File system and log analysis

Catalog

One 、inode And block

Two 、 Hard and soft links

3、 ... and 、 Access file process

Four 、 Delete inode value

5、 ... and 、inode Value size

6、 ... and 、 Classification of log files

summary ：

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One 、inode And block

1、 File data consists of meta information and actual data .

2、 The files are stored on the hard disk , The smallest unit on the hard disk is “ A sector ”, Each sector stores 512 byte

block（ block ）： Eight consecutive sectors make up one block block , Is the smallest unit of file access

inode( The index node )： Also called inode node , Used to store file meta information （ Meta information is quite Window Documents in / Properties of directories and so on ）

（ The smallest unit on the hard disk is sector 512 byte

    The smallest unit of file storage is block  4K

    Successive 8 Sectors make up a block block    512x8=4096 byte =4k ）

3、 see inode Value method ① ls -i file / Catalog

                                 ②stat  file / Catalog ： stat Inquire about inode Value contains information

In use find When searching ,time Represents days , also min It means minute, which means it was modified a few minutes ago

atime Represents the access time of the file

mtime Indicates the content modification time of the file

ctime Indicates the attribute modification time of the file

Two 、 Hard and soft links

1、 The difference between hard link and soft link

Soft link ：

type ： Shortcut   ; Operating range ： It can be used across regions     ; Occupancy space ： Just occupy inode Value size ; Action object ： You can create a directory

Hard to connect ：

type ： copy          ; Operating range ： Non cross region ; Occupancy space ： The size is the same as the original file      ; Action object ： You cannot create a directory

  experimental data

 

 

 

3、 ... and 、 Access file process

1、 When the range has a soft connection , First find the file name ——》 Soft connection inode node ——》 original file name ——》 The original document inode node ——》block block data

analysis ： When deleting the original file , The soft connection fails , Flashing red , When a file with the same name is created, it will be restored

2、 Hard links

Hard links and original documents inode The value is the same . All point to the same inode It's worth it , All deleting soft links or hard links has no effect on each other . But if you delete inode value , There will be no documents .

 

Four 、 Delete inode value

1、 Normally, delete a file . System operation flow

rm -rf file name

Find the filename ——》 Find according to the file name inode value ——》 Finally, delete the data

2、 Delete inode value , The data is deleted （ The file name is only for users , The system recognizes inode value ）

The delete command ①：find ./ -inum Numerical value -exec rm -i {} \;  Find the items that need to be deleted under the current directory inode value , And delete  

               ②：find ./ -inum Numerical value -delete    Find the items that need to be deleted under the current directory inode value , And delete

3、 Delete inode Usefulness （ Use scenarios ）

① The filename contains special characters , It may not be deleted properly . In this case, you can directly delete inode, Can play the role of deleting files

② Move or rename files , Just change the filename , No effect inode number

③ After opening a file , The system is based on inode Number to identify this file , Don't think about file names anymore .

④ After the file data is modified and saved , Will generate a new inode number .

⑤ When the system disk resources are insufficient , When data cannot be deleted by deleting the file name , We can delete inode Value to delete .
 

5、 ... and 、inode Value size

inode It also consumes hard disk space , When the hard disk is formatted , The operating system automatically divides the hard disk into two areas . One is the data area , Store file data ; The other is inode District (inode table) , Deposit inode The information contained .

6、 ... and 、 Classification of log files

Log files are used to record Linux Files of various running messages in the operating system , Be the host first “ Diary ”.

1、 The role of logs ： Auxiliary obstacle removal ; Data recovery ; Data analysis

2、 Classification of log ：

                        Kernel and system log ： This kind of log data is served by the system rsyslog Unified management , According to its main configuration file ./etc/rsyslog.conf The settings in determine where to record kernel messages and various system program messages

                        User logs ： This kind of log data is used to record Linux. Operating system information about user login and logout , Include user name 、 Logged in terminal 、 The login time 、 Source host 、 Process operations in use, etc

                        Program log ： Some applications choose to manage a log file independently （ Not to rsyslog）） Service management ), Used to record all kinds of event information in the process of running this program .

3、 The level of system kernel log messages , common 8 level , We use 3 Level and 4 Level 2 .

The more important the program or service , The log information with lower priority should be saved , In this way, it is convenient to check the fault

Linux Priority of system kernel log messages ( The lower the number level , The higher the priority , The more important the news is ):

0 EMERG( emergency ): It will lead to the unavailability of the host system .

1 ALERT( Warning ): A problem that must be solved immediately .

2 CRIT( serious ): A more serious situation .

3 ERR( error ): There was an error running .

4 WARNING( remind ): It may affect the function of the system , Important events that need to alert users .

5 NOTICE( Be careful ): It doesn't affect normal function , But the things that need attention .

6 INFO( Information ): General information .

7 DEBUG( debugging ): A program or system i Debugging information, etc .

summary ：

To study the inode value , His differences and usage , And delete inode Value to delete the file , Classification of logs and viewing logs