The third Lesson IV speaking 03_04_linux user and authority detailed

The third Lesson IV speaking 03_04_linux user and authority detailed
1. Libraries and processes are siblings. Process can get CPU time, memory address, call various files
2. Permissions: Defines the access capabilities of computer resources and services called permissions
3. Logical container, user-associated permissions are user groups. For assigning permissions, cannot log on independently

4. The document belongs to the owner, the documents belong to the group, other,
5. Users and groups in the computer is an identifier
6. The process also has a group of owners and
The security context of the process, the owner of the process owner and the resource
7. File R,w,x
R:read readable, can use the File View command cat and other commands to view the contents of the file
W:write can be written. You can use file editing or delete command vim,rm and other action files
X:executeable executable. Can be submitted to the kernel at the command prompt as a command
8. Catalogue R,w,x
R: Use the word directory to execute LS to list all internal files
W: can be used to create files in secondary directory
X: Use the CD to switch into this command, or use ls-l to view the details of the internal file
9. User: User ID uid/etc/passwd the database has corresponding records
Group: Group ID gid/etc/group database with corresponding records
Shadow Password: User:/etc/shadow
Group:/etc/gshadow
10. User Category:
admin: uid=0, inner rule, internal build
Normal User: UID range 1-65535
System User: UID range 1-499, background process or service is already running before the user logs in. The owner of these processes and services is called the system user. This type of user is not allowed to log on to the system.
General User: UID range 500-60000
User group category categories the first type:
Administrators group:
Normal Group:
System Group:
General Group:
User Group category Classification the second type:
Basic group: Default group for users
Private group: When a user is created that does not have a group assigned to it, the system automatically creates a group with the same name as its user name
Added value, additional groups: groups other than the default group of users
11:PASSWD detailed
Account: User Name
Password: password,or x is a password placeholder
UID: User ID
GID: Basic Group ID
GECOS: User annotation information, comment
Home dir: Home directory
Shell: User Default Shell
11:shadow detailed
Login Name: Login name
Encrypted password: encrypted password ($1$ddddd$-1 means MD5 encryption, DDDDD is the salt level impurity bit). Or!! Indicates that the user is locked
3 bit: How long has it been since I last changed my password?
4-bit: Password minimum usage time: 0 not Limited
5-bit: Maximum password usage time
6-bit: A few days before password expiration remind users
7-bit: grace period, password expired, the user did not change, give him a few days time grace
8-bit: account validity, regardless of 5-bit.
9-bit: Reserved fields

12. Encryption Method:
Symmetric encryption: Encryption and decryption with the same secret key
Public Key cryptography: each password appears in pairs, one for the private key (secret key) and one for the public key
One-way encryption (also called hash algorithm), hash encryption: Can be encrypted cannot decrypt. Used to extract data signatures for data integrity checks.
1) Avalanche effect, butterfly effect, small changes in initial conditions can cause great changes in results, prevent reverse effects, prevent cracking
2) fixed-length output
One-Way Encryption example: Md5:message digest,128 for fixed-length output (MIT AI Lab development)
Sha1:secure Hash algorithm,160 bit length output (general algorithm convened by American National Standards Committee)
13.useradd
Useradd USERNAME
14.groupadd
15./etc/group file
Group name: Group password: Group ID: User with this group of attachment groups
User Management commands:
Useradd,userdel,usermod,passwd,chsh,chfn,finger,id,chage
Group Management Commands:
groupadd,groupdel,groupmod,gpasswd
Rights Management Commands:
Chown,chgrp,chmod,umask

The third Lesson IV speaking 03_04_linux user and authority detailed