Rhcsa day 9

Just signed in Linux when , First start /etc/profile  file , Then start... In the user directory  ~/.bash_profile、~/.bash_login or  ~/.profile One of the documents

Order of execution by ：~/.bash_profile、~/.bash_login、 ~/.profile.

If  ~/.bash_profile If the document exists , In general, it will also carry out  ~/.bashrc file .

/etc/profile >>>> Of all users

.bash_profile>>>> Current user

/etc/.bashrc>>>> Home catalog

  User's environment variable configuration ：

[[email protected] ~]$ ls /root/.bashrc                 # It is recommended to set it in this file first

/root/.bashrc

[[email protected] ~]$ ls /root/.bash_profile

/root/.bash_profile

Global environment variable configuration ：

[[email protected] ~]$ /etc/profile

[[email protected] ~]$ /etc/bashrc

[[email protected] ~]$ /etc/profile.d/

To initialize or display the loaded content after login , Put the script file in /etc/profile.d/ Then you can （ No need to load execution rights limit ）
1. Create a normal variable local_data=1 And access

  Create environment variables root_data, Only root Users can access

[[email protected] ~]# vim .bashrc
[[email protected] ~]# echo $root_data
1

  Create environment variables normal_user_data, Only ordinary users can access

  Create environment variables root Both users and ordinary users can access

2. establish 3 File test1.txt, test2.txt, test3.txt
  Use find lookup test1.txt,test2.txt, test3.txt

  Use the alias : Name the above command myfind

To take effect automatically every time you log in , Add alias to /etc/profile or ~/.bashrc in . then # source ~/.bashrc . To make every user effective, alias , Add alias to /etc/bashrc Back most , then # source /etc/bashrc

  Remove alias

 
3. View recently used 10 Historical orders

4. Print on one line 123 And from root Switch to normal user

5. Wildcard usage
  establish 3 File file1, file2, file3
  1.* To match 3 File           2.? matching 3 File

 

  3.[] matching file1 and file3
  4.[^] matching file2
  5.[!] matching file2

  6.{} matching file1 and file3

6. Examples of the use of quotation marks : No quotes , Single quotation marks , Double quotes , The quotation marks ,$()

7.linux Type of user in
 linux Type of user group in

Super user's UID——0

System user's UID——1～999

For ordinary users UID——≥1000

linux Which file stores user information in ？ And what do the fields mean

         User account file ——/etc/passwd passwd It's a text file , Used to define the user account of the system , Because all users are right passwd Have the right to read , So this file Only user accounts are defined in , Without saving the password .

passwd In file ： Each line defines a user account Field meaning Login name Login name Encryption port Make Use SHA-512/SHA-256/MD5 The password encrypted by the algorithm ,

If it is empty , Indicates that the user can log in without a password ,

if “*” Indicates that the account cannot be used to log in to the system

if “！！” Indicates that the account password has been locked Finally Time modification Time Date of last password change , With distance 1970 year 1 month 1 The number of days in a day means At the very least Interval How many days can the password not be changed . The default value is 0, Means unrestricted Maximum time Interval How many days must the password be changed . The default value is 99999, It means that there is no restriction When warning between How many days in advance to warn users that the password will expire , The default value is 7 God ,0 Indicates that no warning is provided inactive Time How many days after the password expires, disable this user When the failure between Password expiration date , With distance 1970 year 1 month 1 The number of days in a day means , The default is empty. , Indicates permanently available sign Keep unused ,

For future development Each line by 7 Fields make up , Use... Between fields “:” Separate , The format is as follows ：

Account name : password :UID:GID: The personal data : Home directory :Shell Field description ：

Account name ： The user login Linux The name of the system .

password ： Previously, the location of the password was saved in an encrypted format , Now the password is saved in /etc/shadow In file , This is just a password placeholder “x” or “*”. if “x”, It means that the password has passed shadow The protection of the

UID： User's identity , It's a number , Use it to distinguish different users

GID： Identification of the basic group in which the user belongs , It's a number , Use it to distinguish different groups , The same group has the same GID.

The personal data ： You can record the full name of the user 、 Address 、 Office phone 、 Personal information such as home phone .

Home directory ： similar Windows Personal directory , Usually /home/username, here username Is the user name , User execution “cd～” Command, the current directory will switch to the personal home directory .

Shell： Define the number of users to activate after logging in Shell, The default is Bash Shell
  linux What is the file in which the group information is stored ？ And what do the fields mean ？

         User group account file ——/etc/group Every file in the system has a user and a group owner .

Use “ls –l” The command can see the owner and group of each file .

Each group in the system , stay /etc/group There is a line in the file Any user can read the user group account information profile . The real password of the user group is saved in /etc/gshadow In profile .