Fifth day Linux basic commands

TTY Console terminal tty1~tty6?

CTRL + ALT + F2~F6 switch console

ALT + F1 return

However, after using init 3 in the graphical interface, you cannot use ALT + F1 to return, because the two are not a problem.

Init 3 Toggle Current Run level

CTRL + ALT + F2~F6 Toggle Current Workspace

PTS Virtual Terminal

If we telnet to the host remotely, do we need a terminal interaction?

Yes, this is the virtual Terminal Pty (pseudo-tty)

PTS/PTMX (PTS/PTMX combined to achieve pty)

Use who am I to query the PTS number of the current terminal

Magnification: ctrl+shift+ +

Zoom Out: Ctrl +-

1.1 Linux Terminal introduces shell prompt Bash Shell basic syntax.

[Email protected] ~]#

Where Root refers to the current user

Xiaogan refers to the host name

~ refers to the current directory

#代表当前权限为root

If it's a normal user, it should be.

[Email protected] root]$

$ represents the current user right for normal permissions

We cannot direct the computer to do anything, because it does not understand, this time need a translator, that is, the interpreter shell

We negotiate with the shell, and the outcome of the negotiations is the instructions we use, ls,cd,pwd.

The shell translates the instructions we send into a language that the kernel can understand, and then implements the instructions.

We interact with the Linux kernel through the shell!

The format used for commands in Linux systems is:

command [options] [parameters]

such as: Ls-a/Home

Indicates that all files are listed in the/home directory

LS stands for command list ' list '

-A description command ls, listing all files

/Home Description Command LS Action object is parameter

1.2 use of BASIC commands: LS, pwd, CD

ls command:

function: See what files are in the current directory

Syntax: LS directory, if you do not add a directory to view the current directory

Parameters:

-L display the shortcut in the detailed information system #ll=ls-l

-A Show hidden files

-D View directory (without viewing the contents)

Why do some catalog files have different colors?

Different colors in the Linux system represent different file types

Blue Directory/etc

Black file/etc/passwd

Light blue link/etc/grub2.cfg

Red Compress Package boot.tar.gz

Green executable file/etc/init.d/network

Black bottom Yellow word device file/dev/sda

PWD command: View current path or current location

CD command: Switch the directory to change the current location

. Represents the current directory

.. Represents the upper level directory

1.3 viewing system and BIOS hardware time

To view the BIOS hardware time:

Hwclock

View system time

Date

"Use date-s Time"

can modify the time

For example: Date-s 2016-12-12

1.4 Linux How to get help, Linux shutdown command: shutdown, init, etc.

Date--help

Fdisk–h

Mans find

The above three commands can be used to view the relative command's Help information

Command--help

Command-H

Man command

Powerful man!!!

Shutdown, init, reboot Poweroff

Shutdown

Function: Shutdown, restart, timer shutdown

Syntax: Shutdown [options]

-R = Restart the computer

-H = power off

-H + time = Timer off

Shutdown-h +10

Shutdown after 10 minutes

Shutdown-h 23:30

Specify a specific point in time to shut down

Shutdown-h now

Turn off the machine now

Shutdown-r now restart
Shutdown-r +10 #10 minutes after restart
Shutdown-r 22:22 # 22:22 Restart

1.5 Linux 7 Boot levels

init command

Role: Switching the system operating level

Syntax: Init 0-6

Linux 7 Boot levels:

0 System shutdown mode, the system default operation level cannot be set to 0, otherwise it will not start normally, the machine shuts down.
1 single-user mode, root privilege, for system maintenance, prohibit remote login, like Safe mode login under Windows.
2 Multi-user mode, no NFS network support.
3 full multi-user text mode with NFS, login to console command line mode.
4 The system is unused, reserved for general use, and in some special cases it can be used to do something. For example, you can switch to this mode to do some setup when your laptop's battery is running out.
5 graphical mode, after landing into the graphical GUI mode, X window System.
6 Restart mode, the default run level cannot be set to 6, otherwise it will not start normally. Running the init 6 machine will restart.

RHEL7 no longer uses the/etc/inittab file for the default boot level configuration

The SYSTEMD uses a more free target substitution than the sysvinit run level.

The 3rd run level is replaced with Multi-user.target.

The 5th run level is replaced with Graphical.target.

Runlevel3.target and Runlevel5.target respectively are

Symbolic links to Multi-user.target and graphical.target.

Switch to the 3rd run level

Systemctl Isolate Multi-user.target

Or

Systemctl Isolate Runlevel3.target

Switch to the 5th run level

Systemctl Isolate Graphical.target

Or

Systemctl Isolate Runlevel5.target

Set the default run-level

Set the default third boot level

Systemctl Set-default Multi-user.target

Set the default fifth boot level

Systemctl Set-default Graphical.target

View the current default startup level

Systemctl Get-default

Fifth day Linux basic commands