Linux Essential Skills-User and permissions

Linux Required Skills - detailed user and authority

/etc/passwd File

Account:password:UID:GID:GECOS:directory:shell

login name: password dot character: Uid:gid: Comment Information: Home directory: User's default shell

users can join more than one group:

Basic Group

additional groups, additional groups

/etc/group File:

Group name: group Password locator: GID: comma-delimited list of users belonging to this group (as an additional group)

Useradd Command:

-uuid

-ggid: the base group to which it belongs

-ggid: the attached group to which it belongs

-C ' COMMENT ' annotation information

-d/path/to/somewhere: If this directory exists beforehand, there will be a warning message

-sshell:shell must be a SHELL that exists in the/etc/shells file

-m force user to create home directory

-M does not create home directories for users

-R Create system user

Groupadd Command

-ggid: Specify GID

-R: System Group

passwd

Ordinary users can only modify their own password

Administrator:

Passwd[username]

Password Complexity policy:

10^5 62^5 110^5

numbers, lowercase, uppercase, and special characters at least three classes

Minimum Length 5 bits

don't use easy-to-guess passwords

modify regularly and do not use passwords that have been used recently

encryption Method ;

Symmetric encryption: Encryption and decryption use the same key:

Key Distribution Difficulties

Public Key cryptography: encryption and decryption using a pair of keys

Public key: Public

private key: Confidential

CA: Certification Scheme Agency

Bob Alice

PKI:

One-way encryption: Unique signatures for extracting data

1, fixed-length output:

2, non-reversible:

3. Avalanche effect

md5:128 bits

sha1:160 bits

Bob--> data, Fingerprint--> data,

Digital signatures

passwd

--stdin

-l:lock

-u:unlock

/etc/shadow file Format

User name: encrypted password: Last password change: password minimum Age: Password maximum age: Password Expiration warning interval: password inactivity period: Account expiration: Reserved area

#man5 Shadow

Userdel:

Userdel[options] USERNAME

-r: delete users and their home directories together

Groupdel:

Groupdelgrpname

Usermod:

Usermod[options] USERNAME

-uuid

-ggid Modifying a user's base group

-G GID,...: Modify additional groups for the user , which is modified by using with- A to append the additional group

-C COMMENT:

-d/path/to/somewhere: Modifying the location of the home directory using the-m option ensures that the home directory is created and the user's original files are moved to the new home directory

-S SHELL:

-L login_name: Modify user name

-L Lock user

-u Unlock user

Chshusername

Chfnusername

Chage

Chage[option] USERNAME

To view user information:

Id USERNAME

-G

-G

-N

-U

W.H.O.

WhoAmI

Finger

To switch users:

Su:switch User

su [option] USERNAME

This article is from the "View hardware under Linux" blog, so be sure to keep this source http://4285797.blog.51cto.com/4275797/1619818

Linux Essential Skills-User and permissions