3-4linux User Rights detailed

Permissions:r,w,x

files:R, readable ,w can be edited or deleted , X, executable, run command to kernel at command prompt

directory:r can perform LS on this directory to list all directories. W, can create files in this directory , x available CD switch directory,ls-l View file Details

User: identifier UID, stored in /etc/passwd

User Groups : User's container, associated permissions. Logical concept. GID, deposited in /etc/group

Shadow Password:

Users:/etc/shadow

user group:/etc/gshadow

User Category:

admin:0

Normal users:1-65536

system users:1-499

General users:500-60000

User Group Category :

Administrators group:

Normal Group:

System Group:

General Group:

Private Group: If a user is created without a group specified for the user, a group with the same name as the user name is automatically created for it.

Basic group: User Default group.

Additional groups: Additional groups, groups other than the default group.

Example: User Tom executes the LS command, andtheLS command is located in /bin/lswith permissions of rwx r-x r-x Root Root

TOMWhether you can runlsto seetonWhether it is the owner of the document, whether it belongs to the group of documents, this example does not belong to, thatTomcan only be performed with general user rightsls,General user rights areR-x,readable executable, soTOMcan runlscommand. After runninglsto become a process, the Access file for this process is no longer a filelspermissions, but the initiatorTOMthe permissions. The ability of this process to access a file depends on whether the generic group of the process is coincident with the owner of the file being accessed. All of this is called the security context.

#:cat/etc/passwd

The file is divided into 7 fields per field meaning:

account user name:password password:uid user ID number:GID Basic group ID:comment user comment information is generally empty:home DIR home directory: Shell: User's default Shell

#:Cat/etc/shadow

account username : encrypted password: record Password change time from 1970 Year: Minimum password age, typically 0 : Password Maximum Age: Password Expires: Number of days after password expires: Password never Expires: The reserved field is meaningless.

Encryption method:

Symmetric encryption: Encrypt and decrypt the same password.

Public Key cryptography: each password appears in pairs, one for the private key and one for the public key. Private key encryption public key decryption, public key encryption private key decryption. Basic infrastructure for the implementation of e-commerce. Public key cryptography has high security and slow speed.

Single encryption, hash encryption: The ciphertext is obtained by the plaintext, extracting the data signature.

1, Avalanche effect , Butterfly Effect: The initial effect of small changes, resulting in a huge change in structure.

2, fixed-length output

MD5: The output of the fixed length

SHA1: fixed-length output

# Cat/etc/group

all the information for the user group is stored in the/etc/group file. The format of this file is separated by a colon (:) Several fields, these fields are as follows:

Group name : password : Group identification number : List of users in the group

User management:useradd ,userdel, usermod ,passwd , Chsh , Chfn,finger,id,chage

Group Management:GROUPADD,GROUPDEL,GROUPMOD,GPASSWD

Rights Management:Chown,chgrp,chmod,ummask

3-4linux User Rights detailed