Basic knowledge of Linux Primer 2

file system: Access files by name

• Files and directories are organized into a single inverted tree structure

• Directory: Directory is not a folder, but a path map

• The file system starts with the root directory, denoted by "/"; Root file System (ROOTFS): root filesystem

• Files with a . Start as hidden files

• There are two types of data in a file:

• Metadata (metadata): Data describing Data properties: file name, size, property, date ... For example: A person's height and weight

• Data: Real data within a file

File system hierarchy: LSB Linux standard Base

Fhs:filesystem Hierarchy Standard

(Example: The disk is divided into a, b two partitions, once a is defined as the root partition, the B partition wants to be accessed, must be connected to a directory already existing on the root partition, as the portal of the B partition, can be accessed)

File name rules

• File name up to 255 bytes

• Filenames, including brutishness, have a maximum of 4,095 bytes. 2^10*4=4k

• (ANSI color file name color standard) blue-to-catalog, green-to-executable, red-to-zip, light blue-to-link, purple-to-socket (socket) file, gray-to-other files

• Standard Linux file System (mainstream file system such as EXT4,XFS), file name case sensitive

File system Structure

• /boot: Boot file directory, kernel file (vmlinuz), boot loader (bootloader,grub), Initramfs are stored in this directory

• /bin: A basic command for all users to use, a program that is used by OS startup and cannot be associated to a separate partition

• /sbin: A basic command to store management classes; A program that is used by OS startup and cannot be associated to a separate partition

• /lib: Basic shared library files that the program relies on at startup and kernel module files (/lib/modules)

• /LIB64: storage location for secondary shared library files dedicated to x86_64 systems

• /etc: Configuration file directory (Linux philosophy, with text files to store configuration files)

• /home/username: Normal User home directory

• /root: Administrator's home directory

• /media: Portable Mobile device mount point (for example, USB flash drive is associated with media access)

• /MNT: Temporary file system mount point

• Shorthand for/dev:devices, all device files and special file storage locations

• B:block device (block device) random access, such as disk

• C:character device (character devices) linear access, such as keyboard

• /opt:optional (optional) third-party application installation directory

• /srv:services, data used by services running on the system

• /tmp:temporary abbreviated, temporary file location (file system that is not used for more than 30 days is automatically deleted)

• /usr:universal shared,read-only Data Global shared read-only

Bin: An application that ensures that the system has full functionality

Sbin

Lib:32 bit use

LIB64: Only 64-bit systems exist

Include:c header file for the program (header files)

Share: structured independent data such as Doc, man, etc.

Local: Installation location for third-party applications, 3rd Party:bin, Sbin, lib, lib64, etc, share

• /var:variable data files (variable storage)

Cache: The application caches the data directory

LIB: Application state information data (that is, not a library file)

Local: Dedicated to storing variable data for applications under/usr/local;

Lock: Lock file

LOG: Logs directory and files

OPT: Dedicated to storing variable data for applications under/OPT;

Run: Process-related data in progress, typically used to store process PID files

Spool: Application Data Pool

TMP: Save temporary data generated between system two reboots

• /proc: For the output kernel and the process I west to the related virtual file system

• /sys: For outputting information about hardware devices on the current system virtual file system

• /selinux: storage location for information such as security enhanced linux,selinux related safety policies

Most of the cases, the/selinux is off , it's too strict

All applications on Linux 4 class main constituent files

• Binaries (applications):/bin,/sbin,/usr/bin,/usr/sbin,/usr/local/bin,/usr/local/sbin

• Library files :/lib,/lib64 ...

• configuration Files :/etc,/etc/directory, ...

• Help file :/usr/share/man,/usr/share/doc ...

Types of files under Linux (Distinction on metadata)

• -: Normal file

• D: Catalog Files directory

• L: Symbolic Link file Symbolic link

• B: Block devices blocks device (randomly accessed device files)

• C: Character device character device (linear access to the corresponding equipment file)

• P: Pipe file Pipe,fifo (first in,first out). /Advanced after the call stack/

• S: Socket file socket

Show current working directory PWD

• Each shell and system process has a current working directory

• Pwd:printing working directory displays the current working directory

Absolute path and relative path

• Absolute path:

• To / start

• The location path of the full file

• Can be used for any time you want to specify a file name

• Relative path:

• Do not start with /

• Specify a location relative to the current working directory or a directory

• You can specify a file name as a short form, such as ./

Base name: basename, a file path to the right of the filename,

Directory Name: dirname, all except basename name Directory name

Change Directory

CD changes directory; (change directory)

Use absolute path or relative paths

Switch to Parent directory: CD.

