/etc.conf file.

Command: find/etc/-name "*.conf" | Tr ' A-Z ' A-Z ' >/tmp/etc.conf

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7. Displays the total number of sub-directories or files in the/var directory.

Command: Ll-a/var |wc-l

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8. Remove the names of the 10 groups with the smallest number of the third field in the/etc/group file.

Command: sort-t:-k3-n/etc/group | Cut-d:-f1 | Head

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9, the contents of the/etc/fstab and/etc/issue files are merged into the same content and saved to the/tmp/etc.test file.

Command: cat/etc/fstab/etc/issue >/tmp/etc.test

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10. Summarize the methods used to describe the user and group management commands and complete the following exercises:

• User and Group management class commands:

Create User: Useradd

-U UID: defined in/etc/login.defs

-G GID: Indicates that the user belongs to the basic group, can be a group name, but also GID

-C "COMMENT": User's comment information

-d/path/to/home_dir: Home directory with the specified path

-S Shell: Indicates the user's default shell program, the available list in the/etc/shells file

-G Group, specify additional groups for the user, group must exist beforehand

-R Create System user, CentOS 6 is 0-499,centos 7 is 0-999

Delete User: Userdel

-r: Delete User home directory

Usermod: Modify User

-U uid: New UID

-G GID: New Basic Group

-G Group: New Add-on group

-S SHELL

-l:lock the specified user

Create Group: Groupadd

-G GID: Specify GID number

ID: View information about user-related IDs

passwd: Add change password, need root user rights

-L: Lock the specified user

-U: Unlock the specified user

-n:mindays: Specify the minimum period of use

-x:maxdays: Maximum use Period

-w:warndays: How many days in advance should I start warning

-i:inactivedays: Non-active period

-stdin: Receive user password from standard input

(1), create group distro, its GID is 2016;

Order Groupadd-g distro

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(2), create user Mandriva, whose ID number is 1005; basic group is distro;

Command Useradd-u 1005-g distro Mandriva

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(3), create user Mageia, whose ID number is 1100, home directory is/home/linux;

Command Useradd mageia-u 1100-s/home/linux

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(4), to the user mageia add password, password for mageedu;

echo "Mageedu" | passwd--stdin Mageia

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(5), delete Mandriva, but retain their home directory;

Userdel Mandriva

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(6), create user Slackware, its ID number is 2002, the basic group is distro, additional group Peguin;

Useradd slackware-u 2002-g distro-g Peguin

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(7), modify the Slackware default shell for/BIN/TCSH;

Usermod-s/bin/tcsh Slackware

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(8), add additional Group admins for user Slackware;

Useradd-g Admins Slackware

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(9), add password for Slackware, and require the minimum password age of 3 days, the maximum is 180 days, warning for 3 days;

Passwd-n 3-x 180-w 3 Slackware

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(10), add user OpenStack, whose ID number is 3003, the basic group is clouds, the additional group is Peguin and Nova;

Useradd-u 3003-g clouds-g Peguin,nova OpenStack

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(11), add the system user MySQL, request its shell for/sbin/nologin;

Useradd-s/sbin/nologin-r MySQL

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(12), use the echo command, non-interactive add a password for OpenStack.

echo "Tdl123" | passwd--stdin OpenStack

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Linux Fundamentals three