Introduction and basic concepts of Linux

Posted by joplinfan on Thu, 20 Jan 2022 02:36:48 +0100

Introduction to Linux distribution

Linux branch reference website: http://futurist.se/gldt/

Common Linux distributions

  • debian system: Ubuntu, Deepin, Mint
  • **slackware: openSUSE
  • redhat: Fedora, CentOS, RHEL, Oracle Enterprise

What Linux distributions have in common: the Linux kernel

Linux has many distributions, but they are all considered Linux. Why? The reason is that they all adopt the Linux kernel, which is the core of the operating system. It bridges the work of the system with the underlying hardware. It also includes many device drivers to support the use of various hardware

Differences between Linux distributions

Package manager

Each Linux distribution contains various ways to install software, but they all have an underlying package manager.

  • On Debian based distributions such as Ubuntu and Linux Mint, dpkg can be accessed through the apt dependency parser.
  • For Redhat systems, such as CentOS, RPM is the package manager, which relies on the yum command for parsing

Differences in other configurations

network configuration

  • The CentOS default network configuration file is in the path / etc / sysconfig / network scripts /, usually ifcfg-[ifname]
  • After Ubuntu 17, the default network configuration file is in / etc/netplan / path and ends with yaml. There is no special limit on the file name

Default firewall

  • The default firewall of CentOS 6 is iptables, and the default firewall of CentOS 7 is firewall
  • The default firewall for Ubuntu 20 is ufw

Installing a Linux distribution

Installing CentOS 7.9

VMware installing CentOS 7.9_Sky_Nemo's blog - CSDN blog

Install Ubuntu 20.04.2

Vmware installation Ubuntu 20.04.2_Sky_Nemo's blog - CSDN blog

Common settings after installation

The following settings apply to CentOS 7.9 Ubuntu 20.04.2

Set host name

[root@localhost ~]# hostnamectl set-hostname aiden

# Effective after re login
[root@aiden ~]#

Set time zone

[root@aiden ~]# timedatectl list-timezones | grep Shanghai
Asia/Shanghai
[root@aiden ~]# timedatectl set-timezone Asia/Shanghai

Set the number of history reserved entries and the command execution time

# Temporary settings
[root@aiden ~]# export HISTSIZE=3000
[root@aiden ~]# export HISTTIMEFORMAT="%Y-%m-%d %H-%M-%S "


# Permanent settings
[root@luna ~]# cat > /etc/profile.d/history_set.sh <<EOF 
# history command set
export HISTSIZE=3000
export HISTTIMEFORMAT="%Y-%m-%d %H-%M-%S "
EOF
# Load for settings to take effect
[root@aiden ~]# source /etc/profile

# View effect
[root@aiden ~]# history | head -n3
    1  2021-07-10 23-58-24 vi /etc/sysconfig/network-scripts/ifcfg-ens33 
    2  2021-07-10 23-58-24 systemctl restart network
    3  2021-07-10 23-58-24 ping www.baidu.com

Linux Philosophy

  • All files (including hardware)
  • Small, single purpose program
  • Link programs to complete complex tasks together
  • Avoid confusing user interfaces
  • The configuration data is stored in text

Common command formats for Linux

COMMAND [OPTIONS...] [ARGUMENTS...]
COMMAND [COMMAND] [COMMAND] ....

COMMAND

**OPTIONS, OPTIONS: * * used to enable or disable one or more functions of the command

  • Short options: UNIX style options, - c for example: - l, -h
  • Long options: GNU style options, – word, for example: – all, --human
  • BSD style option: a letter, for example: A, is relatively less used

**ARGUMENTS, parameter: * * the target of the command, such as file name, user name, etc

Example:

# Short options
[root@aiden ~]# echo -e "1\t2"
1	2

# Long option
[root@aiden ~]# date --utc
Sat Jul 10 16:34:37 UTC 2021

# BSD style
[root@aiden ~]# ps a
   PID TTY      STAT   TIME COMMAND
  1351 tty1     Ss+    0:00 -bash
 10446 pts/1    Ss     0:00 -bash
 10630 pts/1    R+     0:00 ps a