Switch to the current user home directory: CD

Switch to the first working directory: CD-

Command ls

Usage: LS [options] [Files_or_dirs]

Example:

Ls-a: List contains hidden files

Ls-l: Displays additional information (Metadate metadata),

Ls-r: Recursive display of all files, including sub-directories under sub-files and subdirectories ... (generally using tree)

LS-LD:-D indicates that the path itself is displayed and is typically used with-l

Example: Ls-a, Ls-l

A total of 10, the first letter for the file type, rwx 3 for the group, is the main/group/other user's use rights

Indicates the number of hard links to a file

Indicates who is the owner and the group

Represents file size, special files are displayed as 2-bit

Represents a modified timestamp (modify Time/mtime) and a file name

Example: Ls-ld

View file status

Stat

File: metadata, data

Three time stamps:

Access time: Atime, reading the contents of a file

Modify Time: Modified, Mtime, change file contents (data)

Change time: Changing times, ctime, meta data changes

(The data changes the metadata must change, the metadata changes the data may not change)

File name wildcard character, Glob,globing,wildcard

• * Match 0 or more characters

• ? Match any single character

• [0-9] Matching number range

• [A-Z]: letters (case insensitive)

• [A-Z]: letters (case insensitive)

• [ABCD] matches any one of the characters in the list

• [^ABCD] matches characters other than all characters in the list (de-inverting)

Pre-defined character class: Man 7 glob

• [:d Igit:]: Any number, equivalent to 0-9

• [: Lower:]: Any lowercase letter

• [: Upper:]: Any uppercase letter

• [: Alpha:]: Any case letter

• [: Alnum:]: Any number or letter

• [: Blank:]: horizontal white space character

• [: Space:]: Horizontal or vertical whitespace characters

• [:p UNCT:]: Punctuation

• [:p rint:]: Printable characters

• [: Cntrl:]: Control (nonprinting) character

• [: Graph:]: Graphic character

• [: Xdigit:]: hexadecimal character

Create File and Refresh time

Touch Command : Change 3 timestamps at the same time; Create an empty file if the file does not exist

Touch [OPTION] ... FILE ...

• -A changes atime and CTime to the current time only

• -M only changes mtime and CTime to the current time

• -t specifies timestamps for atime and Mtime [[CC]YY]MMDDHHMM[.SS]

• -C If the file does not exist, it is not created

copy :cp [OPTION] source target

• -I: Pre-overwrite hint –n: Do not overwrite, note both order

• -R,-r: recursively replicate directories and all internal content

• -A: Archive, equivalent to-DR--preserv=all

• -d:--no-dereference--preserv=links does not copy the original file, only the link name is copied

• --preserv[=attr_list]

Mode: Permissions

Ownership: Belong to the main group

Timestamp

Links

Xattr

Context

All

• -P: Equivalent--preserv=mode,ownership,timestamp

• -V:--verbose, more information

• -F:--force

• -u:--update only copy files that do not exist for the source than the target update file or destination

• --backup=numbered Target exists, back up plus digital suffix before overwriting

Move and rename files

MV Command common option (options):

-I: Interactive

-F: Mandatory

-T: Source behind, target position in front

Delete

RM [OPTION] ... FILE ... (delete files only)

Common options:

-I: Interactive

-F: Force delete

-R: Recursive (used when you want to delete a folder)

--no-preserve-root

Example:

RM-RF/(Delete the root file, i.e. delete all data)

Directory Operations

Tree Display directory trees

-D: Show only directories

-L Level: Specify display layer progression

-P Pattern: Displays only the paths that are matched by the specified pattern

mkdir Creating a directory

-P: exists in no error, and can automatically create the required directories (create an empty directory of purchased only son

