User management commands
useradd
Add user
Syntax: useradd [options] username
passwd
change password command
Syntax: passwd [options] [username]
User password: In the production environment, the length of the user password is more than 8 characters. Set the upper and lower case plus numbers plus special characters, and change the password regularly.
ys ^ h_L9t
userdel（user delete）
delete users
-r Delete the host directory when deleting the account (remove)
Process management commands
The difference between a process and a program:
1. A program is a static concept, which itself is stored for a long time as a software resource; while a process is the execution process of a program, it is a dynamic concept, has a certain life cycle, and is dynamically generated and destroyed.
2. There is no one-to-one correspondence between programs and processes. A program can be shared by multiple processes; on the other hand, a process can execute several programs sequentially in an activity.
The difference between process and thread:
Process: It is the program or command being executed. Each process is a running entity, has its own address space, and occupies certain system resources.
Thread: A lightweight process; a process has an independent address space, a thread does not; a thread cannot exist independently, it is created by a process; relatively speaking, a thread consumes less CPU and memory than a process.
The role of process management?
Determine the health status of the server
View all processes in the system
kill process
ps command
Role: View process information in the system
Syntax: ps[-auxle]
Common options
a: show processes for all users
u: Display username and startup time
x: show processes that do not have a controlling terminal
e: show all processes, including those without a controlling terminal
l: long format display
View all processes in the system
# ps aux #View all processes in the system, use the BSD operating system format, unix
# ps -le #View all processes in the system, using the Linux standard command format
ps application example
# ps -u or ps -l View the details of the processes that belong to you# ps aux | grep sam View processes executed by user sam
# ps -ef | grep init View specified process information
pstree
Role: View the current process tree
Syntax: pstree[options]
-p show process PID
-u show the user of the process
top
Function: View system health status
Displays the processes that consume the most resources in the current system, as well as some load conditions of the system.
Syntax: top [options]
-d seconds, specify a few seconds to refresh once, the default is 3 seconds (dynamic display)
kill
Action: close the process
Syntax: kill [-options] pId
kill -9 process number (forcibly close) commonly used
kill -1 process number (restart process)
authority management
Three basic permissions
r read permission (read)
w write permission (write)
x execute permission (execute)
Permission description
owner group others
Bit 1: file type (d directory, - normal file, l linked file)
Bits 2-4: User (owner) authority, represented by u (user)
Bits 5-7: Group permissions, represented by g (group)
Bits 8-10: other users (others) permissions, represented by o (other)
Bits 2-10: Indicates all permissions, represented by a (all)
Type: f binary file l soft link file d directory
character |
permission |
Implications for the file |
Implications for the directory |
r |
read permission |
Can view file content |
Can list the contents of a directory (ls) |
w |
write permission |
file content can be modified |
Can create delete files in a directory ( mkdir,rm ) |
x |
execute permission |
executable file |
Can enter the directory (cd) |
document:
r-cat,more,head,tail，less
w-echo, i saw
x-command, script
content:
r-ls
w-touch,mkdir,rm,rmdir
x-cd
The permission to delete a file is to have wx permission on the directory where the file is located.
permission change - chmod
英文：change mode(change the permissions mode of a file)
Role: change file or directory permissions
grammar:
chmod [{ugoa}{+-=}{rwx}] [filename or directory]
chmod [mode=421] [file or directory]
Parameters: -R The files and subdirectories below do the same permission operation (Recursive recursive)
Thinking: Who can change the permissions of a file? root owner
root
file owner
For example: chmod u+x a.txt
chmodu+x,o-x a.txt
Permissions are represented by numbers (r=4, w=2, x=1, -=0)
For example: chmod 750 b.txt
rwx and digital representation can be switched at will
Note: The root user is a super user, and root can make changes with or without permissions. Test permissions with a normal user.
You cannot use an ordinary user to modify the permissions of another ordinary user.
change owner - chown
English: change file ownership
Role: Change the owner of a file or directory
Syntax: chown user[:group] file...
-R : recursive modification
Parameter format:
user : the user ID of the new file owner
group: the user group of the new file owner
eg: #chown lee file1 Change the owner of the file1 file to user lee
eg: #chown lee:test file1 Change the owner of the file1 file to user lee, and the group to test
eg: #chown –R lee:test dir Modify the owner and group of dir and its subdirectories
change group chgrp
英文：change file group ownership
Role: Change the group to which a file or directory belongs
Syntax: chgrp [group] file...
eg:chgrp root test.log Change the group of test.log to root
RPM package management
RPM packages are also known as binary packages
RPM is the abbreviation of RedHat Package Manager (RedHat Package Management Tool). Although the name of this file format is marked with the RedHat logo, its original design concept is open. Now, Linux distributions including RedHat, CentOS, SUSE, etc. If adopted, it can be regarded as a recognized industry standard. RPM files are the easiest to install in Linux systems
RPM command usage
Common parameters of rpm
i: Install the application (install)
vh: display the installation progress; (verbose hash)
U: upgrade package; (update)
qa: show all installed packages (query all)
e: Uninstall the application (erase)
Note: If other software packages have dependencies, a prompt message will be generated when uninstalling, you can use --nodeps to force uninstall.
Query all installed rpm packages: # rpm –qa
Query mysql related packages: # rpm –qa | grep mysql
Install: rpm -ivh jdk.rpm
Uninstall: rpm –e mysql*
Forced uninstall: rpm -e mysql* --nodeps
Graphical interface, manual mount
YUM management
yellowdog updater modified package management tool
The benefits of applying yum:
1. Automatically resolve package dependencies
2. Convenient package upgrade
query
yum list Query a list of all available packages
yum search keyword Search all packages related to the keyword on the server
You can find the package name through the yum info keyword
Install
yum -y install package name -y automatically answers yes
upgrade
yum -y update package name
Note: If you don't add the package name, it will upgrade everything, including the kernel. You must add a package name to upgrade a single package, use caution to upgrade all
Detect upgrade yum check-update
uninstall
yum -y remove package name
help
yum --help、man yum
yumclean all clears cache and old packages
yum repolist View currently available yum sources
yum deplist httpd lists all dependencies of a package