System directory usage

Linux directory structure

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  • Files and directories are organized into a single root inverted tree structure
  • The file system starts from the root directory and is represented by /
  • Root file system (rootfs): root file system
  • Standard Linux file system (e.g. ext4). The file name is case sensitive, such as mail, mail, mail and mail The first file is hidden
  • The symbol for path separation is/
  • The maximum length of the file name is 255 bytes
  • The maximum length of the file name including the path is 4095 bytes
  • Blue – > directory, green – > executable, red – > compressed file, light blue – > linked file, gray – > other files
  • All characters are valid except slash and NUL. However, directory names and files with special characters are not recommended. Some characters need to be quoted in quotation marks
  • Each file has two types of related data: metadata, i.e. attribute, and data, i.e. file content

File system hierarchy of Linux: FHS file system Hierarchy Standard: https://www.pathname.com/fhs/

Common directory functions

/bin: Basic commands used by all users; Cannot be associated to a separate partition, OS Start the program that will be used
/boot: Boot file storage directory, kernel file(vmlinuz),boot loader (bootloader, grub)Are stored in this directory
/dev: Storage location of equipment files and special files
	b: block device，Random access
	c: character device，Linear access
/etc: Profile directory
/home/[USERNAME]: Home directory of ordinary users
/root: Administrator's home directory
/sbin: Basic commands of management class; Cannot be associated to a separate partition, OS Start the program that will be used
/tmp: Temporary file storage location
/usr: universal shared, read-only data
	bin: Application program provided to ensure that the system has complete functions
    sbin:
    lib: 32 Bit usage
    lib64: Only 64 bit systems exist
    include: C Program header file(header files)
    share: Structured independent data, e.g doc, man etc.
	local: Installation location of third-party applications
	bin, sbin, lib, lib64, etc, share
/var: variable data files
	cache: Application cache data directory
	lib: Application status information data
	local: Dedicated to/usr/local Applications under store variable data
	lock: Lock file
	log: Log directory and files
	opt: Dedicated to/opt Applications under store variable data
	run: Running process related data,Typically used to store processes pid file
	spool: Application data pool
	tmp: Save temporary data generated between system restarts

/lib: The basic shared library files and kernel module files that the program depends on at startup(/lib/modules)
/lib64: Dedicated to x86_64 Secondary shared library file storage location on the system
/media: Portable mobile device mount point
/mnt: Temporary file system mount point
/opt: Installation location of third-party applications
/srv: Data used by services running on the system
/proc: Virtual file system for outputting kernel and process information
/sys: Used to output information about hardware devices on the current system virtual file system
/selinux: security enhanced Linux，selinux Storage location of relevant security policies and other information

Application common directories

Binary program:/bin, /sbin, /usr/bin, /usr/sbin, /usr/local/bin, /usr/local/sbin

Library files:/lib, /lib64, /usr/lib, /usr/lib64, /usr/local/lib, /usr/local/lib64

Profile:/etc, /etc/DIRECTORY, /usr/local/etc

Help files:/usr/share/man, /usr/share/doc, /usr/local/share/man, /usr/local/share/doc

Changes in directory structure after CentOS 7

Some directories are combined in the form of soft links

  • /Bin and / usr/bin
  • /sbin and / usr/sbin
  • /lib and / usr/lib
  • /Lib64 and / usr/lib64
[root@aiden ~]# ls -ild  /bin /usr/bin
3505 lrwxrwxrwx. 1 root root     7 Mar  7  2019 /bin -> usr/bin
  15 dr-xr-xr-x. 2 root root 36864 Jul  9 11:38 /usr/bin

[root@aiden ~]# ls -ild  /sbin /usr/sbin
33 lrwxrwxrwx. 1 root root     8 Mar  7  2019 /sbin -> usr/sbin
16 dr-xr-xr-x. 2 root root 20480 Feb 28 22:08 /usr/sbin

[root@aiden ~]# ls -ild  /lib /usr/lib
25 lrwxrwxrwx.  1 root root    7 Mar  7  2019 /lib -> usr/lib
17 dr-xr-xr-x. 30 root root 4096 Feb 28 22:27 /usr/lib

[root@aiden ~]# ls -ild  /lib64 /usr/lib64
27 lrwxrwxrwx.  1 root root     9 Mar  7  2019 /lib64 -> usr/lib64
24 dr-xr-xr-x. 51 root root 32768 Jun 15 19:04 /usr/lib64

Topics: Linux

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