Linux Basics-Operating system basics

System call Order

From bottom to top

Hardware →kernel kernel →library API (application program Interface)

System boot Order

Power-on self-Test →bios mapping program → load system kernel → application usage

Cons: Easy to create memory fragmentation

GCC----GNU C complier GNU C compiler

Directory Management:

LS, CD, pwd, mkdir, RM, tree

File Management:

Touch, stat (view modified timestamp), file, CP, MV, Nano

Date Time:

Date, clock, Hwclock, Cal

Text Processing:

Cat, more, less, head, tail, cut, sort, uniq, vim, awk, join, grep, SED

Cut

-D: Specifies the field delimiter, which is the default space

-F: Specifies the field to display (-F 1,3 indicates the first and third fields are displayed. -F 1-3 Indicates the first to third field is displayed)

Cases:

Cut-d:-f1-3/etc/passwd to: Display a 1-3 field in/etc/passwd file for a separator

BASH-supported quotes

": Command substitution

"": weak reference, can implement variable substitution

': Strong reference, do not complete variable substitution

Bash file wildcard

*: Any character of any length

?: any single character

[]: matches any single character within the specified range

[Abc],[a-z],[a-z],[0-9],[a-za-z0-9]

[: Space:] white space character [:p UNCT:] punctuation [: lower:] lowercase [: Upper:] uppercase letters [: Alpha:] Upper case Letters [:D igit:] numbers [: alnum:] numbers and uppercase and lowercase letters

[^] matches any single character outside the specified range

Linux Library types

. So Dynamic shared library

Encryption method

Symmetric encryption: Encrypt and decrypt using the same password

Public key decryption: each password appears in pairs, one for the public key and one for the private key

One-way encryption: Extracting data signatures, used for data validation

Features: 1, Butterfly Effect 2, fixed-length output

Encryption algorithm

MD5: summary information, 128-bit fixed-length output

sha1:160 bit fixed-length output

sha256:256 bit fixed-length output

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Linux Basics-Operating system basics