20141208 Study Notes

Command aliases

Alias cmdalias= ' COMMAND [options] [arguments] '

Aliases defined in the shell are valid only in the current shell life cycle: The valid range of aliases is only the current shell process

Command substitution: $ (command), anti-quote: ' command '

To replace a subcommand in a command with the process of executing the result

Quotes supported by bash:

": Command substitution

"": weak reference, can implement variable substitution

': Strong reference, do not complete variable substitution

File name wildcard, globbing

*: Any character of any length

?: any single character

[]: matches any single character within the specified range

[^]: matches any single character outside the specified range

[: Space:]: white space character

[:p UNCT:]: Punctuation

[: Upper:]: Uppercase

[: Lower:]: lowercase letters

[: Alpha:]: Uppercase and lowercase letters

[:d igit:]: Number

[: Alnum:]: Numbers and uppercase and lowercase letters

Users, Groups, permissions

Permissions:

R,w,x

To the file:

R: Readable, you can view the contents of the file using commands like Cat

W: section write, you can edit or delete this file:

X: Executable, can be submitted to the kernel at the command prompt as a command to run

Directory

R: You can perform LS on this directory to list all internal files

W: You can create files in this directory

X: You can switch to this directory using a CD, or you can use Ls-l to view the details of internal files

Rwx

0---: No permissions

1 001--x: Execution

2 010-w-: Write

3 011-wx: Write and Execute

4 r--: Read-only

5 101 R-x: Read and Execute

6 rw-: Read and Write

7 111 rwx: Read and write execution

Users: UID,/ETC/PASSWD

Group: Gid,/etc/group

Shadow Password:

Users:/etc/shadow

Group:/etc/gshadow

User Category:

Admin: 0

Normal Users: 1-65535

System users: 1-499

General Users: 500-60000

User groups:

Administrators group:

Normal Group:

System Group:

General Group:

User Group Category:

Private group: When you create a user, a group that has the same name as the user name is created automatically for a group that is not a specified member

Basic group: Default group for users

Additional groups: Additional groups: Groups other than the default group

/etc/passwd file

Account: Login Name

Password: password

Uid:

GID: Basic Group ID

Comment: Notes

Home dir: Home directory

Shell: User does not have a default shell

/etc/shadow

Account: Login Name

Encrypted Password: encrypted password

Encryption method:

Symmetric encryption: Encrypt and decrypt using the same password

Public Key cryptography: Each encryption appears in pairs, one for the private key (secret key), and one for the public key

One-way encryption, hash encryption: Extracting data signatures, often used for data integrity checks

1. Avalanche effect

2, fixed-length output

Md5:message digest,128 fixed-length output

Sha1:secure Hash algorithm,160 bit fixed length output

Add Users:

Usreadd NAME: New user

passwd NaME: Modify user Password

To add a group:

Groupadd NAME: New Group

20141208 Study Notes