linux

Filesystem Hierarchy Standard

What is the difference between Unix, Linux, BSD and GNU?

Linux Boot Process

The BIOS/MBR Boot Process

Master boot record

科普贴：BIOS和UEFI的启动项

linux architecture

cpu,ram,disk, device, network;

1. the process of booting

legacy

1. feature: 不知道分区和文件，只能固定读取启动盘的第一个扇区；

2. stage

   1. stage 1: 通过table 知道分区
   2. stage 2: 通过引导程序 知道文件系统；；

3. BIOS: basic input outpt system

   1. check haredware:Power On Self Test (post)
   2. load and excute bootloader in MRB following the boot sequeuce

4. mbr/GPT: master boot recorder,stage 1

   寻找bootable(active) partition

   1. bootloader code;
   2. partition list

5. volume boot record: 真正的引导程序，stage 2,加载os

   1. config

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      #boot=/dev/sda default=0 timeout=5 splashimage=(hd0,0)/boot/grub/splash.xpm.gz hiddenmenu title CentOS (2.6.18-194.el5PAE) root (hd0,0) kernel /boot/vmlinuz-2.6.18-194.el5PAE ro root=LABEL=/ initrd /boot/initrd-2.6.18-194.el5PAE.img

   2. list:
      1. grub: linux

6. kernel

   1. start up
   2. run init program: init programe read

uefi

1. feature:

   1. 是一个完整的程序，知道各个分区和文件系统，不需要额外中介，直接读取引导程序；

2. how to boot

   1. 文件启动: 指定明确目录，window manager –> 在 esp partition目录: /EFI/microsoft/boot/bootmgfw.efi
   2. 设备启动(u盘): 为指定明确目录 boot from usb ，遍历分区,寻找/efi/boot/bootx64.efi

Run level

init program

the first program start after the kernel booting, it is the ancestor of all other programs

1. SysV-style

2. systemed

1. linux base structure

1. linux distribution constitue components

Kernel + gnu(a set of programs) + windows(optional)

2. system famliy

POSIX: portable operateing system interface

1. Bsd and unix are old implementation
2. linux is new comer

directory

1. /home($HOME | ~): it’s the workspace of a particular user;each user have its own individual files
2. /bin: fundamental user program

   cat, cp

3. /sbin:fundamental system program(run by root) > init, route
4. /etc: configure files
5. /usr: contain the majority of user utilities and applications;
   1. /usr/bin: common program
   2. /user/sbin: common system program
   3. /usr/local/: local program

      go,python…

6. /run: runtime variables
7. /tmp: maybe delete at any times
8. /lib: dynamic library for /bin and /sbin
9. /opt optianl application software packagee
10. /var variables data; continually change during normal operation of the system
    1. /var/run: runtime variables

       /var/run/mysqld/mysqld.pid

    2. /var/log
11. /dev: device files： disk,cpu,etc.

1. difference between

/opt vs /usr/local? 1. /usr/local you should mimic the linux hierarchy, seperate your application into different folder /usr/local/bin /usr/local/lib

    /usr/local/etc

2. /opt: don't have these restrictions
  > e.g.our applications

bin sbin

sbin: used for system administrator bin: used for normal user

/bin, /sbin: essential command

1. /bin: ls, cat
2. /sbin: iptables, ip

/usr/bin /usr/bin: distribution-manager; not essential

1. /usr/bin: awk, sed
2. /usr/sbin: httpd ，

/user/local/bin /user/loca/sbin : local-user manager

1. /user/local/bin: go

root user

1. what? hava the high privledge;

2. change user: su change to a substitute user,if user is not given, root is asumed

   1. -, -l: make the shell a login shell

3. /etc/sudoers visudo grant the user root priviliages

   formt: user/%group ALL=(ALL) NOPASSWD: command

           [run as user/group ]
   

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   sys ALL=(ALL) NOPASSWD: ALL # user have root %admin ALL = (ALL) ALL # group have root priviledge rd ALL=(ALL) NOPASSWD: /bin/whoami,/bin/cat,/bin/tail #rd can excute these commnad as root user

4. grant the user root priviledge

   1. add to group: the wheel group %wheel ALL=(ALL): ALL usermod -aG wheel(sudo) rd

   2. grant to the root privilege directly sys ALL=(ALL) NOPASSWD: ALL

manager user

/etc/passwd: user info /etc/shaowd: password;; /etc/group:

vipw：edit /etc/passwd safely

1. query less /etc/passwd

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sys❌1000💯system Adminstrator:/home/sys:/bin/bash
# name userID groupID   userid info   (home directory)  login shell

groups root; # show groups;
id  root; # show id and group;

wheel❌10:tang,rd
# name groupID username

2. add user useradd kafka -p: password -m/M: create/notCreate home director

update:

1. change group

   1	usermod -aG wheel kafka

2. update name group home directory

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groupadd ostechnix
usermod -d /home/ostechnix -m -g ostechnix -l ostechnix vagrant

4. delete userdel username;
   1. -r: remove home directory and mail

group

1. primary group and secondary group when a new user is created useradd,
   it will create a group which is same name with the user, and will be the primary group of the user

2. cat /etc/group tang❌1001: groupname: password: groupID;

linux signal list

1:hangup 2:interrupt(ctrl+c) 3:quit (ctrl+) 9:kill: cant’t be caught or ignored 15:terminate: software termination signal 18: stop signal generated from keyboard

put a process in background,suspended; can be recoverd by fg command;

job manage

job: a proces from current terminal

1. foreground: start process from current terminal
2. background:&
3. stopped: ctrl+z; bg: bring the job into the background fg: bring the job into the foreground jobs: list all jobs

terminal tty console

terminal and console are both hardware which can interact with a host, basically a keyboard with a display; in the early years, it’s tty;

i/o mutiple

linux directory

/srv: data files for a specific service 如 /srv/www/ftpfile, /srv/indexhtml

/opt: 三方软件不是遵循linux的方式安装的，自己编译的；

/srv 和 /opt都可以部署自己的服务；

如 goApp,
/srv/goApp: 此时goAPP二进制文件可以看做服务特别的数据

/var: 程序允许过程中产生的，如日志，cache；

发行版本

RHEL:

1. red hat 维护的或者与其相关的
2. 使用yum 安装包
3. 代表： rhel, fleodra, cento s

debian

1. 开源的
2. 使用apt安装
3. 代表： debian , ubuntu，

Fedora-> centos stream -> rhel->centos fedora 和stream 都是测试版本, centos 和 rhel都是稳定版本