Day5:linux file System (3) + Redirect and pipeline + user group Hull Rights Management (1)

July 29, Marco Linux study on the fifth day, the main content of study:

First, the index node

Second, hard links and soft links

Iii. Redirection and piping

Iv. Users and user groups

First, index node

• 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

  
  

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

  
  

• CP Command and Inode:

  Allocate a free inode number, generate a new entry in the Inode table create a directory entry in the directory, associate the name with the inode number copy data to generate a new file

  Cp-f/etc/issue/f1/etc/issue/Delete and create F1 file

  
  

• RM Command and Inode:

  The number of links is decremented so that the inode number released can be reused

  Put data blocks in the free list

  Delete a catalog item (the data is not actually deleted immediately, but will be overwritten when another file uses the data block)

  
  

• MV Command and Inode:

  Target and source on the same file system: Create a new directory entry with a newer file name delete the old directory entry corresponding to the old file name does not affect the Inode table (except the timestamp) or the data location on the disk: No data is moved!
  Target and source in a different file system: MV equivalent to CP and RM

  
  

Second, hard links and soft links

• Hard Links

  Syntax: ln filename [linkname]

  Creating a hard link adds an additional record entry to reference the file, corresponds to a physical file on the same file system, each directory references the same inode number, the number of links is incremented when the file is deleted, and the RM command decrements the count of links; file to exist, at least one link number when the number of links is zero, the file is deleted ; Cannot cross drive or partition, cannot create hard link to directory.

  
  

• Soft links

  Syntax: ln-s filename [linkname]
  

  A symbolic link points to another file, the name of the Ls-l display link, and the referenced file; the content of a symbolic link is the name of the file it refers to, can be made to a directory, can span a partition, and a path to another file, with the size of the length of the path string pointed to ; does not increase or decrease the reference count of the target file inode.

  
  

Third, redirect

• Standard input and output:

  Linux provides three types of I/O devices to the program:

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

  Standard output (STDOUT)-1 Default output to terminal window

  Standard error (STDERR)-2 default output to terminal window

  
  

• I/O redirection: Changing the default location

  StdOut and stderr can be redirected to a file: command action Symbol file name
  Supported operational symbols include:

  > redirect stdout to file (set-c: Suppresses overwriting of existing files but can append mandatory overrides: >| Set +c: de-disable)

  2> redirect stderr to file

  &> Redirect all output to file
  (> file content will be overwritten >> original content, append content)

  
  

  The standard output and error outputs are directed to different locations:

  COMMAND >/path/to/file.out 2>/path/to/error.out

  
  

  Merge standard output and error output redirect for the same data stream:

  (1) &>: Overwrite redirect &>>: Append redirect

  (2) COMMAND > /path/to/file.out 2> &1 (&1 indicates the correct output directory with standard)

  COMMAND >> /path/to/file.out 2> &1

  Multi-line redirection: Cat <<eof cat > File <<eof
  (): Consolidation of multiple programs (Cal stdout; cal) > All.txt

  
  

• TR command: Convert and delete characters
  TR [OPTION] ... SET1 [SET2]
  -C or--complerment: a complement to the character set

  -D or--delete: Deletes all characters belonging to the first character set

  -S or-squeeze-repeats: the consecutive repeating character is represented by a single character

  -T or--truncate-set1: Converts the corresponding character of the first character set to the corresponding character of the second character set

  tr [A-z] [a-z] converts lowercase to uppercase (cannot be deleted directly when input, can be deleted using Ctrl+backspace)

  
  

• Pipeline

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

  A connection program that implements the output of the previous command directly after a program as an input data stream

  ls | Tr ' A-Z ' A-Z

  StdErr cannot be piped forward by default and can be implemented with 2>&1 or |&
  Less: one page, one page view input: $ ls-l/etc | Less

  Mail: Send input by e-mail: $ echo "Test Email" | Mail \ S "Test" [email protected] LPR: Send input to Printer $ echo "Test print" | Lpr-p Printer_name

  
  

• Tee command: One input, two output (standard output + file)

  $ Command 1 | Tee File name | Command 2
  Save the stdout of command 1 in the file name, and then pipe the input to the command 2

  cat/etc/issue/| Tee/tmp/issue.tee | Tr ' A-Z ' A-Z
  Use: Save different stages of output, troubleshoot complex pipelines, and view and record output at the same time

  
  

• Special Equipment:

  /dev/null

  To use the status result without executing the result, the execution results are put into/dev/null
  

Iv. Users and user groups

• Users user

  Linux Users: Username/uid

  admin: Root, 0

  Normal Users: 1-65535

  System User: 1-499 (CENTOS6), 1-999 (CENTOS7) Assign permissions to the daemon to get resources

  Login User: (CENTOS6) +, + (CENTOS7) +

  Interactive Login

  
  

• Group

  Linux Group: Groupname/gid

  Administrators group: root, 0

  Normal Group:

  System groups: 1-499, 1-999

  General Group: 1000+,

  Primary group of users (primary group):

  The user must belong to one and only one primary group group name with the user name and only one user: private group

  Additional groups for users (secondary groups):

  A user can belong to 0 or more secondary groups

  
  

• Linux security context
  The permissions that a process (a running program) can access to a resource depends on the identity of the process's runner

  
  

• The complexity strategy for passwords
  Use at least 3 of the numbers, uppercase letters, lowercase and special characters

  Long enough (at least 8 digits) to use a random password

  change regularly; Do not use passwords that have been used recently

• Encryption algorithm

  Symmetric encryption: Encryption and decryption using a

  Asymmetric encryption: Encryption and decryption using a pair of keys (public key, private key)
  

  One-way encryption:: Hash algorithm, can only encrypt, not decrypt, extract the data signature (fixed-length output, avalanche effect)

  Algorithm type: MD5 SHA1 sha224 sha256 sha384 sha512

  
  

• Primary profiles for users and groups

  /ETC/PASSWD: User and its attribute information (name, UID, primary group ID, etc.)

  /etc/group: Group and its attribute information

  /etc/shadow: User passwords and their associated properties

  /etc/gshadow: group password and its related properties

  
  

• passwd file format

  ①login Name: Login name (WANG)

  ②PASSWD: Password (x)

  ③uid: User identification Number (1000)

  ④gid: Login Default group number (1000)

  ⑤gecos: User's full name or comment

  ⑥home Directory: Household directory (/home/wang)

  ⑦shell: The user uses the shell by default (/bin/bash)

• Shadow file format
  Login with Name

  User password: Generally with sha512 encryption ($n $salt$ password where n is the encryption type salt is the random number added each time)

  From January 1, 1970 to the time the password was last changed

  The password can be changed in a few days (0 means it can be changed at any time)

  The password must be changed in a few days (99999 means never expire)

  The system reminds the user a few days before the password expires (default is one week)

  Password expires days payback will be locked

  From January 1, 1970 onwards, the number of days after the account expires.

• Group file format

  Group name: is the group name

  Group password: usually does not need to be set, the password is recorded in/etc/gshadow

  GID: Is the ID of the group

  List of users with the current group as additional groups (comma delimiter)

• Gshdow file format

  Group name: is the group name

  Group Password:

  Group Admins list: List of group admins, change groups passwords and members

  List of users with the current group as additional groups: (comma delimiter)
  

This article is from the "Laugh Monkey" blog, please be sure to keep this source http://xiaomonky.blog.51cto.com/11869371/1833394

Day5:linux File System (3) + Redirect and pipe + user group Hull Rights Management (1)