Linux internal commands are also called shell built-in commands or embedded commands. External commands are stored in files and can be found in files when needed. These files are defined in $PATH.

First, all linux files are files. When the operating system loads, we load the shell as a /bin/bash file.

internal command

The built-in command does not need a subprocess to execute, it has been compiled with a shell. As part of the shell tool. Built-in commands do not require external program files to run. Internal commands can be viewed through the enable command.

How does linux display images in ll?

First, use the yumrepolistall command to see which yum sources are currently enabled.

Mirror configuration files in the /etc/yum.repo.d/ directory, ll will see many repos files, and each repos file is configured with a yum source:

The content in square brackets represents the name of this source code, which can be named by itself, but it can't be the same as other source codes, otherwise Yum won't know which source code to look for.

Name: it is equivalent to the source description, and its importance is not high.

Mirrorlist: lists the mirror sites that can be used by this source. You don't need it. You can't write if you set the mirror site directly.

Baseurl: the direct address of the source, specifying a fixed source address. mirrorlist is a yum program to obtain the source address.

Enabled: Whether to enable the mirror.

Gpgcheck: whether to check the digital signature.

Gpgkey: the address of the digitally signed public key file.

After installing the virtual machine linux on the computer, the computer has a blue screen?

1. Check whether virtualization technical support is turned on on the motherboard. Press CTRL+SHIFT+ESC at the same time to open the task manager, and then click-Details-Performance, and the following interface will appear to confirm that virtualization has been turned on. If the display is enabled, skip to the second step. If the display is not enabled, you need to turn on virtualization.

2. After the computer is turned off, press F2 rhythmically to enter the bios. When the computer enters the bios, use the arrow keys to control the cursor to "Configure". After entering the options, move the cursor to "InterVirtualTechnol", press the "Enter" key (Enter key), select "Enable" to indicate opening, and finally press "F 10".

How to make SSH service run automatically under linux?

Under linux, ssh service can be started and run automatically, which can be set by the systemctl command.

1. Set ssh to boot and start. Sudo is privilege elevation, systemctl is service manager, enable is the parameter of systemctl, indicating that startup and automatic operation are enabled, and ssh is the name of the service to be set. After the setting is successful, you can use chkconfig to check the startup status of ssh, and on means that the startup has been set.

2.ssh disables startup and self-startup. Sudo is to elevate the authority, systemctl is the service manager, disable is the parameter of systemctl, which means startup is prohibited, and ssh is the name of the service to be set.