-V: Show more information

-M MODE: Create a directory to specify permissions directly

rmdir Delete empty directories (rarely used)

-P: Recursive deletion of empty parent directory (delete empty directory of one vein only son)

-V: Show more information

rm-r Recursively delete a directory tree (used when a non-empty directory is deleted)

PS: Production environment in not 100% clear what you are doing do not delete any directory (can be manually established to recycle Bin, using the MV command to move to the Recycle Bin)

Inode (Index node)

• The inode(Index node) table contains a list of all file system files

• A node (an index node) is a table item that contains information about the file (metadata), including:

File type, permissions, Uid,gid

Number of links (pointing to the number of path names for this file name)

The size of the file and the different timestamps

Data block pointer to file on disk

Additional data about the file

ls-i Display inode number

Directory

• File reference is an inode number (cross file system/partition, Inode number cannot be shared)

• A person is referring to a file by file name

• A directory is a mapping between a file name and an inode number in a directory

CP and Inode

1. Allocate a free inode number to generate a new entry in the Inode table

2. Create a catalog entry in the directory, associating the name with the inode number

3. Copy data to generate a new file

RM and Inode

1. The number of links is decremented, thus releasing the inode number can be reused

2. Put data blocks in the free list

3. Delete a catalog entry

RM data is not actually deleted immediately, but is overwritten when another file uses a block of data

MV and Inode

If the target and source of the MV command are in the same file system,

1. Create a corresponding directory entry with a new file name

2. Delete old directory entry pairs for older file names

Does not affect the Inode table (except timestamp) or data location on disk: No data is moved

If the target and source are in a different file system, MV is equivalent to CP and RM 2 steps

Hard links and soft links (symbolic links)

Hard Links: Different file paths point to the same inode

ln filename [linkname]

• Creating a hard link adds an additional record entry to reference the file (increasing the reference count of the Inode)

• Hard links correspond to the same file system as the same physical file

• Directory does not support hard links

• Increased number of links when creating hard links

• When deleting files:

• RM command reduces number of hard links

• File to exist, with at least one link number

• When the number of links is 0 o'clock, the file is deleted

• Hard links cannot span drives or partitions

Symbolic link/Soft Link:

ln-s filename [Linkename]

(Original path, link path) The link path does not point to the inode, but instead points to the original path

The path of a symbolic link to another file

Ls-id display the name of the link and the referenced file

Soft links can be used for directory

Can span partitions

A path to another file whose size points to the length of the path string, without increasing or decreasing the target file Inode reference count

Standard inputs and outputs

Program: Instruction + data

Read-in data: Input

Outputs data: Output

The open file is also a file descriptor (Fd:file descriptor)

3 Types of I/O devices for Linux programs

input, default. Standard input: (STDIN)-0 accepts input from the keyboard by default

/dev/stdin,keyboard

output, default. Standard output: (STDOUT)-1 Default output to terminal window

/dev/stdout,terminal Monitor

error, default. Standard error: (STDERR)-2 default output to Terminal

/dev/stdout,

I/O redirection: Changing the default location

Re-export the output and errors to the file

StdOut and stderr can be redirected to a file

Command Action Symbol file name

Supported operational symbols include:

1. > >> redirect stdout to file

2. 2> 2>> redirect stderr to file

3. &> &>> (Command >/path/to/file.out 2>&1, Command >>/path/to/file.out 2>&1) Redirect all output to file

> Overwrite file,>> not overwrite file, append later

Standard output and error outputs are directed to different locations : COMMAND >/path/to/file.out 2>/path/to/error.out

StdOut for merging multiple programs:(Cal 2007;cal) > All.txt

Files can contain multiple types of data

Check the file type, and then determine the appropriate open command or application to use

file [options] <filename>

Pipe (using the symbol "|" Used to connect commands

Command 1 | Command 2 | Command 3 | ...

Send stdout of command 1 to stdin of command 2, stdout of command 2 to stdin of command 3

StdErr cannot be piped forward by default and can be implemented with 2>&1 or |&

The last command executes in the child shell process of the current shell process to

The ability to combine multiple tools

ls | Tr ' A-Z ' A-Z

Basic knowledge of Linux Primer 2